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Ventilation shaft to increase effectiveness of natural ventilation

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Ventilation shaft to increase effectiveness of natural ventilation

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VENTILATION SHAFT TO INCREASE EFFECTIVENESS OF NATURAL
VENTILATION

by

Abhay Nagory

________________________________________________________________________

A Thesis Presented to the
FACULTY OF THE USC SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE

August 2012

Copyright 2012 Abhay Nagory

ii

ACKNOWLEDGMENTS
I would like to extend my deepest gratitude to my thesis committee for guiding and
supporting my research through the entire process of my study. Dr. Peter Simmonds of
IBE consulting Engineers has been the backbone of this study. His constant guidance and
perseverance has helped me reach the goals of this study. His logical thinking, knowledge
and vast experience in a wide range of building science topics have been of great help in
developing me as a professional and develop my thesis. It has been an enriching
experience to work with an exceptionally knowledgeable and experienced person like
him.
I would like to express my deep appreciation to Professor Marc Schiler, Ed Woll and
Pablo La Roche. I thank them for being extremely patient with my work which helped me
see through this study. I would also like to acknowledge the assistance and guidance
extended by Mr. Greg Otto. He has been of immense help in crafting and envisioning the
process of the theses.

I also would like to express my heartfelt gratitude to my mentor Prof. Christopher
Charles Benninger and Prof. Arvind Adarkar who have been and will always be a
constant source of inspiration and guidance through my life.

iii

My parents and elder brother deserve a special mention for their constant guidance and
inspirational words through this year long study. They have been constant piers of
support through this journey and my mentor’s who have helped me reach my goals. My
dear friends Shahan Patel, Rohit Narayan, Pranesh Krishnamurthy, William Vicent and
Sukreet Singh have been constant support through all my endeavors and want to express
my heartfelt gratitude for their love.

iv

TABLE OF CONTENTS
Acknowledgments............................................................................................................... ii
List of Figures ................................................................................................................... vii
List of Tables .................................................................................................................. xiv

HYPOTHESES .............................................................................................................. xxi
ABSTRACT…. ............................................................................................................. ..xxi

CHAPTER 1: BACKGROUND TO NATURAL VENTILATION ..............................1
1.1 Introduction ..................................................................................................2
1.2 Weighing benefits of Natural Ventilation. ...................................................6
1.3 Ventilation Elements ....................................................................................8
1.4 Ventilation Shafts.........................................................................................9
1.5 Precedents ..................................................................................................12

CHAPTER 2: VENTILATION MECHANISMS. ........................................................17
2.1 The key mechanisms for Natural Ventilation. ...........................................18

CHAPTER 3: PRINCIPLES & BACKGROUND OF VENTILATION. ...................23
3.1 Fundamentals & Governing Principles of Ventilation...............................24
3.2 Buoyancy induced Air Flow. .....................................................................29
3.3 Wind induced Air Flow. ............................................................................33
3.4 Combined (wind + buoyancy) induced Air Flow. .....................................36
3.5 Dimensionless Coefficients. ......................................................................38
3.6: Prediction Methods. ...................................................................................41
3.7: Comparative analysis between Numerical & Computational technique. ..46
3.8: Variable in Estimation. ..............................................................................53

v

CHAPTER 4: ADAPTIVE THERMAL COMFORT BY NATURAL
VENTILATION ...............................................................................................................54
4.1 Effectiveness of Naturally Ventilated Spaces ............................................55
4.2 Effect of Airflow on Internal Temperature. ...............................................58
4.3: The effect of External Air Temperature on Air Flow and Internal
Temperature. ..............................................................................................61
4.4 The effect of Wind and on Air Flow and Internal Temperature. ...............65

CHAPTER 5: CALCULATION PROCEDURE AND METHODOLOGY. ..............71
5.1 Methodology ..............................................................................................72
5.2 Technique for Calculating Air flow ...........................................................74
5.3 Study Model ...............................................................................................75
5.4 General Assumptions for Model Analysis. ................................................79

CHAPTER 6: AIR FLOW IN MODEL A – SINGLE SIDED ....................................82
6.1 Buoyancy induced Ventilation Studies. .....................................................84
6.2 Wind induced Ventilation Studies. ..........................................................101

CHAPTER 7: AIR FLOW IN MODEL B – CROSS VENTILATION. ...................113
7.1 Buoyancy induced Ventilation Studies. ...................................................114
7.2 Wind induced Ventilation Studies. ..........................................................128

CHAPTER 8: AIR FLOW IN MODEL C – SINGLE ZONE + SHAFT. .................140
8.1 Buoyancy induced Ventilation Studies. ...................................................141
8.2 Wind induced Ventilation Studies. ..........................................................154

CHAPTER 9: AIR FLOW IN MODEL D – MULTIPLE ZONES + SHAFT. ........163
9.1 Buoyancy induced Ventilation Studies. ...................................................164
9.2 Wind induced Ventilation Studies. ..........................................................171
vi

CHAPTER 10: CONCLUSIONS OF BUILDING COMPONENTS ON
AIR FLOW. ..................................................................................................................174
10.1: Influence of Occupant Zone Height. ........................................................176
10.2: Influence of Opening Height. ..................................................................177
10.3 Influence of Opening Area.......................................................................179
10.4 Influence of Shaft Height. ........................................................................181
10.5 Influence of Shaft Area. ...........................................................................183
10.6 Influence of Ventilation Shaft Outlet .......................................................185

CHAPTER 11: AIR FLOW USING A VENTILATION SHAFT. ............................187
11.1: Air flow in a Single Zone Model. ............................................................190
11.2: Air flow in Multi Zone Model. ................................................................201
11.3: Summary of Conclusions. ........................................................................219

CHAPTER 12: DESIGN AND EFFECTIVENESS OF A VENTILATION SHAFT 222
12.1: Framework for Calculations. ...................................................................225
12.2: Air flow & Thermal Comfort in the Models. ...........................................238
12.3: Summary of Conclusions. ........................................................................257

CHAPTER 13: CONCLUSIONS AND FUTURE WORK. .......................................261
13.1: Conclusions. .............................................................................................262
13.2: Future Work. ............................................................................................275

BIBLIOGRAPHY: ........................................................................................................279

APPENDIX A: VENTILATION SHAFT AND NEUTRAL PRESSURE PLANE. 285
APPENDIX B: AIR FLOW RATES FOR INDOOR AIR QUALITY .....................294
APPENDIX C: COEFFICIENT OF WIND PRESSURE- C
p
. ..................................298

vii

LIST OF FIGURES
Figure 1: Acceptable operative temperature ranges for naturally conditioned spaces. .......5
Figure 2: Shaft extracts used in Mossbourne Community Academy Project ....................10
Figure 3: Schematic working of an Iran wind catcher at different wind and thermal
conditions. ....................................................................................................................14

Figure 4: Wind towers of Iran ............................................................................................15
Figure 5: Ventilation towers of Frederick Lanchester Library ..........................................16
Figure 6: Schematic illustration of Wind induced cross ventilation ..................................19
Figure 7: Schematic illustration of Buoyancy induced air flow .......................................21
Figure 8: Schematic illustration of typical single sided ventilation ...................................22
Figure 9: Pressure gradients across a fixed height – for different air temperature ............31
Figure 10: Resultant pressure gradients across the shaft height for different air
temperatures and the induced air flow. ..............................................................................31

Figure 11: Schematic illustration of wind pressure distribution in a single zone model. ..34
Figure 12: Combining Buoyancy and wind pressures for air flow in a Shaft. ...................37
Figure 13: Single zone model for calculating the pressure and air flow under buoyancy
effects. ....................................................................................................................48

Figure 14: Single zone model for calculating the pressure differences by the two
techniques. ....................................................................................................................50

Figure 15: Comparison of pressure differentials across the two openings using the AIVS
and CONTAM technique. ..................................................................................................52

Figure 16: Change in effective internal temperature for different air flow rates. ..............59
Figure 17: Single zone model calculated under different temperature conditions. ...........62

viii

Figure 18: Decrease in air flow rates when external air temperature increases. ................64
Figure 19: Single zone model having different wind speed and angle in the same
horizontal plane. .................................................................................................................66

Figure 20: Air flow rates for varying wind speed and different wind angle ......................68
Figure 21: Internal temperature for varying wind speeds and different wind angles. .......69
Figure 22: Methodology to estimate the range of influence of building components on
ventilation. ....................................................................................................................73

Figure 23: Model A represented by a Single zone – Single Sided Ventilation type. ........75
Figure 24: Model B represented by a Single zone – Cross Ventilation type. ....................76
Figure 25: Model C represented by a Single zone attached to a ventilation shaft. ............77
Figure 26: Schematic representation of a Model D - Multi zone model ...........................78
Figure 27: Single zone (single sided model) with varying heights. ...................................84
Figure 28: Air flow rates in zones having varying zone heights (single sided model) at
different temperatures. .......................................................................................................86

Figure 29: Single zone (single sided model) with varying opening heights. .....................87
Figure 30: Air flow rates for different opening heights (single sided model) 4m high. ....90
Figure 31: Air flow rates for different opening heights (single sided model) 6m high. ....90
Figure 32: Single zone model (single sided model) with varying opening sizes. ..............92
Figure 33: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (single sided model) - 4m high. ........................................................94

Figure 34: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (single sided model) - 4m high. ........................................................95

Figure 35: Air flow rates for when Outlet size is increased keeping Inlet size constant. ..95
Figure 36: Air flow rates for when inlet size is increased while keeping outlet size
constant at 2m
2
...................................................................................................................96

ix

Figure 37: Single zone – (single sided model) with varying heights. ..............................101
Figure 38: Air flow rates for different single zone (single sided model) heights at 0
0
wind
angle. ..................................................................................................................103

Figure 39: Single zone (single sided model) having different opening heights. .............104
Figure 40: Air flow rates in a Single Sided model 4m high having different opening
height. ..................................................................................................................107

Figure 41: Air flow rates in a single sided model 6m high having different opening
height. ..................................................................................................................107

Figure 42: Single zone (single side model) with varying opening sizes. .........................109
Figure 43: Wind induced air flow rate in a single zone (single sided model) 4m high at
wind speed – 2m/s when opening sizes are changed.. .....................................................111

Figure 44: Wind induced air flow rate in a single zone (single sided model) 4m high at
wind speed – 5m/s when opening sizes are changed. ......................................................111

Figure 45: Single zone (cross ventilated model) with varying heights. ...........................114
Figure 46: Air flow rates in cross ventilated zones having varying heights at different
temperatures. ..................................................................................................................116
Figure 47: Single zone (cross ventilated model) with varying opening heights. .............117
Figure 48: Air flow rates for different opening heights in a single zone (cross ventilated
model) of height 4m. ........................................................................................................120

Figure 49: Air flow rates for different opening heights in a single zone (cross ventilated
model) of height 6m. ........................................................................................................120

Figure 50: Single zone (cross ventilated model) with varying opening sizes. .................121
Figure 51: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (cross ventilated model) - 4m high. ................................................123

Figure 52: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (cross ventilated model) - 4m high. ................................................124

x

Figure 53: Single zone (cross ventilation model) with varying heights. .........................128
Figure 54: Air flow rates for different zone heights at 0
0
wind angle. ............................129
Figure 55: Single zone (cross ventilation model) having different opening heights. ......131
Figure 56: Air flow rates in a cross ventilated zone 4m high having different opening
height. ..................................................................................................................134

Figure 57: Air flow rates in a cross ventilated zone 6m high having different opening
height ..................................................................................................................134

Figure 58: Single zone (cross ventilated model) with varying opening sizes. .................136
Figure 59: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (single sided model) - 4m high at 2m/s wind speed. ......................138

Figure 60: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (single sided model) - 4m high at 2m/s wind speed. ......................138

Figure 61: Single zone + shaft investigated for change in air flow by varying shaft
height. ..................................................................................................................142
Figure 62: Buoyancy driven air flow rates for different shaft height. .............................143
Figure 63: Single zone + shaft investigated for change in air flow by varying shaft area
size. ..................................................................................................................145

Figure 64: Buoyancy Air flow rates for different shaft areas in a shaft 6m high. ...........147
Figure 65: Air flow rates as a function of varying shaft area for different opening sizes.149
Figure 66 Air flow rates as a function of shaft areas for two different shaft heights. .....150
Figure 67: Single zone connected to a shaft for change in air flow by varying shaft outlet
size. ..................................................................................................................151

Figure 68: Air flow rates as a function of varying shaft outlet size for two different shaft
heights. ..................................................................................................................153

Figure 69: Single zone + shaft investigated for change in air flow by varying shaft
height ..................................................................................................................154
Figure 70: Wind driven air flow rates for different shaft heights. ...................................156
xi

Figure 71: Single zone + Shaft wherein the shaft area vary. ...........................................157
Figure 72: Wind driven air flow rates as a function of shaft area for two different shaft
heights. ..................................................................................................................159

Figure 73: Single zone connected to shaft having variable shaft outlet size. ..................160
Figure 74: Wind driven air flow rate for different shaft outlets size at different wind
speeds. ..................................................................................................................162

Figure 75: Multiple zones model connected to a ventilation shaft wherein shaft outlet size
is changed. ..................................................................................................................165

Figure 76: Pressure distribution across shaft height 12m. ...............................................167
Figure 77: Pressure distribution across shaft height 18m. ...............................................168
Figure 78: Air flow for different shaft outlet sizes and two different shaft heights. .......170
Figure 79: Air flow rate as a function of shaft outlet size for different wind speeds and
shaft heights. ..................................................................................................................173

Figure 80: Typical trend of change in air flow rates for different shaft areas. ................184
Figure 81: Methodology applied to investigate potential of building occupant and
ventilation shaft design on inducing air flow. ..................................................................189

Figure 82: Model 1 – Single zone – Single Sided Ventilation ........................................190
Figure 83: Model 2 – Single zone – Cross Ventilation ....................................................190
Figure 84: Model 3 – Single zone attached to a ventilation shaft ....................................191
Figure 85: Air flow rate in Model 1, 2 and 3 by buoyancy effects. .................................194
Figure 86: Air flow rate in Model 1, 2 and 3 by wind pressure effects. ..........................195
Figure 87: Air flow rate in Model 1, 2 and 3 by combined pressure effects. ..................196
Figure 88: The internal temperature in the three models. ................................................199
Figure 89: Model 4 – Multi zone – Single Sided Ventilation ..........................................201
Figure 90: Model 5 – Multi zone – Cross Ventilation. ....................................................202
xii

Figure 91: Model 6 – Multi zone attached to a ventilation shaft. ....................................203
Figure 92: The air flow pattern across the stacked zones under buoyancy effects. .........207
Figure 93: The air flow rates across the three models 4, 5 & 6 by buoyancy pressure. ..208
Figure 94: The air flow pattern across the three zones due to wind pressure effects. .....210
Figure 95: The air flow rates across the three models 4, 5 & 6 by wind pressure. ..........211
Figure 96: The air flow pattern across the three zones due to combined effects. ............213
Figure 97: The air flow rates across the three models 4, 5 & 6 by combined pressure of
buoyancy and wind. .........................................................................................................214

Figure 98: The internal temperature in the three models. ................................................217
Figure 99: Methodology applied to investigate thermal comfort and variation is
ventilation shaft designs. ..................................................................................................224

Figure 100: Design of MODEL X. ..................................................................................227
Figure 101: Design of MODEL Y ...................................................................................230
Figure 102: Temperature range for September in Los Angeles .......................................233
Figure 103: External temperature on 22
nd
September......................................................234
Figure 104: Typical occupancy schedule in a commercial building ................................234
Figure 105: Wind rose diagram for 22September ............................................................235
Figure 106: Air flow pattern in MODEL X & Y for CASE I climate conditions. ..........240
Figure 107: Air flow rates in MODEL X & Y for CASE I climate conditions. ..............241
Figure 108: Internal temperature of the occupant zones of MODEL X & Y under CASE I
climatic conditions. ..........................................................................................................242

Figure 109: Air flow pattern in Model X & Y for CASE II climate conditions. .............245
Figure 110: Air flow rates in MODEL X & Y for CASE II climate conditions. .............246

xiii

Figure 111: Internal temperature of the occupant zones of MODEL X & Y under CASE 2
climatic conditions. ..........................................................................................................248

Figure 112: Air flow pattern in Model X & Y for CASE III climate conditions. ...........252
Figure 113: Air flow rates in MODEL X & Y for CASE III climate conditions. ...........253
Figure 114: Internal temperature of the occupant zones of MODEL X & Y under CASE
III climatic conditions. .....................................................................................................255

Figure 115: Reference shaft for Calculations. .................................................................280
Figure 116: Neutral plane level from opening sizes ........................................................283
Figure 117: Flow directions for vertical openings temperature, opening and neutral plane
dependent ..................................................................................................................284

Figure 118: To illustrate change in Neutral Pressure Plane for different opening size. ..287
Figure 119: Air flow pattern as result of change in Neutral pressure Plane level for
different opening size. ......................................................................................................288

Figure 120: Air flow rate and air changes per hour requirement for different building
types to maintain indoor air quality. ......................................................................290 – 292

xiv

LIST OF TABLES
Table 1: Values of constant – Ks & ‘a’ for calculating wind reduction coefficient. .........40
Table 2: Selected equations to calculate volumetric air flow due to wind effects. ............43
Table 3: Selected equations to calculate volumetric air flow due to buoyancy effects. ....43
Table 4: The different numerical equations to calculate pressure difference due to
buoyancy effects alone .......................................................................................................47

Table 5: The different numerical equations to calculate air flow rates due to buoyancy
effects alone effects. ...........................................................................................................47

Table 6: Conditions when calculating air flow in a single zone.. ......................................48
Table 7: Result of pressure differential across the two openings of the single zone. ........49
Table 8: Result of air flow rates in the single zone. ...........................................................49
Table 9: Conditions to calculating the pressure difference in a single model so as to
compare results from the two methods of AIVC and CONTAM. .....................................51

Table 10: Results of difference in pressure distribution values .........................................51
Table 11: Assumed heat gains for internal heat gain calculations. ....................................58
Table 12: Conditions to calculate the air flow by changing temperature conditions.. .......63
Table 13: Results of Air flow rate in a single zone when external air temperature
increases. ....................................................................................................................63

Table 14: Conditions for calculating change in air flow rates when wind speed and angle
is altered. ....................................................................................................................66

Table 15: Results for change in air flow rates when wind angle is altered. ......................67
Table 16: Building components influencing air flow. .......................................................73
Table 17: Initial - Primary Conditions for calculations. ...................................................74

xv

Table 18: Division of the results table.. .............................................................................83
Table 19: Conditions for calculating air flow by changing overall zone heights. .............84
Table 20: Results of air flow when external temperature is kept at 17
0
C. ........................85
Table 21: Results of air flow when external temperature is kept at 22
0
C. ........................85
Table 22: Conditions for calculating buoyancy driven air flow by changing opening
heights. ....................................................................................................................87

Table 23: Results of air flow rates in a 4m single zone (single sided model) when opening
heights are changed. ...........................................................................................................88

Table 24: Results of air flow rates in a 6m zone when opening heights are changed. ......89
Table 25: Conditions for calculating buoyancy driven air flow in a zone by changing
opening areas. ....................................................................................................................92

Table 26: Results of air flow rates by changing area of inlet to outlet in a single zone
(single sided model) 4m high keeping height difference at 2.5m. .....................................93

Table 27: Results of air flow rates by changing area of inlet to outlet in a single zone
(single sided model) 4m high keeping height difference at 1.5m. .............................97 – 98

Table 28: Comparative analysis of change in buoyancy driven air flow rate by varying
inlet to outlet size ratio to see the percentage difference in corresponding air flow rate
from the air flow rate when openings are equal. ................................................................99

Table 29: Conditions for calculating wind driven air flow in a single zone (single sided
model) by changing the zone heights. ..............................................................................102

Table 30: Results of air flow rates in a single zone (single sided model) by changing
overall zone heights. ........................................................................................................102

Table 31: Conditions for calculating wind driven air flow in a single zone (single sided
model) by changing opening heights. ..............................................................................105

Table 32: Results of air flow in single zone- (single sided model) 4m high by varying
opening heights. ...............................................................................................................105

Table 33: Results of air flow in single zone 6m high by varying opening heights. .........106

xvi

Table 34: Conditions for calculating wind driven air flow rates by varying opening
sizes. ..................................................................................................................109
Table 35: Results of air flow rates for different opening size for different wind speeds.110
Table 36: Conditions for calculating air flow by changing overall zone heights.. ..........114
Table 37: Results of air flow for different zone heights when T
o
is kept at 17
0
C. .........115
Table 38: Results of air flow for different zone heights when T
o
is kept at 22
0
C ..........115
Table 39: Conditions for calculating buoyancy driven air flow by changing opening
heights. ..................................................................................................................117

Table 40: Results of air flow rates in a 4m zone when opening heights are changed. ....118
Table 41: Results of air flow rates in a 6m zone when opening heights are changed. ....119
Table 42: Conditions for calculating buoyancy driven air flow in a zone by changing
opening areas. ..................................................................................................................122

Table 43: Results of air flow rate by changing area of inlet to outlet in a single zone
(cross ventilated model) 4m high, keeping height difference between openings
at 2.5m. ..................................................................................................................122

Table 44: Results of air flow rates by changing area of inlet to outlet in a single zone
(cross ventilated model) 4m high keeping height difference at 1.5m. .............................125

Table 45: Comparative analysis of change in air flow rate by varying inlet to outlet size
ratio to see the percentage difference in corresponding air flow rate from the air flow rate
when openings are equal. .................................................................................................126

Table 46: Conditions for calculating wind driven air flow in a single zone (cross
ventilated model) by changing the zone heights. .............................................................128

Table 47: Results of air flow rates in a single zone by changing overall zone heights. ..129
Table 48: Conditions for calculating wind driven air flow in a single zone by changing
opening heights. ...............................................................................................................131

Table 49: Results of air flow in single zone (cross ventilated model) 4m high by varying
opening heights. ...............................................................................................................132

xvii

Table 50: Results of air flow in single zone 6m high by varying opening heights ..........133
Table 51: Conditions for calculating wind driven air flow rates by varying opening sizes.136
Table 52: Results of air flow rates in a single zone (cross ventilated model) for different
opening size at 2 m/s wind speed at 0
0
wind angle. .........................................................137

Table 53: Conditions for calculating buoyancy driven air flow when changing shaft
heights. ..................................................................................................................142

Table 54: Results of buoyancy driven air flow when shaft heights are changed. ............143
Table 55: Conditions for calculating buoyancy driven air flow rate when shaft area is
changed. ..................................................................................................................145

Table 56: Results of air flow rate for shaft height constant at 6m. ..................................146
Table 57: Air flow rates for as a function of shaft area for different opening sizes. .......148
Table 58: Comparing results of air flow rate for shaft height at 8m and 6m. ..................150
Table 59: Conditions for calculating buoyancy driven air flow rates by changing shaft
outlet size. ..................................................................................................................152

Table 60: Results of air flow rates by changing shaft outlet size. ...................................152
Table 61: Conditions for calculating wind driven air flow by changing shaft heights. ...155
Table 62: Results of air flow rate when shaft heights are altered. ...................................155
Table 63: Conditions for calculating wind driven air flow rate when shaft area
is altered. ..................................................................................................................157
Table 64: Results of air flow rates by changing shaft area for different shaft heights. ...158
Table 65: Conditions for calculating wind driven air flow when shaft outlet size is
altered. ..................................................................................................................161

Table 66: Results of air flow rate by varying shaft outlet size. .......................................161
Table 67: Conditions for calculating buoyancy driven air flow rates in a multi zone
model ..................................................................................................................166
Table 68: Shaft outlet area based on sum of area of inlets. .............................................166
xviii

Table 69: Results of air flow rate and pressure when shaft outlet size is varied. ............167
Table 70: Buoyancy driven air flow rates for different shaft outlet size at two different
shaft heights. ..................................................................................................................169

Table 71: Conditions for calculating wind driven air flow rates in a multi zone model
where shaft outlet is varied. .............................................................................................172

Table 72: Results of air flow rate as a function of shaft outlet size for different wind
speeds and shaft heights. ..................................................................................................172

Table 73: Change in Air flow rates – Q (m
3
/s) by varying inlet (A1) and outlet (A2)
height difference (DH) for both wind (Q
w
) and buoyancy (Q
b
) driven air flow. ............178

Table74: Relative percentage change in air flow rate when the ratio of opening sizes is
altered. ..................................................................................................................180

Table 75: Change in air flow rates when ventilation shaft heights are increased, attached
to an occupant zone 4m high. ..........................................................................................182

Table 76: Method to calculate minimum required shaft are depending on volume flow
and overall shaft height. ...................................................................................................184

Table 77: To compare the difference between the opening design of the three single zone
models – 1,2 & 3. .............................................................................................................191

Table 78: Single zone model – design conditions. ..........................................................192
Table 79: Conditions for calculating air flow in the single zone models.. ......................192
Table 80: Air flow results for CASE A – conditions on single zone models. .................193
Table 81: Air flow results for CASE B – conditions on single zone models. .................193
Table 82: Air flow results for CASE C – conditions on single zone models. .................194
Table 83: Internal temperature by air flow rate generated through combined effect of
buoyancy and wind effects. ..............................................................................................198

Table 84: To compare the difference between the opening design of the three multi zone
models. ..................................................................................................................204

Table 85: Multi zone model – design conditions .............................................................204
xix

Table 86: Conditions for calculating air flow in the multi zone models. ........................205
Table 87: Air flow results for CASE D – conditions on Multi zone models. ..................205
Table 88: Air flow results for CASE E – conditions on Multi zone models. ..................206
Table 89: Air flow results for CASE F – conditions on Multi zone models. ..................206
Table 90: Internal temperature by air flow rate generated through combined effect of
buoyancy and wind effects on Multi zone models. ..........................................................216

Table 91: Summary of the two model design – Model X & Y. .......................................231
Table 92: The climate limitation and criterions for a naturally ventilated space in Los
Angeles. ..................................................................................................................232

Table 93: Day time temperatures on 22
nd
September in Los Angeles. ............................233
Table 94: Summary of the three climate conditions. .......................................................236
Table 95: The units and symbols of the result table. .......................................................237
Table 96: Break down for reporting results of the calculations. ......................................237
Table 97: Results of air flow and temperature compared with each zone of the two
models – when conducted under conditions represented by CASE I. ...................238 – 239

Table 98: Results of air flow and temperature compared with each zone of the two
models – when conducted under conditions represented by CASE II. ..................243 – 244

Table 99: Results of air flow and temperature compared with each zone of the two
models – when conducted under conditions represented by CASE III. ................250 – 251

Table 100: Period of thermal comfort conditions in MODEL X & MODEL Y. .............259
Table 101: Difference in ventilations shaft design used for MODEL X & MODEL Y. .260
Table 102: Trend of change in airflow as a function of height difference for both wind
and buoyancy driven effects on air flow. .........................................................................265

Table 103: Change in air flow rate when the ratio of opening sizes is altered. ...............266

xx

Table 104: Difference in air flow by different models types and the corresponding effect
on internal temperature. ...................................................................................................272

Table 105: Conditions for calculating the Neutral pressure Plane levels. .......................285
Table 106: Relationship of change in neutral pressure plane when inlets to outlet sizes are
changed. ..................................................................................................................285

Table 107: Pressure redistribution by change in neutral pressure plane. .........................286
Table 108: Values of wind pressure coefficient for exposed shielding conditions and 1:1
surface ratios. ..................................................................................................................294

Table 109: Values of wind pressure coefficient for Surrounded by obstruction equivalent
to half the building height shielding conditions and 1:1 surface ratios. ..........................295

Table 110: Values of wind pressure coefficient for Surrounded by equal to height of the
building shielding conditions and 1:1 surface ratios. .......................................................296

Table 111: Values of wind pressure coefficient for exposed shielding conditions and 2:1
surface ratios. ..................................................................................................................297

Table 112: Values of wind pressure coefficient for Surrounded by obstruction equivalent
to half the building height shielding conditions and 2:1 surface ratios. ..........................298

Table 113: Values of wind pressure coefficient for Surrounded by equal to height of the
building shielding conditions and 2:1 surface ratios. .......................................................299

xxi

HYPOTHESIS
The time period of effective natural ventilation in an occupant space can be increased by
using a ventilation shaft.

ABSTRACT
Ventilation shafts can aid natural ventilation in buildings. Natural ventilation provides
ventilation for occupants that can provide thermal comfort conditions. This study
attempts to increase air flow rates, which can provide thermal comfort conditions, in
occupant spaces of a low rise commercial building by using a ventilation shaft. While
doing so the time period of effective natural ventilation also increases. This is achieved
by optimizing the occupant zone and ventilation shaft design to maximize the air flow
inside them. This design optimization is achieved by identifying the range of influence
building and ventilation shaft components of height and openings have on both types of
buoyancy and wind driven air flow.
A comparison of air flow rate and thermal comfort conditions achieved by the airflow on
different models having different ventilation shaft designs are performed to verify the
potential of a ventilation shaft in increasing effectiveness of naturally induced airflow.
Multi zone airflow and contaminant Transport analysis (CONTAM) software by National
Institute of Standards and Technology (NIST) is used to perform all the calculations.

1

CHAPTER 1: BACKGROUND TO NATURAL VENTILATION.
This chapter is a general introduction to natural ventilation. It describes the need for
natural ventilation mechanisms and weighs the benefits and drawbacks of employing
natural ventilation strategies. This chapter introduces the ventilation shaft along with
identifying the various design principles used to design a ventilation shaft

2

1.1: INTRODUCTION
Natural ventilation is the process of providing air for ventilation purposes across
habitable spaces without the use of any mechanical ventilation systems.

After the oil crises in 1973 all developed and developing countries became more
conscious of deteriorating environmental conditions. Extensive administrative polices
and measures have been undertaken and discussed to reduce the impact of rampant
human development on the ecology of our planet. The greatest impact on the
environment is through the built environment – buildings. Buildings consume 40% of the
total energy generated globally (Mazaria 1979). Mechanical systems used for cooling and
heating buildings have direct and indirect environmental impacts. The robust natures of
typical mechanical systems respond sensitively to internal needs and generally have high
energy requirements. Pure natural ventilation, which specifically is ventilation not relying
on fan assistance, avoids the use of any mechanical systems. As natural ventilation varies
as a function of time - prevailing wind characteristics and the thermal state of the
building, the energy consumption of the building also varies making natural ventilation
techniques virtually a free medium with minimal environmental impact.

3

1.1.1 VENTILATION FOR BREATHING
The purpose of ventilation is to provide habitable conditions for building occupants.
Habitable conditions can be achieved by having clean uncontaminated air for breathing
and by maintaining internal temperature within thermal comfort conditions. Natural
ventilation can help in achieving such habitable conditions by inducing air flow.

1.1.2: INDOOR AIR QUALITY
Indoor air quality refers to the quality of air inside and surrounding habitable space which
is required to be maintained within permissible limits of contaminant concentration and
harmful gasses to maintain occupant health and comfort. The acceptable air contaminant
levels are stipulated by the American society of heating refrigerating and air-conditioning
engineer’s (ASHRAE) standard 62.1- 2007 and are tabulated in Appendix B.
Fresh air is necessary as a primary breathing requirement. Ventilation plays an important
role in providing good fresh indoor air quality for breathing and thermal comfort for the
occupants. Inadequate air changes increase pollutant and air contamination levels.
Constant air flow within the building ensures air changes, keeping the pollutants and
contaminant levels in check. As air blows inside a space it pushes out aged stale air from
the occupant space, removing contaminated air having higher concentrations of harmful
gases.

4

It is essential for acceptable indoor air quality that there be a sufficient air supply and also
usually essential for energy conservation to avoid airflow rates that are too high. Thus a
balanced method to control air flow is necessary.

1.1.3: THERMAL COMFORT
Thermal Comfort is that condition of mind that expresses satisfaction with the thermal
environment (ASHRAE/ANSI.55. 2007). A comfort balance between the body’s need to
maintain its temperature with the temperature, humidity and airflow of its immediate
surroundings can also be understood as a condition of relative thermal comfort.
Occupants thermal comfort level cannot be represented only as simple heat balance of the
human body but depends on other psychological processes also. The parameters that
influence thermal comfort can be categorized into physical parameters, physiological
parameters and the external parameters which make it difficult to satisfy everyone in a
space. Physical parameters include temperature, humidity and air velocities,
physiological parameters include age, sex and specific characteristics of the occupant and
the external parameters include clothing, human activity, cultural expectations and social
conditions. Modifying the air movement around the human body can make considerable
difference in thermal comfort levels for the occupants. Air movements are instrumental in
determining the heat and mass exchange of the human body with the surrounding air
(ASHRAE/ANSI.55. 2007). This exchange is primarily through convection.

5

The direct effect of natural ventilation on comfort conditions is to counter the indoor heat
gains generated largely from occupant’s body heat, artificial lighting and mechanical
equipment such as computers. By limiting and controlling the way air changes occur,
internal air temperature can be controlled leading to relative thermal comfort (Dols,
Enunerich and Axley August,2001) .The chart below represents a typical adaptive
comfort range for occupants without natural ventilation under different indoor and
outdoor temperature differences.

Fig 1: Acceptable operative temperature ranges for naturally conditioned spaces
1
.

1
(ASHRAE/ANSI.55. 2007)
6

1.1.4: NIGHT FLUSHING
Natural ventilation is also effective for night flushing. This process extracts heat
generated through the day from the building at night time providing optimum comfort
levels in the morning. This technique is most effective for climates experiencing
considerable diurnal temperature differences. Heat trapped in the building mass during
daytime occupancy hours is flushed out at night providing thermal comfort conditions at
early morning hours for the building occupants.

1.2: WEIGHING BENEFITS OF NATURAL VENTILATION
Natural ventilation is very attractive for engineers or architects because it offers solutions
capable of providing an acceptable indoor air quality and meeting comfort needs
throughout a considerable range of climatic conditions (Dols, Enunerich and Axley
August,2001). Energy savings as compared to mechanical systems are a great advantage
but there are also limits to its applicability. The potential cooling energy that may be
saved depends, of course, on both the climate in which a building is located and the
relative level of internal and other gains that impact the building’s thermal performance.
Clearly, when natural ventilation is not applicable due to extreme conditions these energy
savings cannot be realized.

7

1.2.1: COSTS
The cost of architectural features needed for natural ventilation can to some extent be
incorporated into the cost for building enclosures. Also the space requirements for
naturally ventilating internal space may be minor when compared to space requirements
for equipment and ducting required by mechanical systems. The reduction of space
requirements can contribute to reduction of building construction costs. However first
cost savings represent only a part of the advantage that may be offered. Eliminating the
running costs of mechanical systems and the corresponding maintenance charges can
amount to important additional savings.

