Exterior glare simulation: understanding solar convergence from concave facades using heat maps

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Content 1

EXTERIOR GLARE SIMULATION:

Understanding Solar Convergence from Concave Facades Using Heat Maps

By

Lisha Deng

A Thesis Presented to the
Presented to the
FACULTY OF THE
SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In partial fulfillment of the
Requirements of degree
MASTER OF BUILDING SCIENCE

AUGUST 2016
2
COMMITTEE

Marc Schiler
Professor
USC School of Architecture
marcs@usc.edu
213 740-4576

Douglas Noble, FAIA, Ph.D.
Associate Professor
USC School of Architecture
dnoble@usc.edu
213 740-2723

Kyle Konis
Associate Professor
USC School of Architecture
kkonis@usc.edu

3
Acknowledgement
I owe my thesis committee my sincerest gratitude. Chair Marc Schiler and committee members Douglas
Noble and Kyle Konis have proven invaluable contribution, working to achieve the goal and scope of this
thesis, guilding my methodology, and improving my writing. The inspiration of this thesis comes from
chair Marc Schiler with his expertise in glare and much research experience in the solar convergence
problem. He is the most patient, inspiring and knowledgeable teacher I have ever met. He encouraged my
passion for testing different software to build a simulation framework. His suggestions and instructions
are crucial to this thesis.
I would also like to acknowledge the contributions of the people from the Grasshopper website. The scripts
of UTCI maps, ray tracing, and heat maps are provided by Joseph Oster, Chris Mackey, Claudio Nunez,
Arie-Willem de Jongh and Mostapha Sadeghipour Roudsari. I am especially grateful to Joseph Oster, who
helped with building the simulation framework of the heat maps. I appreciate their time and effort.
My family has been a constant source of support, and without them, I would not have a chance to study
abroad at USC and take on the challenge of writing a master’s thesis. Since I was young, they are always
encouraging me to be brave instead of worrying about being perfect. That is the reason I am excited and
curious to simulate the solar convergence problem and test software though I do not have much experience
in glare simulation.
Finally, I appreciate my MBS family: the students, alumni, faculty and staff. I feel very lucky to be
surrounded by a group of nice and friendly people. I have done so much fun things together with my
classmates, which made my graduate school experience a memorable one. I look forward to having a
chance to work together.
4
Abstract
Concentration of solar radiation reflected from concave and specular facades results in the solar
convergence problem. In extreme cases the solar convergence problem had caused melting automotive
surfaces at the street level. The goal of this thesis was to build a simulation framework and test software
that can be used to simulate the solar convergence problem in the pre-design phase. Grasshopper and its
plug-ins Ladybug & Honeybee were chosen as the simulation tools. This thesis tests three simulations -
ray tracing, Universal Thermal Climate Index (UTCI) maps and heat maps. Ray tracing simulation showed
how the sun rays moved after being reflected from the concave and specular façade. UTCI maps showed
how and where the solar radiation reflected from the concave and specular surface resulted in thermal
discomfort. Absolute and relative heat maps are the distribution of reflected lights on the ground and hot
spots where the most reflected light has been concentrated. Relative and absolute heat map patterns and
their domains for seven different surface forms - ellipse (concave), flat top and bottom, flat top, flat
bottom, concave, convex bottom, and concave sweep were analyzed. Three methods of delivering heat
maps were used to simulate the solar convergence phenomenon for different purposes. The results showed
that flat top and curved bottom surface with a swirl pattern heat map caused the greatest focus effects on
the center of the swirl. Convex bottom surface has the most distributed pattern. For ellipse and concave
surfaces, the heat maps are closely distributed arcs, while flat top and bottom and convex bottom surfaces
delivered more sparsely distributed straight lines and arcs. Convex Sweep and flat top and bottom have a
focus effect on the edges of heat maps.

5
TABLE OF CONTENTS
ACKNOWLEDGEMENT .......................................................................................................................................................... 3
ABSTRACT ............................................................................................................................................................................ 4
TABLE OF CONTENTS ........................................................................................................................................................... 5
LIST OF FIGURES .................................................................................................................................................................. 9
LIST OF TABLES .................................................................................................................................................................. 15
LIST OF EQUATIONS ........................................................................................................................................................... 16
1 INTRODUCTION ........................................................................................................................................................ 17
1.1 AN INTRODUCTION TO SOLAR CONVERGENCE ........................................................................................................................ 17
1.2 DIFFERENT FACTORS CAUSING SOLAR CONVERGENCE .............................................................................................................. 19
1.3 THE IMPORTANCE OF SOLAR CONVERGENCE ANALYSIS ............................................................................................................. 20
1.4 TERMS ........................................................................................................................................................................... 21
1.4.1 Disability Glare and Discomfort Glare ................................................................................................................ 21
1.4.2 Absolute Glare and Relative Glare ..................................................................................................................... 21
1.4.3 Specularity and Reflectivity ................................................................................................................................ 22
1.4.4 Interior Glare and Exterior glare ........................................................................................................................ 22
1.4.5 Highly Specular and Concave Building Facades ................................................................................................. 24
1.4.6 Thermal Index .................................................................................................................................................... 27
1.5 CLASSIFICATION OF REFLECTED GLARE .................................................................................................................................. 31
1.6 STUDY BOUNDARIES.......................................................................................................................................................... 32
1.7 SIMULATIONS .................................................................................................................................................................. 32
1.8 CHAPTER SUMMARY ......................................................................................................................................................... 33
2 PREVIOUS WORKS: LITERATURE REVIEWS ................................................................................................................ 34
2.1 CONCAVE BUILDING FORMS AND SPECULAR FACADES ............................................................................................................. 34
2.2 CAUSTIC FORMATION ........................................................................................................................................................ 35
6
2.3 SIMULATION METHODS OF REFLECTED GLARE ........................................................................................................................ 36
2.4 BOUNDARY OF REFLECTION AREA (BRA) ANALYSIS ................................................................................................................. 37
2.5 GLARE REMEDIATION TECHNIQUES ...................................................................................................................................... 38
2.6 CHAPTER SUMMARY ......................................................................................................................................................... 39
3 METHODOLOGY ....................................................................................................................................................... 40
3.1 COMPARISON IN SIMULATION TOOLS (RADIANCEIES/GRASSHOPPE WITH LADYBUG AND HONEYBEE PLUG-INS/3DS MAX) ................... 40
3.1.1 RadianceIES ........................................................................................................................................................ 40
3.1.2 3ds MAX ............................................................................................................................................................. 43
3.1.3 Ladybug & Honeybee ......................................................................................................................................... 44
3.2 LADYBUG OUTDOOR SOLAR TEMPERATURE ADJUSTOR AND LADYBUG OUTDOOR COMFORT CALCULATOR ......................................... 49
3.2.1 Ladybug Outdoor Solar Temperature Adjustor .................................................................................................. 49
3.2.2 Ladybug Outdoor Comfort Calculator ................................................................................................................ 52
3.3 UTCI MAP ...................................................................................................................................................................... 55
3.4 RAY TRACING................................................................................................................................................................... 56
3.5 HEAT MAP ...................................................................................................................................................................... 56
3.6 CHAPTER SUMMARY ......................................................................................................................................................... 57
4 THE DATA AND THE TOOL ......................................................................................................................................... 58
4.1 CREATING THE UNIFORM THERMAL CLIMATE INDEX (UTCI) MAP .............................................................................................. 58
4.1.1 Hourly UTCI Map of Test Surface ....................................................................................................................... 58
4.1.2 Hourly UTCI of Single Human Geometry ............................................................................................................ 65
4.2 RAY TRACING................................................................................................................................................................... 69
4.2.1 Ray Tracing in Ladybug & Honeybee ................................................................................................................. 69
4.2.2 Ray Tracing in Grasshopper ............................................................................................................................... 73
4.3 HEAT MAP ...................................................................................................................................................................... 76
4.3.1 PLX (line/plane intersection) .............................................................................................................................. 76
4.3.2 Split sorted list of values .................................................................................................................................... 77
4.3.3 Color Range of Heat Map ................................................................................................................................... 79
7
4.4 CHAPTER SUMMARY ......................................................................................................................................................... 80
5 THE INTERPRETATION OF HEAT MAPS ...................................................................................................................... 81
5.1 RELATIVE/ABSOLUTE HEAT MAPS ....................................................................................................................................... 81
5.2 DIFFERENT BUILDING FACADE FORMS .................................................................................................................................. 84
5.3 GRID SIZE - SUN GRID AND TEST SURFACE GRID ..................................................................................................................... 86
5.3.1 Comparison of Grid Size ..................................................................................................................................... 87
5.4 RELATIVE HEAT MAPS ....................................................................................................................................................... 90
5.4.1 Concave Ellipse Surface ...................................................................................................................................... 91
5.4.2 Concave Rectangular Surface ............................................................................................................................ 92
5.4.3 Flat Bottom Surface, Curved Top Surface........................................................................................................... 94
5.4.4 Flat Top, Curved Bottom Surface ....................................................................................................................... 94
5.4.5 Flat top and bottom Surface .............................................................................................................................. 95
5.4.6 Convex Bottom Surface ...................................................................................................................................... 96
5.4.7 Convex Sweep Surface........................................................................................................................................ 97
5.4.8 Comparison of Domains of Relative Heat Maps with Different Building Facade Forms .................................... 98
5.5 ABSOLUTE HEAT MAPS ...................................................................................................................................................... 99
5.5.1 Calibrate Same Threshold Values with Different Building Facades Forms ......................................................... 99
5.5.2 Calibrate the Building Facade Form by the Maximum Density Found throughout the Day ............................. 101
5.6 COMPARISON OF RELATIVE HEAT MAPS WITH DIFFERENT LATITUDES .......................................................................................... 106
5.7 COMPARISON OF ABSOLUTE HEAT MAPS WITH HIGH RESOLUTION .......................................................................................... 108
5.8 VISUALIZATION OF HEAT MAPS WITH BOUNDING BOX ........................................................................................................... 110
5.9 CHAPTER SUMMARY ....................................................................................................................................................... 111
6 CONCLUSION .......................................................................................................................................................... 112
6.1 RAY TRACING................................................................................................................................................................. 112
6.2 UTCI MAPS .................................................................................................................................................................. 112
6.3 HEAT MAPS .................................................................................................................................................................. 113
6.4 FUTURE WORK ............................................................................................................................................................... 114
8
6.5 FINAL SUMMARY ............................................................................................................................................................ 116
7 REFERENCE ............................................................................................................................................................. 117