1.2.2: LIMITATIONS
‘Natural’ also implies that behavior will be somewhat random and cannot necessarily be
effectively controlled, which affects the reliability of the system’s overall performance.
In summer periods, where humidity levels are high with no wind, relying on pure natural
ventilation for comfort conditioning is not possible. Similarly, natural ventilation is not
usually the best solution for extreme climates. In colder climates cold drafts entering
buildings can be uncomfortable for occupants. The need to maintain reliable ventilation
rates and the inherent difficulty in doing so when using natural driving forces must be
seen as a major challenge for the development of natural ventilation systems. (Dols,
Enunerich and Axley August,2001)

8

1.3: VENTILATION ELEMENTS
Ventilation elements have developed through time and extensive research based on
qualitative and quantitative information of interactions between building characteristics
and natural ventilation mechanisms. Various architectural elements have evolved through
time to assist naturally flowing wind to enter, circulate through and condition habitable
spaces. Due to different geographical and climatic conditions these architectural elements
for ventilation and methods have varied but the intent has been the same: getting the
outside air to flush out internal stale air and thus create comfort levels for the habitants.
The Egyptian civilization developed wind scoops to trap the cooler air flowing generally
above the building heights to ventilate the underlying spaces (Ghaemmaghami and
Mahmoudi May 2005). Middle Eastern countries like Saudi Arabia (Alaard 1998) and
Iran (Mumovic, et al. 2009)developed solar chimneys and wind catchers which rely on
air buoyancy and direct wind pressure to achieve regular air changes (Kleiven
March,2003)

9

1.4: VENTILATION SHAFTS
This study focuses on a vertical element used for ventilation purposes. Ventilation shafts
are vertical hollow architectural elements connected to almost all stacked floors
performing various circulation and ventilation functions and many times carrying
essential building services (Lomas 2007).It induces air flow in occupant space by
primarily relying on buoyancy effects inducing pressure differentials across openings
(Kleiven March,2003). However it also responds to wind pressure acting at its outlets.

Not many architectural projects have employed ventilation shafts as their primary natural
ventilation strategy. As a part of this study, extensive time was dedicated to research and
find architectural projects which have used or partly used ventilation shafts as a part of
their ventilation strategy. The key projects which are substantially documented are
Frederick Lanchester Library, Coventry, UK; The School of Slavonic and East European
Studies , London, UK and the Harm A. Weber Library, Elgin near Chicago USA (Lomas
2007). In all these projects, the ventilation shaft volumes have strong architectural impact
on the building aesthetics.

10

This overpowering aesthetical feature may not suit as the preferred choice among
building designers for their ventilation strategies. The rational of the ventilation shaft
design are also not well documented. Data from post design analysis have been relied to
judge the effect of air flow induced by their ventilation shafts on thermal comfort. Thus
this study also focused at methods to reduce overall shaft volume without reducing air
flow rates which affects the thermal comfort conditions.

Fig 2: Shaft extracts used in Mossbourne Community Academy
2
project.

The general design guidelines for ventilation shafts are mentioned in various guide
books. The common design guidelines are compiled and mentioned further.

2
Mossbourne Community Academy - www.vision-environmental.co.uk
11

1.4.1: GENERAL DESIGN GUIDELINES FOR A VENTILATION SHAFT
Based on historical precedents the following rules of thumb aid in designing effective
ventilation strategies using ventilation shafts:

• In multistory office buildings, attention should be paid to the placement of shafts
in plan. They should not function as simple exhaust stack ventilation systems in
order to avoid warm stale air from lower zones entering the top floors. A shaft
partition can be useful in such cases (Kleiven March,2003)
• The outlets of shafts should be placed facing the leeward side of the building,
significantly above the top floor level served. (Kleiven March,2003)
• The height of the outlets’ position and size of the overall opening area should be
chosen as a means of controlling the neutral pressure level and thereby enhancing
the ventilation of the spaces (Alaard 1998)
• The vertical position of the inlet openings in spaces should be lower than the
position of the outlet openings in order to avoid a conflict between cross
ventilation and the stack effect (Alaard 1998).
• The inlets should be placed along the windward side of the building to benefit
from direct winds. (Irving, Ford and Etheridge January,2007)

12

• Establish a workable shaft height for effective stack effect. An effective stack will
usually be twice as tall as the height of the tallest space it is ventilating (Walker
2010).
• Estimate the cooling capacity of the stack ventilation system on the basis of shaft /
stack height and the stack – area-to-floor-area ratio (Alaard 1998).

1.5 PRECEDENTS
Modern ventilation shaft design concepts are deduced from historical precedents – like
the wind towers of Iran or the solar chimneys in Saudi Arabia. It is beneficial to explore
the ventilation techniques adopted by these historical elements of ventilation to
understand the working of a ventilation shaft

1.5.1: IRAN WIND CATCHERS
Wind towers of Iran are a key element of traditional Iranian architecture. They look like
tall chimneys in the sky line of ancient cities of Iran. They are vertical shafts with vents
on top to trap wind for underlying habitable spaces to provide thermal comfort and
necessary air changes.

13

As wind enters from the top it moves vertically down the hollow tower blow to occupant
spaces below. These movements are generally due to wind induced pressure differences.
To enhance wind pressure these towers are oriented directly in the face of the prevailing
wind. Depending on the wind directions these wind catchers have single or multi
directional openings and they vent at the top. Most of the wind towers are also partitioned
inside. This allows reverse and regular air movement due to wind pressure and for stack
effects. This makes the wind catchers functional both in the summer and winter periods.
A wind tower operates as a ventilation-inducing device as a result of the combination of
three types of physical mechanism:

• DOWNDRAUGHT:
In the absences of wind, hot ambient air enters the tower in the early hours
through the openings in the sides and is cooled when it comes in contact with the
tower walls, which have enough thermal inertia to release at night the heat
absorbed during the day (Alaard 1998). A downdraught is thus created when
denser cooler air sinks through the tower.

• THE WIND EFFECT:
Cooling effect from wind operates through the tower which has doors that can be
opened into the central hall and basement of the building. When doors are opened
the cooled air from the tower moves into and across the building and pushes the
stale air out through windows and other openings.

14

Wind at night has a heating effect since the tower walls warm night air before it
enters the building (Alaard 1998).

• THE STACK EFFECT:
When there is no wind at night, heat released by the tower walls warms the air in
the tower thus creating a buoyancy effect up draught,

Fig 3: Schematic working of an Iran wind catcher
3
at different wind and thermal
conditions.

3
www.ecobine.de. The bottom opening connected of the occupant space will act as two-way opening
depending on the temperature and wind conditions of the site. Doors connected at the bottom of the tower
re-direct air movement inside the occupant space or up the tower depending on the thermal and wind
15

Fig 4: Wind towers of Iran
4

1.5.2: LANCHESTER LIBRARY
One of the known architectural projects employing ventilation shafts are Frederick
Lanchester Library, Coventry, UK; The School of Slavonic and East European Studies ,
London, UK and the Hiram A. Weber Library in Elgin near Chicago USA (Lomas 2007)
The ventilation design of the Frederick Lanchester Library, Coventry in United Kingdom
relies on tall ventilation towers similar to a ventilation shaft – Figure 5. A cluster of these
ventilation towers creates an impressive and dramatic landmark on the Coventry skyline.
The ventilation towers in this public building have become a prominent architectural
feature having a strong impact on the overall architectural scheme.

conditions .It can act as inlets for direct wind induced air flow whereas outlets in case for warm air rising
up due to buoyancy effects.
4
albert-videt.eu
16

The floor plate is deeply punctuated by a glazed atrium at its centre and four- large, full
height light wells. Shafts, linked to a plenum under the ground floor, conduct fresh air
into the building while it is removed again via the large central atrium and 20 ventilation
stacks around the perimeter of the building (Kleiven March,2003) (Lomas 2007)
The tall brick ventilation stacks are topped with metal structure designed to react to
changing winds and also to allow rising air to exit without mechanical assistance under
all weather conditions.

Fig 5: Ventilation towers of Frederick Lanchester Library
5
.

Ventilation mechanisms across these shafts are similar to those of the Iran wind catchers.
The present study looks at methods to reduce shaft height so as to reduce the influence on
design.

5
Coventry library - www.safarisue.blogspot.com
17

CHAPTER 2: VENTILATION MECHANISMS.
This chapter introduces the reader to the various natural ventilation mechanisms.
.
18

2.1: THE KEY MECHANISMS FOR NATURAL
VENTILATION
Natural ventilation may be defined as ventilation provided by thermal, wind or diffusion
effects through doors, windows or other intentional openings in the building. The variety
and diversity of purpose-provided natural ventilations systems that have been proposed in
recent years is large. It is important to identify the principal driving mechanisms to
explore different possible strategies under various climatic conditions. Natural ventilation
depends generally on pressure and temperature differences which lead us to categorize it
various mechanisms as (Irving, Ford and Etheridge January,2007)
• Wind – driven cross ventilation.
• Buoyancy – driven stack ventilation and single sided ventilation

2.1.1: WIND DRIVEN VENTILATION
Wind enters form one side of the building and leaves from the opposite side. Wind
driven ventilation is mostly due to wind pressure exerted on building openings.
Therefore it is necessary to understand the wind pressure differences occurring on
building surfaces. Building surfaces which act as obstructions to the prevailing wind
create positive and negative wind pressure on the windward and leeward side of
buildings respectively. Because of these pressure differences wind enters the building
from the windward side and exits from the leeward side- Figure 6.

19

Fig 6: Schematic illustration of Wind induced cross ventilation

The effectiveness of the ventilation induced depends on the speed, angle and height at
which wind enters inside and also the relative size and height of the exit opening.
Sometimes the wind flows are parallel to the building face; under such conditions
architectural features like air scoops can be integrated in building facades to trap the
oncoming air. It is important to avoid any obstructions between the windward inlets and
the leeward outlets.
.
20

2.1.2: BUOYANCY DRIVEN (STACK) VENTILATION
Buoyancy differences can be humidity or temperature induced (Dols, Enunerich and
Axley August,2001). For this study buoyancy effects arising purely by temperature
differences are considered. Buoyancy driven ventilation relies on density differences to
draw cool, outdoor air in through low ventilation openings and exhaust warm, indoor air
through high ventilation openings. These openings can be on the same façade or on the
opposite façade (Liddament June,1986)

A stack effect tower can be devised to use this effect to advantage. The heat given out by
occupants and mechanical equipment increases the temperature of interior air causing it
to rise. The stale heated air escapes from an opening at the top of the tower pulling air
from the bottom of the tower and therefore creating a convective
6
air movement. Stack
effect is especially effective in winter when the indoor to outdoor temperature
differences are at a maximum.
It should be noted that stack effects may be relatively weak; in many cases wind driven
ventilation effects may be much stronger than the stack effects. (Alaard 1998)
Depending on wind conditions wind driven ventilation may either augment or negate
stack effect ventilation.

6
Convective air movement is where in the air moves from lower levels to a higher level. Figure no. 4
illustrates a convective air flow pattern wherein air flows from lower to higher level in that zone and
common shaft.
21

Fig 7: Schematic illustration of Buoyancy induced air flow

2.1.3: SINGLE-SIDED VENTILATION
This ventilation strategy typically serves for single rooms or single zones and relies on
Buoyancy effects to generate air flow. The key to this ventilation system is the height of
inlets and outlets. Ventilation air flow for this condition is driven by room – scale
buoyancy effects and small differences in air pressure and temperature – Figure 8.
Consequently driving forces for single- sided ventilation tend to be small and variable.

22

Compared to other types this type of ventilation may not prove to be efficient (Dols,
Enunerich and Axley August,2001)

Fig 8: Schematic illustration of typical single sided ventilation.

23

CHAPTER 3: PRINCIPLES & BACKGROUND OF VENTILATION.
To understand the principle mechanisms of ventilation it is necessary to study the
physical principles governing ventilation. This chapter explores the fundamentals of
ventilation and the background for calculating ventilation rates by various techniques.
24

3.1: FUNDAMENTALS & GOVERNING PRINCIPLES of
VENTILATION
To understand ventilation as a physical phenomenon one needs to understand the
underlying principles of mass flow and related volume flow mechanisms. Using these
principles various prediction models in the form of empirical formulas have been
developed. These formulas have been derived by integrating natural phenomena of air
speed, temperature and pressure with the ideal gas laws which govern mass flow and
volume flow of gas. Design manuals like the American Society of Heating Refrigerating
and Air-conditioning Engineer’s (ASHRAE/ANSI.55 2004) (ASHRAE/ANSI.62.1
2007) and Chartered Institution of Building Services Engineers (Irving, Ford and
Etheridge January,2007)derive their prescribed methods for air flow through these
prediction methods.

The reliability of the prescribed methods varies due to difficulty in estimating boundary
conditions. This chapter discusses the primary principles governing ventilation and their
employment to help predict ventilation.

25

3.1.1: GOVERNING PRINCIPLES
Principles of natural ventilation processes can be understood in accordance to laws and
physics governing the study of fluid dynamics and the law of conservation of mass.

3.1.1.1: MASS and VOLUME FLOW:
Air flow can be quantified as terms of mass flow or volume flow. The value of mass
flow is directly proportional to the value of volume flow; the factor of proportionality
being density.
........................................................................... Equation 1

Where,
Q = volume flow measured in m
3
/sec.
ρ = Density in kg/m
3
M = mass in kg

However for a given quantity of gas the mass will remain constant but the volume of the
gas can increase or decrease. This variation occurs due the differences in temperature
and static pressure at different locations and heights which in turn affects density of air.
Thus a balance in mass flow does not necessarily mean that there is a balance in volume
flow.

26

It is conceptually simpler to express flow rate in terms of mass but for convenience we
directly consider volume flow rate both because as the numeric variation of density is
quite small and because the most conventional measurement of air flow is in m
3
/second
(or ft
3
/ min).

3.1.1.2: LAW OF CONSERVATION OF MASS:
The law of conservation of energy states that energy may neither be created nor
destroyed. The sum of total energy in a system remains constant but changes in its form.
In parallel to the Law of conservation of Energy, the Law of conservation of Mass for
ventilation means:

Mass of air entering a building = Mass of air leaving the building

In accordance to this – the amount of air entering a space will always be equal to the
amount of air exiting the space. Thus the variations in the air flow patterns will occur
due to pressure differences across the space. This pressure is temperature, density and
height dependent, in the case of stack pressure whereas for wind pressure it is directly
proportional to the prevailing wind velocities.

27

3.1.1.3: DENSITY, PRESSURE and TEMPERATURE:
Considering pressure differences as the primary driver for air movement it is necessary
to understand the relationship among pressure, density of air, temperature of air and
height of building shaft (the variables – pressure, density and temperature which describe
the state of a fluid, known as State Variables.) Changes in either temperature or density
have direct impact on the pressure thus affecting the overall air flow rate. The
relationship among these three variables for a gas is given by the Ideal Gas Law.
............................................................................... Equation 2

Where,
V= Volume in m
3

P = Pressure of gas in Pa

R = Specific gas Constant in J/kg
T = Temperature in K
n = the amount of Substance

Density is directly proportional to pressure and inversely proportional to temperature.
This means that at low temperature the density of air is higher. Inversely at higher
temperatures the density is lower; that is, a given volume of air is lighter, which induces
buoyancy. This is the reason for convective air movement upward in summer and the
opposite flow in winter in a stack ventilation system.

28

As the volumetric flow rate is caused due to pressure drop across openings, the flow rate
across them can be expressed as a simple function of pressure:
............................................................................... Equation 3

Where,
Q = Volumetric flow rate in m
3
/s,
ΔP = Pressure difference in Pa
C = Flow coefficient depends of
building condition.
n = Flow exponent – depends on air
flow type.

3.1.2.4: BERNOULLI’S EQUATION:
In 1738 Bernoulli published his principle on the relation between pressure and overall
energy in fluids (Awbi 2008). Bernoulli’s equation provides a method to calculate the
pressure of fluid flow at any point throughout the system; a direct application of
Bernoulli’s equation to understand pressure differentials between the outside and inside
air can also be made. ..............................................................................................................

..................................................................................................... Equation 4

29

Where,
ρ = Air Density in kg/m
3

ΔP = Pressure drop between 1& 2 in
N/m
2
where: 1 N/m
2
= 1 Pascal.
P
1
, P
2
= entry and exit static pressures
Z
1
, Z
2
= Entry and Exit elevations in m
g = Gravitational acceleration = 9.8m/s
2

V
1
, V
2
= Entry & exit velocities

This principle can be derived from the principle of conservation of energy which states
that the sum of kinetic and potential energy of a fluid remains constant throughout the
system. Any changes in speed or pressure will affect the energy distribution in the fluid
but the sum of energies will remain constant. In other words, if the speed of a fluid
increases due to the physical changes in the system, the dynamic pressure and kinetic
energy increase and the static pressure decrease.

3.2: BUOYANCY INDUCED AIR FLOW
In fluid dynamics the hydrostatic pressure at a point decreases with increase in height,
and the rate of decrease is proportional to the density of the fluid (Awbi 2008). This
implies that pressure of cooler air decreases more rapidly with height than warmer air.
This is because colder air is denser than warmer air. The buoyancy effect is similar which
occurs because of denser cold air sinking to displace the warm air.

30

In this case the warm air rises inside the shaft depending on the thermal state of the shaft.
Because the internal and external pressures change with height
1
there will exist a pressure
difference across the boundary walls of the shaft when the warm air rises-Figure 9.
External or air from outside flows into the shaft through openings in order to balance the
pressure difference when the warm air rises, which results in air to flow up or down the
shaft depending on the temperature conditions. A pressure gradient across the height of
the shaft is thus created – Figure 10. The air flow pattern is governed by this pressure
difference acting on theses openings which are of similar magnitudes acting in opposite
directions. The relative position of the two gradients i.e. inside and outside pressure
gradients adjusts themselves to a level where the pressure difference across the two
openings is the same. This level – or the height at which this gradient intersect is the
neutral pressure plane level which is generally at the midway between the two heights
(Fig 10) (Irving, Ford and Etheridge January,2007).
The air flow and pressure differential is illustrated further in Figure 9 and 10. As
discussed earlier from the Ideal Gas Law equation pressure is proportional to the air
density. If the air is at a uniform temperature, the density is constant and then the gradient
is a straight line (this is the case shown in Figure – 9).
7
If temperature varies, which may
now change with height depending on the thermal state of the shaft, then the slope of the
pressure gradient will also vary with height and become a curved line as seen in Figure 9
and 10.

7
Hydrostatics requires the pressure at a point decreases with height, the rate of decrease being proportional
to the density of fluid. This is shown in Figure 9.(Irving, Ford and Etheridge January,2007). Because the
outside air is colder, it is denser and therefore the pressure decreases with height more rapidly outside the
building(Blue Line) than inside (the red Line)
31

Fig 9: Pressure gradients across a fixed height – for different air temperature
8
.

Fig 10: Resultant pressure gradients across the shaft height for different air
temperatures and the induced air flow
9
.

8
(Irving, Ford and Etheridge January,2007)
9
(Irving, Ford and Etheridge January,2007)
32

3.2.1: PRESSURE
Thus pressure induced across the height of the shaft is calculated using:
................ Equation 5

Where,
ρ
o
= Density of outside air in kg/m
3

T
o
= Temperature of outside air in K
T
i
= Temperature of inside air in K
H
2
= Height of top opening
H
1
= Height of bottom opening
ΔP = Buoyancy Pressure at H2 in Pa.

3.2.2.: AIR FLOW due to BUOYANCY PRESSURE
The equation to calculate the volumetric air flow across the opening will be –
.............. Equation 6

Where,
Q = Volumetric air flow in m
3
/s
T
o
= Temperature of outside air in K
A = Area of Opening in m
2

T
i
= Temperature of inside air in K
Δh = Height Difference in m
C
d
= Discharge coefficient
g = Gravitational acceleration in m/s
2

33

Based on the governing equations mentioned above – building components which
influence air flow and pressure differentials due to buoyancy effects are:

Height of Building Openings & Area of Building openings
Area of opening, opening heights, shaft outlet size and ventilation shaft heights are
building design components examined further to investigate their extent influence on air
flow.

3.3: WIND INDUCED AIR FLOW
Wind driven ventilation is caused by similar physical relationships as buoyancy driven
ventilation, except that the pressures are a result of varying surface pressures acting
across the building envelope rather than differences in hydrostatic pressure (Irving, Ford
and Etheridge January,2007). Generally building surfaces facing wind directly
experience positive wind pressure and the leeward side experiencing no direct wind
experience negative pressure – Figure 11. This suction force, forces wind across building
openings causing cross ventilation.
The velocity pressures of the wind increase as the square of wind speed and so the wind
pressures on high-rise buildings can be very large during periods of high speed wind
(Irving, Ford and Etheridge January,2007).
10

10
The surface pressure acting on the building is related to the velocity pressure of the wind by the wind
pressure coefficient (Section 3.5.1), which will vary from façade to façade, and will also vary across a face.
34

Wind induced pressure generally occurs across the width of the building thus the design
flow patterns are mostly horizontal. This means that the air entering and leaving the
building occur at the same vertical level negating the height variable which instead
creates hydrostatic pressure across the building height.

Fig 11: Schematic illustration of wind pressure distribution
11
in a single zone model.

11
(Irving, Ford and Etheridge January,2007)
35

3.3.1: PRESSURE
Pressure difference across a building is now a function of area of opening and wind speed
which can be expressed as:
.................................................................. Equation 7
Where,
ΔP = Wind induced pressure in Pa C
p
= Coefficient of pressure
ρ=Air Density in kg/m
3
V
r
= Wind velocity in m/s
2

3.3.2: AIR FLOW due to WIND PRESSURE
The volumetric air flow across the opening due to this pressure difference is expressed
as:
............................................................................. Equation 8
Where,
Q = Volumetric air flow in m
3
/s
C
p
= Coefficient of wind pressure
ρ=Air Density in kg/m
3

A = Area of opening in m
2

ΔP = Pressure Difference in Pa
Based on the governing equations mentioned above – building components which
influence air flow and pressure differentials due to buoyancy effects are:

Area of openings & Overall Zone height
36

Areas of opening and zone heights are building design components are examined further
to investigate their influence extent on air flow.

3.4.: COMBINED (wind + buoyancy effects) INDUCED AIR
FLOW
The above discussion provides an ideal presentation of the mechanisms driving stack
induced and wind induced natural ventilation. In reality these effects never occur in
isolation. It must be noted that most of the time there will be significant wind speeds and
also temperature differences inducing a combined stack and wind induced ventilation.
Therefore it is important to understand that natural ventilation is generally a combined
effect of wind and stack – Figure 12. Rarely do these two different mechanisms occur in
isolation for a given location. Therefore if a specific design may be concentrating only at
s single type of mechanism, the effects of the other should not be ignored.

Having mentioned the combined effect of two types of mechanisms the resultant
pressure difference is thus a combined sum.
.............................................................. Equation 9

37

Where,
ΔP = Overall pressure difference in Pa
ΔP
w
= Wind induced pressure in Pa
ΔP
s
= Stack induced pressure in Pa

It should be noted that the overall flow rates cannot be determined by calculating the
flow due to each mechanism separately, then adding the results together. This is because
the flow through a typical ventilation opening is non-linear, and so it is the pressures that
must be added and then the combined pressures used in the flow equation (Irving, Ford
and Etheridge January,2007).

Fig 12: Combining Buoyancy and wind pressures
12
for air flow in a Shaft.

12
(Irving, Ford and Etheridge January,2007)
38

3.5: DIMENSIONLESS COEFFICIENTS
One difficulty when attempting to analyze fluid flow phenomena in buildings is that
there are geometrical and physical barriers to air movement that create turbulent air flow.
Therefore to account for turbulent flows simple equations derived using assumptions of
laminar flow require a number of corrections. The relevant coefficients for the
calculations used in this thesis are:
•
Pressure coefficient - C
p
•
Coefficient of discharge - C
d
•
Wind reduction coefficient - C
v

3.5. 1: PRESSURE COEFFICIENT: C
p

The turbulent flow pattern when, air enters an opening, affects the pressure differential
between immediate interior and exterior of the opening. This pressure difference creates
necessary air flow, however the wind angle at which wind strikes the opening and the
opening conditions relate to a decrease or increase in the static pressure which cannot be
accounted for precisely. This is due to the vast range of building and wind angle
conditions. To account for this effect a coefficient is introduced into the calculations
derived through wind tunnel measurements. The coefficient takes into account the
changes in the wind angle in case of turbulent flow with respect to the building surface
description at which it strikes.

39

There is no rule of thumb values associated with wind pressure coefficient as they
depend on building surface and wind angle conditions. The Cp values for various wind
angles are tabulated in Appendix C.

3.5.2: DISCHARGE COEFFICIENT: C
d

Wind induced static pressure changes when entering through a building opening. This
static pressure is generally more than the dynamic pressure and the pressure due to height
of free unobstructed wind. The pressure difference is due the Venturi effect observed at
the openings. The depth and area of openings determine the range of this pressure
difference. To account for this pressure difference a coefficient derived through extensive
mathematical calculations is introduced in pressure differential calculations. The scale
varies from 0.60 to 0.70 depending on the size of the opening. Generally for all
calculation purposes the typical rule of thumb value of 0.65 is taken as discharge
coefficient.

3.5.3: WIND SPEED REDUCTION
Wind speed is calculated from measured wind velocities recorded at meteorological
stations. These station sites are open sites (like airports), having almost no direct
obstruction to prevailing wind, and recorded at a fixed height of 10m above the ground
level. Wind speed is adjusted in two ways: a height correction is made and a correction is
made to account for the topography of the location and the roughness of the terrain.
40

............................................................... Equation 10

Where,
V = Local wind speed at building height. ............ K
s
& a = Constant dependent on terrain.
Z = Building height in m ............................................. Vm = Wind Speed recorded at 10m

TERRAIN COEFFICIENTS K
s
a
Open flat country 0.68 0.17
Country with scattered windbreaks 0.52 0.20
Urban 0.35 0.25
City 0.21 0.33

Table 1: Values of constant – ‘K
s
’ & ‘a’ for calculating wind reduction coefficient.

41

3.6: PREDICTION METHODS
Designers and engineers employ different techniques to visualize and predict ventilation
flow in spaces. All prediction techniques are governed by principles of fluid flow and the
law of conservation of mass discussed earlier. Recent advances in both mathematical
modeling and experimental techniques have resulted in a considerable improvement in
understanding air infiltration. As a result of these advancements various methods have
developed which aid the designer in predicting air flow paths. These methods depend on
time, level of detail in measurement and infrastructure availability.
To calculate the air flow rates and pressure differentials for this study a comparative
method using the numerical technique prescribed in the Air Infiltration and Calculation
techniques – An application guide: June 1986 by the Air Infiltration and Ventilation
Centre (AIVC) and the computation technique using Multi zone airflow and contaminant
Transport analysis (CONTAM) software by National Institute of Standards and
Technology (NIST) is performed.

3.6.1: NUMERICAL METHOD
Mathematical techniques provide an inexpensive and rapid method for quick analysis of
different design options. By using this method a designer can analyze an infinite variety
of ventilation design options quickly before narrowing down to his final approach. This
method saves time and labor which makes it an extremely efficient technique.

42

Care should be taken in assuming the type of zone models constructed before applying
the equations to derive the desired results.

• SINGLE ZONE: A single zone is a single cell building in which the interior air
mass is assumed to be well mixed and the zone is at a single uniform pressure.
Generally dwellings and open flow plan conform to single zone types. Whenever
possible it is preferable to use single zone approximation because it simplifies the
calculation.

• MULTI ZONE: Multi-zone spaces are characterized by apartment buildings and
multi cell commercial floor plans where every zone behaves different then the
neighboring zone. Calculations for these are complicated because the number of
variables attached with these types of zone modeling is more than for single zone.

A number of calculation methods are available based on different regression techniques.
The governing principles for all these types are similar. A table of different forms of
equations is tabulated below.

43

AIVC
13

ASHRAE method
14

The Aynsley
Method
15

Table 2: Selected equations to calculate volumetric air flow due to wind effects.

Hakim Awbi –
Yuguo Li method
16

Steven Szokolay
method
17

AIVC
18

Table 3: Selected equations to calculate volumetric air flow due to buoyancy effects.

13
(Liddament June,1986)
14
(Awbi 2008)
15
(Awbi 2008)
16
(Awbi 2008)(Wang and Li 2010)
17
(Szokolay 2004)
18
(Liddament June,1986)
44

3.6.1.2 : NUMERICAL TECHNIQUE – AIVC ventilation guide.
Numerical method to calculate pressure and air flow rates prescribed in the Air
Infiltration and Calculation techniques – An application guide: June 1986 by the Air
infiltration and Ventilation Centre is adopted in this study.
Among the many numeric methods recognized in the industry this study performed
calculations only using some of the methods which are tabulated further in Table 4 & 5.
The values calculated from these different numerical methods were compared with values
derived from CONTAM.

3.6.2: COMPUTATIONAL TECHNIQUE – CONTAM
19

CONTAM is a multi-zone indoor air quality and ventilation analysis computer program /
software developed at the National Institute of Standards and Technology. This program
is designed to aid designers in determining primarily airflows, Contaminant
concentrations and personal exposure of occupants to contaminants.
The software is useful for a varied range of applications. Its ability to calculate building
airflows is useful to assess the adequacy of ventilation rates in a building, to determine
the variation in ventilation rates over time and the distribution of ventilation air within a
building, and to estimate the impact of envelope air tightening efforts on infiltration rates
(Walton and Dols December,2011). The indoor air quality of a building can be
determined by the prediction of contaminant concentrations through CONTAM.

19
Multi-zone indoor air quality and ventilation analysis computer program.
45

The predicted contaminant concentrations can then be used to estimate the personal
exposure based on occupancy patterns in habitable spaces. This program also assists in
investigating the impacts of various design decisions related to ventilation system design
and building material selection.
Other than these principle goals of the software, the program also combines special
features in the form of applications, which simulate building pressurization tests,
investigate smoke control systems and the design of building shafts. The special feature
of shaft computation is useful for this study, because of which also, CONTAM is the
preferred choice for computational software.
Similar to other infiltration models, based on empirical relationship between air flow and
pressure difference across openings, the governing power law relationship in CONTAM
for shafts is also:
............................................................................ Equation 11

Where,
Q = Volumetric flow rate in m
3
/s,
C = Flow coefficient - 3.10 for shaft.
ΔP = Pressure difference in Pa
n = Flow exponent

46

3.7: COMPARATIVE ANALYSIS BETWEEN NUMERICAL
TECHNIQUE (AIVC) & COMPUTATIONAL TECHNIQUE
(CONTAM):
Two separate comparative analyses were conducted to verify and validate the results by
the two different prediction methods.

• ANALYSIS A: This calculation was to compare the results of airflow derived by
the various numerical techniques to the results of air flow derived from
CONTAM using a single zone model having two openings on opposite sides.
These comparisons were conducted under similar boundary and physical
conditions. The percentage differences between values are tabulated below.

• ANALYSIS B: This analysis is performed to check the range of difference in
results of pressure and air flow - derived from CONTAM and numerical
calculations using equations prescribed in AIVC guide (Liddament June,1986).

3.7.1: ANALYSIS A
This analysis compared values of pressure and air flow induced by buoyancy effects in a
single zone derived from the under mentioned numerical equations and CONTAM. All
calculations were conducted under similar boundary conditions.

47

AIVC(Liddament June,1986)

Steven Srokolay method(Szokolay
2004)
Hakim Awbi – Yuguo Li method(Awbi
2008)(Wang and Li 2010)

Table 4: The different numerical equations to calculate pressure difference due to
buoyancy effects alone.

Similarly, different numerical methods to calculate Volumetric air flow:
Hakim Awbi – Yuguo Li
method / AIVC
20

Steven Srokolay
method(Szokolay 2004)

Table 5: The different numerical equations to calculate air flow rates due to
buoyancy effects alone effects.

All calculations were conducted under the following boundary conditions assuming a
temperature difference of 3
0
C (ASHRAE/ANSI.55 2004)

20
(Liddament June,1986)(Awbi 2008)
48

• SINGLE ZONE MODEL

Fig 13: Single zone model for calculating the pressure and air flow under buoyancy
effects.

• CONDITIONS FOR CALCULATIONS:
Conditions Units
Zone Height m 4
External Temperature
0
C 25
Assumed Internal Temperature
0
C 28
Height difference between openings Δh 2.5
Zone Area m
2
50
Area of Inlet – A1 m
2
0.7
Area of Outlet – A2 m
2
0.4
Discharge Coefficient C
d
0.61

Table 6: Conditions when calculating air flow in a single zone.
49

• ANALYSIS:
The difference in pressure difference results are:
Pressure difference in kg/m
Percentage difference
in values
CONTAM(Walton and Dols December,2011) 0.78238 -
AIVC Guide (Liddament June,1986) 0.78219 0.14 %
Steven Srokolay Method(Szokolay 2004) 0.78538 0.26 %
Hakim Awbi- Yuguo Li method(Awbi 2008) 0.78585 0.33 %

Table 7: Result of pressure differential (Pa) across the two openings of the single
zone.
Similarly the differences in Volume flow results are:
Volumetric air flow rate – m
3
/s
Percentage difference
in values
CONTAM(Walton and Dols December,2011) 0.285 -
Hakim Awbi – Yuguo Li method / AIVC(Awbi
2008)(Liddament June,1986)
0.27859 2.25 %
Steven Srokolay method(Szokolay 2004) 0.29314 2.78 %

Table 8: Result of air flow rates (m
3
/s) in the single zone.
Results of Table 6& 7 above –display that air flow and pressure values derived using the
numerical technique published in the AIVC guide fall closest to the values of CONTAM.
It also highlights the variation in estimating ventilation rates by using different numerical
methods. All these methods are based on the power law relation of mass flow (Equation
11). The difference in results thus arises because of variation in the coefficients values
used by the different method to estimate air flow and pressure values.
50

3.7.2: ANALYSIS B
Further analyses were conducted to determine the extent of difference in results which
were derived by the two different prediction methods. To determine the difference, the
values of pressure differences due to buoyancy effect only, across two openings for 5
different single cell volumes are compared. The results and differences in pressure values
derived by the two methods on the 5 different single zone volumes are tabulated below:

• SINGLE ZONE MODEL

Fig 14: Single zone model for calculating the pressure differences by the two
techniques.
51

• CONDITIONS FOR CALCULATIONS:
Conditions Units
Zone Height m 4, 5, 6, 7 & 8
External Temperature
o
C 25
Assumed Internal Temperature
o
C 28
Height difference between openings Δh varies
Zone Area m
2
50
Area of Inlet – A1 m
2
0.70
Area of Outlet – A2 m
2
0.40

Table 9: Conditions to calculating the pressure difference in a single model so as to
compare results from the two methods of AIVC and CONTAM.
• RESULTS:
Zone Height – m
Opening -
Height
Pressure
difference (Pa)
from AIVC –
numerical
Pressure
difference (Pa)
from CONTAM
- Computational
Percentage
difference
in %
Z1 -4m
A1 – 1.5m -0.14 -0.15 4.89 %
A2 – 3.5m 0.44 0.48 7.74 %
Z2 – 5m
A1 – 1.5m -0.29 -0.30 4.87 %
A2 – 4.5m 0.59 0.64 8.10 %
Z3 – 6m
A1 – 1.5m -0.43 -0.46 6.20 %
A2 – 5.5m 0.73 0.79 7.54 %
Z4 – 7m
A1 – 1.5m -0.58 -0.61 5.33 %
A2 – 6.5m 0.88 0.96 8.14 %
Z5 – 8m
A1 -1.5m -0.72 -0.77 6.10 %
A2 – 7.5m 1.11 1.11 0.00 %
Table 10: Results of difference in pressure distribution values
52

• ANALYSIS:
Table 10 highlights minor percentage difference in the numeric results of pressure
differentials across the two openings when calculated using the two different prediction
techniques, which allows employing both the prediction techniques for further
calculations.

Fig 15: Results of pressure differentials (Pa) across the two openings using the
numerical (AIVC) and computational (CONTAM) technique.

53

3.8: VARIABLES IN ESTIMATION
Variables in predicting ventilation arise due to some basic uncontrollable processes and
behavior. These issues make designing ventilation systems only statistically reliable and
often beyond human control, some of which are:
• Uncertainty in simulation: The dimensionless coefficients represent a range of
values applicable for initial boundary condition of wind, opening size, building
heights etc.
• Stochastic behavior of weather: Possibly the greatest drawback of the natural
ventilation mechanism is its limited reliability. As wind is intermittent in nature
the dependent ventilation also becomes irregular in nature. Therefore relying only
on natural ventilation is often not a viable option.
• Occupant’s behavior: Elements like operable windows, location of work spaces
in building plan and occupant’s cyclic routine have a considerable influence in
the effectiveness of natural ventilation.
• Building component: Despite all care taken by designers in designing and sizing
building openings for air flow, air does not flow inside and outside a space only
through the predicted paths and openings. Air leakages through building
components, doors and uncertain construction play a role in air distribution inside
the space.

54

CHAPTER 4: ADAPTIVE THERMAL COMFORT BY NATURAL
VENTILATION.
This chapter describes and establishes how naturally induced air flow affects the
internal temperature and thermal comfort conditions in an occupant space.
.

55

4.1: EFFECTIVENESS of NATURALLY VENTILATED
SPACES
Naturally induced air flow is effective only when the induced air flow creates conditions
for thermal comfort. As discussed earlier in section 1.2. - Thermal comfort is that
condition of mind which expresses satisfaction with the thermal environment. Because
there are large variations, both physiologically and psychologically, from person to
person, it is difficult to satisfy everyone in a space. (ASHRAE/ANSI.55. 2007)(5.1)
Modifying the air movement around the human body can make considerable difference in
thermal comfort levels of the occupants (ASHRAE/ANSI.55. 2007). The direct effect of
natural ventilation on comfort conditions is to counter the indoor heat gains generated
largely from occupant’s body heat, artificial lighting and mechanical equipment such as
computers. By limiting and controlling the way air changes occur, internal air
temperature can be controlled leading to relative thermal comfort.(Liddament June,1986)

For achieving thermal conditions by natural conditioning mechanisms the internal
temperatures

should be maintained such that 80% to 90% of people should be
comfortable. The 80% acceptability limits are typical applications and are used when
specific information of final building heat gains, site conditions etc are not available
(ASHRAE/ANSI.55. 2007).

56

For this study, the benchmark for adaptive thermal comfort will be to reach 90%
acceptability
21
. This 90% acceptability levels are for adaptive thermal comfort conditions.
Adaptive thermal comfort introduces the notion that building occupants will tolerate a
wider range of internal temperatures conditions to changing internal environments.
Adjustments to achieve adaptive thermal comfort conditions can be made by change in
clothing, activity, posture, etc. of occupants so that they are comfortable in prevailing
conditions. This happens due to the natural body physiological behavior of developing
greater tolerance to wider range of thermal and humidity conditions.

This section further discusses how natural ventilation will assist in reaching thermal
comfort conditions. As discussed earlier air flow dissipates heat generated around
occupants which improves thermal comfort conditions. This thermal comfort condition is
achieved by maintaining the internal temperature achieved by natural air flow within the
operative temperatures
22
. The operative temperatures for 90% adaptive thermal comfort
conditions are prescribed in ASHRAE 55. 2007 and varies as per the location and climate
of the site. The internal temperature by natural air flow in this case depends mainly on the
internal heat gains of the occupant space and the air flow rate. Human comfort also
depends on the humidity levels of the space but this study does not consider humidity
levels. For this study the internal temperature is the dry bulb temperature.

21
Chapter 12 – discusses the 90% acceptable adaptive thermal comfort conditions achieved by two multi
zone models connected to a ventilation shaft located in the climate of Los Angeles. The limits for achieving
this adaptive thermal comfort conditions are described and explored in detail in Chapter 12.
22
The comfort zone is defined in terms of a range of operative temperatures that provide acceptable
thermal environmental conditions or in terms of the combinations of air temperature and mean radiant
temperature that people find thermally acceptable. (ASHRAE/ANSI.55. 2007)

57

An increased effective natural ventilation mechanism will therefore focus on increasing
air flow rates rather than accepting the minimum rate stipulated by ASHRAE/ANSI 62.1,
2007 (which is 0.45 liters/second
2
or 0.06 meter/second
2
) so that the internal heat
generated is dissipated at a faster rate. This study thus concentrates on maintaining
internal temperature in an occupant space within the operative temperatures of thermal
comfort by increasing naturally induced air flow while assuming constant internal heat
gains throughout. This increased air flow rate may also assist in maintaining indoor air
quality which will make comfort conditions achieved by natural ventilation more
effective
23
.

4.1.2: INTERNAL HEAT GAINS
Air flow across any occupant zone dissipates heat generated inside by building occupants
and building equipment. To evaluate the effectiveness of a natural ventilation mechanism
it’s necessary to consider the internal heat generated by building occupants and occupant
activities which is to be dissipated.
Dissipation of this internal heat brings about change in air temperature which is
investigated further. For this purpose the amount of heat generated by the building
occupant and building equipment is calculated using the following equation:
Q
total heat gain
= Q
occupant
+ Q
equipment
+Q
lighting ................... Equation 12

23
Indoor air quality refers to the quality of air inside and surrounding habitable space which is required to
be maintained within permissible limits of contaminant concentration and harmful gasses to maintain
occupant health and comfort. The benchmark criteria’s for indoor air quality for different building types are
mentioned in Appendix B.

58

Occupant heat 70 Watts per person
24

Lighting heat (Fluorescent) 12 W/m
2

Equipment heat 18 W/m
2

Total number of occupants 3
25

Floor area 50m
2

Heat gain (3 x 70) + (50 x 12) + (50 x 18)
Total heat gain 1710W (1.7 kW)

Table 11: Assumed heat gains for internal heat gain calculations.

Heat generated from Equipment and Lighting is taken from ASHRAE 62.1 – 2007.

4.2: EFFECT of AIRFLOW on INTERNAL TEMPERATURE
To show the influence of increased air flow on reducing internal temperature, a series of
incremental air flow rates was assumed in a single zone. The internal temperature as a
result of this assumed air flow was calculated to realize effectiveness of air flow rate. The
result of this calculation keeping internal heat gains constant at 1710W, for a given
external air temperature is illustrated in Figure 16.

24
Heat generated by building occupant change somewhat with internal temperatures. But for the purposes
of this study the occupant heat generation is taken as 70W per person(ASHRAE/ANSI.55. 2007)
25
As per ASHRAE 62.1 – the occupant density for a commercial building is - 5 persons per100m
2
.For
50m
2
the number of occupants is 3(ASHRAE/ANSI.62.1 2007).

59

It can be observed from results in Figure 16 that when internal heat gains and external air
temperature remain constant, an increased air flow rate can reduce the internal
temperature. An increased air flow reduces the internal temperature. A reduction in
internal temperature will also reduce the temperature difference between the external and
the internal air. This temperature difference is vital to be maintained within the maximum
limit of 3.0
0
C for naturally ventilated spaces to maintain adaptive thermal comfort
conditions (ASHRAE/ANSI.55. 2007).

Fig 16: Change in internal temperature for different air flow rates.

Additionally, the internal temperature does not reduce much at higher air flow rates.
At higher air flow rates the heat gain is now dissipated at a higher rate but the influence
of sensible temperature by the heat gains on internal temperature remains unchanged,
which therefore results in marginal difference on the internal temperature.

60

Therefore by increasing or maintaining air flow rates in a space having constant internal
heat gains and external air temperature, the internal temperature can be reduced and
further maintained within the operative temperatures. Also an increase in air flow rates
reduces the temperature difference between internal and external air temperature
26
.

4.2.1: INTERNAL TEMPERATURE OF NATURALLY CONDITIONED
SPACES
The internal air temperature as a result of naturally induced air flow is calculated
considering the internal heat gains and the external air temperature. To calculate this, the
following equation is used:
................................................ Equation 13
Where,
Qi = Internal heat in W/m
2

C
p
= Specific heat capacity of air at room temperature in kJ/kg.
0
K
Q= Volumetric Air flow rate in zone in m
3
/s calculated assuming ΔT = 3
0
K
ρ = Air Density in kg/m
3

ΔT = Temperature difference in
0
K
In which:
C
p
= 1.0005 kJ / kg.
0
K .................................................................................... ρ = 1.2 kg/m
3

26
For naturally cooled spaces the temperature difference is required to be maintained within 3.0
0
C beyond
which naturally cooled or heated spaces render ineffective for thermal comfort.(ASHRAE/ANSI.62.1
2007)

61

This ΔT is the difference between external air temperature and the internal air
temperature. By assuming a temperature difference of 3.0
o
C (ASHRAE/ANSI.62.1
2007) between external and internal air temperature the value of air flow rates can be
deduced. Based on this result of air flow rate the actual internal temperature of the zone,
depending on the internal heat gains, can be derived using the equation mentioned above.

4.3: THE EFFECT OF EXTERNAL AIR TEMPERATURE ON
AIR FLOW AND INTERNAL TEMPERATURE.
Adaptive thermal comfort conditions are achieved if the internal temperature lies within
the operative temperatures of the occupant zone. As thermal comfort conditions rely on
external temperatures and internal heat gains as discussed earlier the calculations in this
section explore the influence of different external temperature conditions on air flow
while maintaining internal heat gain constant. The intent of this series is to check the
extent of influence of varying external temperature on air flow.
This situation is when the external air temperature increases as the day progresses and
also to highlight the dependency of external air temperature on airflow.

62

Prevailing external air temperature is a naturally occurring parameter beyond the
designer’s control, which can have drastic influence on thermal comfort conditions
achieved by natural air flow.
The results of air flow will change when opening area and opening height changes. Thus
for this series the opening size and opening heights are kept constant throughout. This
assures that any change in air flow will be a result of varying external air temperature
conditions. The internal heat gains are also kept constant at 1710 W for this calculation.
The study examines change in air flow rates for increase in external temperature -T
o
, and
assuming an internal temperature 3
0
C higher than the external air temperature. The
temperature difference is maintained at 3.0
0
C within the 3.0
0
C
limit.(ASHRAE/ANSI.55. 2007).For the purposes of this series we construct a single
zone model having openings on two opposite façades and at different heights.

Fig 17: Single zone model calculated under different temperature conditions.

63

• CONDITIONS FOR CALCULATIONS:
Design Constants Natural Constants Variable conditions
Zone floor area Temperature difference External Temperature
Opening areas 3.0
0
C Internal temperature
Opening heights

Table 12: Conditions to calculate the air flow by changing temperature conditions.

• RESULTS
Openings
External
Temp.
o
C
Assumed
Internal
Temp in
Zone. -
o
C
Volumetric
air flow -
m
3
/s
Actual
Internal
Temperatur
e in Zone
27
-
o
C
Kept
constant
throughout
Inlet Outlet

Height -m 1 3.5 17 20 0.308 22
Area - m
2
1 1 18 21 0.306 23
19 22 0.305 24
Internal heat gain 1710W 20 23 0.303 25
21 24 0.302 26
Zone height 4m 22 25 0.300 27
23 26 0.299 28

Table 13: Results of Air flow rate in a single zone when external air temperature
increases.

27
This is calculated using the internal heat gain equation. Equation 13 – Section 4.2.1.

64

Fig 18: Decrease in air flow rates when external air temperature increases.

• ANALYSIS:
Results from above calculations of air flow with temperature highlight that with increase
in external temperature the air flow rates decrease marginally provided the temperature
difference and internal heat gains are maintained constant throughout – Figure 18. This
observation is when the opening heights and opening areas are kept constant.
Change in external temperature has marginal influence on air flow rate as long as the
temperature difference is maintained constant. Air flow rates remains almost constant for
higher external air temperature. Thus external air temperature has marginal influence on
air flow rates when the internal heat gain and the temperature difference are kept constant
throughout. Based on this conclusion all the further calculations in this study assume
constant temperature difference of 3.0
0
C and constant internal heat gain.

65

Results of actual internal temperature in Table 13 highlight that, keeping constant internal
heat gains can assist in maintaining constant temperature difference between external air
temperature and the internal air temperature
28
. A regular change in internal temperature
due to varying air flow rates changes the temperature difference between internal air
temperature and external air temperature regularly. If this temperature difference exceeds
the 3.0
0
C limit for naturally cooled spaces, natural ventilation renders in effective to
provide thermal comfort (ASHRAE/ANSI.62.1 2007).

4.4: THE EFFECT OF WIND ON AIR FLOW AND
INTERNAL TEMPERATURE.
Prevailing wind speed and wind angle effect pressure which changes air flow rates
(Section 3.3). This wind speed and wind angle may have its influence on the internal
temperature and thus on the thermal comfort conditions. Calculations are conducted to
investigate this influence of varying wind speeds and wind angles on air flow and its
corresponding influence on internal temperature.
The results of air flow will change when opening area and opening heights change. Thus
for this series of calculations the opening size and openings heights are kept constant
throughout. This assures that any change in air flow will be a result of varying wind
conditions.

28
In this case the temperature differences are not within the 3.0
0
C limit for thermal comfort conditions in
naturally cooled space but the temperature difference for different external air temperature and internal air
temperature is constant throughout.

66

Fig 19: Single zone model having different wind speed and angle in the same
horizontal plane.

• CONDITIONS FOR CALCULATIONS:
Design Constant Variable conditions
Zone floor area and height Different wind angles
Opening areas 0
o
and 45
o

Opening heights Wind speed

Table 14: Conditions for calculating change in air flow rates when wind speed and
angle is altered.

67

• RESULTS
Openings Wind Angle - 0
KEPT
CONSTANT
Inlet - A1
Outlet -
A2
Wind
Speed -
m/s
Volumetric
air flow -
m
3
/s
Internal
Temperature
29

-
0
C
Area - m2 1 1
Heights - m 1 3.5 1.0 0.14 29.9
2.0 0.29 24.9
Zone height 4m 3.0 0.43 23.3
External Air temperature 20
0
C 4.0 0.57 22.5
Internal Heat gain 1710 W 5.0 0.71 22.0
6.0 0.86 21.6
7.0 1.00 21.4
8.0 1.14 21.2
9.0 1.29 21.1
10.0 1.43 21.0

Openings Wind Angle - 45
KEPT
CONSTANT
Inlet -
A1
Outlet -
A2
Wind
Speed -
m/s
Volumetric
air flow -
m
3
/s
Internal
Temperature
-
0
C
Area - m2 1 1
Heights - m 1 3.5 1.0 0.13 31.2
2.0 0.25 25.6
Zone height 4m 3.0 0.38 23.7
External Air temperature 20
0
C 4.0 0.50 22.8
Internal Heat gain 1710 W 5.0 0.63 22.2
6.0 0.76 21.9
7.0 0.88 21.6
8.0 1.01 21.4
9.0 1.13 21.2
10.0 1.26 21.1

Table 15: Results for change in air flow rates when wind angle is altered.

29
This is calculated using the internal heat gain equation. Equation 13 – Section 4.2.1.

68

• ANALYSIS:
Air flow rates increase with increase in wind speeds. Winds perpendicular to the opening
exert greater pressure than wind at an angle. Therefore the increase in air flow rates is
gradual for winds at a lower angle then the steady and greater increase in air flow rates
for winds flowing directly perpendicular on the building façade. - Figure 20. However the
difference in air flow rate for the two different wind angles is not high. This minor
difference of wind angle on air flow does not make any difference on internal
temperature as seen in Figure 21.

Fig20: Air flow rates for varying wind speed and different wind angle

69

Higher wind speeds reduce the internal air temperatures – Table 15. With higher wind
speeds the internal temperatures can be kept closer to operative temperatures of thermal
comfort which may increase the period of adaptive thermal comfort conditions -Figure
21. The influence of varying wind angle on air flow is however relatively low when
compared to the influence of wind speed on air flow.

Fig21: Internal temperature for varying wind speeds and different wind angles.

70

Based on the above calculations, conclusions on impact of natural parameters of wind
speed, wind angle and external temperature can be made. These conclusion are based
assuming constant internal heat gains (1710 W) and a constant external and internal air
temperature difference of 3.0
0
C.

The natural parameter of wind speed has a high impact on air flow. This influence on air
flow has a corresponding effect on the internal temperatures which may affect thermal
comfort conditions. Air flow rates change marginally when the wind angles are changed
from 0
0
to 45
0
. This marginal change does have not make substantial difference on
internal temperature as seen from the results in table 15, whereas wind speed makes a
greater difference on internal temperature. Thus wind speed has a higher impact on
thermal comfort than wind angle.

Other natural parameter of varying External air temperature has marginal effect on air
flow unlike wind speed. This marginal influence on air flow is extremely low to have any
effect on internal temperature conditions.

Having explored the influence of natural parameters on natural ventilation in this section,
the following sections now concentrate on examining and investigating the influence of
various building component on air flow.

71

CHAPTER 5: CALCULATION PROCEDURE AND
METHODOLOGY.
This chapter introduces the conditions for all the calculations along with the procedure
used for the ventilation studies on various building components.
.

72

5.1: METHODOLOGY
Previous chapters describe fundamental parameters and building components that
influence air flow under both the regimes of buoyancy and wind pressure. Further it
explores how temperature and wind influence air flow and its effect on thermal comfort
conditions. This study now investigates the extent of influence building components have
on air flow. By doing so typical relationships between different ventilation parameters
can be established which help deduce inferences that aid in prescribing different design
methods to enhance air flow rates. This chapter details the framework and approach
methods adopted in this study in order to achieve desired goals.

The rationale of design for the final model comes from these series of calculations based
on buoyancy and wind driven air flow, performed on various building components. The
building components which influence air flow are tabulated below in Table 16-.These
components are investigated for their influence using four different model types.

73

BUOYANCY WIND
Opening Size Opening Size
Opening Heights Zone Height
Ventilation shaft height Ventilation shaft outlet Size
Ventilation shaft outlet Size

Table 16: Building components influencing air flow.

Fig 22: Methodology to estimate the range of influence of building components on
ventilation

74

5.2: TECHNIQUE for CALCULATING AIR FLOW
To investigate the relationship and influence of building components on ventilation, each
parameter was investigated individually by varying their design under fixed climate
conditions. Four different models are constructed for this purpose and are described
further. Results and values of volumetric air flow rates and pressure difference are
derived from the computational technique using CONTAM (Walton and Dols
December,2011).

5.2.1: CONDITIONS FOR CALCULATIONS
The fixed and varying parameters for these calculations (depending on the type of
ventilation mechanism under investigation) are mentioned below:
PARAMETERS BUOYANCY WIND
1 Wind speed Vary 0 m/s 2 , 3 ,5 , 10 m/s
2 Wind angles Vary 0
0
0
0
& 45
0

3 Height of shaft outlet Vary 0.5 m from shaft top 0.5 m from shaft top
4 Air density Fixed 1.2 kg / m
3
1.2 kg / m
3

5
Assumed Internal
temperature
Vary Varies 20
0
C
6 Outside temperature Vary
Varies keeping ΔT –
3
0
C
20
0
C
7 Discharge coefficient Fixed 0.61 0.61
8 Zone floor area Fixed 50 m
2
50 m
2

Table 17: Initial - Primary Conditions for calculations.

75

5.3: STUDY MODEL
As ventilation shafts assist in inducing air flow by primarily relying on buoyancy effects
the three models are designed such that they can always rely on buoyancy induced
pressure to provide air flow. This is done by creating height differences between the
inlets and outlets as buoyancy depends on height.

5.3.1: MODEL A: SINGLE ZONE – SINGLE SIDED
Inlets placed only on one façade at different heights.
This model represents an occupant space having equal opening sizes.

Fig 23: Model A represented by a Single zone – Single Sided Ventilation type.

76

5.3.2: MODEL B: SNGLE ZONE – CROSS VENTILATION
Inlets placed on opposite facades at different heights.
This model represents an occupant space having equal opening sizes on opposite facades.
By having opening at two opposite facades this model can benefit from cross ventilation
induced by prevailing winds.

Fig 24: Model B represented by a Single zone – Cross Ventilation type.

77

5.3.3: MODEL C: SINGLE ZONE + VENTILATION SHAFT
Third case of a tower added to the room with openings on opposite facades.
This model represents an occupant space having equal opening sizes on opposite facades.
A height difference is between the openings in the zone and the outlet on the shaft. The
two openings of the occupant zone are at the same height. This helps to identify the
influence a ventilation shaft can make in creating pressure differentials across the
opening, which may aid to induce air flow in the occupant spaces.

Fig 25: Model C represented by a Single zone attached to a ventilation shaft.

78

5.3.4: MODEL D: MULTI ZONE + VERTICAL SHAFT
This model is developed in order to study air flow rates and air flow patterns as a
function of shaft height (varying the neutral pressure planes levels). This model closely
represents the final study model – a 3 story commercial building with a ventilation shaft.

Fig 26: Schematic representation of a Model D - Multi zone model

79

5.4: GENERAL ASSUMPTIONS FOR MODEL ANALYSIS

All calculations, irrespective of the prediction method employed, were conducted based
on the following assumptions:

• Internal Temperature – This assumes that for all type of zones – single and
multi – the assumed internal temperature is uniform across the zone height and
the zone width. Also the shaft and occupant zones are at the same temperature.

• Temperature difference:
As discussed earlier in Section 3.5.1 - Natural ventilation can cool the occupant
space by removing internal heat gains providing a cooling effect in the space.
While doing this the internal temperature also changes. Varying air flow rates
will vary the internal temperature but the temperature difference between
external and internal temperature should be limited to a maximum of 3.0
0
C in a
span of 4 hours for naturally ventilated spaces to maintain adaptive thermal
comfort conditions (ASHRAE/ANSI.55. 2007).For this study, except where
mentioned otherwise, the inside to outside air temperature difference is assumed
to be 3.0
0
C. This difference of 3.0
0
C is within the 3.0
0
C limit for temperature
difference prescribed in the ASHRAE/ ANSI 55, 2007.

80

• Conservation of mass – As the study is dealing with only steady state
simulations, the mass of air in each zone is conserved. Thus, the mass of air
entering the zone will be equal to the mass of air leaving the building.

• Building Material and air leakages - All the zones under study are assumed to
have impermeable building partitions. No thermal or air loss is experienced as a
result of material or construction flaws.

• Solar Radiation - Solar radiation effects on the shaft’s external façade is not
accounted for in this study. This simplifies the calculations maintaining uniform
internal temperature in the zone and shaft respectively, for the multi zone models.

• Zone Openings - Air inlet and outlet openings are treated purely as punctures in
zone surfaces. They are not treated as operable windows to avoid computational
complexity when dealing in CONTAM.

• Coefficients: Pressure coefficients for wind induced ventilation are taken as
prescribed in AIVC ventilation guide section 6.1 and also tabulated in appendix
D. For simplicity the discharge coefficient at openings for stack ventilation is
taken to be 0.61. This value is used for all types of openings.

81

• Wind direction and wind angle: For the purposes of this study the wind flow
direction is considered to be uni-directional. The wind angle is taken to 0
0
unless
specified otherwise and the terrain coefficients for the wind reduction coefficient
are taken that of an urban terrain.

• Air flow pattern and openings: For all conditions and model types the air flow
patterns will be visualized only through the vertical section of the building. Air
flows from inlets and flows out from outlets placed on opposite ends of the zone.
No openings are placed on adjacent walls.

• Design of Single Zones: All the single zones are rectangular in plan. The shorter
side of the rectangular plan is connected to the ventilation shaft and has one
opening located on its each short façade. No openings are located on the longer
side of the rectangular floor plan.

• Location and design of shaft: For all the series of investigations the ventilation
shafts are attached to the shorter side of the rectangular floor plan of single and
multi zone models. Also, the openings of the ventilation shafts are along the
shorter facade of the rectangular floor plan of the single zone and only one shaft
outlets s located along on the ventilation shaft wall. The height and area of the
shaft is assumed according to the intent of the investigation undertaken, rational
of which is discussed in the relevant section.

82

CHAPTER 6: AIR FLOW IN MODEL A – SINGLE SIDED.
This chapter reports the results and inferences of air flow calculations conducted on
single zone –Single sided model for Buoyancy and wind induced air flow.

83

Based on the framework established in chapter 5 the results of buoyancy driven
ventilation are reported below followed by wind induced ventilation studies on a single
sided ventilated model.
The series of investigations are reported in the following order:
• Conditions for calculation.
• Results
• Analysis.
The result tables are:
1 2 3 4 5
Design
constant in
Calculation
Variables in
Calculations
Volumetric Air
flow rates in
m
3
/s
Air
Velocity
in m/s
Internal temperature as
a result of air flow
rates.

Table 18: Division of the results table.
Column five of effective internal temperature calculation
30
for analysis is performed only
for buoyancy studies. This column is provided as a reference and estimation of change in
temperature as a result of the induced air flow keeping internal heat gain constant at
1710W. This gives the reader an estimation of effect air flow has on thermal comfort. All
calculations of internal temperature are conducted considering equation mentioned in
section 4.3.

30
This is calculated using the internal heat gain equation. Equation 13 – Section 4.2.1.

84

6.1: BUOYANCY INDUCED VENTILATION STUDIES:
This section reports the results of buoyancy calculations.

6.1.1: INFLUENCE OF ZONE HEIGHT
This case is to determine influence of zone heights on air flow rates.

Fig 27: Single zone (single sided model) with varying heights.
• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Zone Heights External temperatures
Opening heights 4, 5, ,6, 7, 8,10, 20 Assumed Internal
Temperatures Opening areas

Table 19: Conditions for calculating air flow by changing overall zone heights.

85

• RESULTS:
OPTION 1

Zone
height
s - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Internal
temp. -
o
C
Openings 4 0.303 0.0152 21.65
Inlet Outlet 5 0.303 0.0121 21.65
Area - m
2
1 1 6 0.303 0.0101 21.65
Height - m 1 3.5 7 0.303 0.0087 21.65
Assumed Zone
Temperature
20
0
C

8 0.303 0.0076 21.65
External Temperature 17
0
C 10 0.303 0.0061 21.65
Internal heat
gain
35
W/m
2

1710W

12 0.303 0.0051 21.65

Table 20: Results of air flow when external temperature is kept at 17
0
C.
The air flow rate remains constant with change in zone heights. Similar calculations for
higher external temperature were conducted.

OPTION 2

Zone
height
s - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Internal
temp.-
o
C
Openings 4 0.300 0.0150 26.70
Inlet Outlet 5 0.300 0.0120 26.70
Area - m2 1 1 6 0.300 0.0100 26.70
Height - m 1 3.5 7 0.300 0.0086 26.70
Assumed Zone
Temperature
25
0
C

8 0.300 0.0075 26.70
External Temperature 22
0
C 10 0.300 0.0060 26.70
Internal heat
gain
35
W/m
2

1710W

12 0.300 0.0050 26.70

Table 21: Results of air flow when external temperature is kept at 22
0
C.

86

Fig 28: Air flow rates in zones having varying zone heights (single sided model) at
different temperatures.
• ANALYSIS:
The air flows across the zone having varying zone heights remains constant. This is
because the opening size and opening heights, which regulate total amount of air entering
and leaving, remains constant. Thus the volume of air entering and leaving the space will
remain the same. Air velocity inside the singe zones change as the height of the zone
changes. With increase in zone height the air velocity decrease. Thus for buoyancy driven
air flow, varying zone heights while keeping opening area and opening height constant in
a single sided zone design will not have any impact on air flow rates. The marginal
difference in airflow between eh two options is a results of varying external air
temperature.

87

6.1.2: INFLUENCE OF OPENING HEIGHTS
This is to study the influence of different opening heights on air flow. For these series of
calculations the overall zone height are opening areas of the zone are kept constant.

Fig 29: Single zone (single sided model) with varying opening heights (m).

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet heights External temperature 20
0
C
Internal heat gain Outlet heights Internal Temperature 23
0
C
Opening area Zone height – 4m & 6m

Table 22: Conditions for calculating buoyancy driven air flow by changing opening
heights.

88

• RESULTS:
Openings Areas

Opening
Heights -
m
Volume
tric air
flow -
m
3
/s
Air
velocity -
m/s
Internal
tempera
ture -
0
C Inlet - A1
Outlet -
A2
A1 A2
Area - m
2
1 1
0.5
2 0.23 0.012 26.0
2.5 0.27 0.014 25.2
Assumed Zone
Temperature
Ti 23
0
C

3 0.30 0.015 24.7
External
Temperature
To 20
0
C

3.5 0.33 0.017 24.2
Internal heat
gain
35 W/m
2
1710 W

1
2 0.19 0.010 27.3
Zone height 4m 2.5 0.24 0.012 26.0
3 0.27 0.014 25.2
3.5 0.30 0.015 24.7
1.5
2 0.14 0.007 30.4
2.5 0.19 0.010 27.3

3 0.24 0.012 26.0
3.5 0.27 0.014 25.2
2
2 0 0.000 -
2.5 0.14 0.007 30.4
3 0.19 0.010 27.3

3.5 0.24 0.012 26.0
Table 23: Results of air flow rates in a 4m single zone (single sided model) when
opening heights are changed.

Additional calculations were conducted for a zone height of 6m.

89

Table 24: Results of air flow rates in a 6m zone when opening heights (m) are
changed.
Inlet -
A1
Outlet -
A2
A1 A2
Area - m2 1 1 3 0.30 0.010 24.7
3.5 0.33 0.011 24.2
4 0.36 0.012 23.9
Assumed Zone Ti 23 C 4.5 0.38 0.013 23.7
External To 20 C 5 0.41 0.014 23.5
Internal heat gain 35 1710 W 5.5 0.43 0.014 23.3
6m 3 0.27 0.009 25.2
3.5 0.30 0.010 24.7
4 0.33 0.011 24.2
4.5 0.36 0.012 23.9
5 0.38 0.013 23.7
5.5 0.41 0.014 23.5
3 0.23 0.008 26.0
3.5 0.27 0.009 25.2
4 0.30 0.010 24.7
4.5 0.33 0.011 24.2
5 0.36 0.012 23.9
` 5.5 0.38 0.013 23.7
3 0.19 0.006 27.3
3.5 0.23 0.008 26.0
4 0.27 0.009 25.2
4.5 0.30 0.010 24.7
5 0.33 0.011 24.2
5.5 0.36 0.012 23.9
3 0.14 0.005 30.4
3.5 0.19 0.006 27.3
4 0.23 0.008 26.0
4.5 0.27 0.009 25.2
5 0.30 0.010 24.7
5.5 0.33 0.011 24.2
3 0.00 0.000 -
3.5 0.14 0.005 30.4
4 0.19 0.006 27.3
4.5 0.24 0.008 26.0
5 0.27 0.009 25.2
5.5 0.30 0.010 24.7
Internal
Temperature - C
Openings Opening Heights
Volumetric air
flow - m3/s
Air
velocity -
m/s
0.5
1
1.5
2
2.5
3
Zone height

90

Fig 30: Air flow rates for different opening heights (single sided model) 4m high.

Fig 31: Air flow rates for different opening heights (single sided model) 6m high.

91

• ANALYSIS:
Buoyancy driven air flow rates increase with increase in height difference between inlets
and outlets. This increase can be purely attributed to change in height difference as the
area of opening, overall zone height and temperature conditions for every change in
height difference is kept constant. By keeping the area of opening constant the volume
(mass) of air entering the space will also be constant. Increase in height difference
increases pressure differentials across the inlet and outlet. With increase in pressure the
air flow rates increase. Based on this study it can be inferred that air flow rates increase
with an increase in height difference between the openings. Thus to increase buoyancy
driven ventilation rates the height difference between the inlets and outlets should be
extended as much as possible.
No air flows across the space when the openings are at the same height. Air flow rates are
dependent of pressure. As discussed in earlier section 3.2 buoyancy effects depend on
height difference. Thus when there is no height difference between openings no pressure
is generated across the openings resulting in low or no air flow. However, this situation
of negligible air flow cannot be accounted only on height difference between openings.
The area of openings and the height of the actual opening frame can also induce pressure
difference along its height (Dols, Emmerich and Axley August,2001).

92

6.1.3: INFLUENCE OF OPENING SIZE.
Having understood the influence of zone heights and opening heights, this study
examines the influence of opening sizes on ventilation. As these openings control volume
of air flow in and out of the occupant zones, it can be vital to identify the best possible
opening configurations in order to refine the occupant zone opening design. For this
series the opening sizes were altered for a single zone volume. Different inlet sizes for
different outlet sizes were calculated and compared.

Fig 32: Single zone model (single sided model) with varying opening sizes.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet area External temperature – 20
0
C
Internal heat gain Outlet area Internal Temperature – 23
0
C
Opening heights Zone height – 4m & 7m

Table 25: Conditions for calculating buoyancy driven air flow in a zone by changing
opening areas.

93

• RESULTS:
The height difference between inlets and outlets are kept constant at2.5m.
Openings

Opening
Size in m
2

Volumetric
air flow -
m
3
/s
Air
velocit
y - m/s
Internal
temperat
ure -
0
C Inlet - A1
Outlet -
A2
A1 A2
Height
-m
1 3.5

1
1 0.30 0.015 24.7
Height difference ΔH 2.5 m 2 0.38 0.019 23.7
Assumed Zone
Temperature
23
0
C

3 0.41 0.020 23.5
External Temperature 20
0
C 4 0.42 0.021 23.4
Internal heat gain 1710 W
2
1 0.38 0.019 23.7
Zone height 4m 2 0.61 0.030 22.3
3 0.71 0.036 22.0
4 0.77 0.038 21.8
3
1 0.41 0.020 23.5
2 0.71 0.036 22.0
3 0.91 0.045 21.6
4 1.03 0.051 21.4
4
1 0.42 0.021 23.4
2 0.77 0.038 21.8
3 1.02 0.051 21.4
4 1.21 0.061 21.2

Table 26: Results of air flow rates by changing area of inlet to outlet in a single zone
(single sided model) 4m high keeping height difference at 2.5m.