9
LIST OF FIGURES
Figure 1- Solar convergence phenomenon caused by Fenchurch Street, knicknamed the Walkie
Talkie or even the walkie scorchie(source: www.amusingplanet.com) ................................................... 18
Figure 2 - Curving façades act like “solar cooker” (source: www.amusingplanet.com) .......................... 19
Figure 3 - Marquee Photo (left) and Color Coded Isoluminance Plot of Founders Room (right)
(Schiler & Valmont 2005) ........................................................................................................................ 25
Figure 4 - Solar convergence Problem of Walkie Talkie ( Designboom Architecture 2013) ................. 26
Figure 5 - Vdara Hotel( source: http://www.destination360.com/north-america/us/nevada/las-
vegas/vdara) .............................................................................................................................................. 27
Figure 6 - Common thermal index (www.weatherunderground.com) ..................................................... 28
Figure 7 - Different components included in UTCI index ........................................................................ 29
Figure 8 - UTCI Assessment Scale (Journal of Thermal Biology 2003) .................................................. 30
Figure 9 – Test three simulations .............................................................................................................. 33
Figure 10 - Facade glare-intensity false-color analysis for different facade shapes at the summer
solstice (Marcin, 2012) ............................................................................................................................. 34
Figure 11 - Caustic formation in 3D space and individually calculated reflection curves that
contribute to caustic envelope creation. The sun altitude (angle) is 45◦(Marcin 2012) ........................... 36
Figure 12 - Union of RGA for a south-facing test facade at different times of the year for different
facade shapes (Marcin 2012) .................................................................................................................... 37
Figure 13 - Glare volume (left) and the part of building free of reflection (right) (Naai-Jung & Huang
2001) ......................................................................................................................................................... 38
Figure 14 – Radiance (left) and 3ds Max (right) Reflected Glare (Schiler & Kensek 2009) ................... 39
Figure 15 - Import gbXML file to IESVE ................................................................................................ 40
Figure 16 - Illuminance level of the room (plan view) ............................................................................. 41
10
Figure 17 - Show lux grid where DF factor ≤ 1% (area 71.7%) ............................................................. 41
Figure 18 - Eye position setting (left) and perspective view of illuminance level of the room (right) .... 42
Figure 19 - Glare analyze (glare threshold = 100 cd/ ft2) (left) and interior view of glare (right) ........... 42
Figure 20 - GVCP (Guth Visual Comfort Probability) (left) and CIE glare index (right) ....................... 43
Figure 21 - Import the FBX file from Revit to 3ds Max (left) and set sun and location (right) ............... 43
Figure 22 - Create light meter (left) and calculate all light meter (right) ................................................. 44
Figure 23 - Interior rendering (left) and exterior rendering (right) ........................................................... 44
Figure 24 - Relationship between Honeybee and other cooperative software (Grasshopper website) .... 45
Figure 25 - Download weather file from EnergyPlus website .................................................................. 46
Figure 26 - Quick chart of the weather data ............................................................................................. 46
Figure 27 - Generate sky condition using the environmental analysis methods provided from
Grasshopper website (Grasshopper 2015) ................................................................................................ 47
Figure 28 - Radiation analysis using the environmental analysis methods provided from Grasshopper
website (Grasshopper 2015) ..................................................................................................................... 48
Figure 29 - Ladybug Outdoor Solar Temperature Adjustor (Grasshopper 2015) .................................... 50
Figure 30 - Solar Adjusted MRT .............................................................................................................. 51
Figure 31 - Effective Radiant Field (ERF) ............................................................................................... 51
Figure 32 - Ladybug Outdoor Comfort Calculator ................................................................................... 52
Figure 33 - Top view of annually UTCI Mesh for a single location ........................................................ 53
Figure 34 - 3D view of annually UTCI Mesh for a single location .......................................................... 53
Figure 35 - Comfort analysis .................................................................................................................... 54
Figure 36 - Use 0 or 1 to represent comfortable or not ............................................................................. 54
Figure 37 - UTCI map comparison with solar radiation adjustment using the method from Ladybug
comfort tutorials provided by Chris Mackey (Grasshopper 2015) ........................................................... 55
11
Figure 38 - Model the glass facades of the building and test surface on the ground by Chris Mackey
(source: http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-
reflected-solar-heat-gain?xg_source=activity) ......................................................................................... 58
Figure 39 -. Human comfort and climatic forces ...................................................................................... 59
Figure 40 - Components of cumulative radiation ..................................................................................... 60
Figure 41 - Honeybee daylight simulation component for cumulative radiation by Chris Mackey
(source: http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-
reflected-solar-heat-gain?xg_source=activity) ......................................................................................... 61
Figure 42 - Script for generating solar adjusted MRT by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-
solar-heat-gain?xg_source=activity) ......................................................................................................... 61
Figure 43 - Calculating process of UTCI values by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-
solar-heat-gain?xg_source=activity) ......................................................................................................... 63
Figure 44 - Hourly UTCI maps of test surface ......................................................................................... 64
Figure 45 - Radiation analysis of single human geometry by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-
solar-heat-gain?xg_source=activity) ......................................................................................................... 66
Figure 46 - Calculation of solar adjusted MRT by using the relationship between MRT and ERF by
Chris Mackey (http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-
under-reflected-solar-heat-gain?xg_source=activity) ............................................................................... 67
Figure 47 - Hourly UTCI value of single human geometry on test grid................................................... 68
Figure 48 - Simulation result of Hourly UTCI of single human geometry on test grid ........................... 68
Figure 49 - Ray tracing simulation result at different time ....................................................................... 71
12
Figure 50 - Surrounding building ............................................................................................................. 72
Figure 51 - Useful Daylight Illuminance (UDI) Result ............................................................................ 73
Figure 52- Arbitrary Surface ..................................................................................................................... 74
Figure 53 - U.S. Naval observatory website sun altitude/azimuth table (source: http:
//aa.usno.navy.mil/data/docs/AltAz.php)) ................................................................................................ 74
Figure 54 - Surface Grid Points Generation Process ................................................................................ 75
Figure 55 - Ray Tracing Simulation Result .............................................................................................. 76
Figure 56 - Control the grid size by 'Line | Plane' intersections ('PLX') by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ..................... 77
Figure 57 - Bounced sun rays intersected the ground ............................................................................... 77
Figure 58 - "Splitting list of values" by Danny Boyes (source:
http://www.grasshopper3d.com/forum/topics/splitting-list-of-values)..................................................... 78
Figure 59 - Split sorted list of values code and list of values before and after split ................................. 78
Figure 60 - Color range code by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ..................... 79
Figure 61 - Heat Map Simulation Result .................................................................................................. 79
Figure 62 – Comparison of heat maps ...................................................................................................... 82
Figure 63 – Calibrate absolute values of heat map by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ..................... 83
Figure 64 - Comparison of relative (top) and absolute heat map (bottom) ............................................. 84
Figure 65 – Seven different building forms used to test heat maps .......................................................... 85
Figure 66 - Code for selecting different façade forms by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ..................... 85
Figure 67 – Sun grid and test surface grid ................................................................................................ 86
13
Figure 68 - change cell size code by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ..................... 87
Figure 69 - Sun grid size 2, cell size 3 ...................................................................................................... 88
Figure 70- Sun grid size 1, cell size 3 ....................................................................................................... 89
Figure 71 - - Sun grid size 1, cell size 1.................................................................................................... 90
Figure 72 – Bounced lights of ellipse surface ........................................................................................... 91
Figure 73 - Relative heat map of ellipse (concave) surface (domain 1-22) .............................................. 92
Figure 74 - Relative heat map of concave surface (domain 1-24) ............................................................ 93
Figure 75- Top view of relative heat map showing second focus effect .................................................. 93
Figure 76 - Relative heat map of flat bottom surface (domain 1-33) ...................................................... 94
Figure 77 - Relative heat map of flat top surface (domain 1-99).............................................................. 95
Figure 78 - Relative heat map of flat top and bottom surface (domain 1-21) .......................................... 96
Figure 79 - Relative heat map of convex bottom surface (domain 1-4) ................................................... 97
Figure 80 - Relative heat map of convex sweep surface (domain 1-24) .................................................. 98
Figure 81 - Absolute heat maps of different building facades forms with the same calibrating
threshold .................................................................................................................................................. 101
Figure 82 - Absolute heat maps of concave surface ............................................................................... 103
Figure 83- Absolute heat maps of flat bottom surface ............................................................................ 104
Figure 84 - Absolute heat maps of flat top surface ................................................................................. 105
Figure 85 - Code for changing locations by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ................... 106
Figure 86 - Comparison of relative heat maps with different latitudes .................................................. 108
Figure 87 – Comparison of absolute heat maps with high resolution..................................................... 110
14
Figure 88 - Code for bounding box by Joseph Oster (source: source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie) ................... 111
Figure 89 – Visualization of heat maps with bounding box ................................................................... 111

15
LIST OF TABLES
Table 1 – Comparison of domains of relative heat maps with different building facades forms ............. 99

16
LIST OF EQUATIONS
Equation 1 ................................................................................................................................................. 31
Equation 2 ................................................................................................................................................. 35
Equation 3 ................................................................................................................................................. 65
Equation 4 ................................................................................................................................................. 66
Equation 5 ................................................................................................................................................. 66

17
1 Introduction
1.1 An Introduction to Solar Convergence
Reflecting light from the concave glass façade and concentrating heat on some spots on the ground is
similar to the effect of burning items with a magnifying glass (Fedele 2013). The curves of glass façades
can act like mirrors, reflecting light that converges at one single point. It causes the hot spots which
generate much heat and, in its extreme, its temperature can even melt metal (Four-solaire 2016). The
reflected light can raise the temperature of some specific hot spots in the surrounding environment
extremely high, which even can fry an egg, melt vehicle surfaces and greatly affect the thermal comfort
of a pedestrian on that spot (Fedele 2013).
In the laboratory PROMES, combustion demonstration and material melting are conducted outside of the
solar furnace using parabolic mirror wall surfaces as projectors. Unlike the other problemetic buildings,
the Foure Solaire did this intentionally. A solar furnace uses parabolic mirrors or heliostats to concentrate
light onto a focal point (Four-solaire 2016). The Odeillo solar furnace in the Pyrenees-Orientales allows
concentrating solar energy to obtain 1000 kilowatts which can reach temperatures above 3500 ℃. It can
be used to generated electricity, melt steel, make hydrogen fuel or nanomaterials (`PROMES 2016).The
study of cell behavior under very high solar flux is conducted at PROMES. The cell was placed at the
focus of parabolic mirror that achieves maximum concentrations of 10,000 suns. The size of the radiating
source, the faults of specularity of the mirror and the heliostats pointing defects are three factors that
contribute to spreading of the concentrated stream and a decrease in the density of solar flux( PROMES
2016). The architects put considerable effort on its unique appearance in part to test the potential benefits
or risks of solar convergence. In result, solar convergence can pose a significant threat to the surrounding
environment. Typically, fixing the problem by putting exterior shading devices on the facades, after the
fact, is extremely expensive. Thus, it is vital to evaluate the risk and avoid solar convergence problems in
the design phase.
18
Glare from concave façades can cause two adverse effects, one is visual discomfort, and another one is
thermal discomfort. Visual discomfort includes impeding the views of nearby pedestrians and drivers,
which can cause serious car accidents and even temporary blindness of people. It is a noticeably annoying
problem so that some researchers have done before about the visual discomfort aspect of glare (Suk 2015).
Relatively less attention has been put on thermal discomfort. Solar convergence is also a growing problem,
and its damage is serious. Solar convergence can cause from small problems like singed hair, melted
plastic bags to serious ones like causing a fire to nearby constructions and thermal stress on pedestrians.

Many studies have been done on the interior glare problem, and software like Radiance, IES and 3ds Max
are also capable of doing luminance, an illuminance level, and glare analysis. Relatively less attention has
been put on exterior glare. Also, there are no specific thermal index or tools that have been developed to
analyze exterior glare problems. The high dynamic range (HDR) image analysis tool in MATLAB can
analyze digitally captured glare scenes. Moreover, HDR images can show the luminance level and exterior
glare sources (Suk 2015). However, a tool has not been developed that can simulate the thermal discomfort
Figure 1- Solar convergence phenomenon caused by Fenchurch Street, knicknamed the Walkie Talkie or even
the walkie scorchie(source: www.amusingplanet.com)

19
caused by exterior glare. To address this exterior glare problem, we need to select a suitable software that
can accurately simulate this phenomenon.
1.2 Different Factors causing Solar Convergence
The solar convergence phenomenon is caused by the total curved surface area, the mathematical focus
point of the curved surface and the specularity of the surface. Concrete or brick surfaces diffuse light.
Large amounts of a beam of light can be reflected from what hits the concrete or brick façade, but it
scatters in all direction. By contrast, almost all the all the light will be reflected by a glass façade and can
focus on one direction. Moreover, with the south-facing orientation and its concave shape, it will create
some potentially dangerous hot spots on the ground which can cause thermal discomfort for the people
standing there.