94

• ANALYSIS
31
:

Fig 33: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (single sided model) - 4m high.

Plotting air flow rates as a function of varying outlet size for different inlet opening size
highlights that when the size of any of the openings increase the air flow rate also
increase. Further analysis of change in air flow, keeping inlet size constant for varying
outlet size and conversely keeping outlet size constant for varying inlet sizes are
performed - Figure 35.

31
Prior to analyzing the influence of opening it is vital to identify the zone and opening settings. For all
these calculations the outlet opening is kept higher than the inlet opening. The internal temperature is
higher than the external air temperature. Such temperature and height conditions will always induce
convective air movement wherein the assumed inlet opening will always perform as an inlet for air and the
assumed outlet opening will always perform as an outlet for air.

95

Fig 34: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (single sided model) - 4m high.

Fig 35: Air flow rates for when Outlet size is increased keeping Inlet size constant.

96

Figure 35 highlights an increase in air flow rates when the outlet size is greater than the
inlet size of 2m
2
. Furthermore the air flow rates decrease when the outlet size is smaller
than the inlet size. With reduced opening size the air flow rate decreases. An opening
regulates the volume of air flowing in and out of the space. Thus an increase in the size of
any of the opening will increase air flow rate. Similarly when the size of an opening
decreases the volume of air that can now enter and exit the space will also decrease. In
other words when the total are of openings increase the air flow rates increase whereas
when the total area of openings decrease the air flow rates also decrease. To verify this
similar analysis of air flow rate are conducted further in which now the outlet size was
kept constant and the change in air flow for varying inlets sizes are analyzed.

Fig 36: Air flow rates for when inlet size is increased while keeping outlet size
constant at 2m
2
.

97

According to the above Figure 36, air flow rates increase when the inlet size is greater
than the outlet size of 2m
2
. Furthermore the air flow rates decrease when the inlet size is
smaller than the outlet size. The pattern of increase in air flow in this case – Figure 36 is
similar to the change observed in Figure 35. Analysis of both these cases highlights that
by increasing the area of either of the opening (inlet or outlet) the air flow rate can be
increased. According to the buoyancy driven air flow equation (Eq. -6 / section 3.2) the
volumetric air flow rate (Q) depends as a function of the total area of opening. Total area
of opening is the sum of area of inlet and the area of outlet openings. Therefore increase
in the size of any of these openings will result in increase of air flow rate.
These analyses are not conclusive as the change in air flow rates are not purely a function
of varying opening sizes. The openings are placed at a height difference which influence
air flow rate. Additional calculations are performed by changing the opening height
difference to 1.5m for varying openings sizes to identify and verify the influence of
openings on air flow – results of which are tabulated below:.
Openings

Opening
Size
Volumetric
air flow -
m
3
/s
Air
velocity
- m/s
Internal
temp -
0
C Inlet - Outlet - A1 A2
Height -m 1.5 3
1
1 0.23 0.007 26.0
Height difference ΔH 2.5 m 2 0.30 0.008 24.7
Assumed Zone
Temperature
23
0
C

3 0.32 0.009 24.5
External Temperature 20
0
C 4 0.32 0.009 24.4
Internal heat gain 1710W

Table 27: Results of air flow rates by changing area of inlet to outlet in a single zone
(single sided model) 4m high keeping height difference at 1.5m.

98

2
1 0.30 0.008 24.8
2 0.47 0.013 23.0
3 0.55 0.016 22.5
4 0.60 0.017 22.4
3
1 0.31 0.009 24.5
2 0.55 0.016 22.6
3 0.70 0.020 22.0
4 0.80 0.023 21.8
4
1 0.32 0.009 24.4
2 0.59 0.017 22.4
3 0.80 0.023 21.8
4 0.94 0.027 21.5

Table 27: Continued.

Based on the two separate calculations, results show that airflow rates change when area
of opening as well as the height difference between the openings is changed. Therefore to
identify the change in air flow by varying opening size a comparative analysis of
percentage change in air flow using different inlet to outlet configurations is performed,
using the value of air flow rates obtained by from the two different calculations. This
analysis will compare the relative change in air flow rate when opening sizes; inlets and
outlets, are increased for both the 2 cases of different opening heights. This comparative
analysis will help analyze the change in air flow rates as a function of varying opening
size negating the influence of different openings heights used for this calculation. This
will also help is deriving the range of change in air flow rate by different opening size
configurations as a function of the total area of opening.

99

N
o
Inlet
– m
2

Outlet
– m
2

Ratio
Height difference 2.5 m Height difference 1.5 m
Air flow
rate -
m3/s

%
change
from
Q
Differe
nce
Air
flow
rate -
m3/s

%
change
from
Q
Difference
Δ% -
100
Δ% -
100
1
1
1 1 : 1 Q=0.303 100 0 0.234 100 0
2
2 1 : 2 0.384 127 27 0.297 127 27
3
3 1 : 3 0.407 134 34 0.315 134 34
4 4 1 : 4 0.417 138 38 0.322 138 38

5
2
1 2 : 1 0.382 127 27 0.296 127 27
6
2 2 : 2 0.606 200 100 0.470 200 100
7
3 2 : 3 0.714 236 136 0.553 236 136
8 4 2 : 4 0.768 254 154 0.595 254 154

Table 28: Comparative analysis of change in buoyancy driven air flow rate by
varying inlet to outlet size ratio to see the percentage difference in corresponding air
flow rate from the air flow rate when openings are equal.

The comparative analysis of different airflow rates derived by changing opening sizes
under the two different conditions of height differences display similar results. The
similar results of percentage change of air flow assists in concluding and verifying that
the effective change in air flow rate purely as a function of change in opening sizes. The
difference in the actual value of airflow rate for similar opening size can be accounted to
both change in height difference between openings and opening size.

100

Results from table 28 highlight regular and similar change in air flow rate for different
opening size configurations. Row numbers 1,2,3 & 4 give the percentage increase in air
flow rate, when either any one of the opening size increases, from the air flow rate values
when both the openings are of the same size. Moreover Row 1 & 6 of table 28 display
that when the opening sizes are doubled the air flow rates will also double. Similar results
in row 2 & 5 display that to increase air flow rate either inlet or outlet openings can be
increased.

From all the above analysis it can concluded that to increase buoyancy driven airflow in
single sided ventilated models the opening sizes should be increased. Increase in total
opening area accounts for increase of air flow rate. Increase in any of the openings, inlet
or outlets will increase air flow rate.

101

6.2: WIND INDUCED VENTILATION STUDIES
This chapter reports results of wind driven ventilation calculation s on the single zone –
single sided model.

6.2.1: INFLUENCE OF ZONE HEIGHT
This case is to determine influence of zone heights on air flow rates.

Fig 37: Single zone – (single sided model) with varying heights.

102

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Zone Heights - m Different wind speeds
Opening heights 4, 5, ,6, 7, 8,10, 20 2m/s and 5m/s
Opening areas Wind angle – 0
0

Table 29: Conditions for calculating wind driven air flow in a single zone (single
sided model) by changing the zone heights.

• RESULTS:
Openings Zone
heigh
ts - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Volumetri
c air flow
- m
3
/s
Air
velocity -
m/s

Inlet -
A1
Outlet
- A2
Wind speed - 2m/s Wind speed - 5m/s
Area -
m
2

1 1 4 0.0032 0.16*10
-3
0.0081 0.40*10
-3

Height -
m
1 3.5 5 0.0034 0.14*10
-3
0.0085 0.34*10
-3

6 0.0036 0.12*10
-3
0.0089 0.29*10
-3

7 0.0038 0.11*10
-3
0.0093 0.26*10
-3

8 0.0040 0.10*10
-3
0.0096 0.24*10
-3

10 0.0041 0.08*10
-3
0.0102 0.20*10
-3

12 0.0048 0.08*10
-3
0.0121 0.20*10
-3

Table 30: Results of air flow rates in a single zone (single sided model) by changing
overall zone heights.

103

Fig 38: Air flow rates for different single zone (single sided model) heights at 0
0

wind angle.

• ANALYSIS:
Marginal air flow is experienced across the zones having varying height. Wind pressure
is induced when opening are placed on opposite sides such that the two openings have
pressure of almost similar magnitude acting in opposite directions (Evola and Popov
2006). In this model both the openings are located on the same side due to which both
openings experience similar positive pressure. As a result there is no pressure difference,
which does not induce any air flow across the single zone. This model renders ineffective
under prevailing winds thus limiting its use under different climatic conditions.

104

The minor or marginal air flow observed in the Figure 38 above is the air flow
experienced exactly at the center of the openings by the prevailing wind. This air flow is
experienced when the wind first strikes the opening
32
and is due to the direct static wind
pressure exerted at the center of the opening. The air flow experienced at the center at of
the openings is reported by CONTAM (Walton and Dols December,2011).

6.2.2: INFLUENCE OF OPENING HEIGHTS
This series of calculation is to study the influence of different opening heights on air
flow.

Fig 39: Single zone (single sided model) having different opening heights.

32
CONTAM reports results of air flow rates experienced exactly at the center of the openings and for this
study it is conducted for as specific time instead of a period of time(Walton and Dols December,2011)

105

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet heights Wind speed - 2m/s
Zone height – 4m Outlet heights Wind angle – 0
0

Opening areas

Table 31: Conditions for calculating wind driven air flow in a single zone (single
sided model) by changing opening heights.
• RESULTS:
Openings Opening Heights Volumetri
c air flow
- m
3
/s
Air
velocity -
m/s
Inlet- A1 Outlet – A2 A1 A2
Area - m
2
1 1
0.5
2 0.00 0.0001
2.5 0.00 0.0001
3 0.00 0.0002
Internal heat gain 1710 W 3.5 0.00 0.0002
Zone height 4m
1
2 0.00 0.0001
2.5 0.00 0.0001
3 0.00 0.0001
3.5 0.00 0.0002
1.5
2 0.00 0.0001
2.5 0.00 0.0001
3 0.00 0.0001
3.5 0.00 0.0001
2
2 0.00 0.0000
2.5 0.00 0.0001
3 0.00 0.0001
3.5 0.00 0.0001
Table 32: Results of air flow in single zone- (single sided model) 4m high by varying
opening heights.

106

Additional calculations were conducted for a zone height of 6m.

Table 33: Results of air flow in single zone 6m high by varying opening heights.
Inlet -
A1
Outlet -
A2
A1 A2
Area - m2 1 1 3 0.0032 0.000108
3.5 0.0035 0.000118
4 0.0038 0.000127
1710 W 4.5 0.0040 0.000133
5 0.0043 0.000143
6m 5.5 0.0046 0.000152
3 0.0029 0.000096
3.5 0.0032 0.000108
4 0.0035 0.000118
4.5 0.0038 0.000127
5 0.0040 0.000133
5.5 0.0043 0.000143
3 0.0025 0.000083
3.5 0.0029 0.000096
4 0.0032 0.000108
4.5 0.0035 0.000118
5 0.0038 0.000127
` 5.5 0.0040 0.000133
3 0.0020 0.000067
3.5 0.0025 0.000083
4 0.0029 0.000096
4.5 0.0032 0.000108
5 0.0035 0.000118
5.5 0.0038 0.000127
3 0.0014 0.000047
3.5 0.0020 0.000067
4 0.0025 0.000083
4.5 0.0029 0.000096
5 0.0032 0.000108
5.5 0.0035 0.000118
3 0.0000 0.000000
3.5 0.0014 0.000047
4 0.0020 0.000067
4.5 0.0025 0.000083
5 0.0029 0.000096
5.5 0.0032 0.000108
Opening Heights
Volumetric air
flow - m3/s
Air velocity -
m/s
Internal heat gain
Zone height
Openings
3
1.5
2
2.5
1
0.5

107

• ANALYSIS:

Fig 40: Air flow rates in a Single Sided model 4m high having different opening
heights.

Fig 41: Air flow rates in a single sided zone 6m high having different opening height.

108

Analyses under both the cases of different zone heights display no natural deviation or
marginal difference in air flow rates as result of height difference between openings. The
opening sizes in both the cases have been kept constant. This assures the total volume of
air entering and leaving the space as fixed.
Wind induced pressure generally occurs across the width of the building thus the design
flow patterns are mostly horizontal. This means that the air can enter and leave the
building at the same vertical level negating the height variable, which may instead create
hydrostatic pressure across the building height. As a result creating any height difference
between openings will have no effect on wind induced air flow. In the single sided model
both the openings experience positive pressure of equal magnitude. Thus there is no
pressure difference across the width of the space due to its openings which restricts air
flow. The low air flow recorded by CONTAM is experienced when the wind first strikes
the opening
33
and is due to the direct static wind pressure exerted at the center of the
opening.

6.2.3: INFLUENCE OF OPENINGS SIZE.
This section investigates the influence of opening size on wind induced ventilation.
Different inlet sizes for different outlet sizes were investigated. The resulting changes in
volume flow rates are plotted below.

33
CONTAM reports results of air flow rates experienced exactly at the center of the openings and for this
study it is conducted for as specific time instead of a period of time(Walton and Dols December,2011)

109

Fig 42: Single zone (single side model) with varying opening sizes.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet area Wind speeds
Zone height – 4m Outlet area 2m/s & 5m/s
Opening heights

Table 34: Conditions for calculating wind driven air flow rates by varying opening
sizes.

110

• RESULTS:
Opening Heights

Opening
Size in
m
2

Volumetric
air flow -
m
3
/s
Air
velocity
- m/s
Volumetr
ic air
flow -
m
3
/s
Air
velocity
- m/s
Inlet - A1
Outlet -
A2
A1 A2 Wind Speed - 2m/s Wind speed - 5m/s
1 3.5
1
1 0.00 0.0002 0.01 0.0004
2 0.00 0.0002 0.01 0.0005
Zone height 4m 3 0.00 0.0002 0.01 0.0005
Wind Angle 0 4 0.00 0.0002 0.01 0.0006
2
1 0.00 0.0002 0.01 0.0005
2 0.01 0.0003 0.02 0.0008
3 0.01 0.0004 0.02 0.0010
4 0.01 0.0004 0.02 0.0010
3
1 0.00 0.0002 0.01 0.0006
2 0.01 0.0004 0.02 0.0010
3 0.01 0.0005 0.02 0.0012
4 0.01 0.0006 0.03 0.0014
4
1 0.00 0.0002 0.01 0.0006
2 0.01 0.0004 0.02 0.0010
3 0.01 0.0006 0.03 0.0014
4 0.01 0.0007 0.03 0.0016

Table 35: Results of air flow rates for different opening size for different wind
speeds.

111

Fig 43: Wind induced air flow rate in a single zone (single sided model) 4m high at
wind speed – 2m/s when opening sizes are changed.

Fig 44: Wind induced air flow rate in a single zone (single sided model) 4m high at
wind speed – 5m/s when opening sizes are changed.

112

• ANALYSIS:
Air flow across this model is extremely low as pressure difference across the two
openings is negligible. As discussed earlier wind induced pressure generally occurs
across the width of the building thus the design flow patterns are mostly horizontal. Thus
when opening are on the same façade, no pressure difference is created which may
induce air flow.
With increase in opening size a marginal increase in air flow rates is observed. This
increase or marginal air flow cannot be accounted only on increase in opening size. The
area of openings and the height of the actual opening frame can also induce pressure
difference along its height (Dols, Emmerich and Axley August,2001). This pattern of
increase in air flow rates may alter if the openings are of different shape. CONTAM
assumes all openings of a perfect square form. With rectangular opening shapes, wherein
the width is larger than the height, the air flow rates may alter. The height of the actual
opening frame may reduce which may also change the pattern of increase in air flow
rates.
However, in this case the air flow rates are extremely low to have any substantial
difference on temperature which makes them ineffective when analyzing to understand
the relationship between openings and wind induced air flow are not possible.

Model 2 – cross ventilation model is investigated on similar parameters and conditions.
The results and the analysis follow in chapter 7.

113

CHAPTER 7: AIR FLOW IN MODEL B – CROSS VENTILATION.
This chapter reports the results and inferences of air flow calculations on single zone –
Cross ventilated model for Buoyancy and wind induced air flow.

114

7.1: BUOYANCY INDUCED VENTILATION STUDIES
This section reports the results and analysis of calculations using a single zone model.

7.1.1: INFLUENCE OF ZONE HEIGHT
This case is to determine influence of zone heights on air flow.

Fig 45: Single zone (cross ventilated model) with varying heights.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Zone Heights External temperatures
Opening heights 4, 5, ,6, 7, 8,10, 20 Assumed Internal
Temperatures Opening areas

Table 36: Conditions for calculating air flow by changing overall zone heights.

115

• RESULTS:
OPTION 1

Zone
heigh
ts - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Internal
tem -
0
C
Openings 4 0.36 0.018 20.8
Inlet Outlet 5 0.36 0.014 20.8
Area - m
2
1 1 6 0.36 0.012 20.8
Height - m 1 3.5 7 0.36 0.010 20.8
Assumed Zone
Temperature
20
0
C

8 0.36 0.009 20.8
External Temperature 17
0
C 10 0.36 0.007 20.8
Internal heat
gain
35
W/m
2

1710W

12 0.36 0.006 20.8

Table 37: Results of air flow for different zone heights when T
o
is kept at 17
0
C.

The air flow rate remains constant with change in zone heights as long as the relationship
between the opening heights is constant. Similar calculations for higher external
temperature were conducted.

OPTION 2

Zone
heigh
ts - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Internal
tem -
0
C
Openings 4 0.355 0.0177 25.9
Inlet Outlet 5 0.355 0.0142 25.9
Area - m2 1 1 6 0.355 0.0118 25.9
Height - m 1 3.5 7 0.355 0.0101 25.9
Assumed zone
Temperature
25
0
C

8 0.355 0.0088 25.9
External Temperature 22
0
C 10 0.355 0.0071 25.9
Internal heat gain 1710W 12 0.355 0.0059 25.9

Table 38: Results of air flow for different zone heights when T
o
is kept at 22
0
C.

116

Fig 46: Air flow rates in cross ventilated zones having varying heights at different
temperatures.
• ANALYSIS:
Hydrostatic pressure changes with change in height. Buoyancy driven air flow in this
case will therefore depend on height difference of openings and also the opening size
which regulate the volume of air flow. In this model the opening heights and opening size
remain constant. This keeps the air flow rates constant for all different zone heights. The
marginal difference in air flow rates between the two options is purely due to difference
in external air temperature. Air velocity changes with change in zone heights. Thus
varying zone heights will not have any effect on buoyancy driven volumetric air flow rate
and will change only the air velocity due to varying overall height.

117

7.1.2: INFLUENCE OF OPENING HEIGHTS
This is to study the influence of different opening heights on air flow. For this series of
calculations the zone height, opening areas and external air temperature remains constant.

Fig 47: Single zone (cross ventilated model) with varying opening heights.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet heights External temperature 20
0
C
Internal heat gain Outlet heights Internal Temperature 23
0
C
Opening area Zone height – 4m & 6m

Table 39: Conditions for calculating buoyancy driven air flow by changing opening
heights.

118

• RESULTS:
Openings Areas

Opening
Heights
Volumetr
ic air
flow -
m
3
/s
Air
velocity
- m/s
Internal
temp –
0
C
Inlet - A1 Outlet - A2 A1 A2
Area - m
2
1 1
0.5
2 0.23 0.012 26.0
2.5 0.27 0.014 25.2
Zone Temperature 23
0
C 3 0.30 0.015 24.6
External Temperature 20
0
C 3.5 0.33 0.017 24.2
Internal heat gain 1710 W
1
2 0.19 0.010 27.3
Zone height 4m 2.5 0.23 0.012 26.0
3 0.27 0.014 25.2
3.5 0.30 0.015 24.6
1.5
2 0.14 0.007 30.4
2.5 0.19 0.010 27.4
3 0.23 0.012 26.0
3.5 0.27 0.014 25.2
2
2 0 0.000 -
2.5 0.14 0.007 30.4
3 0.19 0.010 27.3
3.5 0.24 0.012 26.0

Table 40: Results of air flow rates in a 4m zone when opening heights are changed.

119

Table 41: Results of air flow rates in a 6m zone when opening heights are changed.
Inlet -
A1
Outlet -
A2
A1 A2
Area - m2 1 1 3 0.30 0.0101 24.7
3.5 0.33 0.0111 24.2
23 C 4 0.36 0.0119 23.9
20 C 4.5 0.38 0.0128 23.7
1710 W 5 0.41 0.0136 23.5
5.5 0.43 0.0143 23.3
6m
3 0.27 0.0090 25.2
3.5 0.30 0.0101 24.7
4 0.33 0.0111 24.2
4.5 0.36 0.0119 23.9
5 0.38 0.0128 23.7
5.5 0.41 0.0136 23.5
3 0.23 0.0078 26.0
3.5 0.27 0.0090 25.2
4 0.30 0.0101 24.7
4.5 0.33 0.0111 24.2
5 0.36 0.0119 23.9
5.5 0.38 0.0128 23.7
3 0.19 0.0064 27.4
3.5 0.23 0.0078 26.0
4 0.27 0.0090 25.2
4.5 0.30 0.0101 24.7
5 0.33 0.0111 24.2
5.5 0.36 0.0119 23.9
3 0.15 0.0049 29.7
3.5 0.19 0.0064 27.4
4 0.23 0.0078 26.0
4.5 0.27 0.0090 25.2
5 0.30 0.0101 24.7
5.5 0.33 0.0111 24.2
3 0.00 0.0000 -
3.5 0.15 0.0049 29.7
4 0.19 0.0064 27.4
4.5 0.23 0.0078 26.0
5 0.27 0.0090 25.2
5.5 0.30 0.0101 24.7
Assumed Zone
External Temperature
Internal heat gain
Air velocity -
m/s
Internal
temperature - C
Opening
Heights
Volumetric air
flow - m3/s
Zone height
Openings Areas
0.5
1
1.5
2
2.5
3

120

Fig 48: Air flow rates for different opening heights in a single zone (cross ventilated
model) of height 4m.

Fig 49: Air flow rates for different opening heights in a single zone (cross ventilated
model) of height 6m.

121

• ANALYSIS:
Air flow in this model increases with increase in height difference between openings.
Buoyancy driven air flow varies as a function of opening area and height difference
between the openings. In this model the opening sizes, zone height and temperature
conditions are kept constant. Therefore the change in air flow can be attributed purely as
a function of change in opening levels which affects the height difference between them.
Thus to increase ventilation rates while maintaining opening size constant, the height
difference between the inlets and outlets levels should be extended as much as possible.

7.1.3: INFLUENCE OF OPENING SIZE.
As openings control volume of air flow in and out of the occupant zones, it can be vital to
identify the best possible opening configurations in order to refine the occupant zone
design.

Fig 50: Single zone (cross ventilated model) with varying opening sizes.

122

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet area External temperature – 20
0
C
Internal heat gain Outlet area Internal Temperature – 23
0
C
Opening heights Zone height – 4m & 7m

Table 42: Conditions for calculating buoyancy driven air flow in a zone by
changing opening areas.

• RESULTS:
Openings

Opening
Size in m
2

Volumet
ric air
flow -
m
3
/s
Air
velocity
- m/s
Internal
temp -
0
C Inlet - A1
Outlet -
A2
A1 A2
Height
-m
1 3.5

1
1 0.30 0.015 24.7
Height difference ΔH 2.5 m 2 0.38 0.019 23.7
Assumed Zone
Temperature
23
0
C

3 0.41 0.020 23.5
External Temperature 20
0
C 4 0.42 0.021 23.4
Internal heat gain 1710 W
2
1 0.38 0.019 23.7
Zone height 4m 2 0.61 0.030 22.3
3 0.71 0.036 22.0
4 0.77 0.038 21.8

Table 43: Results of air flow rate by changing area of inlet to outlet in a single zone
(cross ventilated model) 4m high, keeping height difference between openings at
2.5m.

123

3
1 0.41 0.020 23.5
2 0.71 0.036 22.0
3 0.91 0.045 21.6
4 1.03 0.051 21.4
4
1 0.42 0.021 23.4
2 0.77 0.038 21.8
3 1.02 0.051 21.4
4 1.21 0.061 21.2

Table 43: Continued

• ANALYSIS:

Fig 51: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (cross ventilated model) - 4m high.

124

Fig 52: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (cross ventilated model) - 4m high.

Plotting air flow rates as a function of varying outlet size for different inlet opening size
highlights that when the size of any of the openings increase the air flow rate also
increase - Fig 51. Further analysis of change in air flow, by varying inlets size for
different outlet opening size highlight similar increase in air flow when area of either of
the openings are increased – Fig 52. When the total area of openings increase the air flow
rates increase whereas when the total area of openings decrease the air flow rates also
decrease.

125

Additional calculations are conducted by changing the height difference between
openings to 1.5m. The results of these calculations are tabulated below.

Openings

Opening Size
in m
2

Volumet
ric air
flow -
m
3
/s
Air
velocity
- m/s
Internal
temp -
0
C
Inlet -
A1
Outlet -
A2
A1 A2
Height -m 1.5 3
1
1 0.23 0.007 26.0
Height difference ΔH 2.5 m 2 0.30 0.008 24.7
Assumed Zone
Temperature
23
0
C

3 0.32 0.009 24.5
External Temperature 20
0
C 4 0.32 0.009 24.4
Internal heat gain 1710 W
2
1 0.30 0.008 24.8
Zone height 7m 2 0.47 0.013 23.0
3 0.55 0.016 22.5
4 0.60 0.017 22.4
3
1 0.31 0.009 24.5
2 0.55 0.016 22.6
3 0.70 0.020 22.0
4 0.80 0.023 21.8
4
1 0.32 0.009 24.4
2 0.59 0.017 22.4
3 0.80 0.023 21.8
4 0.94 0.027 21.5

Table 44: Results of air flow rates by changing area of inlet to outlet in a single zone
(cross ventilated model) 4m high keeping height difference at 1.5m.

126

Results from the above calculations highlight a similar trend of increase in air flow with
increase in opening size. This increase is irrespective of increase in either of the inlets or
outlet openings. Based on the two separate calculations, results show that airflow rates
change when area of opening as well as the height difference between the openings is
changed. Therefore to identify the change in air flow by varying opening size a
comparative analysis of percentage change in air flow using different inlet to outlet
configurations is performed, using the value of air flow rates obtained by from the two
different calculations

No Inlet Outlet Ratio
Height difference 2.5 m Height difference 1.5 m
Air flow
rate -
m3/s

%
change
from
Q
Differe
nce
Air
flow
rate -
m3/s

%
change
from
Q
Differenc
e
Δ% -
100
Δ% -
100
1
1
1 1 : 1 Q=0.303 100 0 0.234 100 0
2
2 1 : 2 0.384 127 27 0.297 127 27
3
3 1 : 3 0.407 134 34 0.315 134 34
4 4 1 : 4 0.417 138 38 0.322 138 38

5
2
1 2 : 1 0.382 127 27 0.296 127 27
6
2 2 : 2 0.606 200 100 0.470 200 100
7
3 2 : 3 0.714 236 136 0.553 236 136
8 4 2 : 4 0.768 254 154 0.595 254 154

Table 45: Comparative analysis of change in air flow rate by varying inlet to outlet
size ratio to see the percentage difference in corresponding air flow rate from the air
flow rate when openings are equal.

127

The comparative analysis of different airflow rates, derived by changing opening sizes
under the two different conditions of height differences has similar results. The similar
results of percentage change of air flow assists in concluding and verifying that the
effective change in air flow rate purely as a function of change in opening sizes. The
difference in the actual value of airflow rate for similar opening size can be accounted to
both - change in height difference between openings and opening size.
Results from Table 45 highlight regular and similar change in air flow rate for different
opening size configurations. Row numbers 1,2,3 & 4 give the percentage increase in air
flow rate, when either any one of the opening size increases, from the air flow rate values
when both the openings are of the same size. Moreover Row 1 & 6 of Table 45 display
that when the opening sizes are doubled the air flow rates will also double. Similar results
in row 2 & 5 display that to increase air flow rate either inlet or outlet openings can be
increased.

From all the above analysis it can concluded that to increase buoyancy driven airflow in a
cross ventilated model the opening sizes should be increased. Increase in total opening
area accounts for increase of air flow rate. Increase in any of the openings, inlet or outlets
will increase air flow rate.
.

128

7.2: WIND INDUCED VENTILATION STUDIES
7.2.1: INFLUENCE OF ZONE HEIGHT
This case is to determine influence of zone heights on air flow rates.

Fig 53: Single zone (cross ventilation model) with varying heights.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Zone Heights - m Different wind speeds
Opening heights 4, 5, ,6, 7, 8,10, 20 2m/s and 5m/s
Opening areas Wind angle – 0
0

Table 46: Conditions for calculating wind driven air flow in a single zone (cross
ventilated model) by changing the zone heights.

129

• RESULTS:
Openings

Zone
height
s - m
Volumetri
c air flow
- m
3
/s
Air
velocity
- m/s
Volumetr
ic air
flow -
m
3
/s
Air
velocity
- m/s

Inlet
- A1
Outlet
- A2
Wind speed - 2m/s Wind speed - 5m/s
Area - m
2
1 1 4 0.29 0.0143 0.71 0.0357
Height - m 2 2 5 0.30 0.0121 0.76 0.0302
Wind angle 0
o
6 0.32 0.0105 0.79 0.0264
7 0.33 0.0094 0.82 0.0235
8 0.34 0.0085 0.85 0.0213
10 0.36 0.0072 0.90 0.0180
12 0.43 0.0071 1.07 0.0178

Table 47: Results of air flow rates in a single zone by changing overall zone heights.

Fig 54: Air flow rates for different zone heights at 0
0
wind angle.

130

• ANALYSIS:
Wind induced airflow rates increase with increase in zone heights. Static wind pressure
exerted on openings increases with height. Therefore with increase in zone height the air
flow rate increases due to higher wind pressure acting on the openings.
Also, for this calculation the wind speed, opening levels and the size of the openings are
kept constant throughout. Thus increase in pressure in this case is due to increase in zone
heights. This increased negative and positive pressure at the openings increases the
airflow rates.
This increase in pressure also depends on wind speed, localized wind turbulence
generated by local terrain and climate conditions along with the site location. Thus an
exact numerical relation for increase in pressure with increase in height cannot be
established. In this case, the static wind pressure acting on the openings increases with
increase in zone height which increases airflow across the space.
Wind speed also influences air flow rate. This influence can be observed in the relative
difference of air flow rates for two different wind speeds of 2m/s and 5m/s for similar
zone heights. However, this wind driven ventilation also depends on wind angles and the
local terrain which changes with the site.

131

7.2.2: INFLUENCE OF OPENING HEIGHTS
This is to study the influence of different opening heights on air flow.

Fig 55: Single zone (cross ventilation model) having different opening heights.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet heights – m Wind speed - 2m/s
Zone height – 4m Outlet heights - m Wind angle – 0
0

Opening areas

Table 48: Conditions for calculating wind driven air flow in a single zone by
changing opening heights.

132

• RESULTS:
Openings

Opening
Heights - m
Volumetri
c air flow
- m
3
/s
Air
velocity
- m/s Inlet - A1 Outlet - A2 A1 A2
Area - m
2
1 1
0.5
2 0.286 0.014
2.5 0.286 0.014
3 0.286 0.014
Internal heat gain 1710 W 3.5 0.286 0.014
Zone height 4m
1
2 0.286 0.014
2.5 0.286 0.014
3 0.286 0.014
3.5 0.286 0.014
1.5
2 0.286 0.014
2.5 0.286 0.014
3 0.286 0.014
3.5 0.286 0.014
2
2 0.286 0.014
2.5 0.286 0.014
3 0.286 0.014
3.5 0.286 0.014

Table 49: Results of air flow in single zone (cross ventilated model) 4m high by
varying opening heights.

Additional calculations using a single zone 6m high were done.

133

Table 50: Results of air flow in single zone 6m high by varying opening heights.
Inlet - A1 Outlet - A2 A1 A2
Area - m2 1 1 3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
1710 W 4.5 0.286 0.010
5 0.286 0.010
6m 5.5 0.286 0.010
3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
4.5 0.286 0.010
5 0.286 0.010
5.5 0.286 0.010
3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
4.5 0.286 0.010
5 0.286 0.010
5.5 0.286 0.010
3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
4.5 0.286 0.010
5 0.286 0.010
5.5 0.286 0.010
3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
4.5 0.286 0.010
5 0.286 0.010
5.5 0.286 0.010
3 0.286 0.010
3.5 0.286 0.010
4 0.286 0.010
4.5 0.286 0.010
5 0.286 0.010
5.5 0.286 0.010
2
2.5
3
0.5
1
1.5
Zone height
Openings Opening Heights Volumetric air
flow - m3/s
Air velocity -
m/s
Internal heat gain

134

Fig 56: Air flow rates in a cross ventilated zone 4m high having different opening
height.

Fig 57: Air flow rates in a cross ventilated zone 6m high having different opening
height.

135

• ANALYSIS:
The calculations show no change in air flow rates when opening levels or height
difference between openings are changed. Wind induced air flow changes a function of
change in static wind pressure acting on the openings, wind speed and the area of
openings at which it flows and is not dependent on the height difference between the
openings at this scale.
Air thus flows in this model when the openings are at the same level. It only requires two
openings having pressure acting in opposite direction and equal magnitude. This makes a
single zone cross ventilation model work under different wind conditions.
Thus, varying openings levels will have no difference on the air flow rates flowing across
the space at this scale.

136

7.2.3: INFLUENCE OF OPENING SIZE.
For this series of calculations the opening sizes were altered for a single zone – cross
ventilated model. Different inlet sizes were investigated for different outlet sizes.

Fig 58: Single zone (cross ventilated model) with varying opening sizes.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Zone floor area Inlet area Wind speeds
Zone height – 4m Outlet area 2m/s
Opening heights Wind angles – 0
o

Table 51: Conditions for calculating wind driven air flow rates by varying opening
sizes.

137

• RESULTS:
Opening Heights
Opening
Size in
m
2

Volumetri
c air flow
- m
3
/s
Air
velocity
- m/s
Opening
Size in
m
2

Volumetr
ic air
flow -
m
3
/s
Air
velocit
y - m/s
Inlet -
A1
Outlet -
A2
A1 A2 Wind angle – 0
o
A2 A1 Wind angle – 0
o

1 3.5
1
1 0.29 0.014
1
1 0.29 0.014
2 0.36 0.018 2 0.36 0.018
Zone
height
4m 3 0.38 0.019 3 0.38 0.019
Wind
speed
2m /s 4 0.39 0.012 4 0.39 0.012

2
1 0.36 0.018
2
1 0.36 0.018
2 0.57 0.029 2 0.57 0.029
3 0.67 0.034 3 0.67 0.034
4 0.72 0.036 4 0.72 0.036

3
1 0.38 0.019
3
1 0.38 0.019
2 0.67 0.034 2 0.67 0.034
3 0.86 0.043 3 0.86 0.043
4 0.97 0.049 4 0.97 0.049

4
1 0.39 0.012
4
1 0.39 0.012
2 0.72 0.036 2 0.72 0.036
3 0.97 0.049 3 0.97 0.049
4 1.14 0.057 4 1.14 0.057

Table 52: Results of air flow rates in a single zone (cross ventilated model) for
different opening size at 2 m/s wind speed at 0
0
wind angle.

138

• ANALYSIS:

Fig 59: Air flow rates as a function of varying outlet size for different inlet opening
size in a single zone (single sided model) - 4m high at 2m/s wind speed.

Fig 60: Air flow rates as a function of varying inlet size for different outlet opening
size in a single zone (single sided model) - 4m high at 2m/s wind speed.

139

When the opening size increases the air flow rates increases. This increase in airflow rate
is similar under both the conditions, that is when the size of inlet openings are increased
and also when the size of outlet openings are increased. Thus increase in total area of
openings increases air flow rates and conversely with decrease in total area of openings a
decrease in air flow rates can be expected.
According to the wind driven air flow equation (Eq. -8 / section 3.3.2) the volumetric air
flow rate (Q) varies as a function of the total area of opening. Total area of opening is the
sum of area of inlet and the area of outlet openings. Therefore increase in the size of any
of these openings will result in increase of air flow rate.
From all the above analysis it can concluded that to increase wind driven airflow in cross
ventilated model the opening sizes should be increased. Increase in total opening area
accounts for increase of air flow rate. Increase in any of the openings, inlet or outlets will
increase air flow rate.

140

CHAPTER 8: AIR FLOW IN MODEL C – SINGLE ZONE + SHAFT.
This chapter reports the results and inferences derived from investigations performed on
single zone model attached to a ventilation shaft.

141

8.1: BUOYANCY INDUCED VENTILATION STUDIES
This section reports the results and analysis of buoyancy induced air flow calculations
using on a single zone model attached to a vertical shaft.

8.1.1: INFLUENCE OF SHAFT HEIGHT
In the earlier two chapters the effect of varying zone heights on air flow rate were
explored. This section continues to explore similar physical component of height wherein
now the zone is kept at a fixed height and the shaft heights are changed.
As inferred from earlier investigations, buoyancy driven air flow is influenced by area of
opening and height difference between openings. Therefore in this model and for all the
calculations all the openings are kept at a constant size. The height difference between
the two opening s in the zone is zero. This assures that the two openings in zone will not
contribute to any increase or decrease in air flow by virtue of their height difference. The
shaft outlet level is kept constant. The height difference between the zone opening and
the shaft outlet height is kept constant at 2.5m. Thus by keeping the opening and height
difference between openings constant any change in air flow rate can now be attributed to
change in overall shaft height.

142

Fig 61: Single zone + shaft investigated for change in air flow by varying shaft
height.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft heights External temperature
Opening areas 20
0
C
Opening heights

Table 53: Conditions for calculating buoyancy driven air flow when changing shaft
heights.

143

• RESULTS:
Openings Shaft
height -
m
Volumetric
air flow -
m
3
/s
Air
velocity
- m/s
Internal
temperature -
0
C
Zone Inlet
Shaft
Outlet
Height -m 1, 1 3.5 4 0.25 0.012 25.7
Area - m
2
1, 1 1 5 0.25 0.012 25.7
6 0.25 0.25 0.012
Internal heat gain 1710 W 7 0.25 0.25 0.012
External Temperature 20
0
C 8 0.25 0.25 0.012
Internal Temperature 23
0
C 10 0.25 0.25 0.012
Zone height 4m 12 0.25 0.25 0.012

Table 54: Results of buoyancy driven air flow when shaft heights are changed.

• ANALYSIS:

Fig 62: Buoyancy driven air flow rates for different shaft height.

144

For buoyancy driven air flow change in shaft height makes no difference on air flow
rates. Buoyancy driven air flow depends on height difference between the openings. As
discussed earlier, in this case the openings are maintained a constant height difference of
2.5 throughout the calculations. The level of the shaft outlet does not change with change
in shaft height. The air flow rates which are generated across the zone are by virtue of
this constant height difference and the fixed opening size. As the height difference or
opening size do not vary the air flow rates also not vary when the shaft heights are
altered.

8.1.2: INFLUENCE OF SHAFT AREA
The study explores various building design components that may influence natural
ventilation. Shaft area contributes to the overall shaft volume and thus is another
ventilation shaft design component which may influence air flow. By exploring the
influence of shaft area on air flow methods to reduce overall shaft volume can also be
explored.
For this series of calculations the shaft height, shaft opening, zone height, zone opening
size and the height difference between all the openings are kept constant. By doing so the
zone and shaft combined will have a constant volume of air and fixed air flow rate. The
change in air flow rates for change or increase in shaft area is reported.

145

Fig 63: Single zone + shaft investigated for change in air flow by varying shaft area
size.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft area External temperature
Opening areas Different shaft heights Assumed internal
temperature Opening heights 6m and 8m

Table 55: Conditions for calculating buoyancy driven air flow rate when shaft area
is changed.

146

• RESULTS:
Openings Shaft area - m
2
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s

Area -
m
2

Height
- m
Length Breadth
Area
- m
2

A1 - Zone
inlet
1 1
1
1 1 0.639 0.064
A2 - Shaft
inlet
1 1 2 2 0.709 0.071
A3 - Shaft
outlet
1 5.5 3 3 0.725 0.073
4 4 0.731 0.073
External temperature 20
0
C 5 5 0.734 0.073
Zone temperature 23
0
C
Shaft height 6m
2
1 2 0.709 0.071
2 4 0.731 0.073
3 6 0.735 0.074
4 8 0.737 0.074
5 10 0.737 0.074
3
1 3 0.725 0.073
2 6 0.735 0.074
3 9 0.737 0.074
4 12 0.738 0.074
5 15 0.738 0.074
4
1 4 0.731 0.073
2 8 0.737 0.074
3 12 0.738 0.074
4 16 0.738 0.074
5 20 0.738 0.074
5
1 5 0.734 0.073
2 10 0.737 0.074
3 15 0.738 0.074
4 20 0.738 0.074
5 25 0.738 0.074
Table 56: Results of air flow rate for shaft height constant at 6m.

147

• ANALYSIS:

Fig 64: Buoyancy craven air flow rate for different shaft areas in a shaft 6m high.

Ventilation shaft should be designed to allow free unobstructed air movement across its
volume. Thus the shaft volume should be big enough to accommodate the total volume of
air flowing across the occupant zones.
From the above Figure – 64 - for smaller shaft areas the air flow rates is low. With
increase in shaft area the air flow rates also increase. The increase in air flow stops and is
relatively constant as soon as the shaft area reaches the minimum size which is required
to allow free air movement up its height. The constant air flow rate represents the total
volume of air which is flowing inside the occupant space and up into the shaft.

148

Thus with low shaft areas this air flow rates decrease as the shaft area is not large enough
to accommodate the total volume of air expected to flow up the shaft.
As seen in Figure 64 – the air flow rates remains constant even for higher shaft areas
when shaft height remains constant at 6m. Thus shaft areas depend on the volume of air
flowing inside the shaft as well as the shaft height. To verify this additional series of
calculations were conducted by changing the opening sizes while keeping the shaft height
constant at 6m.
Openings
Shaft
area - m
2

Volumetric air flow - m
3
/s

Area - m
2

Height
- m
Smaller
openings
Larger
openings
1 0.400 0.631
Smaller openings 2 0.444 0.863
A1 - Zone inlet 1 1 3 0.454 0.943
A2 - Shaft inlet 1 1 4 0.458 0.977
A3 - Shaft outlet 1 5.5 5 0.459 0.993
6 0.460 1.003
Larger openings 8 0.461 1.013
A1 - Zone inlet 2 1 9
0.461
1.015
A2 - Shaft inlet 2 1 10 0.462 1.017
A3 - Shaft outlet 3 5.5 12 0.462 1.020
15 0.462 1.021
External temperature 20
0
C 16 0.462 1.022
Zone temperature 23
0
C 20 0.462 1.023
Shaft height 6m 25 0.462 1.024

Table 57: Air flow rates for as a function of shaft area for different opening sizes.

The pattern of change in air flow rates observed in Figure 65 is similar to the change
observed in Figure 64. Larger openings allow larger volume of air to flow up the shaft
due to which the minimum required shaft area to allow free air movement will be greater.

149

Fig 65: Air flow rates as a function of varying shaft area for different opening sizes.

This increase in shaft area is also because the shaft height is kept constant restricting the
volume of shaft. Thus to accommodate even larger air volumes the shaft area needs to
increase till it reaches the minimum required size configurations which will allow free
unobstructed air flow up its height. To verify this additional calculation were performed
by varying shaft heights. The change in air flow rates for different shaft heights follows
similar trend as seen in Figure 66. The results of air flow rates for two different shaft
heights of 8m and 6m are compared below.

150

Openings Shaft
area –
m
2

Volumetric air flow - m
3
/s

Area - m
2
Height -
m
Shaft height
8m
Shaft
height 6m
A1 - Zone inlet 1 1 1 0.4460 0.401
A2 - Shaft inlet 1 1 2 0.4949 0.445
A3 - Shaft outlet 1 7.5 3 0.5059 0.454
4 0.5099 0.458
External temperature 20
0
C 5 0.5118 0.460
Zone temperature 23
0
C 6 0.5128 0.461
8 0.5139 0.462
9 0.5142 0.462
10 0.5144 0.462
12 0.5146 0.462
15 0.5148 0.462
16 0.5149 0.463
20 0.5150 0.463
25 0.5151 0.463

Table 58: Comparing results of air flow rate for shaft height at 8m and 6m.

Fig 66 Air flow rates as a function of shaft areas for two different shaft heights.

151

8.1.3: INFLUENCE OF SHAFT OUTLET
This series of calculations examines the influence of different shaft outlet sizes on air
flow rates. For this the height difference between all the openings, the zone openings
size, shaft area and zone volume are kept constant for varying shaft outlet size. Thus any
change in shaft outlet size can be attributed to a change in shaft outlet size. The
calculations are performed using two different shaft heights to compare the trend of
change in airflow rate

Fig 67: Single zone connected to a shaft for change in air flow by varying
shaft outlet size.

152

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft outlet area – A3 External temperature
Opening areas Varying shaft height Assumed internal temperature
Opening heights

Table 59: Conditions for calculating buoyancy driven air flow rates by changing
shaft outlet size.
Pressure changes with height. Thus the parameter of height is also considered for the
calculation. For these calculations all the opening are kept at 1m
2
constant size
34
.

• RESULTS:
Openings Shaft
Heigh
t
Outlet
area –
m
2

Volumetric
air flow -
m
3
/s
Air
velocity -
m/s

Area -
m
2

Height -
m
A1 - Zone inlet 1 1
4m
1 0.398 0.011
A2 - Shaft inlet 1 1 2 0.460 0.013
A3 - Shaft
outlet
1
0.5 from
shaft top
3
0.475 0.014
4 0.481 0.014
Internal zone temperature 23
0
C 5 0.484 0.014
External Temperature 20
0
C
6m
1 0.589 0.017
2 0.681 0.019
3
0.703 0.020
4
0.711 0.020
5
0.715 0.020

Table 60: Results of air flow rates by changing shaft outlet size.

34
The sum of inlets is equal to sum of outlets. By doing this the neutral pressure plane remains stationary.

153

• ANALYSIS:
Buoyancy driven air flow rate varies as a function of total area of opening. In this
case the air flow rates increase with increase in shaft outlet size. The zone opening
size, shaft height, external temperature and the height difference between all the
openings are kept constant. Thus the increase in air flow rates is purely by the virtue
of increase in outlet size. Moreover the pattern of increase in air flow rate for increase
in shaft outlet size for two different shaft heights is similar. Thus it can be concluded
that buoyancy driven air flow rate an increase with increase in shaft outlet size.

Fig 68: Air flow rates as a function of varying shaft outlet size for two different shaft
heights.

154

8.2: WIND INDUCED VENTILATION STUDIES
This section reports the results and analysis of wind induced air flow calculations
performed on a single zone model attached to a vertical shaft.

8.2.1: INFLUENCE OF SHAFT HEIGHT
Opening heights, opening size and zone volumes are kept constant for these calculations.
Only the shaft height is varied to investigate its effect on air flow.

Fig 69: Single zone + shaft investigated for change in air flow by varying shaft
height.

155

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft heights External wind speed
Opening areas 2m/s
Opening heights Constant wind angle

Table 61: Conditions for calculating wind driven air flow by changing shaft heights.

• RESULTS:
Openings
Shaft
height - m
Volumetric
air flow -
m
3
/s
Air
velocity -
m/s
Area -
m
2

Height - m

A1 - Zone inlet 1 1 4 0.23 0.0117
A2 - Shaft inlet 1 1 5 0.25 0.0125
A3 - Shaft outlet 1
0.5 from
shaft top
6 0.26 0.0130
7 0.27 0.0134
External Wind speed 2 m/s 8 0.27 0.0137
External Wind Angle 0
0
10 0.29 0.0144
Zone Height 4m 12 0.30 0.0150

Table 62: Results of air flow rate when shaft heights are altered.

156

Fig 70: Wind driven air flow rates for different shaft heights.

• ANALYSIS:
A gradual rise in air flow rates is observed with increase in shaft height. As the shaft
height increases the static wind pressure acting on the shaft outlet increases. This
increased pressure at the outlets increases the air flow rates across the occupant zones.
However this increase is not steep as shaft height increases.
The increase in air flow rate is because of increase ins haft height as all the other design
components of opening size, opening heights and zone heights influencing air flow are
kept constant for this series of calculations..

157

8.2.2: INFLUENCE OF SHAFT AREA
For this series of calculations the shaft height, shaft opening, zone height, zone opening
size and the height difference between all the openings are kept constant

Fig 71: Single zone + Shaft wherein the shaft area vary.

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft area Wind speed of 2m/s
Opening area and height Different shaft heights
Wind speed 6m and 8m

Table 63: Conditions for calculating wind driven air flow rate when shaft area is
altered.

158

• RESULTS:
Openings
Shaft area –
m
2

Volumetric air flow –
m
3
/s

Area –
m
2

Height -
m
L B m
2
Shaft
height 6m
Shaft
height 8m
A1 - Zone inlet 1 1
1
1 1 0.225 0.238
A2 - Shaft inlet 1 1 2 2 0.250 0.264
A3 - Shaft
outlet
1
0.5m from
shaft top
3 3 0.255 0.270
4 4 0.257 0.272
External Wind speed 2 m/s 5 5 0.258 0.273
External Wind Angle 0
0

2
1 2 0.250 0.264
2 4 0.257 0.272
3 6 0.258 0.273
4 8 0.259 0.274
5 10 0.260 0.274
3
1 3 0.255 0.269
2 6 0.258 0.273
3 9 0.259 0.274
4 12 0.259 0.274
5 15 0.259 0.274
4
1 4 0.257 0.272
2 8 0.259 0.274
3 12 0.259 0.274
4 16 0.259 0.274
5 20 0.259 0.274
5
1 5 0.258 0.273
2 10 0.259 0.274
3 15 0.259 0.274
4 20 0.259 0.274
5 25 0.259 0.274

Table 64:Results of air flow rates by changing shaft area for different shaft heights.

159

Fig 72: Wind driven air flow rates as a function of shaft area for two different shaft
heights.

• ANALYSIS:
The increase in air flow rates stabilizes when the shaft area reaches the minimum
required area, to allow free unobstructed air movements up the shaft without creating any
pressure difference due to its reduced volume. The observations in this series of
investigations are similar to the observations made for the buoyancy driven air flow
calculations for varying shaft areas. Thus shaft area, for both the mechanisms of wind and
buoyancy driven air flow, vary as a function of shaft height and area of openings which
regulate the volume of air flowing up the shaft.

160

8.2.3: INFLUENCE OF SHAFT OUTLET
This series of calculations are to examine the influence of different shaft outlet size on air
flow rates. For these the height difference between all the openings, the zone openings
size, shaft area and zone volume are kept constant for varying shaft outlet size. Thus any
change in shaft outlet size can be attributed to a change in shaft outlet size. The
calculations are performed using two different shaft heights to compare the trend of
change in airflow rate

Fig 73: Single zone connected to shaft having variable shaft outlet size.

161

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume and shaft height Shaft outlet area Wind speed
Opening area and height 2m/s & 5m/s
Wind angle

Table 65: Conditions for calculating wind driven air flow when shaft outlet size is
altered.
• RESULTS:
Wind induced air flow changes with wind speed. Thus this parameter is also considered
for the calculations.
Openings
Win
d
spee
d
Outlet
area in
m
2

Volumetric
air flow –
m
3
/s
Air
velocity
- m/s

Area -
m
2

Height -
m
A1 - Zone inlet 1 1
2
m/s
1 0.259 0.0130
A2 - Shaft inlet 1 1 2 0.300 0.0150
A3 - Shaft outlet 1
0.5 from
shaft top
3 0.309 0.0155
4 0.313 0.0156
Shaft height 6 m 5 0.314 0.0157
Wind Angle 0
o

5
m/s
1 0.238 0.0119
2 0.275 0.0137
3 0.284 0.0142
4 0.287 0.0143
5 0.288 0.0144

Table 66: Results of air flow rate by varying shaft outlet size.

162

Fig 74: Wind driven air flow rate for different shaft outlets size at different wind
speeds.
• ANALYSIS:
The air flow rates increase as long as the shaft outlet size reaches the minimum required
size to allow unobstructed air flow up the shaft. This volume of air flowing up the shaft
depends also on the size of the zone inlets due to which a further increase in shaft outlet
size does not increase air flow rate. Therefore when the shaft outlet size (> 2m
2
) is equal
or more than the sum of zone inlets (2m
2
) the angle of increase in air flow rate reduce.
Thus the air flow rate and the shaft outlet size are also dependent on the other zone
openings which control the volume of air flowing inside. Air flow pattern for wind
induced ventilation is not subject to the neutral plane level. Due to which the air flow
pattern will be convective or reverse depending on the wind direction irrespective of the
shaft height. This negates the need to investigate the influence of wind induced pressure
on air flow pattern in a multi zone model with three inlet openings in the shaft.

163

CHAPTER 9: AIR FLOW IN MODEL D – MULTIPLE ZONES +
SHAFT.
This chapter reports the results and inferences of air flow and pressure differential
calculations performed on a multi zone model connected to a ventilation shaft for both
buoyancy and wind induced ventilation

164

9.1: BUOYANCY INDUCED VENTILATION STUDIES
This section reports the results of calculations performed using a multi zone model.

9.1.1: INFLUENCE OF SHAFT OUTLET SIZE
Appendix A discusses the potential and the effect of neutral pressure plane level on
buoyancy driven air flow. This neutral pressure plane level can change air flow patterns
which may also influence air flow rates. This series of calculations are to investigate the
change in air flow rates when multiple openings are connected to a ventilation shaft.
Under such conditions the neutral pressure plane will affect the air flow pattern.
The air flow pattern across multiple zones can be visualized by calculating the pressure
differences across the multiple openings. Thus pressure differential calculations are
performed for this series for investigations. The pressure distribution graph represents the
air flow pattern across the shaft.
Moreover the change in air flow rates as a function of varying shaft outlet sizes is also
explored further.

165

Fig 75: Multiple zones model connected to a ventilation shaft wherein shaft outlet
size is changed.

166

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft outlet areas Different external
temperature –
0
C Inlet areas 0.5 , 1, 2 , 3 , 4, 5 m
2

Inlet heights Different shaft heights - m

Table 67: Conditions for calculating buoyancy driven air flow rates in a multi zone
model

Pressure changes with height. Thus the parameter of height is also considered for these
calculations. Inferences from the study in Appendix A
35
, the shaft outlet size
configurations are based on the sum of all the inlet opening sizes.

CASE Sum of inlets – A1 + A2 + A3 Area of Outlet – A4 Inlet : Outlet
1 1 + 1+ 1 = 3 1 m
2
3 : 1
2 1 + 1+ 1 = 3 2 m
2
1.5 : 1
3 1 + 1+ 1 = 3 3 m
2
1 : 1
4 1 + 1+ 1 = 3 4 m
2
0.75 : 1
5 1 + 1+ 1 = 3 5 m
2
0.6 : 1

Table 68: Shaft outlet area based on sum of inlet areas (m
2
).

35
Neutral pressure plane level becomes relative when outlet size and height is altered so as to achieve
regular and convective air flow pattern.

167

• RESULTS:
Openings
Shaft
Height
CASE
Pressure Difference - ∆P in Pa

Area -
m
2

Height - m A1 A2 A3 A4
A1 - Shaft inlet 1 3.5
12 m
1 0.94 0.15 -0.33 -0.63
A2 - Shaft inlet 1 7.5 2 1.15 0.35 -0.13 -0.43
A3 - Shaft inlet 1 10 3 1.26 0.47 -0.02 -0.31
A4 - Shaft outlet varies
0.5 from shaft
top
4 1.32 0.52 0.03 -0.26
5 1.38 0.58 0.09 -0.20
Internal zone temperature 23
0
C
External Temperature 20
0
C
18 m
1 0.92 0.15 -0.32 -0.61
2 1.11 0.34 -0.13 -0.41
3 1.23 0.46 -0.01 -0.30
4 1.28 0.50 0.03 -0.25
5 0.90 0.56 1.33 -0.19

Table 69: Results of air flow rate and pressure when shaft outlet size is varied.

• ANALYSIS:

Fig 76: Pressure distribution across shaft height 12m.

168

Fig 77: Pressure distribution across shaft height 18m.

Shaft outlets have the potential to change the pressure distribuiton across the shaft. This
change in pressure changes the air flow patterns across the shaft. This observation is
similar to the inference derived from Appendix A, thus also validating the observations of
Appendix A.It can be observed from Figure 77 that shaft outlets sizes which are equal or
larger then the sum of all inlets areas induce convective
36
air flow across the multi zone
model. When the shaft outlet size is 1& 2 m
2
which is lower than the sum of inlets, the
top zone in the model will have air entering in from lower zones. This is because the
opening A3 lies above the shaft’s neutral pressure plane level.

36
Under this condition all occupant zone have fresh external air flowing inside and air flows from lower to
higher levels.

169

Thus to achieve convective air flow and reduce the influence of neutral pressure plane
level the shaft outlet size should preferably be equal or greater than the sum of area of all
the inlets feeding air inside shaft
37
.This increase in shaft outlet size also will help
increasing the air flow rates as seen in the Figure 78. The increase in air flow for every
increase in shaft outlet size is steep.
The air flow rates at the outlet across the two differnet shaft heights increase with
increase in outlet size.

Openings
Shaft
outlet
size - m
2
Volumetric air flow rate
(m
3
/s) at A4

Area –
m
2

Height - m

Shaft height
– 12 m
Shaft
height – 18
m
A1 - Shaft inlet 1 3.5 1 0.62 1.00
A2 - Shaft inlet 1 7.5 2 1.03 1.82
A3 - Shaft inlet 1 10 3 1.32 2.36
A4 - Shaft
outlet
varies
0.5 from
shaft top
4 1.61 2.68
5 1.77 2.88

Table 70: Buoyancy driven air flow rates for different shaft outlet size at two
different shaft heights.

37
Additionally the inlet closest to the shaft outlet can also be altered to reduce the large size of the outlet.

170

Fig 78: Air flow for different shaft outlet sizes and two different shaft heights.

Thus to increase air flow rates and negate the effect of the neutral pressure plane in a
multi zone model the shaft outlet sizes should be more than the sum of the area of inlets
connected to the shaft.

171

9.2: WIND INDUCED VENTILATION STUDIES
This section reports the results and analysis of wind induced air flow calculations
performed using a multi zone model connected to a ventilation shaft.

9.2.1: INFLUENCE OF SHAFT OUTLET SIZE
Air flow pattern for wind induced ventilation is not subject to the neutral plane level.
Thus irrespective of shaft heights the air flow pattern will be convective or reverse
depending on the wind direction. Thus for this series the influence of shaft outlets on air
flow rates is only investigated. The height difference between the zone openings, the
zone openings and the shaft opening are kept constant. Also the shaft height, zone height
and the shaft area are kept constant throughout. Any change in air flow rates will now be
only because of change in shaft opening size.
The opening area configurations are deduced in a similar order of the buoyancy studies
conducted in section 9.1. - Table 68.

172

• CONDITIONS FOR CALCULATIONS:
Design Constant Design Variables Variable conditions
Single zone volume Shaft outlet areas Different wind speeds
Inlet areas 0.5 , 1, 2 , 3 , 4, 5 m
2

Inlet heights Different shaft heights –m

Table 71: Conditions for calculating wind driven air flow rates in a multi zone
model where shaft outlet is varied.
• RESULTS:
Openings
Wind speed - 2m/s
Area Height

Shaft
outlet
size - m
2
Volumetric air flow rate (m
3
/s)
at A4
A1 - Shaft inlet 1 3.5

Shaft height –
12 m
Shaft height –
18 m
A2 - Shaft inlet 1 7.5 1 0.2808 0.3142
A3 - Shaft inlet 1 10 2 0.3054 0.3418
A4 - Shaft outlet varies
0.5 from
shaft top
3 0.3107 0.3477
4 0.3127 0.3510
Wind Angle 0
0
5 0.3136 0.3524

Wind speed - 5m/s
Shaft
outlet
size - m
2
Volumetric air flow rate (m
3
/s)
at A4
Shaft height –
12 m
Shaft height –
18 m
1 0.5973 0.6442
2 0.6496 0.7007
3 0.6609 0.7129
4 0.6651 0.7173
5 0.6669 0.7194

Table 72: Results of air flow rate as a function of shaft outlet size for different wind
speeds and shaft heights.

173

• ANALYSIS:
As wind speed increases the air flow rates increases. Similarly with increase in shaft
height the air flow rates also increase. However the increase in air flow rates for different
shaft outlet size is marginal and almost negligible. With increase in shaft height the
negative wind pressure exerted at the shaft openings increase. This increase in pressure
increases air flow rates.
Thus shaft outlet height has greater influence on wind induced air flow than the shaft
outlet size.

Fig 79: Air flow rate as a function of shaft outlet size for different wind speeds and
shaft heights.

174

CHAPTER 10: CONCLUSIONS OF BUILDING COMPONENTS ON
AIR FLOW.
This chapter combines the analysis of all the calculations performed on the four different
Model types in Chapter 6, 7, 8 & 9. It informs of the general relationship derived between
building components and air flow.

175

Calculations reported in chapter 6, 7, 8 & 9 highlight the influence of various building
components on air flow. All these building components were investigated under
controlled boundary conditions of temperature, wind speed and wind angle in order to
establish a relationship between them and air flow. This relationship is to identify the
extent of influence building components can have on both buoyancy and wind induced
air flow. Based on these relationships, methods to increase air flow in an occupant space
can be deduced.
This chapter collates all the analysis of these calculations from the four models – Single
sided; Cross ventilation, single zone+ shaft and the multi zone ; that will serve as a
reference guide to design the final model (Chapter 13). The conclusions from all the
analysis are presented in the following order:

1. Occupant zone height.
2. Opening heights.
3. Opening Areas
4. Ventilation shaft height
5. Ventilation shaft area
6. Ventilation shaft - outlet area.

176

10.1: INFLUENCE OF OCCUPANT ZONE HEIGHT
For the buoyancy and wind driven calculations on the two models – single sided and
cross ventilated mode - opening size and the height difference between the openings were
kept constant. Thus the change in air flow rates was as a function of change of zone
height. Under such design conditions buoyancy driven air flow rates remain constant for
varying zone heights, whereas a marginal change in air flow rate is reported for wind
induced air flow.
Buoyancy driven air flow rates depends on opening size and the height difference
between the openings. Therefore when the zone heights are increased while keeping the
openings at the same level, the air flow rates do not increase or change. Thus as long as
the openings are kept at the same level any increase in the height of the zone will not
affect air flow rate.
In the case of wind induce air flow the rise in air flow rates is because the wind pressure
exerted directly on the building openings increases with increase in the zone height. Wind
pressure as per the wind pressure equation (Eq 7 / Section 3.3.1) changes according to
wind speed and height. Wind speed adjusts according to building height. (Eq 10 / Section
3.5.3).such that increases in building height will increase the wind speed.(Awbi 2008)

177

Therefore, when the building height increases the wind pressure exerted directly on the
opening also increases. This increase in wind pressure increases the air flow rates.
However the increase in air flow rates is marginal as their effect on internal temperature
is negligible (as seen from the results in Section 6.2 and 7.2).

10.2: INFLUENCE OF OPENING HEIGHTS
Buoyancy driven air flow rate differs as a function of height difference between
openings. Buoyancy calculations on a single zone models display a change in air flow
rate when the height difference between openings are changed. This change is observed
in all three single zone models
38
.The change in air flow rates in these series of analysis
are attributed purely to change in height difference because the area of openings, zone
heights and the external temperature conditions are kept constant throughout.
A similar pattern of change in air flow in zones having different overall heights aids in
deducing a generalized relation to estimate change in air flow when the height difference
between openings are changed. This generalized relationship is tabulated below in table
73.

38
Single sided ventilated model; cross ventilated model; single zone attached to a ventilation shaft.

178

For wind induced air flow, no natural deviation or marginal difference in air flow rates is
observed when the height difference between openings is increased. Wind induced
pressure generally occurs across the width of the building thus the design flow patterns
are mostly horizontal.
The typical change in air flow by varying height difference between openings induced by
buoyancy and wind effects respectively is tabulated below.

Height difference - m
Change in air flow rates
by Wind effects - Q
w

Change in air flow
rates by Buoyancy
effects – Q
b

Outlet (A2) – Inlet (A1)
0 Q
w
0
1 Q
w
Q
b

1.5 Q
w
Q
b
+ 2.5 Q
b

2 Q
w
Q
b
+ 5.0 Q
b

2.5 Q
w
Q
b
+ 7.5 Q
b

3 Q
w
Q
b
+ 10 Q
b

3.5 Q
w
Q
b
+ 12.5 Q
b

4 Q
w
Q
b
+ 15 Q
b

4.5 Q
w
Q
b
+ 17.5 Q
b

5 Q
w
Q
b
+ 20 Q
b

Table 73: Change in Air flow rates – Q (m3/s) by varying inlet (A1) and outlet (A2)
height difference (DH) for both wind (Q
w
) and buoyancy (Q
b
) driven air flow.

179

Therefore to increase buoyancy driven ventilation rates the height difference between the
inlets and outlets should be extended as much as possible. Whereas in the case of wind
effects, air flow rates remained unchanged when opening heights are changed.

10. 3: INFLUENCE OF OPENING AREA
Governing equations for both, buoyancy driven air flow and wind driven air flow,
express air flow as a function of the total area of opening. This function is such that air
flow rates are directly proportional to the area of opening. Therefore an increase in area
of opening will correspond to an increase in air flow rates.
Airflow calculations on both the zones; single sided and cross ventilated model; highlight
similar results of change in air flow rate when opening sizes are changed. This change is
such that when the area of either of the openings – inlets or outlets is increased the air
flow rates in the zone also increase. This observation is constant for both buoyancy and
wind driven effects on airflow. The increase in air flow rates as a function of varying
opening sizes was similar when the height differences between the openings were
changed, in the case of buoyancy driven effects. Whereas a similar trend of increase in air
flow rates was also observed when the wind speeds were altered when calculated for
wind driven effects.

180

This similar trend aids in deducing a generalized pattern of change in air flow rates when
the opening sizes are changed. The relative change in air flow rates for varying opening
sizes can now be expressed as:

Opening rationale
Change in Volumetric air flow rate –
m
3
/s Inlet : Outlet OR Outlet : Inlet
1 : 1 Q
1 : 2 Q + 27% Q
1 : 3 Q + 34% Q
1 : 4 Q + 38% Q

Table74: Relative percentage change in air flow rate when the ratio of opening sizes
is altered.

This percentage change in air flow rate remains constant for different external
temperature conditions as well as when the height between the openings is changed.
Similar trend of relative change in air flow rates is observed for varying wind speeds and
wind angles.
Moreover results from the investigations display that when the total area of openings
double the air flow rates in the zone also double. This result and observation is in
accordance to the relation expressed by the governing equation of buoyancy and wind
driven air flow rate.

181

10.4: INFLUENCE OF SHAFT HEIGHT
Shaft heights were varied to examine the influence on wind and buoyancy driven airflow
by keeping the shaft outlet level, inlet level and the opening sizes constant throughout.
The corresponding effect on buoyancy air flow rate is negligible as the air flow rates
remains constant for different shaft heights. The air flow rates increase in the case of
wind driven air flow effects.
Buoyancy depends on height difference. This height difference is subject to opening
levels and not the overall height of the zone. This conclusion is similar to the analysis
reported for the single zone – varying zone height investigations. Similar to those results
the air flow rates in this case of varying shaft heights remains unaltered. For increase in
shaft heights the air flow rates remains constant. This air flow rate depends on the
opening area, height difference between the openings and the external temperature
conditions. Shaft heights have not direct effect on air flow rate.
Following this analogy if the shaft outlet level had followed the increase in the shaft
height the air flow rates would increase. This is because the height difference between the
shaft inlet and the shaft outlet would increase.

182

Wind pressure induces a gradual rise in air flow rates when shaft heights are increased.
This rise in air flow is due to stronger wind pressure at shaft outlets. This increased
pressure at the outlets increases the air flow rates across the occupant zones. However
this increase is not steep and regular as shaft height increases. This increase also depends
on the site terrain conditions and the wind angles.
The typical increase in air flow rates are for both wind and buoyancy effects are
compared with the zone height to which the shafts are attached
Zone Height Zone Height
Change in air flow
rates by Wind effects -
Q
w

Change in air flow
rates by Buoyancy
effects – Q
b

Z
h
S
h

4 4 Q
w
Q
b

4 5 Q
w
+ 7.5 Q
w
Q
b

4 6 Q
w
+ 10 Q
w
Q
b

4 7 Q
w
+ 15 Q
w
Q
b

4 8 Q
w
+ 20 Q
w
Q
b

4 10 Q
w
+ 25 Q
w
Q
b

4 12 Q
w
+ 30 Q
w
Q
b

Table 75: Change in air flow rates when ventilation shaft heights are increased,
attached to an occupant zone 4m high.

Buoyancy driven airflow rate remains unaltered whereas for wind driven air flow rates
increase with increase in shaft height. This increase is gradual and regular.