Figure 2 - Curving façades act like “solar cooker” (source: www.amusingplanet.com)
20
1.3 The Importance of Solar Convergence Analysis
A shiny coating can reflect most sunlight which means less solar heat has been absorbed in the building.
So an extremely specular façade is often considered eco-friendly and energy saving regarding less
cooling load. Also, people inside can experience a better indoor environment. However, to those on the
outside the building, it can be uncomfortable or even dangerous. Also, more severe problems may occur,
like blinding a driver’s eyes, melting the vehicles alongside the street and causing interior glare to the
surrounding buildings.
Solar convergence can cause serious damage and also cost a significant amount of money to fix. So it is
necessary to evaluate the design and glare potential in the pre-design phase. Many questions should be
asked before giving a sound architecture design: How to avoid a concave and reflective building affect
to surrounding buildings and people? How to regulate solar convergence in built environment? Are there
any computer simulation techniques to prevent solar convergence of building in pre-design phase? Are
there any techniques to mitigate the existing solar convergence damages? What is the most efficient and
economically reasonable way to address this problem? Are there any shading devices that cost relatively
less and are effective to solve the problem? How do the people feel who are in the area of hot spots
caused by the highly specular building? What metrics or index is there to measure it?
The solar convergence may have a small relative impact on urban heat island effect (Ferro 2013), which
means many hard surfaces made of asphalt can absorb an enormous amount of heat and thus causing the
cities to be hotter than the rural area. However, buildings also have an impact on their surrounding
environment; the reflected light can cause great impact on the surrounding building, transportation, and
people.
Solar convergence has not been regulated by specific standards or codes. Building rating systems like
LEED do not include solar convergence evaluation as one part of the credits. Not only are there limited
21
standards regulating this problem, but solar convergence also may have many difficulties regarding
simulation. Besides, the sun is a moving target and will always reflect light in the growing built
environment. Architects and developers must consider that this concave facades design could hold a
significant threat to the immediate environment (Ferro 2013).
1.4 Terms
1.4.1 Disability Glare and Discomfort Glare
Disability glare happens when the light source is so dazzling that people are unable to finish their task,
In this case, people avoid looking at the light source to prevent its damage to their eyes. Either the
extremely bright light source or the extreme contrast between the glare source and background is the
cause of disability glare (Suk 2015). Discomfort glare happens when the light source adversely affects
the human comfort level and their work performance (Suk 2015).
Veiling Reflection will mask the things people look at, such as a specular magazine or a computer
monitor. By changing the angle of the incident angle or light source placement, some veiling can be
avoided (Suk 2015).
1.4.2 Absolute Glare and Relative Glare
Absolute glare happens with an excessively bright glare source, such as while looking directly into the
sun, absolute glare happens due to the exceeding brightness of glare source (Suk 2015). Absolute glare
is beyond the threshold of certain brightness (Schiler & Valmont, 2005).
Relative glare is created by the contrast between the brightness of glare source and its surroundings.
When human eye adapts to the relatively darker background conditions, the glare source can cause their
discomfort even without exceeding brightness. (Suk 2015) Relative glare might be below the absolute is
threshold but still hard for the eye to adapt to, owing to a lower background level in the field of view
22
(Schiler & Valmont, 2005). For example, when people look at the headlights of an oncoming car at
night, discomfort glare happens to cause to the eye adaption to a black background. In contrast, the
headlights of oncoming at daytime may not cause this problem (Suk 2015).
1.4.3 Specularity and Reflectivity
“Solar reflectance is a measure of the ability of a surface material to reflect sunlight, including the
visible, infrared, and ultraviolet wavelengths (Suk 2015).” Reflected lights include diffuse, spread and
specular reflection, the remaining light is either absorbed, transmitted, or both. When light is striking a
specular surface like glass, stainless steel or mirror material, the angle of incoming incident light is
exactly equal to the angle of the outgoing reflected light. Matte surfaces distribute light almost equally
in all directions while specular surfaces reflection light in a preferred direction (Reinhard 2010). By
changing the angle of the surface or changing the beam spread of the reflected light from a specular
reflection to a diffuse one, some discomfort glare problems can be avoided (Suk 2015).
High specularity, instead of high reflectivity is the cause of solar convergence. This can be true for three
different kinds of surfaces, black specular reflective surface, black specular low-reflective surface, white
specular reflective surfaces. Both white and black specular surfaces reflect a beam. The lights hit on
them can have a diffuse and/or specular reflection. For the black specular low-reflective surface, even it
is low-reflective, it still can cause solar convergence problem with high specularity. Both white and
black matte surfaces do not reflect a beam. The light hit on them only have a diffuse reflection. For a
white matte reflective surface, even if it has high reflectivity, it diffuses light so that it will not have the
focus issue (Suk 2015).
1.4.4 Interior Glare and Exterior glare
Much research had been done with interior glare which focused on the indoor environment and the
energy consumption of the building itself, and software like RadianceIES and 3ds Max are also capable
23
of doing luminance levels, an illuminance level, and glare analysis. Relatively less study is focusing on
exterior glare, which affects the surrounding buildings and streets. Also, there is no specific thermal
index or tools that have been developed to analyze the exterior glare problem.
Daylight plays a vital role in sustainable design because it saves energy consumption of electric lighting
and improves the comfort and productivity of occupants. Besides, sunlight can also provide a heating
effect in winter. Thus, more opening, windows, and transparent façade are applied to building to
optimize the daylight effect. On the one hand, it indeed saves a significant amount of energy. On the
other hand, it introduces glare problems to the interior and exterior environment and causes human
discomfort (Suk 2015).
1.4.4.1 Interior glare
Interior glare can significantly affect people’s comfort and work efficiency. Sometimes buildings are
designed to maximize their daylight to save energy, however, too much sunlight can cause glare.
Although there are several interior glare indices, there is still considerable disagreement among them.
The discomfort feeling of people from minor to disturbing glare is hard to clarify. So the design of glass
ratio of the wall should be balanced between indoor comfort and energy-saving effect (Patterson 2014).
Interior glare can adversely affect some activities like reading books and watching TV. However, on the
other side, sufficient daylight also plays a vital role in the comfortable indoor environment and greatly
affect people’s mood inside. So calculating how to make the balance becomes necessary, and there are
some ways to reduce the interior glare without sacrificing too much daylight (Miller & Media 2015).
Window films can be used to reduce fabric damage and eye damage. Rolling solar shades or Venetian
blinds are also an excellent choice regarding flexibility. From morning to midday when glare is a big
problem, they can be pulled down to block sunlight. However, they typically trap heat gain on the
24
inside. For natural shading, some trees should be planted surrounding the building, especially providing
the shading for windows on the west side and east side (Schiler 1981).
Changing the color of walls can also make an improvement. Paint the wall in a higher reflectance so that
window seems less bright compared with it. The comparison is significant, because when the room is
dark, the windows seem brighter. By painting the wall brighter, the room is almost as bright as a
window so that glare will not be a problem (Miller & Media 2015). However, the ratios are so high that
it is often insufficient.
1.4.4.2 Exterior glare
While interior glare is more clearly defined, a clearer definition for exterior glare is needed. Exterior
glare will affect both the thermal comfort and visual discomfort of people nearby. There is a lack of
research, codes and regulations of this exterior glare problem.
1.4.5 Highly Specular and Concave Building Facades
More and more cuboid-shaped buildings are replaced with contemporary, free-form structures in design
trends. New forms of buildings bring many challenges to the civil, mechanical and electrical engineers.
The free-form structures with the highly specular material can cause exterior glare. Many articles have
now reported the solar convergence problem caused by concave building facades with a glass material.
The following buildings are some examples of highly specular buildings.
1.4.5.1 Walt Disney Concert Hall
Walt Disney Concert Hall in Los Angeles was studied by Professor Marc Schiler and his students,
Jonathan Tedjakusuma (Schiler & Valmont 2005) and Jae Suk (Suk 2015). This building created
extreme exterior glare, with highly polished panels as a facade that amplified the sunlight onto a nearby
building. This research focuses on how the building has an impact in the microclimate of their
25
immediate surroundings. Schiler claims that there are two kinds of glare. One is “absolute value” glare
which beyond the threshold of certain brightness. While another is “relative glare" or “adaptation glare”
that might be below the threshold but still hard for the eye to adapt to owing to a lower background level
in the field of view. Moreover, solar convergence issues and visual glare issue are addressed separately
(Schiler & Valmont 2005).

Figure 3 - Marquee Photo (left) and Color Coded Isoluminance Plot of Founders Room (right) (Schiler & Valmont 2005)
In the Walt Disney Concert Hall (WDCH) Research, a survey of the employees of Walt Disney Concert
Hall, an infrared thermometer gun, and dataloggers were used to find thermal glare issues. Digitized
photographs, computer simulations, and luminance histograms were used to analyze visual glare issues.
This building causes overheating in the surrounding environment and adversely affects traffic safety
(Schiler & Valmont 2005).
1.4.5.2 20 Fenchurch Street
20 Fenchurch Street is a skyscraper at 20 Fenchurch Street in London. It has a concave structure and
glass façade which reflects intensified heat onto nearby buildings, streets and roads. Moreover, it melted
automotive surfaces because concentrated light reflected by its southern-facing, glass-and-steel concave
façade. To deal with this problem, a sunshade system known as 'brise soleil' was planned for the 500-
foot elevation of the building (Mullin 2014).
26

Figure 4 - Solar convergence Problem of Walkie Talkie ( Designboom Architecture 2013)
1.4.5.3 Vdara Hotel
The Vdara Hotel in Las Vegas is famous for its death ray, which is also owing to its curving, south-
facing and highly specular façade (D + D News 2013). The Vdara hotel is LEED Gold certified. Many
buildings are LEED-certified, which means they are designed, constructed and managed to make the
least impact on the environment and saving energy and resources. However, these building may ignore
the solar convergence issue, which causes potential dangerous heat to surrounding buildings or people.
The sunlight is reflected from the glass façade and focuses on the swimming pool area. The area is
approximately 20 degrees hotter than another area. The plastic bags melted are often made from some
material like polyethylene, which can stand for temperature over 120 degrees. (NBCNEWS Website
2010) There is no building in front of it to block the sunlight so that swimming pool area can receive all
the sunlight hitting on it. Some people who came to the pool for relaxing reported that they experience
uncomfortably hot temperatures just after a short period. Some of them even experienced singed hair
with the odor coming from their head. People instinctively run into the shade to avoid being burned by
converged sunlight. (D+D News 2013)
27
Though the film which supposedly can scatter sunlight had been installed to the glass panes, many
customers in this hotel still complain about being uncomfortable in the swimming pool area. This is
because the film reduces the reflectivity, but does not successfully scatter the light. Adding more natural
shading is one solution. Also, more large sun umbrellas and other artificial shading devices should be
added. An effective configuration of shading devices should also be considered and analyze (Leckert
2014). In the case of the Vdara, it is the change in the MRT and effective temperature that affect thermal
comfort. Other factors like realitive humidity will also affect thermal comfort.

Figure 5 - Vdara Hotel( source: http://www.destination360.com/north-america/us/nevada/las-vegas/vdara)
1.4.6 Thermal Index
Outdoor comfort is usually measured by some kind of temperature scale. Moreover, it is expressed by a
common thermal index that is often oversimplified. As Figure 6 shows, the air temperature can be only
84.5℉, and yet it feels like 95 ℉. The explanation of it is that the humidity is higher than usual, which is
78%. So it is hot enough for people to sweat and the humidity reduces evaporation which contributes to
an overheated feeling. So a suitable thermal index should be given to show human thermal comfort.
28

Figure 6 - Common thermal index (www.weatherunderground.com)
1.4.6.1 UTCI
Universal Thermal Climate Index (UTCI) is a thermal comfort index that indicates how the temperature
feels. The motivation for developing this thermal index is finding a sound and accurate way to assess the
thermal comfort with the consideration of human biometeorology factors. This temperature metric is
universal because it encompasses a review of both heat exchange conditions and physiological factors,
the balancing of the human thermoregulatory heat budget, meteorological factors, and discomfort
sensations (Fiala, 2009).
29

Figure 7 - Different components included in UTCI index
UTCI thermal index is the result of the cooperation of experts in many fields including thermal-
physiology, energy modeling, meteorology and data analysis (Fiala 1957). This multidisciplinary
research provides a human health related and physiological and meteorological based thermal index.
It is made by a very complex energy model. Thousands of simulations of this complicated energy model
were run. The developing of UTCI includes the consideration of the assessment of the outcome of the
model and its application to different situations, comparison of the result of the model with available
field data, identification of input data and estimate its effect on the result. The UTCI value is the
outcome of the complete simulation, including both body thermal effects and local effects.This thermal
index is an approximation of thermal comfort based on these simulation results (Fiala 1999).
The UTCI was developed as an index like temperature. It shows the equivalence between the real
condition and human physiological response. As figure10 shows, different ranges of UTCI value stands
for the different level of thermal stress. People will experience extreme cold stress if the value is below -
40, and will experience extreme heat stress if the value is above +46. (Jendritzky 2000)
30

Figure 8 - UTCI Assessment Scale (Journal of Thermal Biology 2003)
1.4.6.2 MRT
Mean radiant temperature is defined as “ the uniform temperature of an imaginary enclosure in which
the radiant heat transfer from the human body is equal to the radiant heat transfer in the actual non-
uniform enclosure (ISO 1998)”. It not only depends on the temperature of surrounding surfaces buts also
the relative positions and viewed angles between human and surfaces. MRT as thermal index could be
used as one factor to evaluate the IEQ (indoor environment quality) and building performance. It
assesses the effect of surface temperature on human thermal comfort.
1.4.6.3 ERF
ERF (Effective Radiation Field) is a thermal measure of the net radiant energy flux to or from the human
body. ERF is used to describe the additional long-wave radiation energy at the body surface when
surrounding surface temperatures are different from the air temperature. The ERF on the human body
from long-wave exchange with surfaces is related to MRT by (Edward etc. 2015):
31
Equation 1
ERF = f
eff
h
r
(MRT - T
a
)
f
eff
is the fraction of the body surface exposed to radiation from the environment (=0.696 for a seated
person and 0.725 for a standing person); h
r
is the radiation heat transfer coefficient (W/m
2
K); and T
a
is
the air temperature (ºC) (PO 1970).
1.5 Classification of Reflected Glare
Based on the relative movement between the building facades and the objects affected by the glare,
reflected glare can be classified into three categories including fast, moderate and slow speed. A fast
speed happens between the reflected glare from facades and a driver in moving automotive surfaces on a
nearby street. A moderate speed exists between the glare source and a moving pedestrian. Lastly, slow
speed happens when glare from reflective glass façade interacts with a worker in a fixed location for a
period. (Naai-Jung & Huang 2001)
Depending on the relationship between site conditions and glare type, reflection glare is categorized as
neighborhood reflection, face-to-face reflection, and irregular reflection. Face-to-face happens when the
buildings are located next to a wide road. Neighborhood reflection happens when buildings are located
close to roads running east-west. Moreover, irregular reflection happens when an office building is next
to old residential areas. Because of the irregular building reflected area, it is very hard to predict glare.
(Naai-Jung & Huang 2001)
Moreover, depending on the neighborhood conditions and a reflection’s appearance, it can also be
classified as fragmental reflection, masked reflection and/or full reflection. The edge of fragmental
reflected glare is blurred. The fragment of glare is divided by the window frames. The edge of masked
reflected glare is discontinuous or distorted because of the mask on the façade. The edge of fully
reflected glare is clear. (Naai-Jung & Huang 2001)
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1.6 Study Boundaries
Different softwares were compared to give accurate simulations of the solar convergence phenomenon.
Conceptual concave surfaces were built, and simulation frameworks were built. The simulation process
includes showing the distribution of reflected light on the ground and then finding relatively hot spots that
concentrated the most reflected light. Also, there will be an analysis of this solar heat gain concentrated
by the concave facade to determine likely thermal discomfort of the people on those spots. A heat map
was built to show light concentration on a given ground surface and thermal stress of an individual
standing on the potential hot spots. Analysis of heat maps revealed that concave glass façades could cause
potentially dangerous hot spots in the surrounding environment and thermal discomfort of a person
standing on the spots. This thesis proposes and tests the simulation framework for solar convergence of
concave glass façades and the discussion of its limitation and future work. The purpose of this thesis is
achieved by the simulation of building with a different shapes, and result applied in pre-design phase can
avoid solar convergence phenomenon. The effect of incident light angle on the solar radiation heat gain
on the human body was not taken into consideration in this thesis.
1.7 Simulations
This thesis tests three simulations. The first simulation is the UTCI map that represents the thermal
comfort of a person standing at one point on the test surface at certain period with the consideration of the
additional solar radiation portion from the concave building. The second simulation is the ray tracing
simulation to trace the reflected lights from concave glass façade at different sun positions and their effect
on surrounding buildings. The third simulation is a colored heat map that indicates how much-reflected
light is focusing on each test grid.
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Figure 9 – Test three simulations
1.8 Chapter Summary
In this chapter, backgrounds, technical terms, study boundaries, simulations of this thesis were
discussed. The next chapter (chapter 2) discusses the previous research people have done.

Test Three
Simulations
UTCI Maps Ray Tracing Heat Maps
34
2 Previous Works: Literature Reviews
2.1 Concave Building Forms and Specular Facades
“Concave and convex facades make rays of sunlight converge or scatter according to the laws of geometric
optics” (Marcin 2012). In Marcin’s research, the effect of reflected glare from different forms of building
facades has been studied and tested including rectangular, angular, concave and convex shapes. Among
these forms of building facades, the concave shape can cause the highest solar convergence effect. The
false color simulation results showed the illuminance level on the ground and the glare intensity. Concave-
shaped facades had the highest glare intensity. A significant amount of heat concentrated on a small area,
which could cause significantly surface temperature rise and potential ignition (Marcin 2012).

Figure 10 - Facade glare-intensity false-color analysis for different facade shapes at the summer solstice (Marcin, 2012)
When the surface is smooth, it evolves toward specular or mirror-like behavior. When the surface is
rough, it diffuses light because of diffraction and interference effects (He etc. 1991). “The specular term
accounts for mirror-like reflection from the mean plane of the reflecting surface (He etc. 1991).” For
rough surfaces, the specular term is reduced by the roughness and shadowing factors. For the smooth
surfaces, as the wavelength of the incident light becomes large about the projected surface roughness,
the specular component dominates the first surface reflection process. The usual form of the
bidirectional reflectivity for a specular surface is (He etc. 1991):
35
Equation 2
|𝐹 |
2
= 𝑐𝑜𝑠𝜃𝑖 𝑑𝑤𝑖
|𝐹 |
2
- Fresnel reflectivity
𝜃 - polar and azimuthal angles
ω - solid angle
A solar light reflectivity analysis had been conducted for the Alkira Apartment in Rhodes about its
adverse effect on surrounding traffic, buildings and pedestrians. Seven locations have been identified for
detailed analysis. A maximum of 20% reflectivity index is recommended for all glazing on the facades
(WINDTECH 2011). However, specularity instead of reflectivity is the cause of solar convergence
problem. The reduction in reflectivity of facades does not necessarily solve the problem, and specular
surfaces with low reflectivity can still cause solar convergence.
2.2 Caustic Formation
In Marcin’s research, the simulation result showed the potentially dangerous caustic vertex formation of
concave facades. By analysis of the result, dimensions of concave façades could be modified to reduce
the intensity of the caustic vertex considerably. Architects could change the shape and size of the
concave facades of buildings to avoid solar convergence. Also, an appropriate choice of cladding
material should be chosen (Marcin 2012).
Figure 11 shows the caustic formation in 3D space, “the red dashed lines represent the individually
calculated reflection curves that contribute to the creation of the caustic envelope (where h ≤
1
2
r).
Moreover, the continuous black lines represent the curves reflected from the arcs at the surface of the
mirror when h >
1
2
r). These considerations allow for the calculation of the conditions to form a caustic
envelope” (Marcin 2012).
36

Figure 11 - Caustic formation in 3D space and individually calculated reflection curves that contribute to caustic envelope creation. The
sun altitude (angle) is 45 ◦ (Marcin 2012)
2.3 Simulation Methods of Reflected Glare
In He, Torrance, Sillion, and Greenberg’s research, a physical model was built to simulate specular,
directional diffuse, and uniformly diffuse reflections. The reflected light pattern depends on incidence
angle, surface roughness parameters, wavelength, and refractive index. The reflection model simulates
from specular to diffuse-like reflection. The model predicts when the specular reflection will happen by
increasing wavelength or angle of incidence, or decreasing surface roughness. (He 1991)
In J.C, Deville and Winkler’s research, radiative properties of light sources and materials were modeled
by a radiosity computation algorithm. It gave a photo-realistic rendering of the simulation result. Based
on the spatial and spectral emittance distribution of the light source, and surface reflectance and
transmittance, the accurate colorimetric properties of the reflecting surface and light source were
calculated. (J.C, Deville &Winkler 1995) However, when the complexity of radiosity input increases,
the computing time increased significantly. Further research should reduce the algorithmic complexity
of radiosity to speed up the simulation process. (J.C, Deville &Winkler 1995)
37
2.4 Boundary of Reflection Area (BRA) Analysis
The simulation of BRA has been done by Naai-Jung and Huang. In their research, glare simulation of
BRA was given at each hour. Then the union of BRA combining reflected areas at the different period
was used to calculate the boundary and glare intensity at each intersection on the ground. The simulation
results are in a daily total, but not a momentary heat gain. (Naai-Jung & Huang 2001)
3dssMax can give photon-emission ray-trace rendering and give RGA (reflection glare area ) result. It
traces light paths by the “Generate Caustic” option. The area of reflected light from glass facades was
measured. By inputting the threshold value, the software helps to outline the area that is affected by the
glare. Concave surfaces can also be molded in 3ds Max to get the simulation result of BRA (Naai-Jung
& Huang 2001)

Figure 12 - Union of RGA for a south-facing test facade at different
times of the year for different facade shapes (Marcin 2012)
38
Besides the reflected area on the ground, simulation results can also show the reflection volume with
volumetric data. It also shows how deep the reflected sunlight can penetrate the interior space by
subtracting the affected interior space from the building. (Naai-Jung & Huang 2001)
It quantifies BRA by the summation of all boundary areas. But it ignored overlay occurring between the
boundaries. It listed the BRA of the 1x1x1 test cube in three locations on summer solstice, spring or
autumn equinox, and the winter solstice. The larger the BRA is, the more setbacks or more shading
strategies have to take into consideration.
It also tested the BRA of normalized cube, tilted walls, and rotated plans in Taipei. It showed that tilting
the walls of a building inward reduces the influence of BRA to a smaller area. It gave instantaneous
numerical values. When a 10◦ tilt is applied, the ratio of reduction falls within 32– 47%. At a tilt of 20◦ ,
the ratio falls within 54 – 67%. The reduction increases when the tilted angle is enlarged.

Figure 13 - Glare volume (left) and the part of building free of reflection (right) (Naai-Jung & Huang 2001)
2.5 Glare Remediation Techniques
In Schiler and Kensek’s paper (Schiler & Kensek 2009), different categories of solutions to mitigate glare
in the urban microclimate were mentioned including surface treatments, additional surface articulation,
freestanding shielding and landscape elements. Three simulation tools were tested including: Lightscape,
Radiance and 3ds Max. The undulations produced multiple concave surfaces at varying heights on the
buildings. Heretofore Lightscape was used to find the luminance mapping viewed from specific locations.
39
3ds Max can check multiple glare focus points for a single simulation by showing the specular secondary
reflections as mapped onto matte surfaces. “The undulations produced multiple concave surfaces at
varying heights on the buildings. Heretofore Lightscape was used to find the luminance mapping viewed
from specific locations.” (Schiler & Kensek 2009) The daily pattern of reflection could be seen in both
3ds Max and Radiance time series. (Schiler & Kensek 2009)

Among those glare remediation techniques, surface articulation, surface treatment and the modification of
form are most required for taller buildings. And surface articulation, freestanding trellises, fins, overhangs
and landscaping become prime possibilities for shorter buildings. (Schiler & Kensek 2009)
2.6 Chapter Summary
In this chapter, previous researches in concave and specular facades, caustic formation, reflected glare
field and glare remediation techniques were discussed. The next chapter (chapter 3) discusses the
methodology of this thesis.

Figure 14 – Radiance (left) and 3ds Max (right) Reflected Glare (Schiler & Kensek 2009)
40
3 Methodology
3.1 Comparison in Simulation Tools (RadianceIES/Grasshoppe with Ladybug and
Honeybee plug-ins/3ds Max)
In the first step, three simulation softwares were compared including RadianceIES, 3ds Max and
Grasshopper with Ladybug & Honeybee plug-ins, and simple geometry was put inside to see the
characteristics of each software.
3.1.1 RadianceIES
RadianceIES is good at visualizing how brightness and glare influences a building’s ambiance and
effectiveness. For the exterior and interior glare analysis, by entering a threshold value of luminance, it
will circle the area in red where there may be potential glare. For interior space illuminance level analysis,
by putting the threshold value of daylight factor or illuminance level, the area will be colored in green if
the illuminance level is under the threshold. So a sense will be given that which part of space may need
artificial lighting. Also, the contour band or false color simulation results can be generated for
visualization.

Figure 15 - Import gbXML file to IESVE

41
3.1.1.1 Illuminance Level Analysis
A daylight factor is the ratio of internal light level to external light level. In the threshold setting, value
of daylight factor was put equals to 1%, the green area represent the area that daylight factor is less than
1%. In this bedroom space, it makes up the 71.7% of the whole area. The result can help to decide the
location of artificial lighting.

Figure 16 - Illuminance level of the room (plan view)

Figure 17 - Show lux grid where DF factor ≤ 1% (area 71.7%)
42
In the sky/Eye section, the view can be changed from plan view to perspective view by eye position
setting.

Figure 18 - Eye position setting (left) and perspective view of illuminance level of the room (right)

Figure 19 - Glare analyze (glare threshold = 100 cd/ ft2) (left) and interior view of glare (right)
3.1.1.2 Luminance level analysis
For the exterior and interior glare analysis, by putting the threshold value of glare, it will circle the area in
red where to have potential glare. Also, final simulation report includes the (Guth Visual Comfort
Probability) and CIE glare index at different view angles. GVCP (Guth Visual Comfort Probability) is
defined as “the percentage of people that will find a certain scene (viewpoint and direction) comfortable
with regard to visual glare (Sylvester K 1966).” The CIE stands for the Commission International
d'Eclairage (International Commission on Illumination). The CIE is an independent, non-profit,
43
professional organization, based in Vienna, Austria who contribute largely to the exchange of information
in lighting, both technical and aesthetic as well as color, vision and image technology. (CIE Board of
Administration 2016)

Figure 20 - GVCP (Guth Visual Comfort Probability) (left) and CIE glare index (right)
3.1.2 3ds MAX
Research have been done in exterior glare simulation of specular surfaces using 3ds Max. (Schiler &
Kensek 2009). 3ds Max is excellent at producing photo-realistic rendering images based on detailed
real-life lighting simulations (AUTODESK 2016). The setting of the sunlight and skylight are very
detailed; the exposure level can be adjusted to get the desired rendering. Moreover, the mental ray sun
&sky solution enables physically plausible daylight simulations and accurate rendering of daylight
scenarios.