183

10.5: INFLUENCE OF SHAFT AREA
Influence of shaft area on air flow rates so as to reduce shaft volume is similar for both
buoyancy and wind effects. The minimum shaft area requirement depends on the volume
of air and the assumed shaft height. This gives greater flexibility to the designer to
control the shaft volumes in order to reduce its architectural impact. Air flow rates in the
shaft stabilize when the shaft area reaches the minimum required size to allow free
unobstructed air movements. This obstruction can be in relation to pressure induced by
lower shaft area. Reduced shaft areas act as a small hollow opening affecting the pressure
differentials across the main inlets. This pressure difference will be due to ventury effect
of air entering from a larger volume of the occupant space to a smaller undersized shaft.
The trend of change in air flow rates as a function of shaft area for different shaft heights
and opening size is similar. This trend in air flow rates for different shaft areas is
determined by the volume of air flowing up the shaft volume. Opening areas and shaft
height determine volume of air flowing across the zone. The shaft volume needs to be big
enough to accommodate this air volume. The point at x-axis of shaft area – Figure 80
from where the air flow rates become almost constant is the minimum required shaft area
for that respective air volume flowing up the shaft. The line in Figure 80 above provides
an approximate point at which the air flow rates become constant.

184

Fig 80: Typical trend of change in air flow rates for different shaft areas.
39

To verify this approximation a reverse calculation of shaft volume from the air flow rates
at that point was performed.
Terms Calculations Units
Volumetric air flow rate 0.735 m
3
/s
Thus volume of air
0.735 x 60 m
3

44.1 m
3

Height of shaft 6 m
Area of shaft 44.1 / 6 m
3
/ m
Approximate shaft area 7.35 m
2

Table 76: Method to calculate minimum required shaft are depending on volume
flow and overall shaft height.

39
Illustration based on results calculated in Section 8.1.2 ; Page : 147 - 155

185

Shaft areas make marginal difference on air flow rates. As observed from the data Table
76 above – shaft areas depend on air flow rates and shaft height. By determining shaft
heights or minimum required air flow rates the shaft area can be re-calculated to best suit
the space and architectural needs.

10. 6: INFLUENCE OF VENTILATION SHAFT OUTLET
As inferred from calculations performed and reported in Appendix A, shaft outlets have
tendency to affect the neutral pressure plane and also the air flow rates. Series of
calculations performed on the muti zone model reported results of pressure distribution
and air fow rates when the shaft outlet sizes were varied. The pressure distribution graphs
aids in visulaing the air flow pattern up a shaft which is connected to multiple inlets along
its height. Thus the effect of changing shaft outlet size on air flow rates and air flow
pattern on such a shaft model can be easily visualised.Observations based from multi
zone model analysis display change in pressur edistribtuion and air flow rates when the
shaft outlet sizes are changed. Change in shaft outlet size changes the pressure
distribution which helps in achieving convective air flow pattern by changing the neutral
pressure plane level.

186

This observation is similar to the inference derived from Appendix A, thus also validating
the observations of Appendix A.. Additionally when the shaft sizes are increases the air
flow rates also increase. The increase in air flow rates is in accordance to the governing
equations of buoyancy driven air flow. Air flow rates being directly proportional to the
total area of opening – an increase in opening size will increase air flow rates.Similar to
the conclusions of variable opening sizes in a sinlge model, the air flow rates in the shaft
increase with increase in opening size. Here the increase in opening size is that of the
shaft outlet. The effect of shaft outlet on buoyancy driven pressure distribution increases
when the opening size is equal or greater than the sum of area of all the shaft inlet
openings. Air flow patterns are convective
40
and regular when the shaft outlet is equal to
or greater than the sum of all the shaft inlets connected to the shaft. Therefore in order to
achieve convective air flow pattern across all the zones and increase air lfow rates in a
multi zone model the shaft outlets should be equal or greater than the sum of area of all
the inlets connected directly to the ventilation shaft.
Whereas in the case of wind driven air flow rates the effect of shaft height is greater than
the effect of increasing shaft outlet size. The air flow rate increase marginally when the
shaft outlet sizes are increased whereas a steeper rise in air flow rates is observed when
the shaft heights are increased. This is because taller shafts expereince higer direct
pressur e at its openings which results in higher air flow rates. The effect of pressure in
this case is stronger than the effect of total opening area when deriving the air flow rates.

40
In this case convective and regular air flow pattern is when all the three occupant zones connected to the
shaft have direct fresh air coming from outside. There is no re-distribution of stale and contaminated air
flowing from the lower zones into the upper zones and airflows from bottom to up.

187

CHAPTER 11: AIR FLOW USING A VENTILATION SHAFT.
This chapter explores the potential of ventilation shaft in increasing and inducing air
flow in occupant spaces, represented by single and multi zone models. The air flow
results are compared using three model type design of single sided, cross ventilated and
single zone + shaft for all combined, buoyancy and wind induced pressure.

188

This study focuses on exploring the potential of a ventilation shaft and other building
components in inducing and increasing natural ventilation in occupant spaces. For this
series of investigations were performed earlier which explored the potential influence of
various building components on air flow .Using the conclusions and inferences from
those studies, further analysis are conducted to explore the potential of ventilation shaft in
inducing air flow.

This series of calculations are purely to explore and highlight the influence of a
ventilation shaft in generating air flow rates and its effect on internal temperature. Thus,
for these studies similar models A, B & C are used.

Based on conclusion made in chapter 10 – the three Models A, B & C, which are single,
sided, cross ventilated and single zone+ shaft respectively, are designed to allow air flow
across their respective zones. These models are examined under three different design
conditions and separately for wind, buoyancy and then combined air flow effects.

189

Fig 81: Methodology applied to investigate potential of building occupant and
ventilation shaft design on inducing air flow.

190

11.1: AIR FLOW IN SINGLE ZONES MODELS
11.1.1: MODELS FOR THE STUDY
• MODEL 1 – S.D (single sided):
This model is similar to Model A – single sided ventilated single zone model.

Fig 82: Model 1 – Single zone – Single Sided Ventilation

• MODEL 2 – C.V (cross ventilated):
This model is similar to Model B – cross ventilated single zone model.

Fig 83: Model 2 – Single zone – Cross Ventilation

191

• MODEL 3 – S+S (single zone + shaft):
This model is similar to Model C – single zone attached to a ventilation shaft. The height
of the ventilation tower was assumed as 8m equal to the zone height
41
.

Fig 84: Model 3 – Single zone attached to a ventilation shaft
MODEL
OPENING
ORIENTATION
OPE NING AREA: m
2
OPENING HEIGHT: m
MODEL 1 Same facade
A1 1 A1 1
A2 1 A2 3.5
MODEL 2 Opposite Facades
A1 1 A1 1
A2 1 A2 3.5
MODEL 3
Opposite facades
with outlet on
shaft exterior
facade
A1 1 A1 1.5
A2 1 A2 1.5
A3 1 A3 7.5

Table 77: To compare the difference between the opening design of the three single
zone models – 1,2 & 3.

41
SECTION :1.4.1: Establish a workable shaft height for effective stack effect. An effective stack will
usually be twice as tall as the height of the tallest space it is ventilating (Walker, 2010).
192

11.1.2: CONDITIONS FOR CALCULATIONS AND METHODOLOGY
Three different opening design conditions are used on each model to estimate the
change in air flow rate. The design change for the three different series of calculations
is kept constant in all models such that changes in opening heights and opening sizes
are similar in all the three models. As discussed earlier ventilation rates change with
change in opening size and opening heights. Thus opening areas and opening heights
are altered for design Case B and C from the base design Case A.
CASE A Base case for opening height and opening area
CASE B Opening sizes are doubled.
CASE C
Height of openings change.
MODEL 1 – S.D
A1 – 1.5
A2 – 3m
MODEL 2 – C.V
A1 – 1.5
A2 – 3m
MODEL 3 – S+S
A1 – 1.5m
A2 – 1.5m
A3 – 6.5m

Table 78: Single zone model – design conditions.

Conditions Units
Internal Temperature
0
C 23
External Temperature
0
C 20
Wind Speed m / s 2
Wind Angle Degrees 0
o

Table 79: Conditions for calculating air flow in the single zone models.
193

11.1.3: RESULTS - Air flow rates are in m
3
/s

CASE A– base case:
Ventilation
mechanism MODEL 1 – S.D MODEL 2 – C.V MODEL 3 – S+S
Buoyancy air flow 0.302 0.302 0.508
Wind air flow 0.003 0.285 0.253
Combined air flow 0.302 0.415 0.559

Table 80: Air flow results for CASE A –conditions on single zone models.

CASE B – change in opening area:
Ventilation
mechanism MODEL 1 – S.D MODEL 2 – C.V MODEL 3 – S+S
Buoyancy air flow 0.604 0.604 0.987
Wind air flow 0.006 0.571 0.526
Combined air flow 0.604 0.830 1.112

Table 81: Air flow results for CASE B – conditions on single zone models.

194

CASE C – change in opening height:
Ventilation
mechanism
MODEL 1 – S.D MODEL 2 – C.V MODEL 3 – S+S
Buoyancy air flow 0.234 0.234 0.483
Wind air flow 0.002 0.284 0.252
Combined air flow 0.234 0.369 0.536

Table 82: Air flow results for CASE C – conditions on single zone models.

11.1.4: ANALYSIS

Fig 85: Air flow rate in Model 1, 2 and 3 by buoyancy effects.

195

For buoyancy effects MODEL 1 (Single sided) and MODEL 2 (Cross ventilated) single
zone model experience similar air flow rates. The air flow rates in MODEL 3 – connected
to a ventilation shaft are higher than the air flow rates in the other two MODELS’s 1 & 2.

Fig 86: Air flow rate in Model 1, 2 and 3 by wind pressure effects.
In the case of wind driven air flow MODEL 1 (single sided) does not experience any air
flow across its zone. This zone is constructed of two openings on the same facade.
Whereas the other two models – MODEL 2 (cross ventilated) & MODEL 3 (single zone
+ ventilation shaft) have air flowing across its zone. The difference in airflow between
MODEL 2 & 3 highlights the difference partitions makes on cross ventilated air flow
mechanism. In MODEL 2 air enters from the designed inlet and exits from the outlet
located at the opposite façade. This air flow is unobstructed and free flowing. No re-
distribution of air flow pattern is experienced in this model.
196

Whereas the air flow rate in MODEL 3 changes. The common wall joining the occupant
zone to the shaft and also housing the opening A2, acts as a partition reducing the wind
induced pressure lowering the air flow rates. This observation also concludes that to
maximize the benefit of a cross ventilation mechanism the two openings on opposite
facades should have unobstructed air flow - free of any internal partitions.

Fig 87: Air flow rate in Model 1, 2 and 3 by combined pressure effects.

Model 3 which is connected to a ventilation shaft has the highest air flow rates across its
occupant spaces under the combined effect of wind and buoyancy effects. MODEL 1
(single sided) in this case has air flow unlike negligible air flow under wind induced
effects. This air flow rate is purely buoyancy driven as the air flow rate in this model is
similar to the air flow rates when the model was calculated for Buoyancy effects in
Figure -85
197

• AIR FLOW RATES:
Comparative analysis of air flow rates illustrated in Figure 85, 86 & 87 represent the air
flow rates across the three models under the three different design conditions. Single
sided ventilation represented by MODEL 1 favors only buoyancy driven ventilation
whereas the air flow in MODEL 2 which allows cross ventilation, increases under all
temperature and wind conditions. Air flow rates in the single zone employing a
ventilation shaft MODEL 3 - increases in all cases of combined, buoyancy and wind
induced ventilation. This increase in air flow can be attributed purely due to ventilation
shaft as the openings A1 and A2 in this model are at the same level. This negates
additional pressure difference occurring in the occupant zone due to buoyancy which may
increase air flow rates. The change in air flow is due to shaft opening A3 and the shaft
height.

Thus evident from the single zone analysis – a ventilation shaft increases the air flow
rates in the zone to which it is connected under the combined effects of wind and
temperature. However the rise in air flow rate is marginal and the effect of this air flow
on internal temperature and the adaptive thermal comfort conditions are explored
further.

198

• THERMAL COMFORT BY AIR FLOW:
The table below represents the internal temperature achieved by the air flow induced in
the three different models. For this analysis the air flow rates generated under the
combined effect of buoyancy and wind effects are used
42
.For this analysis the external
temperature is 20
0
C (Table 79) which are used for all the air flow calculations and the
internal heat gains in kept constant at 1710W
43
. The internal temperature is calculated
using the internal heat gain equation mentioned in Section 4.2.1 – Equation13.

Combined
air flow
MODEL 1 – S.D MODEL 2 – C.V MODEL 3 – S+S
Air flow
rate - Q
(m
3
/s)
Internal
temperature
-
0
C
Air flow
rate – Q
(m
3
/s)
Internal
temp -
0
C
Air flow
rate – Q
(m
3
/s)
Internal
temp -
0
C
CASE 1 0.302 24.67 0.415 23.40 0.559 22.52
CASE 2 0.604 22.33 0.830 21.70 1.112 21.27
CASE 3 0.234 26.02 0.369 23.82 0.536 22.63

Table 83: Internal temperature by air flow rate generated through combined effect
of buoyancy and wind effects.

42
Generally a combined effect of buoyancy and wind effect induced air flow on a site(Awbi 2008)(Alaard
1998).
43
Section 4.1.2 – Table no. 11.
199

Fig 88: The internal temperature in the three models.

The temperature difference between the external temperature and the internal temperature
for the single sided model (MODEL 1) is more than 3.0
0
C
44
under design conditions A
& B which makes this single zone model ineffective as a naturally ventilated space. The
difference between internal temperatures of MODEL 2 & 3 is marginal. The difference in
the air flow between these two models does not change the temperature to a degree that
its effect may not be able to be substantially felt by the occupant which may then change
their adaptive thermal conditions. This difference ranges from 0.
0
8 to 0.21
0
C.

44
Temperature difference between external and internal temperature should be limited to a maximum of 3.0
0
C in a span of 4 hours for naturally ventilated spaces to maintain adaptive thermal comfort conditions
(ASHRAE/ANSI.55. 2007).
200

Thus increase in air flow rates using a ventilation shaft may not necessarily imply that
it may be much effective in providing considerable difference on the internal
temperature. A single zone having a cross ventilated design with a height difference
between its openings can also provide almost similar results.

• DESIGN OF OCCUPANT SPACES:
Wind induced air flow in MODEL 1 (single sided model) and MODEL 2 (cross
ventilated model) highlight the difference orientation and location of openings can make
on air flow. MODEL 1 & 2 have similar opening size and height; however the single –
sided ventilation design in MODEL 1 does not experience any air flow when there are no
air temperature differences. Whereas, MODEL 2 – cross ventilated single zone; model
has air flow under both the conditions of wind flow and temperature difference.

This identifies the influence of opening location on building façade in inducing
natural ventilation. Thus cross ventilation model is the most effective design for a
single zone occupant space, which can have air flow under all climate conditions. This
difference also highlights limits the time and capability of a single sided ventilation
design which has air flow only under thermal differences.
This study quantifies the influence of ventilation shaft on air flow only in a single zone.
The effect of multiple openings in the ventilation shaft cannot be examined using this
model. Thus a multi zone model of similar dimensions and similar ventilation design is
constructed.
201

11.2: AIR FLOW IN MULTI ZONES MODELS
Similar air flow studies were conducted on these single zone models now placed over
each other having similar volumes calculated for air flow under similar boundary
conditions. The design rational for these models is to represent a low rise commercial
building.

11.2.1: MODELS FOR THE STUDY
• MODEL 4: – S.D (single sided):
This model has three single zones with equal opening size.

Fig 89: Model 4 – Multi zone – Single Sided Ventilation
202

• MODEL 5: C.V (cross ventilated)
This model has three single zones which have equal opening size placed on opposite
facades. The height difference between openings assists in generating hydrostatic
pressure across the height by buoyancy effects.

Fig 90: Model 5 – Multi zone – Cross Ventilation.

203

• MODEL 6: – M.S+S (Multiple zones + shaft):
This model has three single zones which have equal opening size placed on opposite
facades connected to a ventilation shaft. The height difference is only between the
openings in the zone and the outlet on the shaft. This helps to identify the difference a
ventilation shaft can make in creating pressure differentials across the opening thus
inducing air flow in the occupant spaces. The height of the ventilation tower was
assumed as 16m.

Fig 91: Model 6 – Multi zone attached to a ventilation shaft.
204

MODEL
OPENING
ORIENTATION
OPE NING
AREA: m
2

OPENING HEIGHT: m –
from zone base
MODEL 4 Same facade
A1 1 A1 1
A2 1 A2 3.5
MODEL 5 Opposite Facades
A1 1 A1 1
A2 1 A2 3.5
MODEL 6
Opposite facades
with outlet on shaft
exterior facade
A1 1 A1 1.5
A2 1 A2 1.5
A3 1 A3
15.5 – from shaft
base

Table 84: To compare the difference between the opening design of the three multi
zone models.

11.2.2: CONDITIONS FOR CALCULATIONS AND METHODOLOGY:
CASE D Base case for opening height and opening area
CASE E Opening sizes are doubled.
CASE F
Height of openings change.
MODEL 4
A1 – 1.5 from zone base
A2 – 3m from zone base
MODEL 5
A1 – 1.5 from zone base
A2 – 3m from zone base
MODEL 6
A1 – 1.5m from zone base
A2 – 1.5m from zone base
A3 – 14.5 m from shaft base

Table 85: Multi zone model – design conditions
205

The Climate and design conditions for the multi zone models are similar to the single
zone models.

Conditions Units
Internal Temperature
0
C 23
External Temperature
0
C 20
Wind Speed m / s 2
Wind Angle Degrees 0
o

Table 86: Conditions for calculating air flow in the multi zone models.

11.2.3: RESULTS - All air flow rates are reported in m
3
/s .
CASE D – base case:
Ventilation
mechanism
Zone MODEL 4 MODEL 5 MODEL 6
Buoyancy air
flow
ZONE A 0.302 0.302 0.732
ZONE B 0.309 0.309 0.485
ZONE C 0.316 0.316 0.282
Wind air flow
ZONE A 0.003 0.284 0.188
ZONE B 0.064 0.344 0.206
ZONE C 0.090 0.399 0.186
Combined air
flow
ZONE A 0.302 0.415 0.746
ZONE B 0.309 0.458 0.521
ZONE C 0.316 0.502 0.152

Table 87: Air flow results for CASE D – conditions on Multi zone models.

206

CASE E – change in opening area:
Ventilation mechanism Zone MODEL 4 MODEL 5 MODEL 6
Buoyancy air flow
ZONE A 0.604 0.604 1.432
ZONE B 0.617 0.618 0.939
ZONE C 0.631 0.631 0.542
Wind air flow
ZONE A 0.006 0.568 0.364
ZONE B 0.127 0.687 0.403
ZONE C 0.180 0.799 0.375
Combined air flow
ZONE A 0.604 0.830 1.457
ZONE B 0.617 0.917 1.007
ZONE C 0.631 1.004 0.274

Table 88: Air flow results for CASE E – conditions on Multi zone models.

CASE F – change in opening heights:
Ventilation mechanism Zone MODEL 4 MODEL 5 MODEL 6
Buoyancy air flow
ZONE A 0.234 0.234 0.723
ZONE B 0.239 0.239 0.470
ZONE C 0.244 0.245 0.308
Wind air flow
ZONE A 0.002 0.283 0.187
ZONE B 0.049 0.341 0.203
ZONE C 0.070 0.396 0.181
Combined air flow
ZONE A 0.234 0.369 0.740
ZONE B 0.239 0.415 0.512
ZONE C 0.244 0.646 0.184

Table 89: Air flow results for CASE F – conditions on Multi zone models.

207

11.2.4: ANALYSIS
For the multizone models - Buoyancy driven, wind driven and combined air flows are
analyzed separately.

• BUOYANCY DRIVEN AIR FLOW:
1. AIR FLOW PATTERN:

Fig 92: The air flow pattern across the stacked zones under buoyancy effects.

MODEL 4 (single sided) & MODEL 5 (cross ventilated) experience convective air flow
pattern in all the zones – wherein air enters through the inlets and leaves from the outlets.
The air flow pattern across the three zones in MODEL 6 is not convective. Zone 6 C (Top
zone) has air entering from its outlet opening A2 instead of the designed inlet A1. Air
from the shaft fed by the lower two zones – Zones 6A & 6B enters Zone 6C. Stale air
from the lower zones is not suitable to provide thermal comfort as it is pre heated by heat
gains from the lower zones.

208

Moreover this stale air is contaminated and thus cannot maintain the indoor air quality
levels for the upper zone. The benefits of natural ventilation are lost in case of this model
type. This is due to the effect of the neutral pressure plane of the ventilation shaft. This
neutral pressure plane lies below the openings of Zone 6C which regulates the air flow
direction
45
.

2. AIR FLOW RATES:

Fig 93: The air flow rates across the three models 4, 5 & 6 by buoyancy pressure.

45
The effect of neutral pressure plane can be understood by also comparing Model 6 for both buoyancy and
wind induced air flow. No irregular air flow occurs for wind induced ventilation in Model 6. Thus neutral
pressure plane is active as long as there exits temperature differences. A detailed study for methods to
reduce the effect of the neutral pressure plane was conducted as part of this study reported in appendix A
209

Zones B & C in MODEL 4 (single sided) & MODEL 5 (cross ventilated) have higher air
flow rates than those in Zone A (Lowest zone). – Figure 93. This difference is marginal.
MODEL 6 – attached to the ventilation shaft experience highest air flow rates. The air
flow rates in the lower two zones – Zone A & B in this model is almost double than the
air flow rates in Model 4 & 5 under all the three design conditions. The opening area,
opening heights and temperature conditions under which the three models were
calculated are similar and constant. Therefore the steep rise in air flow for MODEL 6 is
can be attributed to the effect of the ventilation shaft.

Zone C – the topmost zone in MODEL 6 has reduced air flow rates. The height
difference between the shaft outlet and the opening in Zone C is the least which reduces
the air flow rates. However the difference in air flow of ZONE 6 C is not much when
compared to similar zones 4C of MODEL 4 (single sided) and zone 5C of MODEL 5
(cross ventilated).

The air flow rates in the three zones of MODEL 6 (ventilation shaft) under buoyancy
effects are not constant as seen in Figure 93. The lowest zone experiences highest air
flow rate whereas when the openings move closer to the shaft outlet level the air flow
rates in their respective zones decrease. This is not suitable condition to maintain internal
air temperature constant through all the zones. Thus to maintain thermal comfort in
multiple zones by natural ventilation mechanisms it is preferable to have regular and
approximately similar air flow rates in all the zones.
210

Ventilation shaft increases air flow under buoyancy effects for multi zone models.
Methods to avoid re-circulation of stale contaminated air in the top zone are mentioned
in Appendix A.

• WIND DRIVEN AIR FLOW
1. AIR FLOW PATTERN:

Fig 94: The air flow pattern across the three zones due to wind pressure effects.

Unlike air flow patterns observed in Figure 92 for buoyancy induced air flow – the air
flow patterns in MODEL 6 (ventilation shaft) remain regular – convective. Fresh air
flows through all the zones in all the three types of models. Thus neutral pressure plane
depends on pressure induced by temperature differences and not by wind induced
pressure. MODEL 4 (single sided) does not have any air flow generated by wind pressure
whereas MODEL 5 (cross ventilated) has air flow in all the zones.

211

2. AIR FLOW RATE:

Fig 95: The air flow rates across the three models 4, 5 & 6 by wind pressure.

The bottom Zone 4A of MODEL 4 (single sided) is devoid of any air flow. As the zones
move higher in altitude the air flow rate in Zone 4B & 4C increase marginally. This
marginal increase of increase in air flow observed and experienced exactly at the center
of the openings by the prevailing wind. This air flow is generated when the wind first
strikes the opening
46
. The air flow generated at that moment is reported for this study.
Also with increase in height the direct wind pressure acting on the openings also
increases due to which the air flow in Zone 4C is greater than Zone 4B in MODEL 4.

46
CONTAM reports results of air flow rates experienced exactly at the center of the openings and for this
study it is conducted for as specific time instead of a period of time
212

MODEL 5 – cross ventilation model -performs best as it assists free air movement in and
out its zones. The air flows inside and outside of all its zones unobstructed. No internal
partitions affect air flow in its occupant zones. It has the highest air flow rates when
compared to the other two MODELS - 4 (single sided) & 6 (ventilation shaft).

All the three zones in MODEL 6 connected to the ventilation shaft have constant air flow
but lower than the air flow in MODEL 5 (cross ventilated) and greater than the air flow in
MODEL 4 (single sided) The wall housing inlets of the shaft and connecting the shaft to
the zones acts as a partition to the free air flow induced by direct positive wind pressure
acting on the zone inlets. This wall reduces the air flow rates as it acts as an obstruction
to free air flow across the occupant space into the shaft. The pressure induced by wind
flowing directly inside is reduced. Thus the difference in air flow MODEL 5 & 6.As the
zones move higher from the ground the air flow rates for both the cases of buoyancy and
wind increase. This is as free wind exerts greater static pressure at higher altitudes and air
density decreases increasing the buoyancy pressure. The upper Zone 6C has therefore
highest air flow rate when compared to its lower zone 6A & 6B in MODEL 6.

Ventilation shafts induce air flow under wind pressure effects. The air flow rates can
be increased further by creating height differences between the zone openings, similar
to the cross ventilated model. Thus a combination of cross ventilated occupant zone
and a ventilation shaft can render higher air flow rates.

213

• COMBINED AIR FLOW
1. AIR FLOW PATTERN:

Fig 96: The air flow pattern across the three zones due to combined effects.

Combined air flow is the effect of buoyancy and wind pressure combined. The air flow
patterns is thus a result of a combined effect of direct wind pressure acting on the
openings and the neutral pressure plane level in the shaft. Results from this calculation
highlight similar air flow patterns that observed from buoyancy driven air flow
investigations.

MODEL 4 (single sided) & MODEL 5 (cross ventilated) have convective airflow
wherein fresh air flows directly inside its zones. The air flow pattern the air flow patterns
driven by combined effects is irregular in MODEL 6 (ventilation shaft). This is because
the buoyancy induced pressure is stronger than the wind induced pressure. Thus Zone 6C
has contaminated stale air passing through.

214

2. AIR FLOW RATE:

Fig 97: The air flow rates across the three models 4, 5 & 6 by combined
pressure of buoyancy and wind.

Air flow rates in MODEL 4 (dingle sided) for a combined effect is similar to air flow
rates deduced in the buoyancy driven air flow calculations. All the zones in this model
have almost constant and regular air flow rates.

215

The airflow rates in MODEL 5 (cross ventilated) increase with increase in the zone
height. Wind pressure increases at higher altitudes thus the upper level zones have higher
air flow rates. This MODEL 5 has air flow due to the combined pressure effect of
buoyancy and wind. The height difference between its two openings induces buoyancy
driven air flow whereas the opposite location of its openings induces cross air flow,
benefitting from wind pressure.

The lower two zones – zone 6A and Zone 6B in Model 6 – connected to the ventilation
shaft experience highest air flow rates for all the three design case conditions. The lowest
zone 6A has the maximum height difference from its inlet to the shaft outlet. This height
difference aids in increasing the air flow rate for that zone. Similar analogy of difference
in opening heights is responsible of increasing air flow rates in the middle Zone 6B.The
neutral pressure plane level re-circulates contaminated air in the top zone 6C. Moreover
Zone 6C is located closest to the shaft outlet. The reduced height difference between its
openings and the outlet reduces the airflow rates generated inside the shaft.

Ventilation shaft aids in increasing air flow rates under combined effect of wind and
buoyancy effects.

216

3: THERMAL COMFORT BY AIR FLOW:
The table below represents the effective internal temperature achieved by the combined
air flow induced in the three different models.
Combined
Air flow
MODEL 4: S.S MODEL 5: C.V MODEL 6: M.S + S
Air flow
rate – Q
(m
3
/s)
Internal
temp -
0
C
Air flow
rate – Q
(m
3
/s)
Internal
temp -
0
C
Air flow
rate – Q
(m
3
/s)
Internal
temp -
0
C
CASE D
ZONE A 0.30
24.7
0.42
23.4
0.75 21.9
ZONE B
0.31
24.6
0.46
23.1
0.52 22.7
ZONE C
0.32
24.5
0.50
22.8
0.15 29.3
CASE E
ZONE A 0.60 22.3 0.83 21.7 1.46 21.0
ZONE B
0.62 22.3 0.92 21.5 1.01 21.4
ZONE C
0.63 22.2 1.00 21.4 0.27 25.1
CASE F
ZONE A 0.23 26.0 0.37 23.8 0.74 21.9
ZONE B
0.24 25.9 0.41 23.4 0.51 22.8
ZONE C
0.24 25.8 0.65 22.2 0.18 27.7

Table 90: Internal temperature by air flow rate generated through combined effect
of buoyancy and wind effects on Multi zone models.
217

Fig 98: The Internal temperature in the three models.

The temperature difference between the external temperature (20
0
C) and the internal
temperature in all the models is more than 3.0
0
C under conditions of Case D & Case F.
When the area of openings is increased in CASE E the air flow rates increase and the
temperature difference decreases. The air flow generated in all the three models in CASE
E conditions assists in providing adaptive thermal comfort conditions.

218

This difference also highlights that area of openings has greater influence than the height
difference between openings for changing air flow rate. Similarly area of openings will
have greater influence on thermal comfort than the height difference between the
openings.
As CASE E provides temperatures within the range to provide adaptive thermal comfort
conditions, analysis for the effectiveness of a ventilation shaft is performed using the
results of the CASE E calculations. Regular and constant air flow rates in MODEL 4 & 5
results in similar internal temperatures in its three single occupant zones. This maintains
constant thermal comfort conditions in all the three zones of MODEL 4 & MODLE 5.

Different air flow rates in the three zones of MODEL 6 (ventilation shaft) results in
different temperature conditions across the three zones. These varying conditions are
such that the thermal comfort conditions across the three zones connected to the
ventilation shaft are not constant. The resultant internal temperature is closer to the
external temperature in the lowest zone which has the highest air flow rates. In the middle
zone the temperature difference between the external and the internal temperature
increase whereas the low air flow rates in the upper zone do not provide thermal comfort
conditions. Different airflow rates have varied effect on thermal comfort conditions
reducing the potential and impact of having a ventilation shaft. Methods to balance
airflow rate across the three zones by altering the component design is explored in the
next series of investigation of multi zone models.
219

Ventilation shaft impart air flow across the zones to which it is connected in all
conditions. This induced air flow may not necessarily provide thermal comfort
conditions.

11.3: SUMMARY OF CONCLUSIONS
• Single zone analysis of the single sided and cross ventilated model display the
influence of opening location on building façade in inducing natural ventilation.
Single sided model, which has openings at a height difference and the openings
are located on the same façade, fails to induce air flow under prevailing wind
conditions. The single sided model experiences air flow only under buoyancy
effects. Whereas the cross ventilated single zone model, wherein the openings are
kept at a height difference and openings on opposite faces, has airflow under both
the effects of buoyancy and wind. Thus cross ventilation model can be the most
effective design for a single occupant zone, which can have air flow under all
climate conditions. This difference also highlights limits the time and capability
of a single sided ventilation design which has air flow only under thermal
differences.

220

• Air flow calculations and analysis on single zone model identifies that a
ventilation shaft increases the air flow rates in the zone to which it is connected.
However the affect of this increased airflow rate is not so high to create any
substantial difference on the internal temperature of the zone. The difference
made by air flow generated in a cross ventilated model and the single zone model
connected to a ventilation shaft on temperature is extremely low. This low
difference does not affect the thermal comfort conditions. Thus a ventilation shaft
may not have much influence in increasing the effectiveness of natural ventilation
in a single zone occupant space.

• For multi zone models a ventilation shaft increases buoyancy induced air flow
rate in the occupant zone. However the neutral pressure plane level reduces the
impact and efficiency of the shaft in providing balanced and equal air flow across
all the zones it’s connected to. All the zones connected to the shaft have different
airflow rates which creates different internal temperature conditions in the
occupant zone.

• In the case of wind induced air flow the ventilation shaft reduces the direct wind
pressure acting on zone inlets. The cross ventilated multi zone model has
unobstructed air flow when entering and leaving the zone. The ventilation shaft’s
internal wall connected to the occupant zones acts as partitions to the wind
induced air flow and reduces the wind pressure differentials inside the model.
221

This obstruction reduces the air flow rates inside the zones. However in this case
the air flow rates across the three zones are relatively balanced and similar.

• The combined air flow calculations on the multi zone model highlight the
difference opening sizes make on air flow when compared to the relative
difference changing opening levels can have on air flow. This difference in air
flow also impacts the thermal comfort conditions. Only under the conditions
wherein the opening sizes were doubled, the multiple zones had internal
temperatures not exceeding the 3.0
0
C temperature difference of naturally
conditioned spaces. This analogy can be so applied that – when trying to achieve
thermal comfort conditions in a zone via natural ventilation the first step to
consider would be simply to increase the area of openings

• The air flow generated in the multiple zones connected to the ventilation shaft is
not constant. This inconsistent air flow rate between the zones changes the
internal temperature conditions in all zones which may alter the thermal comfort
conditions. This may reduce the effectiveness of natural ventilation of the whole
model. The effect of air flow induced by a ventilation shaft in a multi zone model
is higher than the effect of air flow induced by the shaft in single zone model.
Potential of ventilation shaft increases when it is connected to multiple zones
instead of single zones.

222

CHAPTER 12: DESIGN AND EFFECTIVENESS OF A
VENTILATION SHAFT.
This chapter explores the potential of ventilation shaft in creating thermal comfort
conditions and also the possibility of reducing its occupied volume. Two models of
similar volumes connected to different ventilation shafts are compared for their thermal
comfort conditions as a result of the air flow induced by ventilation shafts. The
calculations are performed for a specific day and site.

223

Investigations in the earlier chapter report potential of using a ventilation shaft in
influencing airflow and also compare the difference made by ventilation shafts on air
flow when compared to other ventilation designs. Results of calculations on multi zone
model connected to a shaft highlight undistributed and varying air flow rates across the
three zones to which the shaft is connected. The varying air flow rates have considerable
influence on the internal temperature which may affect the thermal comfort conditions in
the occupant zone.
This chapter examines methods to avoid this irregular airflow generated across the three
zones which are connected to ventilation shaft and also the potential of ventilation shafts
in providing adaptive thermal comfort conditions. For this two separate models are
constructed. The ventilation designs of the two models vary based on the research and
inferences from the air flow investigations performed on single and multi zone models.
The design of the ventilation shaft in the first model (MODEL X) is based on the general
design guidelines recognized and reported in section 1.4.1. The design of the ventilation
shaft used in the second model (MODEL Y) - is based on the series of calculations
performed in Chapter 6, 7, 8 & 9 which are focused on finding methods to increase air
flow rates in occupant zones. Observations and inferences derived from these
investigations were used to construct a model which attempts to maximize the influence
of natural ventilation on thermal comfort. These two models were examined for air flow
rates under different climatic conditions. The procedure and analysis methodology for the
calculations in this section are illustrated in the flow chart below.
224

Fig 99: Methodology applied to investigate thermal comfort and variation is
ventilation shaft designs.