Figure 21 - Import the FBX file from Revit to 3ds Max (left) and set sun and location (right)
The light meter was created in lighting analysis, which reads out simulation results in each section of the
segments. For the whole rendering process, the following processes are included. In rendering setup,
44
view of rendering should be verified first. In exposure control, outdoor daylight and sky condition were
chosen. In the render frame window, material accuracy and other properties were checked before
rendering with different exposure level.

Figure 22 - Create light meter (left) and calculate all light meter (right)

Figure 23 - Interior rendering (left) and exterior rendering (right)
3.1.3 Ladybug & Honeybee
Ladybug & Honeybee are two plug-ins in Grasshopper that can be used to do some environmental
analysis. Ladybug & Honeybee are the bridge between drafting software and simulation software.
45
Geometry is built in Rhino, and daylight analysis of it will be given by the combination of Rhino and
Radiance or Daysim. Energy Modeling is achieved by the cooperation between Rhino between
EnergyPlus or OpenStudio. Ladybug & Honeybee are more suitable to analyze this solar convergence
phenomenon because their variable ability in radiation analysis, solar analysis, psychrometric chart and
comfort analysis (Grasshopper 2015).

Figure 24 - Relationship between Honeybee and other cooperative software (Grasshopper website)
These two plugins for Grasshopper help architects to give an environmentally friendly design. Weather
data is downloaded from standard EnergyPlus Weather files and imported to Ladybug. Using the method
provided in Grasshopper website, a quick graph of weather data was generated by inputting the address
of the weather file (Grasshopper 2015). In the preliminary design, the simulation results and 3D graphics
generated from Ladybug & Honeybee can help with the decision-making process. A comprehensive
energy modeling and daylighting simulation could be given by the connection between Honeybee and
other software including Daysim, Radiance, EnergyPlus, and OpenStudio. Ladybug & Honeybee also
enables environmental analysis in a parametric way. The following figures are some simulation results of
46
the environmental analysis following the methods provided from Grasshopper website (Grasshopper
2015). Figure 27 shows the simulation result of generating sky condition. Figure 28 shows the radiation
analysis of several conceptual buildings.
Grasshopper was chosen as the simulation tool to produce a heat map for this thesis. Ladybug &
Honeybee (Grasshopper plug-ins) were used to produce a UTCI map that represents the thermal comfort
of a person standing at one point on the test surface with the consideration of the additional reflected
solar radiation from the concave building.

Figure 25 - Download weather file from EnergyPlus website

Figure 26 - Quick chart of the weather data
47

Figure 27 - Generate sky condition using the environmental analysis methods provided from Grasshopper website (Grasshopper 2015)
48

Figure 28 - Radiation analysis using the environmental analysis methods provided from Grasshopper website (Grasshopper 2015)
49
3.2 Ladybug Outdoor Solar Temperature Adjustor and Ladybug Outdoor
Comfort Calculator
Ladybug & Honeybee are chosen as computer tools to build the simulation framework for the solar
convergence phenomenon Because there will be an analysis of whether additional solar heat gain
concentrated by the concave façade to determine likely thermal discomfort of the people on those spots,
Ladybug outdoor solar temperature adjustor, and Ladybug Outdoor comfort calculator were used.
3.2.1 Ladybug Outdoor Solar Temperature Adjustor
Figure 29 is the Ladybug outdoor solar temperature adjustor that calculated solar adjusted MRT
(Grasshopper 2015). With the input values of dry bulb temperature, MRT, direct radiation and diffuse
radiation from weather files, it adjusted the MRT with solar radiation. However, when the original MRT
data are not available, it assumed the MRT as ambient air temperature, so it expected that there is no
sunlight falling on the person for the first step. It only suits some extreme case that the individual is under
the shading device like an umbrella. To get a more accurate solar adjusted MRT, original values of MRT
should be input instead of ambient air temperature. Moreover, sky should be generated to simulate the
diffuse radiation that evenly distributed by it. Comfort mannequin is automatically generated with this
component. Body posture, rotation angle and body location can be adjusted with this mannequin. The
simulation colors the mannequin depending on the average value of solar radiation on its surfaces in the
analysis period.
50

Figure 29 - Ladybug Outdoor Solar Temperature Adjustor (Grasshopper 2015)
When a person is exposed to the sun, air temperature itself is not an accurate index to represent human
thermal comfort owing to the extra solar heat gain. Mean radiant temperature (MRT) is the thermal
index usually used to describe surrounding surface temperatures. Outdoor solar temperature adjustor
takes solar radiation into consideration. The output of solar adjusted MRT can more accurately show
human thermal comfort. It can also be used to calculate Effective radiant field (ERF). ERF is used to
describe the additional (positive or negative) long-wave radiation energy at the body surface when
surrounding surface temperatures are different from the air temperature.” (Edward 2015).
51

Figure 30 - Solar Adjusted MRT

Figure 31 - Effective Radiant Field (ERF)
52
3.2.2 Ladybug Outdoor Comfort Calculator
Ladybug outdoor comfort calculator is used to do comfort analysis. With the input values of dry bulb
temperature, wind speed, relative humidity and MRT from EnergyPlus weather file, Ladybug outdoor
comfort calculator calculates universal thermal climate index (UTCI) values showing the thermal
comfort of human on the test point during the analysis period.

Figure 32 - Ladybug Outdoor Comfort Calculator
The UTCI values were calculated using the method in Ladybug comfort tutorial provided by Chris
Mackey (Grasshopper 2015). After Solar adjusted MRT was output, they were plugged into the Ladybug
outdoor comfort calculator to calculate UTCI values representing human thermal comfort. After
inputting weather data and location information to ladybug outdoor comfort calculator, annually
universal thermal climate index (UTCI) graph was shown in Rhino. It makes a 3D view of a mesh of
every single hour of the year for a single location. After adjusting the scale and preview preference, a
top view of annually UTCI mesh was generated.
53

Figure 33 - Top view of annually UTCI Mesh for a single location

Figure 34 - 3D view of annually UTCI Mesh for a single location
As the UTCI mesh in figure 41 shows, there are just a few extreme conditions that are either too hot or
cold in London. From April to November, most temperatures are in the range of 18-24 ◦C. Moreover, in
the rest of the months most are in the range of 0 -12 ◦c. So in most condition weather is pretty cool, and
only several hours in July and August are hot.
54
Ladybug outdoor comfort calculator also gives comfort analysis. Use 0 or 1 to represent comfortable or
not. The red hours are comfortable and the blue hours are not comfortable. It seems in London, 1/3 of
the hours of all year are comfortable, and the rest 2/3 hours are not comfortable.

Figure 35 - Comfort analysis

Figure 36 - Use 0 or 1 to represent comfortable or not
55
3.3 UTCI Map
UTCI maps were calculated using the method from Ladybug comfort tutorials provided by Chris Mackey
(Grasshopper 2015). Human thermal comfort was compared with and without solar radiance adjusted. As
Figure 37 shows, the first UTCI map was generated by plugging MRT into Ladybug outdoor comfort
calculator, while the second UTCI map was generated by plugging solar adjusted MRT into Ladybug
outdoor comfort calculator. However, here it assumed the MRT as air temperature, so this simulation has
limitations. To get a more accurate result, original values of MRT should be input instead of air
temperature. Still, the result gives the sense of different human thermal comfort when people are standing
inside or outside the sun at the mannequin’s location. If a person stands in the sun continuously, it could
be dangerous for him to get a heat attack. So in summer, the solar convergence caused by concave
reflective building can pose a significant threat to the pedestrians.

Figure 37 - UTCI map comparison with solar radiation adjustment using the method from Ladybug comfort tutorials provided by Chris
Mackey (Grasshopper 2015)
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3.4 Ray Tracing
The Ray tracing component is a new component in Ladybug. Geometries were built and ray tracing
simulation were run following the method provided by Arie-Willem de Jongh from Grasshopper website
(Grasshopper 2015). It is an excellent way to perform preliminary glare analysis for a concave glass
façade. By this component, a preview could be given to show how the sun ray moves after being reflected
from the concave façade. The process includes generating the sun path, defining the location, inputting
the latitude, using Ladybug construct time component to change the hours and generating test points. The
output of the sun vectors component indicates the direction of sunlight at each sun position. The Ladybug
forward raytracing component is used to trace how sunlight is reflected by a contextual geometry. Also,
it is useful to evaluate the diffusion of light by a light shelf or to see whether a parabolic building geometry
might converge sunlight to potentially dangerous levels at certain times of the year. This component
assumes that all sunbeams are reflected off of a specular facade (as if they were a mirror). It is an excellent
way to perform a preliminary analysis of solar convergence. Simulation results show how sun rays are
reflected and concentrated on certain points. However, how much light is concentrated on each point of
the ground and the resulting surface temperature needs further discussion. The surface temperature would
depend on the absorptivity, the emissivity and the thermal mass attached to the surface. However, the heat
gain values could be shown in W/𝑚 2
or Btu/hr 𝑓𝑡 2
.
3.5 Heat Map
Heat maps were built in Grasshopper showing the reflected glare area on the ground. Joseph Oster from
Grasshopper website helped with building the simulation framework of the heat maps (Grasshopper
2015). The concept of heat maps was very simple: points were counted where the bounced sun rays
intersected "the ground" at each grid cell and grid cells were colored depending on how many points
struck within. Different building facades forms were built to test the heat maps. The number range of
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intersections was used as input for color range. As the number of reflected light point on the ground
increased, the color changes from green to red. However, the effect of incident light angle of the solar
radiation heat gain on the human body was not taken into consideration here. When the color is red,
there is a relatively high potential for a hot spot.
3.6 Chapter Summary
In this chapter, different simulation tools were compared and the ideas of UTCI maps, ray tracing and
heat maps were discussed. The next chapter (chapter 4) discusses the more detailed simulation process.

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4 The Data and The Tool
4.1 Creating the Uniform Thermal Climate Index (UTCI) Map
Before creating a UTCI Map, a glass facade of the building was modeled as mirror material with input
values of reflectance, roughness, and specularity (Figure 38). The script was written by Chris Mackey
from Grasshopper website (Grasshopper 2015). The test surface on the ground was built to give a grid-
based simulation.

Figure 38 - Model the glass facades of the building and test surface on the ground by Chris Mackey (source:
http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-gain?xg_source=activity)
4.1.1 Hourly UTCI Map of Test Surface
UTCI values were calculated using the method provided by Chris Mackey in Grasshopper website
(Grasshopper 2015). This simulation used Ladybug outdoor comfort calculator and calculated 133 UTCI
values with each test grid on the ground. The hourly UTCI map shows the human thermal comfort on the
test surface.
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However, there are some limitations of this simulation. Solar adjusted MRT was calculated by Ladybug
outdoor solar temperature adjustor. With the input values of direct radiation, diffuse radiation, and MRT,
it adjusted the MRT with solar radiation. Because it was difficult to obtain the original MRT from the
EnergyPlus simulation, the MRT is assumed to be the dry bulb temperature, which is not accurate. To get
a more accurate solar adjusted MRT, original values of MRT should be input instead of dry bulb
temperature. However, it is beyond the scope of work.
The simulation results only show the hourly UTCI map, but a set of animated temperature maps can be
produced by animating the time slider. The relation between human comfort and climate forces is
illustrated in Figure 39.

Figure 39 -. Human comfort and climatic forces
A radiation analysis was conducted using the Honeybee daylight simulation component. The cumulative
radiation values comprise of direct radiation and diffuse radiation (Figure 40). Direct radiation includes
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direct sun beams and beams reflected off of a concave glass facade while the diffuse radiation is
radiation distributed evenly across the sky. Figure 41 shows the process of generating cumulative
radiation, and the script was written by Chris Mackey.

Figure 40 - Components of cumulative radiation
Cumulative radiation
Direct radiation
Direct sun beams
Reflected sun beams
from a concave glass
facade
Diffuse radiation
Diffuse radiation
across the sky
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Figure 41 - Honeybee daylight simulation component for cumulative radiation by Chris Mackey (source:
http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-gain?xg_source=activity)

Figure 42 - Script for generating solar adjusted MRT by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-gain?xg_source=activity)
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In Figure 42, part 1 is the weather file component, which output the values of dry bulb temperature,
relative humidity, wind speed, direct normal radiation and diffuse horizontal radiation. Part 2 used the
cumulative radiation values that come from the Honeybee daylight simulation (Figure 41). There is no
very accurate method to separate the direct radiation portion and the diffuse radiation portion from the
cumulative radiation values. To give an extreme range estimate, all of the cumulative radiation values
were plugged into the diffuse radiation portion. Part 3 is the Ladybug outdoor solar temperature adjustor
that calculated solar adjusted MRT. With the input values of direct radiation and diffuse radiation, it
adjusted the MRT with solar radiation. After Solar adjusted MRT had been calculated, it was plugged
into the Ladybug outdoor comfort calculator to calculate UTCI values representing human thermal
comfort
63

Figure 43 - Calculating process of UTCI values by Chris Mackey (http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-
gain?xg_source=activity)
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Figure 43 shows the script for generating the UTCI Map. Part 1 is the weather file, which outputs the
values of dry bulb temperature, relative humidity, wind speed, direct normal radiation and diffuse
horizontal radiation. Part 2 is the Ladybug outdoor solar temperature adjustor that calculated solar adjusted
MRT. Part 3 allows the user to select an hour of the day. Finally, Part 4 is the Ladybug outdoor comfort
calculator that delivers a UTCI map. Each simulation with the Ladybug outdoor comfort calculator
provides 133 UTCI values on a test grid, which shows the thermal comfort of a human.
This method is not accurate enough for generating UTCI values; another method is explained in the next
sub-chapter.

Figure 44 - Hourly UTCI maps of test surface
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4.1.2 Hourly UTCI of Single Human Geometry
This simulation calculates MRT by using the relationship between MRT and ERF following the method
from Grasshopper website (Grasshopper 2015). Effective radiant field (ERF), “a measure of the net radiant
energy flux to or from the human body. ERF is used to describe the additional (positive or negative) long-
wave radiation energy at the body surface when surrounding surface temperatures are different from the
air temperature” (Edward, Tyler, Xin, Li, Hui & Stefano, 2015).
One study was done by the Center of the Built Environment in UC Berkeley where they built a whole-
body model that simulates the solar radiation on personal heat gain and thermal comfort. In the research,
a method was provided to calculate solar gain to the human body using the relationship between ERF and
MRT. ERF times the long-wave emissivity/absorptivity is the energy flux absorbed by the body. Solar
radiation heat gain on humans can be equated to an additional amount of long-wave flux, which is defined
by the following formula:
Equation 3
𝛼 𝐿𝑊
𝐸𝑅𝐹 𝑠𝑜𝑙𝑎𝑟 = 𝛼 𝑆𝑊
𝐸 𝑠𝑜𝑙𝑎𝑟
𝐸𝐹𝑅 𝑠𝑜𝑙𝑎𝑟 -- Long-wave radiation energy at the body surface;
𝛼 𝑆𝑊
-- Short-wave absorptivity, ≈0.67 for (white) skin and average clothing.
𝛼 𝐿𝑊
-- Long-wave emissivity/absorptivity, typically equal to 0.95.
𝐸 𝑠𝑜𝑙𝑎𝑟 -- Short-wave solar radiant flux on the body surface (W/𝑚 2
), or cumulative radiation that includes
direct radiation coming from the sun, diffuse radiation coming from sun and reflected radiation from the
floor. Diffuse radiation that coming is from the sky is assumed to be even distributed on the upper half of
the radiative exposed part of the body.
The relationship between EFR and MRT is then defined by this formula
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Equation 4
𝐸𝑅𝐹 = 𝑓 𝑒𝑓𝑓 ℎ
𝑟 (𝑀𝑅𝑇 − 𝑇 𝑎 )
𝑓 𝑒𝑓𝑓 -- Fraction of the body surface exposed to radiation from the environment (=0.696 for a seated
person and 0.725 for a standing person;
ℎ
𝑟 -- Radiation heat transfer coefficient (W/𝑚 2
K);
𝑇 𝑎 -- Air temperature (ºC)
Therefore, the MRT is calculated by using:
Equation 5
𝑀𝑅𝑇 =
𝛼 𝑆𝑊
𝐸 𝑠𝑜𝑙𝑎𝑟 𝛼 𝐿𝑊
𝑓 𝑒𝑓𝑓 ℎ
𝑟 + 𝑇 𝑎
This method of obtaining the MRT is more appropriate. Based on this formula, a code was developed to
get the solar adjusted MRT values. To get the cumulative radiation on the human body, a radiation
analysis was conducted. Figure 45 is the radiation analysis of single human geometry on the test grid.

Figure 45 - Radiation analysis of single human geometry by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-gain?xg_source=activity)
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In Figure 45, Part 1 is used to generate a sky condition to perform radiation analysis. Part 2 is used to
insert a comfort mannequin on the test point. Part 3 is used to build a concave mirror façade (Honeybee
surface). Part 4 is the Honeybee Grid Based Simulation component using sky file (Part 1), the
mannequin (Part 2), and simulation type. Here value “1” was the input for simulation type, which means
a radiation (kW) analysis will be completed (Value “0” will provide illuminance level analysis and “2”
will provide luminance level analysis). Finally, part 5 is the Honeybee Run Daylight Simulation
component, with the input of Honeybee Surface (Part 3) and Grid Based Simulation (Part 4). Part 5
outputs the cumulative radiation values.
Using Equation 5, a script was created to generate solar adjusted MRT based on different cumulative
radiation values (Figure 46).

Figure 46 - Calculation of solar adjusted MRT by using the relationship between MRT and ERF by Chris Mackey
(http://www.grasshopper3d.com/group/ladybug/forum/topics/surface-temperature-under-reflected-solar-heat-gain?xg_source=activity)
In this case, 𝐸 𝑠𝑜𝑙𝑎𝑟 equals to 224.8 W/𝑚 2
from the radiation simulation, with the input values of 𝛼 𝐿𝑊
and
𝛼 𝑆𝑊
, the ERT values can be calculated. MRT Delta was output using the following formula, which equals
37.8℃. 𝑇 𝑎 equals 16.1℃ from the inputted weather file. And solar adjusted MRT equals to 53.9℃.
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Solar adjusted MRT was plugged into the Ladybug outdoor comfort calculator. Using this method, the
UTCI value equals 27.09℃. Although the air temperature 𝑇 𝑎 is at 16.1℃, the human feels hotter, at
27.09℃, due to solar radiation (Figure 47).

Figure 47 - Hourly UTCI value of single human geometry on test grid

Figure 48 - Simulation result of Hourly UTCI of single human geometry on test grid
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4.2 Ray Tracing
4.2.1 Ray Tracing in Ladybug & Honeybee
Ray tracing simulation was run following the method provided by Mostapha Sadeghipour Roudsari from
Grasshopper website (Grasshopper 2015). The Ray tracing component is a new component in Ladybug.
It is an excellent way to perform preliminary glare analysis for a concave glass façade. By this component,
a preview could be given to show how the sun ray moves after being reflected from the concave glass
façade. The process includes generating the sun path, defining the location, inputting the latitude, using
Ladybug to construct the time component to change the hours and generate test points. The output of the
sun vectors component indicates the direction of sunlight at each sun position. The Ladybug forward
raytracing component is used to trace how sunlight is reflected by a contextual geometry. Also, it is useful
to evaluate the diffusion of light by a light shelf or to see whether a parabolic building geometry might
converge sunlight to potentially dangerous levels at certain times of the year. Simulation results show how
sun rays are reflected and concentrated on certain points. However, how much light focuses on each point
of the ground and the resulting surface temperature needs further discussion. The surface temperature
would depend on the absorptivity, the emissivity and the thermal mass attached to the surface. The
following figures show the ray tracing simulation results at different times.
70

DEC 21th 8:43 a.m.

DEC 21th 10:43 a.m.
71

DEC 21th 12:43 p.m.

DEC 21th 3:43 p.m.
Figure 49 - Ray tracing simulation result at different time
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Reflected glare will also affect the occupants of surrounding buildings. The influence depends on many
factors including the intensity of glare, duration of glare impact, the type of building, and the glazing
and shading devices used in the neighboring building. The level of tolerance of the occupant will also
affect the outcome. (WINDTECH Consultants Pty Ltd, 2011)
Multiple boxes were built as the surrounding buildings and windows, and shading devices were added to
them. The simulation result shows how the reflected light from the concave glazing façade or the ground
will affect the surrounding buildings, how well the shading devices function, and how to adjust the
shading device angle to maximize the daylight without causing too much solar heat.

Figure 50 - Surrounding building
Useful Daylight Illuminance (UDI) it is an output value of Honeybee daylight simulation component.
Useful Daylight Illuminance (UDI) is an index to evaluate daylight level. This metric has three
illumination ranges: 0-100 lux, 100-2000 lux, and over 2000 lux. Although high levels of illuminance do
not necessarily mean great potential for glare, a value of 2000 lux is the upper threshold and values
above it are not wanted due to potential glare or overheating. So the UDI value stands for the annual
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percentage of illuminance level within the range of 100 -2000lux. The angle of shading devices can be
adjusted to optimize the result. Here the indoor thermal comfort analysis is beyond the scope of work, so
there is no further discussion about it.

Figure 51 - Useful Daylight Illuminance (UDI) Result
4.2.2 Ray Tracing in Grasshopper
4.2.2.1 Surface/ Altitude/Azimuth
The geometry of a concave façade was built in Grasshopper. The surface is arbitrary and was created in
the 'Surface' group. First a 3D ellipse object and an XZ plane w ere built in Rhino, and the concave
surface is the section of this ellipsoid and XZ plane.
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Figure 52- Arbitrary Surface
As Figure 53 shows, this is the U.S. Naval Observatory website. The sun altitude and azimuth table were
computed after inputting time, tabular interval and location. It generated a table of altitude and azimuth
at each point of time. The table of values was input into grasshopper to control the direction of the sun's
rays.

Figure 53 - U.S. Naval observatory website sun altitude/azimuth table (source: http: //aa.usno.navy.mil/data/docs/AltAz.php))
75
4.2.2.2 Surface Grid Points
The next step is to generate test points on the surface. First, a bounding box was built to contain the
concave surface inside. Then the surface was extracted from the bounding box which is tangent to the
concave surface. Divide surface component was used to generate a grid of (UV) points on the tangent
surface. At last, point project component was used to project a point onto the concave surface (Figure
54).

Figure 54 - Surface Grid Points Generation Process
4.2.2.3 Simulation Result
Ray tracing simulation was run following the simulation framework provide by Joseph Oster from
Grasshopper website (Grasshopper 2015). The yellow lines are the sun rays, which are controlled by the
altitude and azimuth angles. The line length and color of the sun rays were defined at each test point.
The blue lines are the surface normal vectors at each test point. Bouncing light was added by using the
angle between the sun ray and normal and rotate with this angle and use normal axis. The orange lines
stand for the bounced sun rays.
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Figure 55 - Ray Tracing Simulation Result
4.3 Heat Map
The simulation framework was provide by Joseph Oster from Grasshopper website (Grasshopper 2015).
The concept of a heat map was very simple: points were counted where the bounced sun rays intersected
"the ground" at each grid cell, and grid cells were colored depending on how many points struck inside.
4.3.1 PLX (line/plane intersection)
'PLX' is the intersections of bounced lights and ground. However, plane line intersections would be
missed at some 'Altitude' and 'Azimuth' angles. When 'Altitude' angle is low, the 'PLX' spread out
widely, requiring a considerable amount of time for the computer to simulate, so a better algorithm
needs to be developed. The effect of the cosine factor on these angles reduces their impact significantly.
77

Figure 56 - Control the grid size by 'Line | Plane' intersections ('PLX') by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie)

Figure 57 - Bounced sun rays intersected the ground
4.3.2 Split sorted list of values
Because the intersected points within the same square cell will have the same values, this code was used
to automatically calculate the number of intersected points in each square cell. The result is a vast
improvement in simulation time when 'Altitude' and 'Azimuth' angles are changed. Figure 58 shows the
example forum written by Danny Boyes.
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Figure 58 - "Splitting list of values" by Danny Boyes (source: http://www.grasshopper3d.com/forum/topics/splitting-list-of-values)
So the basic idea is splitting a list of integers into "runs". The number was counted for consecutive
recurrences of the same integer. For example, a list of numbers like 2,2,0,0,2,2,2,2 would be split into
three separate lists: (2,2), (0,0), (2,2,2,2). Then the length of each of these lists was measured. Figure
59 shows the list of value before and after the split. The length of each list means the number of
intersected points in each cell.

Figure 59 - Split sorted list of values code and list of values before and after split
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4.3.3 Color Range of Heat Map
The number range was used as the input for the color range. As the number of intersected points
increases, the color of grid cells changes from green to red. However, the effect of incident light angle
on the solar radiation heat gain on the human body was not taken into consideration here. When the
color is red, there is a relatively high potential for a hot spot (Figure 60). The detailed illustration of heat
maps is given in next chapter.

Figure 60 - Color range code by Joseph Oster (source: http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-
talkie)

Figure 61 - Heat Map Simulation Result
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4.4 Chapter Summary
In this chapter, detailed simulation processes of UTCI maps, ray tracing and heat maps were discussed.
The next chapter (chapter 5) interprets the meanings of heat maps.

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5 The Interpretation of Heat Maps
Heat maps were built on the ground showing the reflected glare area. The simulation framework
was provide by Joseph Oster from Grasshopper website (Grasshopper 2015). The concept of heat
maps was very simple: points were counted where the bounced sun rays intersected "the ground"
at each grid cell and grid cells were colored depending on how many points were inside.
Different shapes of simple concave facades were built to test the heat maps. Density of
intersections per square cell which represents magnitude of radiant heat gain.
5.1 Relative/Absolute Heat Maps
There are three methods to deliver heat maps (Figure 62). In the first method, the simulations were
run on an “as is basis”. There were always some cells in red, even though there were not many
intersected points in them. Because the values are relative to the respective building forms, they
cannot be compared. For comparison reasons, there are two methods to generalize heat maps.
Using absolute values, the red cells only appear when the density of intersected points in it is above
the threshold value. The next method includes using the same threshold value to calibrate all the
heat maps of different building forms; then the results can be used to compare focus effects. The
third method uses the highest density found throughout the day; red cells then represent the greatest
risk potential of hot spot locations through this day. This calibration method can be used to spot
the most dangerous location for the respective building form.
These three methods have their characteristics and can be used to simulate solar convergence
phenomenon for different purposes. For method one, the relative heat maps can be employed when
one building façade form has already been chosen. Simulation processes could be applied to some
existing buildings or buildings that have already finished design phase. The simulation results
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show the relative hot spots under this building façade form. The second method can be used for
comparison reason, so it helps designers to choose building forms in the conceptual design phase.
When using the same threshold value to calibrate heat maps with different building forms, the
comparison result can be used for designers to avoid the building form that has the largest number
of red cells. The third method can be used to spot out the locations where the highest density
achieved under respective building forms. The number of the red cells can also be outputted to see
how many places achieved the highest density throughout the day.

Figure 62 – Comparison of heat maps

To illustrate the methods explained above, an example is used where the absolute value is set as
16 (Figure 63). Filter stream command is used to filter the values above 16. Only values above
16 will be colored in red. In Figure 64, the relative and absolute heat maps of the concave
Comparison of heat maps
Method 1
Relative - run as usual
Absolute - calibrate with
threshold values
Method 2
Calibrate same threshold
values with different
building facades forms
Method 3
Calibrate the building
facade form itself by the
maximum density found
throughout the day
83
surface were compared, showing the absolute map has more red cells, owing to the red cell
happens above the set threshold value. The largest number of intersected points is 24, and the
cells with values above 16 are all colored in red in the absolute heat map. However, the color
range in relative heat map is based on the number range (1-24) of intersected points in each cell.

Figure 63 – Calibrate absolute values of heat map by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie)

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Figure 64 - Comparison of relative (top) and absolute heat map (bottom)
5.2 Different Building Facade Forms
Seven surfaces were added to test the heat map. The same two circular arcs were used as the edges
of the surface. The top and bottom of the surfaces were changed to a straight line, concave (arc of
circle) or convex line by using the sweep command. Parabolic surfaces with four edges of same
parabolas could cause more extreme focus in the air, which is out of the scope of this thesis. Here
seven different building forms were discussed (Figure 65): ellipse (concave), flat top and bottom,
flat top, flat bottom, concave, convex bottom, and concave sweep. Figure 66 shows the code for
selecting different forms.
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Figure 65 – Seven different building forms used to test heat maps

Figure 66 - Code for selecting different façade forms by Joseph Oster (source:
http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie)
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5.3 Grid size - Sun Grid and Test Surface Grid

Figure 67 – Sun grid and test surface grid
Sun Grid refers to the surface of the building façade, where the value means the distance between
sun ray points. Test Surface Grid refers to the ground surface within the immediate distance of the
building. When the sun-grid size and cell size of the test surface on the ground are smaller, the
simulation result of the heat map is more accurate owing to the more detailed division and analysis
of the test surface. Figure 68 illustrates the coding for selecting cell sizes.
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Figure 68 - change cell size code by Joseph Oster (source: http://www.grasshopper3d.com/forum/topics/thermal-glare-
simulation-of-walkie-talkie)
5.3.1 Comparison of Grid Size
When the cell size is large, it will show a cumulative intersected points of that cell. Breaking this
cell into smaller grids will show the same number of intersected points. However, it shows more
refined details about where the intersected position is located within that large cell. Therefore,
using larger grid size, even though there are many intersected points inside, they do not necessary
show the focus effect which is the essence of this study. So with a smaller grid size, it is more
accurate to evaluate the focus effect on the smaller area. To illustrate this idea, the following
figures show the comparison of the change in sun grid and test surface grid and its effect on the
accuracy of the heat maps generated. The original grid settings had the sun grid size of 2 and
surface cell size equals to 3 (Figure 69). It can be seen there are few red cells at the edge of the
heat map.
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Figure 69 - Sun grid size 2, cell size 3
Then sun grid size was changed to 1 (Figure 70). When the sun grid size becomes smaller, it
gives more reflected sun rays, producing a denser heat map with the same pattern. Here, the area
of the focus effect is similar, but with more reflected sun rays. The user can pinpoint focus effect
spots more easily compared to the previous. The range of domain changed from 1-4 to 1-18. The
domain of heat maps means the smallest to the largest number of intersected points found in test
surface grid cells.
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Figure 70- Sun grid size 1, cell size 3
Next, both the sun grid size and test surface grid size were changed to 1(Figure 71). The domain
was changed to 1-5. Moreover, the accuracy of heat map increased. It provided a refined heat
map showing the how much the intersected points at each cell with more specific locations and
its focus effect. Breaking this cell into smaller grids will show the same number of intersected
points however it shows more refined details about where the intersected position is located
within that large cell.
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Figure 71 - - Sun grid size 1, cell size 1
5.4 Relative Heat Maps
All the heat maps in this section are relative heat maps. The patterns of different building forms
were analyzed at the same location (San Francisco) and time (12:30 p.m. on Nov 19, 2015). Cell
size was 0.25. The meaning of the relative map is to compare the focus effect by itself and
understand the potential for relatively hot spots for this form of building facades.
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5.4.1 Concave Ellipse Surface
When the preview of bounced lights is enabled, it helps to understand how the heat map pattern
is generated (Figure 72). It shows the bounced sun rays and how are stops at the ground surface.

For the heat map pattern of an ellipse (concave) surface, there were some red points at the edge
of the heat map. It shows a series of arcs from inside to outside. The outside edge has the most
focus effect with some red points and yellow points while the inside arcs have relatively low
focus effect with green color. For the number of intersected points in each grid cell, the domain
is 1 to 22.
Figure 72 – Bounced lights of ellipse surface
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Figure 73 - Relative heat map of ellipse (concave) surface (domain 1-22)
5.4.2 Concave Rectangular Surface
The concave surface is the section of an ellipse (concave) slid along a shallow arc. The result is
similar to the ellipse in that it is focusing, but rectangular in shape. However comparing the
results, there are slight differences. The heat map here has two parts. First, the reflected glare
field shapes like a “Chinese fan”, which is similar to the ellipse surface, the edge has some focus
effect. The second part is the reflection from the lower part of the building where it produces
some focus effect at where they cross paths (Figure 74). If seen from the top view of the heat
map, some focus effect happens at the cross area at the end point of the sector. Here also there is
a high potential for the hot spots. The domain here of intersected points is 1 to 24.

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Figure 75- Top view of relative heat map showing second focus effect
Figure 74 - Relative heat map of concave surface (domain 1-24)
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5.4.3 Flat Bottom Surface, Curved Top Surface
The top edge is a concave line and bottom of the surface was changed to a straight line. The
reflected glare field shapes like an arrow, the focus effect happens at the tip of the arrow. In the
domain of the number of intersected point in each grid, the smallest number is 1, and the largest
number is 33.

Figure 76 - Relative heat map of flat bottom surface (domain 1-33)
5.4.4 Flat Top, Curved Bottom Surface
The top was changed to a straight line and bottom of the surface was a concave line. The reflected
glare field is shaped like swirl, the largest number of intersected points is in the grid cells achieved
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at the center of the swirl. In the domain of the number of intersected point in each grid, the smallest
number is 1 and the largest number is 99.

Figure 77 - Relative heat map of flat top surface (domain 1-99)
5.4.5 Flat top and bottom Surface
The top and bottom of the surface were changed to straight lines. The reflected glare field was a
set of straight lines, with more focus effects at the end of the heat map. In the domain of the number
of intersected points is 1 to 21.
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Figure 78 - Relative heat map of flat top and bottom surface (domain 1-21)
5.4.6 Convex Bottom Surface
The top of the surface was a concave line and bottom was changed to the convex line. The reflected
glare field contains many dispersed and intersected arcs. Owing to the scatter effect of the convex
bottom, the reflected lights are more distributed than the concave surface. The overall heat map
looks like a “fountain”. There were no high focus effects on the ground. In the domain of the
number of intersected point in each grid, the smallest number is 1 and the largest number is 4.
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Figure 79 - Relative heat map of convex bottom surface (domain 1-4)
5.4.7 Convex Sweep Surface
The top and bottom of the surfaces were changed to convex lines. The reflected glare field was a
set of arcs. It caused the focus effect at the edge of the field. Convex Sweep surface causes more
dispersed arcs compared to concave. The domain of the number of intersected point is 1 to 24.
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Figure 80 - Relative heat map of convex sweep surface (domain 1-24)
5.4.8 Comparison of Domains of Relative Heat Maps with Different Building Facade Forms
There are some interesting findings after a comparison of intensity domains of relative heat maps.
Although it may seem that ellipse or concave surfaces will have the most focus effects, the
simulation results show that flat bottom and flat top surfaces caused more focus effects than the
ellipse and the concave surfaces. Especially the flat top surface with a swirl pattern heat map
caused the greatest focus effects on the center of the swirl. The heat map pattern of ellipse and
concave surface are highly similar to each other, and their domains are also close. The only
difference is that concave surface also has some focus effects at the cross area at the end point of
the sector. Also, flat top and bottom and concave sweep surfaces were assumed to have little focus
99
effects on the ground, but simulation results show that they have similar focus effects as ellipse
and concave surface on edges of heat maps. The maximum density for these four building forms
is all close to 20. The differences are the densities of layouts for these four heat maps. For ellipse
and concave surfaces, the heat maps are closely distributed arcs, while flat top and bottom and
convex bottom surfaces delivered more sparsely distributed straight lines and arcs. If compared,
heat maps of the convex bottom surface with convex sweep surface, convex bottom and concave
top instead of both convex top and bottom would cause more scatter effect (Table 1). The next
sub-chapter discusses the absolute heat maps for better comparison.
Table 1 – Comparison of domains of relative heat maps with different building facades forms
Building
Facades
forms
ellipse concave flat
bottom
flat top flat top
and
bottom
convex
bottom
concave
sweep
domains 1-22 1-22 1-33 1-99 1-21 1-4 1-24

5.5 Absolute Heat Maps
5.5.1 Calibrate Same Threshold Values with Different Building Facades Forms
The first calibration method includes using the same threshold value to calibrate all the heat
maps of different building forms; then the results can be used to compare focus effects. Here the
threshold value was set as 16, so the cells with a number of intersected points above 16 will be
colored in red. The reason that 16 was chosen as the calibrating value is based on the simulation
results of domains above. Most heat maps have maximum densities around 20, so 16 was
selected as a value close to 20. But in real projects, the calibrating values should depend on
different situations and requirements. Here is a simple illustration of this calibration method. The
comparison of absolute heat maps shows that flat top surface has the largest number of red cells
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while the convex bottom surface has the least number of red cell (Figure 81). The locations of
red cells are similar to the relative heat maps, but this method allows better comparison between
building forms with the same calibrated values.

101

5.5.2 Calibrate the Building Facade Form by the Maximum Density Found throughout the Day
The second calibration method uses the highest density found throughout the day. Red cells then
represent the highest risk potential of hot spots locations through this day. The simulation results
can be used to spot the most dangerous location for the respective building form. Of the seven
building forms, the following three were chosen to simulate to illustrate this calibration method.
Figure 81 - Absolute heat maps of different building facades forms with the same calibrating threshold
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For the concave surface, the pattern of heat maps at different times was shown in the following
picture. During 10:30 a.m. – 13:30 p.m., the surface has some focus effect, the most intensified
focus effect happens at 11:30 a.m. The edge and cross paths have some focus effects. At 14:30
p.m., the pattern starts to spread out; similar to the opposite of the pattern at 8:30 a.m. Finally at
15:30, the intersected points were widely dispersed. Using this method, the user can easily spot
out the locations where the highest density achieved (Figure 82)
For the flat bottom surface, the surface has some focus effect during11:00 a.m. – 14:00 p.m. with
the highest intensity at 12 p.m. At the 8:00 a.m., the sun is still behind the surface, giving almost
no effect to the front. However, from 10 a.m., the “arrow” pattern starts to appear on the heat
map. The arrow size becomes smaller and denser until the most number of red cells appears at
12:00 p.m. at the tip of the arrow. After 14:00 p.m., the size of the arrow on the heat map starts
to increase, and the intersected points start to disperse (Figure 83).
For the flat top surface, the heat map pattern shows a swirl on it and focus effects happens at the
center of the swirl. During 10:30 a.m. to 13:30 p.m., large part of heat map shows the highest
density occurred in the center of the swirl. Even in the morning at 8:30 a.m. and in the afternoon
at 15:30 p.m., the heat map still shows some locations achieving the highest density. So this
building form gives the most threat to the immediate environment. (Figure 84)
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Figure 82 - Absolute heat maps of concave surface
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Figure 83- Absolute heat maps of flat bottom surface
105

Figure 84 - Absolute heat maps of flat top surface
106
5.6 Comparison of relative heat maps with different latitudes
In the conceptual design phase of building, the location is also an important factor to analyze
solar convergence problems due to the differences in latitude. Three cities were chosen -
Honolulu, San Francisco, and Fairbank to test this. The locations of the sun for each city
throughout the day were obtained using the altitude and azimuth values. These values were
tabulated and used as the input to the script. This helps control the direction of sun rays of three
cities with different latitudes thus providing different effects on the heat map. The latitudes of
these three cities are Honolulu, Hawaii (21°N), San Francisco, California (38°N) and Fairbanks,
Alaska (65°N). Based on the above simulations, the flat top surface was chosen as the test
surface owning to the highest focus effects. Sun grid size is 2.5 and cell size is 4.

Figure 85 - Code for changing locations by Joseph Oster (source: http://www.grasshopper3d.com/forum/topics/thermal-glare-
simulation-of-walkie-talkie)
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For the city Fairbank, the largest number of intersected points was found in the test grid 4. In San
Francisco, the largest number was 17. And lastly in Honolulu, the largest number was 30. This
shows that the latitude of the city plays an important role and very much affects the solar
convergence. When the value of latitude decreased, the solar convergence increased. From the
simulations, the latitude of the city location also affects the location of the focus effect. In
Fairbanks the effect was seen farthest from the building while compared to Honolulu, the focus
effect was closer to the building (Figure 86).

Fairbanks (latitude 65, the highest density 4)

San Francisco (latitude 38, the highest density 17)
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Honolulu (latitude 21, the highest density 30)
Figure 86 - Comparison of relative heat maps with different latitudes
5.7 Comparison of Absolute Heat Maps with High Resolution
The following simulation shows heat maps with higher resolutions. When the sun grid size and
cell size of a test surface on the ground were smaller, the accuracy of simulation results
increased. Here both the sun grid size and test surface grid size were changed to 0.1. The sun
rays get as close as it can, and the accuracy of heat map significantly improved. However, the
computation time could be further decreased. Currently, it takes more than two minutes for each
simulation. Three typical building forms were compared for the simulation results with high
resolution. The concave surface, flat top surface, and convex bottom surface were chosen as the
test surface. All the heat maps are absolute heat maps with the same threshold value as 16.
In these three building forms, the flat top surface still has the most focus effect, which is the
same as the simulations showed before. The largest density number throughout the day for the
flat top is 144. For the concave surface, the largest number of intersected points 15. Moreover,
109
because of the scatter effect of the convex surface, the surface with concave top and the convex
bottom has the largest number of 6 (Figure 87).

Concave surface (domain 1-15)

Flat top surface (domain 1-144)
110

Convex bottom surface (domain 1-6)
Figure 87 – Comparison of absolute heat maps with high resolution
5.8 Visualization of Heat Maps with Bounding Box
This version of heat maps uses the component in Grasshopper calling bounding box ( 'BBox').
This component helps to visualize the movement of the sun’s rays using a box bounding the
entire surface. This version provides a clear visualization of the movement of sun rays. The
script shows in Figure 88. Figure 89 shows about the bounding box visualization of
sun rays at different time periods.
111

Figure 89 – Visualization of heat maps with bounding box
5.9 Chapter Summary
In this chapter, the heat maps generated with different methods were discussed. In addition,
changed sun grid and test surface grid size were compared to improve the accuracy of heat maps.
The next chapter (chapter 6) discusses the conclusion and future work.
Figure 88 - Code for bounding box by Joseph Oster (source:
source: http://www.grasshopper3d.com/forum/topics/thermal-glare-simulation-of-walkie-talkie)
112
6 Conclusion
From the outset of this research, the intended goal was to build a simulation framework and test
software that can be used to simulate the solar convergence problem caused by buildings with a
concave shape, and highly specular materials in pre-design phase to avoid its damage. Grasshopper
and Ladybug & Honeybee (Grasshopper plug-ins) were chosen as the simulation tool. This thesis
produces three simulations including ray tracing, UTCI maps and heat maps.
6.1 Ray Tracing
The first simulation is the ray tracing simulation resulted from simulation framework in
Grasshopper website to trace the reflected lights from a concave glass façade at different sun
positions and their effect on surrounding buildings. A preview was given in section 4.2 to show
how the sun rays move after being reflected from the concave façade.
6.2 UTCI Maps
The second simulation is the UTCI map and UTCI values were calculated using the method
provided by Chris Mackey from Grasshopper website that represents the thermal comfort of a
person standing at test point on the ground at the certain period with the consideration of the
additional solar radiation portion from the concave building. Ladybug outdoor solar temperature
adjustor that calculated solar adjusted MRT and Ladybug Outdoor comfort calculator was used to
do comfort analysis. Two UTCI maps were developed. One is the Hourly UTCI Map of Test
Surface. This simulation used Ladybug outdoor comfort calculator and calculated 133 UTCI
values with each test grid on the ground. The hourly UTCI map shows the human thermal comfort
on the test surface. This method is not accurate enough for generating UTCI values. Another
method is hourly UTCI of single human geometry. One human geometry was run by Honeybee
113
Run Daylight Simulation Component. The hourly cumulative radiation value was the output,
which can be used to calculate Effective radiant field (ERF). MRT was calculated by using the
relationship between MRT and ERF. UTCI value was calculated by Ladybug outdoor comfort
calculator that represent human thermal comfort and human heat gain from the solar radiation part.
Using this method, the UTCI value equals 27.09℃. Although the air temperature 𝑇 𝑎 is at 16.1℃,
the human feels hotter, at 27.09℃, due to solar radiation reflected by the concave and specular
facades.
6.3 Heat Maps
The third simulation is a colored heat maps using the framework built by Joseph Oster from
Grasshopper website that indicates how much reflected light is focusing on each test grid. Seven
surfaces were added to test the heat map including ellipse (concave), flat top and bottom, flat top,
flat bottom, concave, convex bottom, and concave sweep. Three methods of delivering heat maps
were used to simulate solar convergence phenomenon for different purposes. Relative and absolute
heat maps patterns and color distributions of different building facades forms throughout the day
were analyzed. The simulation results show that the flat top surface with a swirl pattern heat map
caused the greatest focus effects on the center of the swirl. Owning to the scatter effect of the
convex bottom surface, the reflected lights of it are more distributed than the concave surface. So
there were not highly focus effect on the ground. Convex Sweep and flat top and bottom still have
a focus effect at edges. Besides building the simulation framework for the building reflected glare,
the computation time of simulation is also a great part concern of this thesis. The simulation time
obviously reduced through improved algorithm.
114
Heat maps with high resolution were also developed. The accuracy of heat maps greatly depends
on sun grid and test surface grid size. When the sun grid size and cell size of a test surface on the
ground are smaller, the simulation result of the heat map is more accurate owning to the most
detailed division and analysis of test ground.
Heat maps with different latitudes were compared. Three cities including Honolulu, San Francisco,
and Fairbank provided the tables of altitude and azimuth values. Simulation results show that
latitude of the city where building built also affect the solar convergence. When the value of
latitude decreased, the solar convergence increased.
Different visualization of heat maps was provided. One is a visualization of heat maps with yellow
sun ray arrow. A yellow arrow was used to standard for the inject angle of all parallel sun lights.
Second is a visualization of heat maps with the bounding box. This version of heat maps using a
box to visualize the movement of sun ray. One side of the box determines the planar grid for the
sun rays. This version can provide a more clear visualization of the movement of sun rays.
6.4 Future work
All of the above work was done using circular arcs. That is, no parabolic or catenary curves were
considered. Such curves should be examined. All of the above tests were conducted with
relatively upright buildings, perpendicular to the ground. Building that lean, especially facades
that lean forward, may produce different results. Often there were focal points in midair. The flux
at these points would be substantially greater than the flux measured on a horizontal ground
surface. Similarly, all tests were done for flat sites. Sloping sites might also intersect these midair
focal points. There should be tests done to find the maximum flux generated by these forms,
independent of whether they strike a flat horizontal surface. Such tests could be done by
115
calculating sloping ground surfaces in front of the facades. These situations might prove far more
dangerous than the cases tested.
For the ray tracing simulation, future work can focus on interior glare. The surrounding
environment should be molded to simulated how the reflected light from the concave glazing
façade or the ground will affect the surrounding building, how well is the shading device functional
and how to adjust the shading device angle to maximize the daylight without bringing the too much
solar heat. Useful Daylight Illuminance (UDI) it is an output value of Honeybee daylight
simulation component. UDI is an index to evaluate daylight level. An analysis of UDI of
surrounding buildings can be given to evaluate the daylight performance and adjust the angle of
shading devices.
For the first Hourly UTCI map of test surface. There are some limitations of this simulation. Here
it assumed the MRT as ambient air temperature. To get a more accurate solar adjusted MRT,
original values of MRT should be input instead of ambient air temperature. In future work, more
refined sense of this MRT is by looking at outdoor surface temperature from an EnergyPlus
simulation. Besides, there is no accurate way to separate the direct radiation portion and the diffuse
radiation portion from the cumulative radiation values. A better way to separate direct and diffuse
radiation should be given.
For the heat maps, the largest numbers of intersected points in the grid cell were founded manually
by changing the time slider through the whole day and check the largest values in the domain. The
better algorithm could be given to automatic spot out the biggest number during the day. It can
save much time to calibrate the absolute heat map by its maximum value.
116
Besides, when changing the size of sun grid and test surface grid, the accuracy of heat map
improved. However, the computation time increased. The better algorithm could be given to
decrease the computation time.
For the simulation of real projects, more information should be collected from surrounding
buildings, streets, traffic, pedestrian, construction details of the concave glass façade to give a
more accurate simulation. Site survey of thermal comfort of pedestrians, drivers, and occupants in
surrounding buildings could be conducted.
6.5 Final Summary
The methods shown can be employed to find possible dangers prior to the start of construction,
allowing solutions to be developed before they become extremely expensive.
The cases tested alert designers to the possible dangers from forms which were not expected to be
dangerous, most notably the flat top and concave bottom form, which develops very high
concentrations.
This work is the first step in solving an extremely complex, but interesting and important issue in
contemporary buildings, as reflective and specular geometric forms become more common due to
the improvements in design software and construction capabilities which are currently on the
leading edge of building.

117
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Asset Metadata

Creator Deng, Lisha (author)

Core Title Exterior glare simulation: understanding solar convergence from concave facades using heat maps

Contributor Electronically uploaded by the author (provenance)

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Publication Date 06/30/2016

Defense Date 04/29/2016

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag heat maps,OAI-PMH Harvest,ray tracing,solar convergence,thermal comfort,UTCI maps

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Language English

Advisor Schiler, Marc (committee chair), Konis, Kyle (committee member), Noble, Douglas (committee member)

Creator Email lishaden@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-259077

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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

Abstract (if available)

Abstract Concentration of solar radiation reflected from concave and specular facades results in the solar convergence problem. In extreme cases the solar convergence problem had caused melting automotive surfaces at the street level. The goal of this thesis was to build a simulation framework and test software that can be used to simulate the solar convergence problem in the pre-design phase. Grasshopper and its plug-ins Ladybug & Honeybee were chosen as the simulation tools. This thesis tests three simulations—ray tracing, Universal Thermal Climate Index (UTCI) maps and heat maps. Ray tracing simulation showed how the sun rays moved after being reflected from the concave and specular façade. UTCI maps showed how and where the solar radiation reflected from the concave and specular surface resulted in thermal discomfort. Absolute and relative heat maps are the distribution of reflected lights on the ground and hot spots where the most reflected light has been concentrated. Relative and absolute heat map patterns and their domains for seven different surface forms—ellipse (concave), flat top and bottom, flat top, flat bottom, concave, convex bottom, and concave sweep were analysed. Three methods of delivering heat maps were used to simulate the solar convergence phenomenon for different purposes. The results showed that flat top and curved bottom surface with a swirl pattern heat map caused the greatest focus effects on the center of the swirl. Convex bottom surface has the most distributed pattern. For ellipse and concave surfaces, the heat maps are closely distributed arcs, while flat top and bottom and convex bottom surfaces delivered more sparsely distributed straight lines and arcs. Convex Sweep and flat top and bottom have a focus effect on the edges of heat maps.