225

12.1: FRAMEWORK FOR CALCULATIONS
12.1.1: MODELS FOR THE STUDY
12.1.1.1: MODEL X:
This model represents a three story commercial building with three single zones stacked
over each other. The floors are connected to a ventilation shaft. The dimensions and
design of the ventilation shaft is based on the general design guidelines mentioned in
section 2.3.1.
Zone height: The occupant zone height is 4m.
Zone area: A rectangular floor plate of 50m
2
area, the shorter dimension is 5m.
Zone opening height: The inlets and outlets are placed at different heights. The centre of
the inlet is at 1.25m whereas the outlet is at 3.5m such that the height difference is 2.25m.
All these dimensions are from the floor level of their respective zones.[Section 2.3.1 –
point 4].
Zone opening size: Openings are placed on the West and East facade. These exterior
walls have 40% of its wall area as openings. The 40% complies with the California
TITLE 24 requirement as minimum opening size requirements so as to achieve
acceptable daylighting and ventilation. This computes to 8m
2
as minimum opening area
requirement. The openings are assumed to be 50% operable. Thus the effective opening
area which regulates air flow is 4m
2
. The opening sizes for this model are then
recalculated, such that they allow similar amount of mass flow across. The total sum of
opening is 8m
2
; the inlets are 3m
2
and the outlets are 5m
2
. [The ratio of inlet to outlet
openings is now 1:1.7.] [Section 2.3.1 – point 7].
226

Overall height: This model is constructed of three single zones the overall building
height is 12m.
Shaft height: The total shaft height is 16m. This height is twice the height of the tallest
zone. . [Section 2.3.1 – point 6].
Shaft area: Minimum required shaft area is calculated according to the method
mentioned in section 10.5. The total amount of air flowing up the shaft is calculated from
the air flow in model 1. The shaft height is assumed as 16 m as mentioned earlier. Thus
the shaft area computes to 26.25 m
2
as the minimum required, to allow free air movement
up the shaft.
Shaft outlet: The design, orientation and the size of the shaft outlet is based on
guidelines mentioned in section 2.3.1 – point 2 & 3. The shaft outlet height is at 15.5m
from the ground and the outlet size is 12m
2
.

227

Fig 100: Design of MODEL X.

228

12.1.1.3: MODEL Y:
This model represents a three story commercial building similar to Model X. with three
single zones stacked over each other. The floors are connected to a ventilation shaft. The
design of openings in the occupant zones and the design of the ventilation shaft are based
purely on inferences derived from the ventilation studies concluded in chapter 10.
Zone height: The occupant zone height is 4m.Varying zone height makes no difference
to air flow. [Section: 10.1]
Zone area: A rectangular floor plate of 50m2 area, the shorter dimension is 5m.
Zone opening height: The inlets and outlets are placed at different heights. By increasing
the height differences between inlets and inlets the airflow increases. This is based on
inference in Section 10.2. The height difference between inlets and outlets vary from
2.75m to 1.25m.
Zone opening size: As observed from previous investigations on the multi zone model
(MODEL 6) all its three zones have different air flow rates. This may induce drastic
internal temperature differences across the three zones and may affect thermal comfort
conditions. The openings in this model are designed so as to regulate air flow at a
constant rate and maintain internal temperature close to the prevalent external air
temperature in all the zones. This rational of design is based on inference from Section
10.3.

229

Overall height: This model is constructed of three single zones the overall building
height is 12m.
Shaft height: The total shaft height reduced to 13.5m. This is 1.5 m higher from the roof
top of zone 3. This is done to reduce the overall shaft volume.
Shaft area: Minimum required shaft area is calculated according to the method
mentioned in Section 10.5. The total amount of air flowing up the shaft is calculated from
the mass flow in model 1. The shaft height is assumed as 13.5 m as mentioned earlier.
The shaft area is reduced from 26.25m
2
which was as calculated for model B to 24m
2
for
this model.
Shaft outlet: To raise the neutral pressure plane the outlet size is increased. The outlet
size is 15m
2
. The basis of this re-configuration is in accordance to inferences from
Section 10.6

230

Fig 101: Design of MODEL Y

231

Thus to summarize the design of the three different models:
PARAMETER MODEL X MODEL Y
Zone area - m
2
50 50
Zone height - m 4 4
Opening height
- m
Zone 1
A1 x 1 A1 y 1.5
A2 x 3.5 A2 y 3.25
Zone 2
A3 x 5 A3 y 5.5
A4 x 7.5 A4 y 7.5
Zone 3
A5 x 9 A5 y 8.75
A6 x 11.5 A6 y 11
Opening area –
m
2

Zone 1
A1 x 3 A1 y 2
A2 x 5 A2 y 3
Zone 2
A3 x 3 A3 y 3
A4 x 5 A4 y 3
Zone 3
A5 x 3 A5 y 2
A6 x 5 A6 y 3
Overall height - m 12 12
Shaft height - m 16 13.5
Shaft area – m
2
26.25 24
Shaft volume – m
3
420 324
Outlet area – m
2
A7 12 15
Outlet height - m A7 15.5 13

Table 91: Summary of the two model designs – Model X & Y.

232

12.1.2: CLIMATE PARAMETERS
Methods to increase air flow performed and reported earlier in this study are not climate
specific. They offer general relationships between various building physical parameters
and air flow. To verify these methods a series of calculations under different climatic
conditions were performed. Thus only for this final study a climate zone is considered.

12.1.2.1: CLIMATE ZONE:
The climate of a typical summer day in Los Angeles is considered for this study. The
climate data for this period is taken from Climate Consultant 5.1
47
.According to the
ASHRAE handbook of Fundamentals Comfort model, 2005 and the Adaptive Comfort
model in ASHRAE 55- 2004, following are the criteria’s for a zone ventilated by natural
ventilation mechanisms.
Terrain Category to modify Wind speed 2 - Suburban
Minimum Indoor Velocity to effect Indoor comfort: 0.2 m/s
Maximum comfortable velocity 1.5 m/s
Maximum perceived temperature reduction 3.6
0
C
Adaptive thermal comfort acceptability 90 %
Comfort Low – Minimum Operative Temperature 19.4
0
C
Comfort high – Maximum Operative Temperature 26.7
0
C

Table 92: The climate limitation and criterions for a naturally ventilated space in
Los Angeles.

47
Climate Consultant – Milne & Liggett; UCLA Energy Design Tools Group.
233

These criteria are intended as guidelines and limitations to verify the effectiveness of
cooling effect by air flow in the two models.

12.1.2.2: TEMPERATURE:
The temperature range for the month of September in Los Angeles is as illustrated below:

Fig 102: Temperature range in
0
C for September in Los Angeles
48
.

The daytime temperature on 22
th
September is:
H 0 1 2 3 4 5 6 7 8 9 10 11
T 18.8 17.8 15.2 15.8 15.6 13.4 14.6 14.7 18.4 22.7 21.8 22.5

H 12 13 14 15 16 17 18 19 20 21 22 23
T 23.2 23.1 23.6 25.7 24.6 23.6 21.5 21.5 22.1 19.8 20.1 19.4

Table 93: Day time temperatures (
0
C) on 22
nd
September in Los Angeles.

48
Climate Consultant – Milne & Liggett; UCLA Energy Design Tools Group.
234

The weather data for 22
nd
September is taken from the United States department of
Energy weather resources and processed in the Autodesk Weather tool -2010.

Fig103: External temperature on 22
nd
September.(ASHRAE/ANSE.62.1 2007).

Fig104: Typical occupancy schedule in a commercial building (ASHRAE/ANSE.62.1
2007).

235

12.1.2.3: WIND SPEED AND WIND DIRECTION:
The average wind speed in Los Angeles for September is 3m/s.

Fig105: Wind rose diagram for 22September
49
.

The prevalent wind direction is from the South West. For the purposes of this study we
assume the wind direction to be only from the west. The wind angles changes as per site
location. As this is a generic study we assume the wind angle to be 0
o
throughout the day.
The site terrain for the wind speed modifier is assumed as suburban which is in
accordance to the criteria’s set forth by ASHRAE handbook of Fundamentals Comfort
model, 2007 for Los Angeles.

49
Climate Consultant – Milne & Liggett; UCLA Energy Design Tools Group.
236

12.1.3: CALCULATION METHODOLOGY
The models are calculated for air flow for different temperature and wind direction
conditions.
Temperature: The air flow rates are calculated for 11 different external temperatures-
from 08.00 hrs to 18:00 hrs on 22
nd
September. The temperature difference between the
assumed internal and external temperature is 3
0
C.
Wind Direction: The models are calculated for two wind directions. For the first set of
calculations the wind direction will be from West to East and the second series of
calculations will be assuming wind from East to West.
Wind speed: All the models will be experience a constant wind speed of 3m/s. Internal
Heat gain: The heat gain will be kept constant at 1710 W.

CASE I Hour T
o
–
0
C
Assumed T
i

–
0
C
External Temperature Te 8:00 18.4 21.4
Internal Temperature Ti 9:00 22.7 25.7
Wind speed 3m/s 10:00 21.8 24.8
Wind Direction W to E 11:00 22.5 25.5
CASE II 12:00 23.2 26.2
External Temperature Te 13:00 23.1 26.1
Internal Temperature Ti
14:00 23.6 26.6
Wind speed 3m/s
15:00 25.7 28.7
Wind Direction E to W 16:00 24.6 27.6
CASE III 17:00 23.6 26.6
External Temperature Te 18:00 21.5 24.5
Internal Temperature Ti 19:00 21.5 24.5
Wind speed 0 m/s

Table 94: Summary of the three climate conditions.
237

12.1.4: RESULTS

RESULTS

Time H Hours
Internal Temperature T
i

0
C
External Temperature T
e

0
C
Volumetric air flow Q m
3
/s
Air velocity - V m/s

Table 95: The units and symbols of the result table.

CASE I, II & III
Air flow pattern
Air flow rates across the three zones
Thermal comfort of the occupant zones

Table 96: Break down for reporting results of the calculations.

238

12.2: AIR FLOW & THERMAL COMFORT IN THE MODELS
12.2.1: RESULTS OF CASE I CLIMATE CONDITIONS: wind directly on
inlets.

Conditions ZONE 1- LOWEST LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 3.61 0.181 18.8 2.45 0.122 19.0
9 22.7 3.54 0.177 23.1 2.40 0.120 23.3
10 21.8 3.56 0.178 22.2 2.40 0.120 22.4
11 22.5 3.55 0.177 22.9 2.40 0.120 23.1
12 23.2 3.53 0.177 23.6 2.39 0.120 23.8
13 23.1 3.54 0.177 23.5 2.40 0.120 23.7
14 23.6 3.53 0.176 24.0 2.39 0.120 24.2
15 25.7 3.50 0.175 26.1 2.37 0.118 26.3
16 24.6 3.51 0.176 25.0 2.38 0.119 25.2
17 23.6 3.53 0.176 24.0 2.39 0.120 24.2
18 21.5 3.56 0.178 21.9 2.41 0.121 22.1

Table 97: Results of air flow and temperature compared with each zone of the two
models – when conducted under conditions represented by CASE I.

239

Conditions ZONE 2 - MID LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 3.09 0.154 18.9 2.70 0.135 18.9
9 22.7 3.03 0.152 23.2 2.65 0.132 23.2
10 21.8 3.04 0.152 22.3 2.65 0.132 22.3
11 22.5 3.04 0.152 23.0 2.65 0.133 23.0
12 23.2 3.03 0.151 23.7 2.64 0.132 23.7
13 23.1 3.03 0.151 23.6 2.65 0.132 23.6
14 23.6 3.02 0.151 24.1 2.64 0.132 24.1
15 25.7 3.00 0.150 26.2 2.62 0.131 26.2
16 24.6 3.01 0.150 25.1 2.63 0.132 25.1
17 23.6 3.02 0.151 24.1 2.64 0.132 24.1
18 21.5 3.05 0.152 22.0 2.66 0.133 22.0

Conditions ZONE 3 - TOP LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 2.44 0.122 19.0 1.76 0.088 19.2
9 22.7 2.41 0.120 23.3 1.73 0.087 23.5
10 21.8 2.41 0.121 22.4 1.73 0.087 22.6
11 22.5 2.41 0.120 23.1 1.74 0.087 23.3
12 23.2 2.40 0.120 23.8 1.73 0.087 24.0
13 23.1 2.40 0.120 23.7 1.74 0.087 23.9
14 23.6 2.40 0.120 24.2 1.73 0.086 24.4
15 25.7 2.38 0.119 26.3 1.72 0.086 26.5
16 24.6 2.39 0.120 25.2 1.72 0.086 25.4
17 23.6 2.40 0.120 24.2 1.73 0.086 24.4
18 21.5 2.41 0.121 22.1 1.74 0.087 22.3

Table 97: Continued -.

240

12.2.1.1: ANALYSIS
AIR FLOW PATTERN:
The air flow rates across the three zones of the two models for CASE I climate conditions

Fig106: Air flow pattern in Model X & Y for CASE I climate conditions.

Air flow pattern across all the zones in both MODELS’ X & Y is regular – convective.
All the occupant zones receive direct fresh air flow from the inlets on the west façade of
the model. Air exits from the designed zone outlets into the shaft. It moves up along the
shaft height finally exiting from the shaft outlet.
Both the types of ventilation shafts induce regular convective air flow pattern when the
wind flows directly perpendicular to the zone inlets.

241

AIR FLOW RATE:

Fig 107: Air flow rates in MODEL X & Y for CASE 1 climate conditions.

The air flow rates in all the zones of MODEL X are higher than the corresponding zones
of MODEL Y. MODEL X which has taller ventilation shaft induces higher air flow rates
when compared to MODEL Y. However the difference between the air flow rates in each
of individual zones in MODEL X is greater when compared to the difference in air flow
rates of the occupant zones in MODEL Y. The air flow rates in MODEL Y are lower but
the difference in air flow rates among its occupant zones is relatively low.

Both these models induce air flow when wind flows directly perpendicular on its
designed inlet openings.

242

INTERNAL TEMPERATURE and THERMAL COMFORT:

Fig 108: Internal temperature of the occupant zones of MODEL X & Y under
CASE I climatic conditions.

The induced air flows in the two models are sufficient and regular over a period of time
which helps to dissipate the internal heat gains of the occupant zones to which they are
attached. The air flow aids in maintaining the internal temperature of the zones within the
operative temperatures for achieving 90% adaptive thermal comfort conditions in its
zones. This also verifies that when the air flow difference between the zones in multi
zone model are less thermal comfort conditions can be achieved. The internal
temperatures in all these zones are also approximately the same.

243

12.2.2: RESULTS OF CASE II CLIMATE CONDITIONS: wind opposite to
inlets.

Conditions ZONE 1- LOWEST LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 3.02 0.151 18.9 1.94 0.097 19.1
9 22.7 2.95 0.148 23.2 1.89 0.094 23.4
10 21.8 2.97 0.148 22.3 1.90 0.095 22.5
11 22.5 2.96 0.148 23.0 1.89 0.095 23.2
12 23.2 2.94 0.147 23.7 1.88 0.094 23.9
13 23.1 2.95 0.147 23.6 1.89 0.094 23.8
14 23.6 2.94 0.147 24.1 1.88 0.094 24.3
15 25.7 2.91 0.145 26.2 1.86 0.093 26.5
16 24.6 2.92 0.146 25.1 1.87 0.094 25.4
17 23.6 2.94 0.147 24.1 1.88 0.094 24.3
18 21.5 2.97 0.149 22.0 1.90 0.095 22.2

Table 98: Results of air flow and temperature compared with each zone of the two
models – when conducted under CASE II Climate conditions.

244

Conditions ZONE 2 - MID LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 2.13 0.106 19.1 1.72 0.086 19.2
9 22.7 2.08 0.104 23.4 1.67 0.083 23.5
10 21.8 2.09 0.105 22.5 1.68 0.084 22.6
11 22.5 2.08 0.104 23.2 1.67 0.083 23.3
12 23.2 2.07 0.104 23.9 1.66 0.083 24.0
13 23.1 2.08 0.104 23.8 1.66 0.083 23.9
14 23.6 2.07 0.104 24.3 1.66 0.083 24.5
15 25.7 2.04 0.102 26.4 1.64 0.082 26.6
16 24.6 2.06 0.103 25.3 1.65 0.082 25.5
17 23.6 2.07 0.104 24.3 1.66 0.083 24.5
18 21.5 2.10 0.105 22.2 1.68 0.084 22.3

Conditions ZONE 3 - TOP LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 0.05 0.003 45.8 0.22 0.011 24.8
9 22.7 0.14 0.007 32.9 0.11 0.006 35.5
10 21.8 0.11 0.005 35.1 0.14 0.007 32.0
11 22.5 0.13 0.007 33.3 0.12 0.006 34.6
12 23.2 0.15 0.008 32.3 0.09 0.005 38.4
13 23.1 0.15 0.008 32.4 0.10 0.005 37.7
14 23.6 0.17 0.008 32.0 0.08 0.004 41.9
15 25.7 0.23 0.011 31.9 0.05 0.003 52.9
16 24.6 0.20 0.010 31.7 0.04 0.002 59.1
17 23.6 0.17 0.008 32.0 0.08 0.004 41.9
18 21.5 0.09 0.005 36.4 0.15 0.007 31.1

Table 98: Continued.

245

12.2.2.1: ANALYSIS:
AIR FLOW PATTERN:
The air flow rates across the three zones in the three models are:

Fig 109: Air flow pattern in Model X & Y for CASE II climate conditions.
The top Zone 3X of MODLE X, designed from design guidelines, does not receive direct
fresh when the wind blows directly perpendicular towards the shaft. In this zone the inlets
are now outlets for air flow. Stale and contaminated air from the lower two Zones 1X and
2X feeds air to zone 3X. This is due to the effect of the Neutral pressure plane which lies
below the Zone 3X openings. Thus with taller ventilation shafts and having all the
openings at similar level and size the air flow is not always regular and convective.
Whereas in case of MODEL Y, where the shaft is designed as per conclusions derived
from building component and air flow studies, the air flow pattern remains convective.
Zone 3Y receives fresh direct air from its designed inlets. A shorter shaft and different
opening sizes can aid inducing regular convective air flow across all the zones.

246

Multi zone models designs based on general design guidelines may not always aid
convective air flow. Furthermore the height of a ventilation shaft is not detrimental in
achieving convective air flow movement.

AIR FLOW RATES:

Fig 110: Air flow rates in MODEL X & Y for CASE II climate conditions.

In this case conditions the wind and buoyancy pressure induced air flow move in opposite
directions. Buoyancy induced air flow flows from inside the occupant zones towards the
shaft outlet whereas wind induced air flow are exerted from the shaft outlet inside the
shaft.
247

Thus the air flow rates in the two MODELS X & Y for CASE 2 (wind east to west)
climate conditions are lower than the air flow rates experienced in CASE 1 ( wind west to
east) climate conditions.
The air flow rates in the lower two Zones – 1X & 2 X of MODEL X are greater than the
air flow rates in all the three zones of MODEL Y. The difference between the air flow
rates in these two zones (1X & 1X of MODEL X) is high and may result in drastic
difference in internal temperature between the two zones.
The airflow rate in the lower tow Zones – 1Y & 2Y of MODEL Y have relatively lower
than the air flow in MODEL X. The difference between the air flow rates of the two
zones is also lower compared to the air flow rate difference in the two lower zones of
MODEL X. The two zones of MODLE Y have regular and almost similar air flow rate.
The air flow rate in the top zones - 3X and 3Y in both the MODEL X & Y is extremely
low. This is because the height difference between its zone outlets and the shaft outlet is
the least reducing the air flow. Along with this the wind induced air flow acts in the
opposite direction of the buoyancy driven air flow. The resultant air flow is reduced.
Zone 3Y receives fresh air from its inlets. This is because the design of MODLE Y aids
in increasing the buoyancy driven pressure along the height of the ventilation shaft. The
buoyancy pressure being stronger than the wind induced pressure. Whereas in case of
MODEL X the ventilation shaft and occupant zone ventilation design is not successful in
generating buoyancy pressure as strong as that developed in MODEL Y design.

248

Buoyancy induced pressure differentials can be increased using a ventilation shaft.
This increase in pressure is also not completely dependent on the ventilation shaft
height or shaft outlet size. Ventilation shaft induces air flow in the occupant spaces
when wind flows directly towards the shaft outlet. The occupant zone design also
affects the air flow rate and air flow patterns.

INTERNAL TEMPERATURE and THERMAL COMFORT:

Fig 111: Internal temperature of the occupant zones of MODEL X & Y under
CASE II climatic conditions.

249

Air flow induced by ventilation shaft in the lower two zones – Zone 1X, 2X, 1Y & 2Y of
models X & Y respectively is regular and sufficiently strong to provide thermal comfort
conditions in the occupant zones. Thus the design of the two MODEL’s are successful in
providing effective natural ventilation for the lower two zones.
Zone 3X (top) of Model X has low air flow rates. The resulting internal temperature is
extremely high – beyond thermal comfort conditions. This is because the air entering this
zone is pre heated by the heat gains of the lower two zones 1X & 1X. This pre heated air
and the internal heat generated in that Zone itself adds to the internal temperature Thus
the design of MODEL X is inapt in providing thermal comfort conditions through natural
ventilation mechanisms in its top ZONE 3X.
The air flow induced in top Zone 3Y is low. It is lower than Zone 3X. But the internal
temperature due to this induced air low is lower than the internal temperature of Zone 3X.
This is because Zone 3Y receives fresh air which is not pre heated form the lower zones.
This low air flow rate is not strong enough to dissipate the internal heat generated in the
zone. Thus this zone may need additional fan –forced air flow to help it achieve thermal
comfort conditions.

It is essential to have direct fresh air entering the occupant zones to provide thermal
comfort conditions through natural ventilation.

250

12.2.3: RESULTS OF CASE III CLIMATE CONDITIONS: No Wind.
Conditions ZONE 1- LOWEST LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 3.29 0.164 18.8 2.19 0.110 19.0
9 22.7 3.22 0.161 23.1 2.15 0.107 23.4
10 21.8 3.23 0.162 22.2 2.15 0.108 22.5
11 22.5 3.22 0.161 22.9 2.15 0.107 23.2
12 23.2 3.21 0.161 23.6 2.14 0.107 23.9
13 23.1 3.22 0.161 23.5 2.14 0.107 23.8
14 23.6 3.20 0.160 24.0 2.14 0.107 24.3
15 25.7 3.17 0.159 26.1 2.11 0.106 26.4
16 24.6 3.19 0.159 25.0 2.12 0.106 25.3
17 23.6 3.20 0.160 24.0 2.14 0.107 24.3
18 21.5 3.24 0.162 21.9 2.16 0.108 22.2

Table 99: Results of air flow and temperature compared with each zone of the two
models – when conducted under CASE III climate conditions.

251

Conditions ZONE 2 - MID LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 2.61 0.131 18.9 2.25 0.112 19.0
9 22.7 2.56 0.128 23.3 2.20 0.110 23.3
10 21.8 2.57 0.128 22.3 2.21 0.110 22.4
11 22.5 2.56 0.128 23.1 2.20 0.110 23.1
12 23.2 2.55 0.128 23.8 2.19 0.110 23.8
13 23.1 2.56 0.128 23.7 2.20 0.110 23.7
14 23.6 2.55 0.127 24.2 2.19 0.109 24.2
15 25.7 2.52 0.126 26.3 2.17 0.108 26.4
16 24.6 2.53 0.127 25.2 2.18 0.109 25.2
17 23.6 2.55 0.127 24.2 2.19 0.109 24.2
18 21.5 2.57 0.129 22.0 2.21 0.111 22.1

Conditions ZONE 3 - TOP LEVEL
H Te
MODEL X MODEL Y
Q V Ti Q V Ti
8 18.4 1.68 0.084 20.9 1.25 0.062 19.5
9 22.7 1.64 0.082 25.3 1.22 0.061 23.9
10 21.8 1.65 0.082 24.4 1.22 0.061 23.0
11 22.5 1.64 0.082 25.1 1.22 0.061 23.7
12 23.2 1.64 0.082 25.8 1.22 0.061 24.4
13 23.1 1.64 0.082 25.7 1.22 0.061 24.3
14 23.6 1.63 0.082 26.2 1.21 0.061 24.8
15 25.7 1.62 0.081 28.3 1.20 0.060 26.9
16 24.6 1.63 0.081 27.2 1.21 0.060 25.8
17 23.6 1.63 0.082 26.2 1.21 0.061 24.8
18 21.5 1.65 0.083 24.1 1.23 0.061 22.6

Table 99: Continued

252

12.2.3.1: ANALYSIS:
AIR FLOW PATTERN:
The air flow rates across the three zones in the three models are:

Fig 112: Air flow pattern in Model X & Y for CASE III climate conditions.

For pure buoyancy driven air flow conditions the air flow pattern across all the zones in
both MODELS’ X & Y is regular – convective. All the occupant zones receive direct
fresh air flow from the inlets on the west façade of the model. Air exits from the designed
outlets into the shaft and then exit finally from the shaft outlet.

By having smaller ventilation shafts, convective airflow patterns can be achieved
purely from buoyancy effects negating the effect of the neutral pressure plane level.

253

AIR FLOW RATES:

Fig 113: Air flow rates in MODEL X & Y for CASE III climate conditions.

Air flow rates decrease with increase in height in Model X. The lowest zone 1X of
MODEL X has the highest air flow rates. The airflow rates in the top zone of the same
model are the lowest. This difference is due to the difference in height between its zone
outlets and the shaft outlet. The difference in air flow rates between the three zones is
high. As observed from earlier analysis this difference in air flow rate may affect the
internal temperature in the occupant zones.

254

Whereas in MODEL Y the lower and the mid level occupant zones – 1Y & 2Y have
almost similar air flow rates. This is achieved by creating pressure balance across the two
zones by controlling their opening area and opening heights. This also highlights the
difference opening area and opening heights make on ventilation by varying the pressure
differentials. The internal temperature of the two zones will be almost similar.
The top zones – Zone 3X and 3Y of the two models have lower air flow rates. As
discussed earlier the openings of these zones lie closer to the shaft outlet which reduces
the height difference across its openings. As discussed earlier lower height differences
have lower buoyancy driven air flow.

The design of building components - opening area and opening heights of the
occupant zone can help regulate pressure and balance airflow rates between multiple
zones connected to a ventilation shaft.

255

INTERNAL TEMPERATURE and THERMAL COMFORT:

Fig 114: Internal temperature of the occupant zones of MODEL X & Y under
CASE III climatic conditions.

Air flow rates generated by the ventilation shaft and occupant zone design of MODEL X
and MODEL Y are sufficient to provide adaptive thermal comfort conditions in all the
zones except the top Zone 3X of MODEL X
Air flow rates generated in Zone 3X are not strong enough to keep the internal
temperature in the zone within the operative temperatures for achieving adaptive thermal
comfort conditions. The internal temperatures exceed the maximum operative
temperature of 26.7
0
C between 14:00 hrs to 17:00 hours.

256

This three hour time period in which temperatures are higher than 26.7
0
C reduce the
period of effectiveness of natural ventilation in MODEL X. Additional air flow through
mechanical sources need to be induced in the occupant zone to provide thermal comfort
conditions for the occupant for the 3 hours.
However, the air flow rate generated by the ventilation shaft in MODEL Y is enough to
dissipate the internal heat gains and maintain the internal temperature within the
operative temperature of 26.7
0
C & 19.4
0
C. Thus the period of natural ventilation using a
ventilation shaft (MODEL Y) is the maximized.

The air flow generated from Ventilation shafts, when designed using the general
design guidelines may not always provide thermal comfort conditions. Designing
occupant zones and ventilation shaft as one combined unit helps achieving maximized
benefits from natural ventilation.

257

12.3: SUMMARY OF CONCLUSIONS
12.3.1: DESIGN APPROACH COMPARISON
The series of investigations conducted in this section used two separate models
represented by similar occupant space connected to ventilation shafts. The ventilation
designs of these two models differ. MODEL X design was based on the general design
guidelines whereas MODEL Y design developed from inferences and analysis of studies
performed on building and ventilation shafts, as a part of this study. This section
enumerates key observations from the conclusions derived through the air flow and
thermal comfort calculations performed in this section.

• Both the design approaches can induce air flow in the multi zone model when
wind flows directly perpendicular on its designed inlet openings. Under such
conditions both the design approaches can help achieve 90% acceptable adaptive
thermal comfort conditions, thus maximizing the effectiveness of natural
ventilation.
• Ventilation shaft designs based on general design guidelines may not always aid
convective air flow in a multi zone model when the air flows directly into the
shaft outlets. The height of ventilation shaft is not instrumental in help achieving
convective air flow pattern. The occupant zone design also affects the air flow
rate and air flow patterns. The design of building components of opening area and
opening heights in occupant zone can help regulate pressure and balance airflow
rates between multiple zones connected to a ventilation shaft.
258

Designing occupant zones and ventilation shaft as one combined unit helps
achieving maximized benefits from natural ventilation.
• The air flow generated from Ventilation shafts, when designed using the general
design guidelines may not always provide thermal comfort conditions. It is
essential to have direct fresh air entering the occupant zones to provide thermal
comfort conditions through natural ventilation. By having smaller ventilation
shafts, convective airflow patterns can be achieved.
• Ventilation shafts designed from design guidelines induce air flow and their
potential to negate the effect of the neutral pressure plane is relative and climate
dependent. As observed from buoyancy air flow calculations in climate
conditions – CASE 3 of no wind, the air flow rate generated using this shaft is not
strong enough to reduce the internal temperature.
• Ventilation shaft induces air flow in the occupant spaces when wind flows
directly towards the shaft outlet. However when it blows directly on the outlet of
ventilation shafts constructed using the general design guidelines the model fails
in providing fresh air to all the zones it is connected with. This failure maybe due
to high wind speeds. The conclusion can be comprehensive only when this shaft is
examined under low wind speeds while keeping the wind direction directly
perpendicular to its outlet.
259

• Buoyancy induced pressure differentials can be increased using a ventilation shaft
which can increase the air flow rates in the occupant zones the shaft is connected
to. This increase in pressure is also not completely dependent on the ventilation
shaft height or shaft outlet size.
• The air flow generated from Ventilation shafts, when designed using the general
design guidelines may not always provide thermal comfort condition. Whereas
the ventilation shaft designed, based on conclusion from ventilation studies
conducted a part of this study, provides thermal comfort conditions throughout
under all climate conditions.
CASE I

CASE II

CASE III
Model X 12 hrs

Model X 8 hrs

Model X 9 hrs
Model Y 12 hrs

Model Y 8 hrs

Model Y 12 hrs

Table 100: Period of thermal comfort conditions in MODEL X & C MODEL Y.

This comparison of thermal comfort conditions can change when the opening
areas and height difference are changed. This comparison is based on the two
design conditions used for these specific study. As opening area and opening
heights have potential to increase air flow rate, the corresponding impact of
increased air flow rate on thermal comfort can change.

260

12.3.2: VENTILATION SHAFT VOLUMES
Ventilation shafts used in these two models – X & Y have different heights and area size.
The previous conclusions highlight the difference these two different shafts have on air
flow pattern, air flow rate and thermal comfort. Both these ventilation shafts serve to
similar occupant zone volumes and were examined under similar climatic conditions.
This makes it possible to compare the difference on leveled grounds.

PARAMETERS

MODEL X

MODEL Y

DIFFERENCE
Height - m

16

13.5

2.5
Area - m
2

26.25

24

2.25
Volume - m
3

420

324

96

Table 101: Difference in ventilations shaft design used for MODEL X & MODEL Y.

The table above and the studies conducted in this chapter highlight the potential of
ventilation shafts to reduce the volume they occupy while providing thermal comfort
conditions by inducing air flow.

261

CHAPTER 13: CONCLUSIONS AND FUTURE WORK.
This chapter concludes the findings derived from this study along with the scope of future
work.

262

13.1: CONCLUSIONS
This chapter discusses the conclusions drawn from observations made through the
process of this study and how these observations serve in fulfilling the intent of this
study.

13.1.1: AIR FLOW THROUGH OCCUPANT ZONES:
This study concentrated on finding methods to increase air flow inside occupant spaces
using a ventilation shaft so as to increase the effectiveness of natural ventilation.
A brief investigation of various ventilations mechanisms by which air is induced inside a
space establishes the framework for all ventilation studies. A detailed study of the
fundamentals and governing principles of the various ventilation mechanisms helped
identify the two key methods by which air flows inside an occupant space. The governing
equations of buoyancy and wind pressure indentify the building components that
influence air flow. Among them the building components which affect air flow under
both buoyancy and wind pressure effects are opening size. The other two building
components are opening heights and building heights. As pressure is height dependent
these two aspects of height have their influence on changing the pressure differentials
across openings.

263

The three building components were analyzed under different wind and temperature
conditions to examine their respective influence on air flow. These building components
were investigated on three different ventilation design models – single sided, cross
ventilation and a single zone attached to a shaft. Air flow calculation under fixed
boundary conditions help identifies the extent of influence of the three parameters of
height, opening height and opening areas.
The single sided model consisted of two openings places on the same façade whereas the
cross ventilation model models contained two openings located on opposite facades.

• ZONE HEIGHT
Results and analysis of the results display marginal and negligible influence of zone
heights in inducing airflow. This observation is assuming that the opening sizes and the
opening heights are kept constant when the zone heights are varied.
No difference is observed for buoyancy driven air flow when heights are varied. Air flow
rates change as a function of difference in opening heights and opening heights instead of
the overall zone heights. Thus overall zone height will not contribute in influencing any
change in buoyancy driven airflow.
Static wind pressure varies with height such that it increases with increase in height. Thus
when the zone heights are changed wind induced air flow will also change.

264

The pressure exerted on the openings will increase increasing the air flow rates across the
zone. This marginal increase in air flow rate will however not have substantial effects on
the internal temperature which may affect thermal comfort conditions.
By increasing zone heights buoyancy driven air flow will remain unchanged whereas a
marginal increase for wind induced air flow can be expected.

• OPENING HEIGHT
Pressure is height dependent. In case of buoyancy pressure this height difference is
between openings whereas in case of wind the overall zone height influences pressure.
When the opening levels are altered the height difference between these opening also
changes. Increase in height difference increases buoyancy driven air flow rate. This
change can be expected when keeping the zone height and the opening size constant.
Buoyancy induced air flow change with every change in height difference of openings.
The influence is such that when the height difference between openings is nullified the
resulting air flow rates also nullify. The studies conducted on the single zones for varying
opening heights highlight this influence of height difference in influencing air flow.

265

Wind induced air flow does not change with change in opening levels. Air flows through
even when the openings are at the same level. Wind and buoyancy air flow calculations
on single zone models assist in deducing a generalized trend of influence opening heights
have on airflow. This trend of change is tabulated below.

Height difference - m
Change in air flow rates
by Wind effects - Q
w

Change in air flow
rates by Buoyancy
effects – Q
b

Outlet (A2) – Inlet (A1)
0 Q
w
0
1 Q
w
Q
b

1.5 Q
w
Q
b
+ 2.5 Q
b

2 Q
w
Q
b
+ 5.0 Q
b

2.5 Q
w
Q
b
+ 7.5 Q
b

3 Q
w
Q
b
+ 10 Q
b

Table 102: Trend of change in airflow as a function of height difference for both
wind and buoyancy driven effects on air flow.

266

• OPENING SIZE
The governing equations to estimate buoyancy and wind driven airflow highlight air flow
as a function of the total area of openings. This total area of openings is the sum of inlet
and outlet opening areas combined. Therefore a change in any of the openings; inlets or
outlets will affect air flow. This effect is such that when the area of openings increases
the air flow rates increase and conversely the potential of a single zone in inducing air
flow decreases when the openings sizes are reduced.
Analysis of the single zone and ventilation shaft studies highlight the regulatory function
of openings. The volume of air entering and leaving an occupant space depends on the
opening size. Moreover as air flow rate is a function of opening size, the air flow rates
double when the total area of openings also double. Airflow rate also increase when the
ration of openings between inlet and outlets are changed. This change in air flow for
different inlet to outlet size configurations are illustrated and tabulated below.
Opening rationale Change in Volumetric air flow rate
– m
3
/s Inlet : Outlet OR Outlet : Inlet
1 : 1 Q
1 : 2 Q + 27% Q
1 : 3 Q + 34% Q
1 : 4 Q + 38% Q

Table 103: Change in air flow rate when the ratio of opening sizes is altered.
267

• OPENING LOCATION
Series of calculations were performed (chapter 11) to verify and highlight the influence
of ventilation shaft in aiding air flow and its corresponding effect on internal temperature.
Analysis through the results of these calculations helped highlight the effect of locating
opening on zone facades. For these studies three single zone models – Single sided, cross
ventilated model and single zone attached to a ventilation shaft were constructed. Both
the zones had height difference between its openings so as to benefit from buoyancy
driven air flow.
For the single sided model both the opening were located on the same façade whereas the
cross ventilated model had the two openings located on opposite facades with a height
difference.
Results display that the single sided model failed to induce air flow under wind blew
directly at its openings. Whereas it induced air flow only under buoyancy driven
temperature conditions. The cross ventilated model had air flow for both conditions of
wind and buoyancy. This difference affected the overall air flow rates even for combined
effects of buoyancy and wind air flow. The cross ventilated model had greater air flow
across its zones than the single sided model. The difference in airflow rates affected the
internal temperature of the zone. The thermal comfort conditions were thus achieved only
for a limited period of time in the single zone model whereas the design of the cross
ventilated model helped achieve thermal comfort conditions almost throughout the time
when the climate conditions were appropriate for natural ventilation.
268

Thus, location of openings on the zone façade also influences the effectiveness of natural
ventilation. An occupant zone which has inlets and outlets located on opposite façades
and have height difference between each other can generate greater airflow rates. Such a
design is represented by MODEL 2; single zone - cross ventilated model used for air flow
analysis in Chapter 11.
Building components of opening size and opening heights are vital in determining the air
flow rate across the occupant spaces. However, the location of openings on building
façade plays the defining role in increasing the time period of air flow across the
occupant space.

All the general relations between building components and air flow are intended to serve
as a quick reference guide when designing the occupant space and a ventilation shaft. The
tables serve as a rule of thumb for designers at the preliminary stages of design. Instead
of recalculating the change in air flow rate for every change in opening size a designer
can now have an approximation of the effect on air flow for every change he makes in the
opening size. Similarly a height difference between openings will increase the period of
natural ventilation as the design will assist buoyancy effects to induce air flow. Knowing
this the designer can make necessary changes on the building elevation design in the
early design stages, without affecting the building aesthetics.

269

13.1.2: AIR FLOW THROUGH VENTILATION SHAFT
Investigations on various aspects of a ventilation shaft –shaft height, shaft area and shaft
outlet size, were conducted under both temperature and wind conditions. The results and
conclusions drawn from these studies were similar to the inferences from the single zone
models.

• VENTILATION SHAFT HEIGHT
The result s and conclusions for the air flow calculations conducted for varying
ventilation shafts is similar to the results from the zone height studies. Keeping shaft
outlet level constant any increase in shaft height will not change buoyancy driven air
flow. Marginal increase in wind driven air flow is observed with increase in shaft height.
This marginal increase however does not have a substantial effect on changing the
internal temperature of the zone.
Thus as long as the shaft outlet is kept at a constant level, an increase in shaft height will
not or only marginally change air flow rate depending on the temperature and wind
conditions of the site.

270

If the shaft outlet follows the rise in shaft height the increase in buoyancy driven air flow
will be by virtue of the increase in height difference between the zone inlets and shaft
outlets. The change in shaft outlet levels will have no effect on wind induced air flow.
Additionally, care must be take when locating the orientation of these outlets. The large
size of these outlets may result in them acting as wind scoops to trap in wind blowing at
higher altitudes. Thus as infered from pressure calcualtion of single zone opening
analysis the area of inlets should be changed in order to increase the negative pressure on
shaft outlets to counter windinduced pressure. By doing this the outlet size also reduces.
Size of a shaft outlet does not have much effect on wind induced air flow. This is because
the height of the shaft outlet has greater influence on air flow. Higher the shaft outlet
greater is the wind induced negative pressure which increases air flow. The shaft outlet
size as observed from the calculation earlier make marginal difference on air flow. Thus
when designing the shaft outlet - the shaft height, cumulative area of inlets and the site
temperature conditions need to be considered.

• VENTILATION SHAFT AREA
Ventilation shaft area is as a function of the volume of air flowing up across the zone and
then up the shaft. The minimum shaft area requirement depends on the volume of air and
the assumed shaft height.

271

This gives greater flexibility to the designer to control the shaft volumes in order to
reduce its architectural impact. The shaft area should be big enough to allow free
unobstructed air flow such that its size does have any impact on the air pressure
distribution across the height of the shaft.

• VENTILATION SHAFT & THERMAL COMFORT
Three single zone models and three multi zone models having different ventilation
designs were examined for their air flow under different climate conditions. These studies
were to examine the potential and extent of influence of ventilation shafts in inducing air
flow along with its effect on adaptive thermal comfort conditions in an occupant zone.
Analysis of results rendered the single zone model ineffective for specific climate
conditions. Whereas the cross ventilation and the model connected to a ventilations haft
was effective in inducing air flow for varied time and climate range. A comparative
analysis of air flow and the resulting effect of air flow on internal temperature between
these two separate models – single and multi zone models are performed. For this
analysis the results of combined air flow rates have been considered.
Observations from results in Chapter 11 –highlight that when the opening sizes were
doubled – the models achieved adaptive thermal comfort conditions. Thus the air flow
values from these calculations –CASE B and CASE E have been considered.

272

Model type
Zone
Level
- m
Air flow
rate – Q
(m3/s)
Difference
in Q
(m3/s)
Internal
temperature
–
0
C
I

Difference
in
0
C
I

SINGLE ZONE
Cross Ventilated 0.830
0.282
21.7
0.4
Single + Shaft 1.112 21.3
MULTI ZONE
Cross Ventilated Lower
zone
0.830
0.627
21.7
0.7
Single + Shaft 1.457 21.0
Cross Ventilated Middle
Zone
0.917
0.09
21.5
0.1
Single + Shaft 1.007 21.4
Cross Ventilated Upper
zone
1.004
0.73
21.4
3.7
Single + Shaft 0.274 25.1

Table104: Difference in air flow by different models types and the corresponding
effect on internal temperature.

Results of air flow difference on the single zone model highlight that using a ventilation
shaft makes marginal difference in increasing air flow. Similarly the effect on internal
temperature is also marginal.

273

A cross ventilated model having openings at a height difference, can provide almost
similar thermal comfort conditions that are provided by using a ventilation shaft.
Therefore the potential and use of a ventilation shaft for a single zone occupant space is
not large.
Using a ventilation shaft for a multi zone model has varied effects on the occupant zone.
The lowest zone connect to the shaft has the maximized benefit as the height difference
between its opening and the shaft outlet is maximum. This generates high air flow rates
inside reducing the temperature difference and increasing the thermal comfort period in
that zone only. As the zones moves close to the shaft outlet and the neutral pressure plane
level of the shaft, the advantage and effect of a ventilation shaft reduce. As seen from the
comparative chart the cross ventilated model performs better for the upper and middle
zone.
Using a ventilation shaft to increase air flow rates in an occupant space is always not
beneficial. The air flow and thermal comfort conditions achieved when using a shaft can
be achieved by different ventilation design and strategy.

274

• DESIGN OF VENTILATION SHAFT
Ventilations shafts and occupant zone design based on general design guidelines perform
only for specific time and climate conditions. This is verified from the analysis of
calculations performed and reported in Chapter 12 –using two different multi zone
models having similar overall occupant zone volumes and two different ventilation shaft
designs. The calculations also highlight the influence various building components
collectively have on changing air flow pattern and air flow rates which then assist in
achieving thermal comfort conditions through natural ventilation.
Ventilation shafts and the occupant zone should not be designed separately. A combined
approach towards designing the occupant zone and the ventilation shaft should be
adopted so as to maximize air flow rates. This combined approach should be aimed to
achieve a regular and almost similar air flow rates across multiple occupant zones and
also regular convective air flow pattern across all the occupant zones.

Based on inferences from all the air flow studies and calculations conducted using a
ventilation shaft, it can be concluded that a ventilation shaft can always serve as a passive
design strategy to marginally increase the effectiveness of natural ventilation in climatic
zones where the diurnal temperatures from night to day differ and also in places which do
not experience direct prevailing wind.

275

Ventilation shafts respond to both buoyancy and wind pressure effects which make them
functional for most of the time period in which natural ventilation is possible.
From the studies it can be inferred that to achieve regular and higher air flow with lower
shaft size, a piece by piece evaluation of all building parameters affecting air flow needs
to be performed. Based on these evaluations, a designer can then achieve a best fit
ventilation shaft design which will perform in almost all temperature and wind conditions
depending on the climatic zone and site conditions in which it’s located.

13.2: FUTURE WORK
Ventilation shafts has the potential to serve ventilation needs and can perform additional
building functions (Heiselberg and Murakami 1998). This study focused only on
exploring the potential of a ventilation shaft in increasing effectiveness of natural
ventilation in occupant spaces. Additional research could help find ways to take
advantage of the large volume occupied by these shafts. Looking at ways to house
building functions and building services without disturbing free air movement up the
shaft height can be explored. In the case of hybrid ventilation mechanisms the ventilation
shaft can be used to house mechanisms exhaust fans to assist air flow.

276

Ventilation shafts assumed for this study are hollow cubical in shape and form. Similar
analysis using different ventilation shaft forms can be further conducted. Different forms
can be cylindrical or conical in shape. Additionally, for all the series of investigations the
ventilation shafts were attached to the shorter dimension of a rectangular floor plate.
Series of investigations assuming ventilation shaft attached to the longer façade of a
rectangular floor plan can also be conducted. The zone openings in this case can be
relocated on the longer facades. Instead of having a single inlet and single outlet opening
the zone can be designed with multiple inlets and once common outlet connecting to the
ventilation shaft. The airflow pattern inside the single zone in this case may alter and also
the air flow rates might change.
The air flow pattern for this study was visualized only along the vertical section. Further
air flow pattern analysis concentrating at only the horizontal section of a single zone
connected to a ventilation shaft can be conducted. By doing this the effect of opening,
connecting the shaft to zone, on air flow pattern inside the shaft can be investigated.
Any change in air flow pattern and air flow rate by change in the location of ventilation
shaft outlet can be examined. The ventilation shaft outlets for all the calculations are
located only on a single façade, on the shorter side of the single zone model such that all
the openings are on a linear horizontal axis when visualized along the plan view of the
study model. For further investigations the shaft outlet can be relocated on the other three
facades of the ventilation shaft.

277

The shaft outlet is positioned on the ventilation shaft walls. Relocating the shaft outlet on
the shaft roof can be another possible design option which may affect the air flow pattern
and air flow rate. Instead of having just one shaft outlet multiple shaft outlets can be
relocated along the shaft facades.
Increasing the number of openings on different facades of a rectangular single zone plan
might alter the air flow pattern inside the occupant space. Locating the openings on the
adjacent facades of the rectangular single zone plan might change the volume of air flow
and the air flow rate flowing inside the shaft. Similarly increasing the number of
ventilation shafts connected to a single and multi zone model might affect the air flow
rates across the various regions inside the occupant zone and also might influence the
architectural impact of ventilation shafts on the building form.
Possibilities and effects of constructing internal partitions inside the ventilation shaft may
also serve as future research work. Creating openings inside the partitions wall in a shaft
may assist in regulating and changing air flow according to the temperature and wind
conditions. This might help increase the effectiveness of ventilation shafts by inducing
airflow for longer time periods and also changing the air flow pattern thus reducing the
effect of neutral pressure plane level.
For all the wind driven air flow investigations the wind angle was assumed to be at 0
0
and
in some cases at 45
0
. The effect of varying wind angles, oblique and acute wind angles on
wind driven air flow can be further investigated.

278

Similarly, wind directions are assumed to be unidirectional in all the conditions of
calculations. The effect of varying wind directions on air flow inside the zone and the
ventilation shaft can also be studied.
This study assumes similar internal temperature inside the occupant zones and the
ventilation shafts. Different internal temperatures inside the occupant space and the
ventilation shaft may vary buoyancy driven air flow rate. Similarly by including the
effect of solar radiation on the ventilation shaft walls may also change the internal
temperature of the shaft, which might result to a change in the air flow rates. For this
present study the effect of solar radiation on the ventilation shaft walls is not considered.
For this study numerical and computational calculations are employed to estimate air
flow rate and pressure differentials across the openings. Other prediction technique using
computational fluid dynamics can also be adopted to investigate the potential of
ventilation shafts. By doing so an approximate variation in the air flow rate and pressure
differential results using different prediction techniques can be observed. Computational
fluid dynamics may also provide a greater detailed visualization of air flow pattern which
might aid in deducing methods to enhance zone and ventilation shaft design.

279

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285

APPENDIX A: VENTILATION SHAFT AND NEUTRAL PRESSURE
PLANE.

As mentioned in Section 3.2– to examine the influence of the neutral pressure plane
simple shaft was constructed. The shaft consists of an inlet at the bottom and an outlet at
the top. Both the opening sizes were altered to see corresponding change on the neutral
plane levels of the shaft.

Fig 115: Reference shaft for Calculations.
286

Appendix A Continued
Based on Bernoulli’s equation the pressure difference between inside to outside is:
................................. Equation 12

Where,
ρ
o
= Density of air outside in kg/m
3

ρ
i
= Density of air inside in kg/m
3

P = Pressure in Pa
H
s
= Stack height in m

H
npl
= Height of neutral plane level in m
g = Gravitational acceleration in m/s
2

K
p
= Constant – depends on building
condition.

As mentioned earlier this pressure difference determines the mass of air flowing inside
the building, the mass flow equation derived from power law equation based on McGuire
and Tamoura (Awbi, 2008) analysis is:
.......................... Equation 13

Where,
M
z
= Mass flow
ΔP = Pressure difference

C
d
= Discharge coefficient
A = Area of opening in m
2

ρ
o
= Pressure in kg/m
3
.

287

Appendix A Continued
By law of conservation of energy: Mass of air entering = Mass of air leaving
........................................................................................ Equation 14
By substituting equation 12 and 13 in equation 14 we get an approximate height of the
neutral plane level – equation 15.
Pressure difference due to thermal differences can be altered by limiting the thermal
interaction between outside and inside air. This can be done by regulating points of
interaction via openings controlling air entering and leaving the zone. By doing this the
amount of air now entering an enclosed shaft is limited thus influencing the overall
pressure gradient in the shaft. Therefore to calculate the neutral plane level the function
of opening area is vital – Figure 116. The neutral pressure plane equation is now
expressed as:

........ Equation 15

Where,
T
o
= Temperature of outside air in K
T
i
= Temperature of inside air in K
A
b
& A
a
– Size of openings in m
2

H
s
= Stack height in m

H
n
= Height of neutral plane level in m

288

Appendix A Continued

Fig 116: Neutral plane level from opening sizes
50
.

To highlight the influence of opening size on neutral plane level – a simple shaft having
an inlet at the bottom and outlet at the bottom was examined for stack effect. In case of
shafts where bottom openings are bigger than the upper opening the resistance offered by
the lower opening is less than the top opening. Therefore in order to fulfill the law of
mass conservation, the pressure drop across the lower opening must decrease, and that
across the upper will increase until the flow equalize once more. (Irving, Ford, &
Etheridge, January,2007)

50
(Liddament, June,1986)

289

Appendix A Continued
The neutral plane is still defined by the point at which the two pressure gradients level
which in this case now occurs lower down the wall. This change in level shall then affect
the direction of air flow through the openings in the stack determining also the air flow
rates through the occupied spaces – Figure 117. (Irving, Ford, & Etheridge,
January,2007). For all buoyancy calculations it is assumed that all internal zones have
uniform temperature distribution As neutral plane level depends on opening heights and
temperature difference, the direction of air flow depends on position of openings with
respect to neutral plane level.

Fig117: Flow directions for vertical openings temperature, opening and neutral
plane dependent

290

Appendix A Continued
The change in neutral pressure plane as a function of varying opening size is calculated
and reported further. The conditions for calculations and the results are tabulated below.

Shaft Height 4m
External temperature 23
0
C
Internal Temperature 20
0
C

Table 105: Conditions for calculating the Neutral pressure Plane level.

Area of opening - m
2
Ratio of A1: A2 Neutral pressure
Plane
51
- NPL
Difference
Inlet - A1 Outlet- A2 A1 : A2
4 1 4 : 1 0.24 m NPL - 88% NPL
3 1 3 : 1 0.40 m NPL - 80% NPL
2 1 2 : 1 0.81 m NPL - 60% NPL
1 1 1 : 1 2.01 m NPL
1 2 1 : 2 3.21 m NPL + 60% NPL
1 3 1 : 3 3.60 m NPL + 80% NPL
1 4 1 : 4 3.77 m NPL + 88% NPL

Table 106: Relationship of change in neutral pressure plane when inlets to outlet
sizes are changed.

51
This neutral pressure plane level is from the base of the zone.

291

Appendix A Continued

Area of opening - m
2
Neutral pressure
Plane - m
Pressure at Openings – ΔP in Pa
Inlet - A1 Outlet- A2 A1 (at 1m height) A2 - (at 3.5m
height)
4 1 0.24 -0.06 0.25
3 1 0.40 -0.05 0.24
2 1 0.81 -0.01 0.21
1 1 2.01 0.08 0.11
1 2 3.21 0.17 0.02
1 3 3.60 0.20 -0.01
1 4 3.77 0.21 -0.02

Table 107: Pressure redistribution by change in neutral pressure plane.

292

Appendix A Continued

Fig118: To illustrate the difference in Neutral pressure Plane for different openings
size.

293

Appendix A Continued

Fig119: Air flow pattern as result of change in Neutral pressure Plane level for
different opening size.

294

APPENDIX B: AIR FLOW RATES FOR INDOOR AIR QUALITY.

The purpose of ventilation is to provide habitable conditions for building occupants.
Habitable conditions can be achieved by having clean uncontaminated air for breathing.
The acceptable air contaminant levels are stipulated in the American Society of Heating
Refrigerating and Air-conditioning Engineer’s (ASHRAE) Standard 62.1- 2007 which
are illustrated below.

295

Appendix B Continued

Fig 120: Air flow rate and air changes per hour requirement for different building
types to maintain indoor air quality.

296

Appendix B Continued

Fig 120: Continued

297

Appendix B Continued

Fig 120: Continued

298

APPENDIX C: COEFFICIENT OF WIND PRESSURE - C
P.

The coefficient of pressure values for various wind angles and building surface
conditions are tabulated below (Irving, Ford, & Etheridge, January,2007).

Wind pressure coefficient: The turbulent flow pattern when, air enters an opening,
affects the pressure differential between immediate interior and exterior of the opening.
To account for this effect a coefficient is introduced into the calculations. This coefficient
has been derived through wind tunnel measurements. The coefficient takes into account
the changes in the wind angle in case of turbulent flow with respect to the building
surface description at which it strikes. The data derived under wind tunnel include Cp
values for 16 different wind directions.

299

Appendix C Continued
C.1: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 1:1
Shielding condition: ................................................................................................. Exposed
Wind speed reference level: ......................................................................... Building Height

Table 108: Values of wind pressure coefficient for exposed shielding conditions and
1:1 surface ratios.

0 45 90 135 180 225 270 315
0.7 0.35 ‐0.5 ‐0.4 ‐0.2 ‐0.4 ‐0.5 0.35
‐0.2 ‐0.4 ‐0.5 0.35 0.7 0.35 ‐0.5 ‐0.4
‐0.5 0.35 0.7 0.35 ‐0.5 ‐0.4 ‐0.2 ‐0.4
‐0.5 ‐0.4 ‐0.2 ‐0.4 ‐0.5 0.35 0.7 0.35
Front ‐0.8 ‐0.7 ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.7
Rear ‐0.4 ‐0.5 ‐0.6 ‐0.7 ‐0.8 ‐0.7 ‐0.6 ‐0.5
‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6
Front ‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5
Rear ‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5
‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5
Front 0.3 ‐0.4 ‐0.6 ‐0.4 ‐0.5 ‐0.4 ‐0.6 ‐0.4
Rear ‐0.5 ‐0.4 ‐0.6 ‐0.4 ‐0.3 ‐0.4 ‐0.6 ‐0.4
‐0.1 ‐0.4 ‐0.6 ‐0.4 ‐0.1 ‐0.4 ‐0.6 ‐0.4
Average
Average
Roof ( > 30 Deg pitch)
Average
Wind Angle
Location
Roof ( < 10 Deg pitch)
Roof ( 11 ‐ 30 Deg pitch)
Face 1
Face 2
Face 3
Face 4

300

Appendix C Continued
C.2: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 1:1
Shielding condition: ........ Surrounded by obstruction equivalent to half the building height
Wind speed reference level: ......................................................................... Building Height

Table 109: Values of wind pressure coefficient for Surrounded by obstruction
equivalent to half the building height shielding conditions and 1:1 surface ratios.

0 45 90 135 180 225 270 315
0.4 0.1 ‐0.3 ‐0.35 ‐0.2 ‐0.35 ‐0.3 ‐0.1
‐0.2 ‐0.35 ‐0.3 0.1 0.4 0.1 ‐0.3 ‐0.35
‐0.3 0.1 0.4 0.1 ‐0.3 ‐0.35 ‐0.2 ‐0.35
‐0.3 ‐0.35 ‐0.2 ‐0.35 ‐0.3 0.1 0.4 0.1
Front ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5
Rear ‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5
‐0.6 ‐0.5 ‐0.4 ‐0.5 ‐0.6 ‐0.5 ‐0.4 ‐0.5
Front ‐0.35 ‐0.45 ‐0.55 ‐0.45 ‐0.35 ‐0.45 ‐0.55 ‐0.45
Rear ‐0.35 ‐0.45 ‐0.55 ‐0.45 ‐0.35 ‐0.45 ‐0.55 ‐0.45
‐0.35 ‐0.45 ‐0.55 ‐0.45 ‐0.35 ‐0.45 ‐0.55 ‐0.45
Front 0.3 ‐0.5 ‐0.6 ‐0.5 ‐0.5 ‐0.5 ‐0.6 ‐0.5
Rear ‐0.5 ‐0.5 ‐0.6 ‐0.5 0.3 ‐0.5 ‐0.6 ‐0.5
‐0.1 ‐0.5 ‐0.6 ‐0.5 ‐0.1 ‐0.5 ‐0.6 ‐0.5
Roof ( < 10 Deg pitch)
Average
Roof ( 11 ‐ 30 Deg pitch)
Average
Roof ( > 30 Deg pitch)
Average
Location
Wind Angle
Face 1
Face 2
Face 3
Face 4

301

Appendix C Continued
C.3: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 1:1
Shielding condition: ......................................Surrounded by equal to height of the building
Wind speed reference level: ......................................................................... Building Height

Table 110: Values of wind pressure coefficient for Surrounded by equal to height of
the building shielding conditions and 1:1 surface ratios.

0 45 90 135 180 225 270 315
0.2 0.05 ‐0.25 ‐0.3 ‐0.25 ‐0.3 ‐0.25 0.05
‐0.25 ‐0.3 ‐0.25 0.05 0.2 0.05 ‐0.25 ‐0.3
‐0.25 0.05 0.2 0.05 ‐0.25 ‐0.3 ‐0.25 ‐0.3
‐0.25 ‐0.3 ‐0.25 ‐0.3 ‐0.25 0.05 0.2 0.05
Front ‐0.5 ‐0.5 ‐0.4 ‐0.5 ‐0.5 ‐0.5 ‐0.4 ‐0.5
Rear ‐0.5 ‐0.5 ‐0.4 ‐0.5 ‐0.5 ‐0.5 ‐0.4 ‐0.5
‐0.5 ‐0.5 ‐0.4 ‐0.5 ‐0.5 ‐0.5 ‐0.4 ‐0.5
Front ‐0.3 ‐0.4 ‐0.5 ‐0.4 ‐0.3 ‐0.4 ‐0.5 ‐0.4
Rear ‐0.3 ‐0.4 ‐0.5 ‐0.4 ‐0.3 ‐0.4 ‐0.5 ‐0.4
‐0.3 ‐0.4 ‐0.5 ‐0.4 ‐0.3 ‐0.4 ‐0.5 ‐0.4
Front 0.25 ‐0.3 ‐0.5 ‐0.3 ‐0.4 ‐0.3 ‐0.5 ‐0.3
Rear ‐0.4 ‐0.3 ‐0.5 ‐0.3 0.25 ‐0.3 ‐0.5 ‐0.3
‐0.08 ‐0.3 ‐0.5 ‐0.3 ‐0.08 ‐0.3 ‐0.5 ‐0.3
Roof ( < 10 Deg pitch)
Average
Roof ( 11 ‐ 30 Deg pitch)
Average
Roof ( > 30 Deg pitch)
Average
Location
Wind Angle
Face 1
Face 2
Face 3
Face 4

302

Appendix C Continued
C.4: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 2:1
Shielding condition: ................................................................................................. Exposed
Wind speed reference level: ......................................................................... Building Height

Table 111: Values of wind pressure coefficient for exposed shielding conditions and
2:1 surface ratios.
0 45 90 135 180 225 270 315
0.5 0.25 ‐0.5 ‐0.8 ‐0.7 ‐0.8 ‐0.5 0.25
‐0.7 ‐0.8 ‐0.5 0.25 0.5 0.25 ‐0.5 ‐0.8
‐0.9 0.2 0.6 0.2 ‐0.9 ‐0.6 ‐0.35 ‐0.6
‐0.9 ‐0.6 ‐0.35 ‐0.6 ‐0.9 0.2 0.6 0.2
Front ‐0.7 ‐0.7 ‐0.8 ‐0.7 ‐0.7 ‐0.7 ‐0.8 ‐0.7
Rear ‐0.7 ‐0.7 ‐0.8 ‐0.7 ‐0.7 ‐0.7 ‐0.8 ‐0.7
‐0.7 ‐0.7 ‐0.8 ‐0.7 ‐0.7 ‐0.7 ‐0.8 ‐0.7
Front ‐0.7 ‐0.7 ‐0.7 ‐0.6 ‐0.5 ‐0.6 ‐0.7 ‐0.7
Rear ‐0.5 ‐0.6 ‐0.7 ‐0.7 ‐0.7 ‐0.7 ‐0.7 ‐0.6
‐0.6 ‐0.65 ‐0.7 ‐0.65 ‐0.6 ‐0.65 ‐0.7 ‐0.65
Front 0.25 0 ‐0.6 ‐0.9 ‐0.8 ‐0.9 ‐0.6 0
Rear ‐0.8 ‐0.9 ‐0.6 0 0.25 0 ‐0.6 ‐0.9
‐0.18 ‐0.45 ‐0.6 ‐0.45 ‐0.18 ‐0.45 ‐0.6 ‐0.45
Roof ( < 10 Deg pitch)
Average
Roof ( 11 ‐ 30 Deg pitch)
Average
Roof ( > 30 Deg pitch)
Average
Location
Wind Angle
Face 1
Face 2
Face 3
Face 4

303

Appendix C Continued
C.5: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 2:1
Shielding condition: ........ Surrounded by obstruction equivalent to half the building height
Wind speed reference level: ......................................................................... Building Height

Table 112: Values of wind pressure coefficient for Surrounded by obstruction
equivalent to half the building height shielding conditions and 2:1 surface ratios.

0 45 90 135 180 225 270 315
0.25 0.06 ‐0.35 ‐0.6 ‐0.5 ‐0.6 ‐0.35 0.06
‐0.5 ‐0.6 ‐0.35 0.06 0.25 0.06 ‐0.35 ‐0.6
‐0.6 0.2 0.4 0.2 ‐0.6 ‐0.5 ‐0.3 ‐0.5
‐0.6 ‐0.5 ‐0.3 ‐0.5 ‐0.6 0.2 0.4 0.2
Front ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6
Rear ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6
‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6 ‐0.6
Front ‐0.6 ‐0.6 ‐0.55 ‐0.55 ‐0.45 ‐0.55 ‐0.55 ‐0.6
Rear ‐0.45 ‐0.55 ‐0.55 ‐0.6 ‐0.6 ‐0.6 ‐0.55 ‐0.55
‐0.5 ‐0.6 ‐0.55 ‐0.6 ‐0.5 ‐0.6 ‐0.55 ‐0.6
Front 0.15 ‐0.08 ‐0.4 ‐0.75 ‐0.6 ‐0.75 ‐0.4 ‐0.08
Rear ‐0.6 ‐0.75 ‐0.4 ‐0.08 ‐0.15 ‐0.08 ‐0.4 ‐0.75
‐0.2 ‐0.4 ‐0.4 ‐0.4 ‐0.2 ‐0.4 ‐0.4 ‐0.4
Roof ( < 10 Deg pitch)
Average
Roof ( 11 ‐ 30 Deg pitch)
Average
Roof ( > 30 Deg pitch)
Average
Location
Wind Angle
Face 1
Face 2
Face 3
Face 4

304

Appendix C Continued
C.6: LOW – RISE BUILDINGS (UP TO 3 STOREY’S)
Length to width ratio:....................................................................................................... 2:1
Shielding condition: ......................................Surrounded by equal to height of the building
Wind speed reference level: ......................................................................... Building Height

Table 113: Values of wind pressure coefficient for Surrounded by equal to height of
the building shielding conditions and 2:1 surface ratios.

0 45 90 135 180 225 270 315
0.06 ‐0.12 ‐0.2 ‐0.38 ‐0.3 ‐0.38 ‐0.2 ‐0.12
‐0.3 ‐0.38 ‐0.2 ‐0.12 0.06 ‐0.12 ‐0.2 ‐0.38
‐0.3 0.15 0.18 0.15 ‐0.3 ‐0.32 ‐0.2 ‐0.32
‐0.3 ‐0.32 ‐0.2 ‐0.32 ‐0.3 0.15 0.18 0.15
Front ‐0.49 ‐0.46 ‐0.41 ‐0.46 ‐0.49 ‐0.46 ‐0.41 ‐0.46
Rear ‐0.49 ‐0.46 ‐0.41 ‐0.46 ‐0.49 ‐0.46 ‐0.41 ‐0.46
‐0.49 ‐0.46 ‐0.41 ‐0.46 ‐0.49 ‐0.46 ‐0.41 ‐0.46
Front ‐0.49 ‐0.46 ‐0.41 ‐0.46 ‐0.4 ‐0.46 ‐0.41 ‐0.46
Rear ‐0.4 ‐0.46 ‐0.41 ‐0.46 ‐0.49 ‐0.46 ‐0.41 ‐0.46
‐0.49 ‐0.46 ‐0.41 ‐0.46 ‐0.45 ‐0.46 ‐0.41 ‐0.46
Front 0.06 ‐0.15 ‐0.23 ‐0.6 ‐0.42 ‐0.6 ‐0.23 ‐0.15
Rear ‐0.42 ‐0.6 ‐0.23 ‐0.15 ‐0.06 ‐0.15 ‐0.23 ‐0.6
‐0.18 ‐0.4 ‐0.23 ‐0.4 ‐0.18 ‐0.4 ‐0.23 ‐0.4
Roof ( < 10 Deg pitch)
Average
Roof ( 11 ‐ 30 Deg pitch)
Average
Roof ( > 30 Deg pitch)
Average
Location
Wind Angle
Face 1
Face 2
Face 3
Face 4

Abstract (if available)

Abstract Ventilation shafts can aid natural ventilation in buildings. Natural ventilation provides ventilation for occupants that can provide thermal comfort conditions. This study attempts to increase air flow rates, which can provide thermal comfort conditions, in occupant spaces of a low rise commercial building by using a ventilation shaft. While doing so the time period of effective natural ventilation also increases. This is achieved by optimizing the occupant zone and ventilation shaft design to maximize the air flow inside them. This design optimization is achieved by identifying the range of influence building and ventilation shaft components of height and openings have on both types of buoyancy and wind driven air flow. ❧ A comparison of air flow rate and thermal comfort conditions achieved by the airflow on different models having different ventilation shaft designs are performed to verify the potential of a ventilation shaft in increasing effectiveness of naturally induced airflow. Multi zone airflow and contaminant Transport analysis (CONTAM) software by National Institute of Standards and Technology (NIST) is used to perform all the calculations.

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University of Southern California Dissertations and Theses

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Asset Metadata

Creator Nagory, Abhay (author)

Core Title Ventilation shaft to increase effectiveness of natural ventilation

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 07/31/2012

Defense Date 03/19/2012

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag effectiveness of natural ventilation,natural ventilation,OAI-PMH Harvest,ventilation shaft

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Woll, Edward (committee chair), Roche, Pablo La (committee member), Simmonds, Peter (committee member)

Creator Email abhaynagory@gmail.com,nagory@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-79813

Unique identifier UC11289114

Identifier usctheses-c3-79813 (legacy record id)

Legacy Identifier etd-NagoryAbha-1086.pdf

Dmrecord 79813

Document Type Thesis

Rights Nagory, Abhay

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA