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Office natural lighting effective of a reflective light plenum
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Office natural lighting effective of a reflective light plenum
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Content
OFFICE NATURAL LIGHTING
EFFECTIVE OF
A REFLECTIVE LIGHT PLENUM
by
Peng-Chih Wang
A Thesis Presented to the
FACULTY OF THE SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE
August 1993
Copyright 1993 Peng-Chih Wang
UMI Number: EP41434
All rights reserved
INFORMATION TO ALL USERS
The quality of this reproduction is dependent upon the quality of the copy submitted.
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
*
Dissertation Publishing
UMI EP41434
Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author.
Microform Edition © ProQuest LLC.
All rights reserved. This work is protected against
unauthorized copying under Title 17, United States Code
ProQuest LLC.
789 East Eisenhower Parkway
P.O. Box 1346
Ann Arbor, Ml 4 8 1 0 6 -1 3 4 6
UNIVERSITY O F SO U T H E R N CALIFORNIA
THE SCHOOL OF ARCHITECTURE
UNIVERSITY PARK
LOS ANGELES. CALIFORNIA 900894)291
This thesis, written by
.PBjer.'C.HJ.H W M 6 r ....
under the direction of h .1$. . . . Thesis Com m ittee,
and approved b y all its mem bers, has been pre
sented to and accepted b y the Dean of The School
o f Architecture, in partial fulfillm ent of the require
m ents fo r the degree o f
W k x s t e x . o i I d { . . S c i en C £
Dean
D ate & / '
THESIS COMMITTEE
“ Chair
! ACKNOWLEDGMENTS
I ;
I would like to thank Professor Marc Schiler, my Committee Chair, for
contributing valuable insights from his own experience and expertise
which helped simplify and direct my approach to the problem. I am
also grateful to Professors Goetz Schierle and Pierre Koenig for their
help and encouragement in researching and writing this study.
Moreover, I also appreciate the generosity of Murray Milne, UCLA
Professor, for supporting the testing equipment.
TABLE OF CONTENTS
!'
LIST OF FIGURES v
LIST OF TABLES viii
ABSTRACT ix
1. INTRODUCTION 1
2. NATURAL LIGHTING IN BUILDINGS 5
2.1 Why Daylighting 6
2.2 The Importance of Natural Lighting in Buildings 7
2.2.1 Natural lighting is a rational design factor 7
2.2.2 Natural lighting lowers energy cost for the building
2.2.3 Natural lighting provides a good quantity and high
quality environment 11
3. LITERATURE REVIEW 13
3.1 The concept of daylighting systems 14
3.2 The Development of Daylighting Systems 15
3.2.1 Lightpipe 15
3.2.2 Mirror systems 17
3.2.3 Prismatic systems 20
3.2.4 Lens systems 21
3.2.5 Holographic diffracting systems 22
3.2.6 Light shelves 22
3.2.7 Light plenum 25
iii
4. EMPIRICAL DAYLIGHT TESTS
28
4.1 Hypotheses 29
4.2 Description of experiment 30
4.3 Description of the model 37
4.4 Instrumentation 38
4.5 Data collection procedures 41
4.6 Problems 42
5. DATA ANALYSIS 44
5.1 Base light plenum vs. conventional offices 46
5.2 Impact of inner light plenum depth 52
5.3 Impact of clerestory height 60
5.4 Light plenum with control device 68
5.5 Duct work integration 75
6. CONCLUSION 85
6.1 Summary 86
6.2 Design guidelines 89
APPENDIX
A. Test data (Foot-candles) 92
B. Test data (Daylight Factor) 103
REFERENCES
114
LIST OF FIGURES
1.1 Three strategies of office daylighting 2
2.1 Great Temple of Ammon, Kamak 8
2.2 Basilica of Constantine, Rome 9
2.3 Saint Apollinare in Classe, Ravenna 9
3.1 Lightpipe 15
3.2 Mirror system — reflective louver 17
3.3 (a) Light scoop and (b) rooflight system 18
3.4 Prismatic glass 20
3.5 Light shelf 23
3.6 Light shelf with sloping ceiling 24
3.7 Light plenum concept in office building with integrated
daylighting, electric lighting and ventilation at ceiling 25
3.8 Light plenum concept 26
3.9 Light plenum, illumination gradient curves 27
4.1 Basic office module 31
4.2 Light plenum vs. base cases 33
4.3 Clerestory height 33
4.4 Light plenum inner depth 34
V
4.5 Control device applications 35
4.6 Integration of duct work 35
4.7 Testing data form 42
5.1 Light plenum vs. base cases, illumination comparison,
clear sky 47
5.2 Light plenum vs. base cases, illumination comparison,
overcast 48
5.3 Light plenum vs. base cases, contrast ratio comparison 50
5.4 Light gain and lost through light plenum 51
5.5 Impact of light plenum inner depth, illumination
comparison, clear sky 53
5.6 Impact of light plenum inner depth, illumination
comparison, overcast sky 54
5.7 Impact of light plenum inner depth, DF(25') & DF(Avg)
comparison, clear sky 55
5.8 Impact of light plenum inner depth, DF(25') &DF(Avg)
comparison, overcast sky 56
5.9 Impact of light plenum inner depth,
contrast ratio comparison 57
5.10 Impact of clerestory height, illumination comparison,
clear sky 61
5.11 Impact of clerestory height, DF(25') & DF(Avg)
comparison, clear sky 62
vi
5.12 Impact of clerestory height, illumination comparison,
overcast sky 63
5.13 Impact of clerestory height, DF(25') & DF(Avg)
comparison, overcast sky 64
5.14 Impact of clerestory height, contrast ratio comparison 65
5.15 Light plenum vs. control devices, interior illumination
comparison, clear sky 69
5.16 Light plenum vs. control devices, DF(25') & DF(Avg)
comparison, clear sky 70
5.17 Light plenum vs. control devices, interior illumination
comparison, overcast sky 71
5.18 Light plenum vs. control devices, DF(25') & DF(Avg)
comparison, overcast sky 72
5.19 Light plenum vs. control devices, contrast ratio
comparison 73
5.20 Light plenum vs. duct work, interior illumination
comparison, clear sky 76
5.21 Light plenum vs. duct work, DF(25') & DF(Avg)
comparison, clear sky 77
5.22 Light plenum vs. duct work, interior illumination
comparison, overcast sky 78
5.23 Light plenum vs. duct work, DF(25') & DF(Avg)
comparison, overcast sky 79
5.24 Light plenum vs. duct work, contrast ratio comparison 80
VII
LIST OF TABLES
2.1 Daylighting parameters: lumens/watt, solar heat gain,
illuminance
5.1 Light plenum vs. conventional offices, DF comparison
summary, clear sky
5.2 Light plenum vs. conventional offices, DF comparison
summary, overcast sky
5.3 Light plenum inner depth, DF comparison summary,
clear sky
5.4 Light plenum inner depth, DF comparison summary,
overcast sky
5.5 Clerestory height, DF comparison summary, clear sky
5.6 Clerestory height, DF comparison summary, overcast sky
5.7 Light plenum vs. control device, DF comparison summary,
clear sky
5.8 Light plenum vs. control device, DF comparison summary,
overcast sky
5.9 Light plenum vs. duct work, DF comparison summary,
clear sky
5.10 Light plenum vs. duct work, DF comparison summary,
overcast sky
10
49
49
58
58
66
66
74
74
84
85
via
ABSTRACT
This project is an experimental study of daylighting for office
buildings. It focuses on the effectiveness of a light plenum as a device
for improving the quantity and quality of natural light available for
interior illumination. The variables of light plenum rear openings,
clerestory and ceiling height, inner light plenum depth, control devices,
and duct work integration are examined using physical scale model
tests. All cases were tested under both clear and overcast sky
conditions. Test results show that:
1) A light plenum with diffuse rear opening to the space below gives a
better combination of high light levels and good quality of light.
2) A larger plenum opening will result in good daylighting, but can also
cause a glare problem.
3) A smaller clerestory has higher interior light level, but worse light
distribution. A larger clerestory results in lower light level, but better
light distribution.
4) An overhang helps to solve the glare problem but decreases the
general light level of the room. A rear mirror in the plenum can
enhance the light level at the back of the room.
5) Placing the ducts perpendicular to window wall within the
plenum did not affect light distribution throughout the room. A
system with ducts parallel to window wall caused significant
reduction of light level within the room.
CHAPTER 1
INTRODUCTION
Natural lighting has recently become one of the important ways of
i
i
planning energy efficiency, especially in non residential buildings
• [Harvey Bryan, Architectural Record 1988]. In the United States, about
one half of the commercial building floor area is in multistory
| buildings. Natural lighting to date has been applied to these type of
i buildings, including office buildings, either by side lighting through
! windows in exterior walls, through large interior atria, or through
I skylights (Figure 1-1). Nevertheless, atria often require the sacrifice of
too much usable floor space to be economically practical. Skylights are
generally limited to the upper story of any building. Therefore, side
lighting seems to be the simplest strategy for natural lighting in office
building.
i
i
ATRIUM
i
i
Figure 1-1 Three strategies o f office daylighting
As we can expect, the growth rate in multistory building is higher than
for single-story building, because of the increasing cost of real estate
2
and because a small surface-to-volume ratio for a building reduces the
construction costs associated with skin insulation and water proofing.
On the other hand, the small surface-to-volume ratio of large office
buildings also limits the area that can be effectively influenced by
natural side lighting to a zone usually within 15 to 20’ of the building's
perimeter [Stephen Selkowitz, 1979]. Since the illuminance decreases
with increasing distance from the openings, deep and enclosed spaces
are usually lit artificially. Due to the growing concern for energy
conservation and recognition of the value in the variability and natural
qualities of daylight [ Evan, 1981], it becomes more desirable to devise
natural lighting systems that illuminate space not immediately adjacent
to the perimeter surfaces in the multistory office buildings.
Some familiar techniques which are assumed with building designs are
available for extending the depth of this perimeter zone. For example,
glass blocks have been used extensively to direct sunlight deeper into
rooms to complement diffuse light near the windows. One concept
which we call "beam sunlighting" involves reflecting direct sun light
from silvered reflective Venetian blinds mounted in the upper two feet
of typical window. The reflected rays are aimed towards the ceiling of
the room to maximum depth of approximately 30 to 40 feet. The ceiling
then acts as a diffuse reflector providing normal diffuse illumination
deep inside the room. Although the lighting quality achieved by such a
scheme is satisfactory, the control of reflected light as sun angles
3
change is a significant problem. A variety of controllable reflecting or
reflector-type devices have been examined. These mostly depend on
the redirection of sun light using mirror, light shelves, louvers, lenses or
a single large rotating panel [Gutherz and Schiler, 1990] via overhang
and other glare-free paths. However, the real issue of these applications
is one of simplicity and low cost in these devices, without sacrificing
the potential performance.
Consequently, in an attempt to enhance daylight contribution without
utilizing complex configurations and high-tech materials, the purpose
of this thesis is to develop and study an efficient natural daylighting
system -- light plenum that can be incorporated into typical office
buildings' design. In other words, the light plenum concept simply
enlarges the functions of an air plenum which is the space between
floor and ceiling and accommodate the structural and mechanical
systems to serve as not only a ventilation (return air) path but also a
light trap. By starting with discussing the benefits of introducing the
daylight in buildings, several daylighting systems are also reviewed.
The character of the light plenum is experimented with physical
models. As a result, some guidelines are listed, and I hope these will
help those who are interested in this application.
4
CHAPTER 2
NATURAL LIGHTING IN BUILDINGS
2.1 Why Daylighting
Talking about the importance of natural lighting in buildings, first of
all, we should ask ourselves "Why daylighting ?" This seems a very
simple question; however, it may cost us several years to figure it out.
People have been chasing the answers for many years quantitatively
and qualitatively. Although the results can not leave the topics of
economics, comfort, and so on, we might satisfy with these response.
After all, there are many studies support these ideas. The question here
is "Why daylighting ?" " Why not? It is free." The answer may be
superficial, but it is true. Think about it. The sun and the whole vault of
the sky provide free limitless light. It is something we take for granted;
it is part of our daily life, like walking or breathing. Indeed, people do
care about daylight in buildings. According to Charles C. Benton's poll
in his research, when people were asked their favorite architectural
space, he quoted " A predominant common denominator for the spaces
chosen was the presence of daylight. Over 95% of the spaces named
were daylit, many with rather special lighting characters. A corollary is
that skills in the manipulation of environmental variables, like daylight,
are still admired by our profession." In fact, the rights to direct
sunlight, skylight and even reflected light off other structures should
belong to all people and would last as long as the buildings they
protected. Basically, adequate lighting for the conduct of human
activities is, of course, a necessity in the built environment. Moreover,
6
there are numerous aspects of daylight that make its use for lighting in
buildings not only desirable, but also valuable from the standpoint of
economics, aesthetics, as well as in the quality and quantity of light that
can be provided. There are three major motivations for utilizing the
natural daylight in buildings.
1. Natural lighting is a rational design factor.
2. Natural lighting lowers energy cost for the building.
3. Natural lighting provides a good quantity and quality
environment.
2.2 The Importance Of Natural Lighting In Buildings
2.2.1 Natural lighting is a rational design factor.
In Vitruvius' trinity stated this " Sun lighting is not a faddish aesthetic
following a trendy concept but the intelligent application o f the
natural environment to the achievement o f programmatic needs."
[Lam, 1986: p.3] Natural daylighting predetermines the appearance of
buildings from the outside, by fenestration, and the interior is modeled
in a specific manner by the light admitted. As a design factor,
daylighting design is based on the universal everlasting human needs,
so it will remain beautiful in its surroundings. In fact, natural
daylighting has produced buildings of classic beauty and lasting value
the world over. For example, in Great Temple of Ammon, Karnak
7
(Figure 2-1), the quantity of light was intentionally varied to reinforce
the axial sequence through the great Hypostyle Hall and finally to the
darkest inner sanctum.
pierced elebe of stone fitter light
fully op an lotus
•fteir capital
(fu p o n aa to
piarcad slab# of
Stpna filter Pght
•mslMigtitsfil#
Figure 2-1 Great Temple o f Ammon, Kamak, 1530- 323 B.C.
In Basilica of Constantine, Rome (Figure 2-2), the building's plan was
rectilinear, elongated east and west to provide greater exposure to the
south. A flat roof covered a serior of north-south running concrete
vaults. This flat side-aisle roof, together with the raised center roof
8
permitted the use of very large clerestory openings (or windows) to
illuminate deep into the vast interior.
\
|
*
5
i
■ I
1
plan
so a a
larg e cleresto ry
ad m itted g re a t
s h e e ts of light
low s id e a is le roof
allow ed la rg e c le re sto ry
4— s
Figure 2-2 Basilica o f Constantine, Rome, A.D. 310-313.
m
v
light, timber trusses reduce
bearing on side wa Its
allowing larger openings,
but height limited by sloped
side aisle roof geometry windows focus
attention
toward apse
Figure 2-3 Saint Apollinare in Classe, Ravenna, A.D. 534-539.
't
In Saint Apollinare in Classe, Ravenna (Figure 2-3), a new
technology of timber trusses resulted in the building sloped side-aisle
roofs that reduced the wall area of available for clerestory windows,
and served to enhance the mystical nature of the new religious
functions [Fuller Moore, 1985].
j
2.2.2 Natural lighting lowers energy cost for the building
Electric light is a significant component in the energy consumption of a
t
j technological society. About 16% of all energy used in this country,
j according to Dubin [Dubin, 1979: p.205], goes to operate commercial
building, and some sources claim that 40 to 50% of the energy used in
office buildings goes for lighting [Evans, 1981: p.35]. On the other
! hand, daylight is as efficient as the best electric lighting systems in its
| ability to deliver illumination. Study shows that light from the sun is
j
. about 10,000 footcandles, while typical offices are only lit to 50-100
| footcandles, and obviously it is a comparatively efficient source of
j illumination (Table 2-1).
Direct Skylight (incident on
beam vertical window)
1. Lumens/watt
(a) Measured, clear day 106 + 2 116 + 7
(b) Nominal values 100 120
2. Solar heat gain (Btu/ft2 h) 300 35
3. Illuminance (footcandles) 9000 1200
• Table 2-1 Daylighting parameters: lumens/watt, solar heat gain, illuminance [
! Rosenfeld; Selkowitz. Energy and Building, 1977: p.44]
10
! As we can see in Table 2-1, the light from the sun can produce 100-
120 lm/w, as compared with nearly 70 lm/w of light for the thermal
| energy delivered from incandescent bulbs. As a matter of fact, the sun
I light can provide high levels ilhimination and more efficient
j lumens/watt. Therefore, the use of daylight in buildings no doubt
: allows for some reduction of electricity for lighting purposes, and can
thereby reduce the consumption of energy in the buildings.
; Farthermore, the advantage of using the wattage from the daylight is
free charge, as compared with electrical sources. In conclusion, all of
these tells us that even modest increases in daylighting for office
buildings could save substantial amount of fuel and money.
2.2.3 Natural lighting provides a good quantity and high quality
environment
Natural lighting could theoretically provide a good quantity of light
inside the buildings , if applied properly. The lumens contained in a
j single square foot of sunlight could provide 50 FC of illumination over
[ i
an area of 180 sqft. In addition, even in the cloudiest regions of North
America, studies have showed that there is ample daylight to make its
j ;
use in the lighting of building interiors definitely feasible [Kingsbury,
H. F.,1957, Boyd, R. A., 1958]. This may confirm the potential of
daylighting application as well. The quality of lighting is another
concern for daylight performance in the buildings, even though veiling
reflection is the most critical issue in this topic. Nevertheless, by
li
reducing the loss of contrast from veiling reflections, the horizontal
nature of window light can help to define surface textures and to
improve the modeling of objects within the interiors. Studies have also
shown that the variation of sun light levels has a relaxing effect on the
eyes and produce advantageous psychological reactions in people.
Moreover, light from the sun is pleasant to us owing to its color
temperature. Vischer, J. C. indicated that people have strong
preference for daylight in their office.
To sum up, the use of daylight is not only for energy conservation and
operating cost benefits. The fact of creating delightful environment for
working and living is even important. In order to achieve thoughtful
daylighting design more easily, as well as a general understanding of
this field, a literature review is then necessaiy.
12
CHAPTER 3
A REVIEW OF THE LITERATURE
3.1 The Concept Of Daylighting Systems
Good daylight design does not simply mean large windows. It must be
approached both quantitatively and qualitatively on broader and more
sensitive design terms. In fact, daylighting systems have lately been
innovated to meet these two main objectives: to bring daylight deeper
into a space (quantitatively), and to control and to distribute direct
sunlight (qualitatively) so that this can be used as an effective working
illuminance. A large number of devices has been proposed; however,
little has been done to show rigorously whether they do in fact save
energy or improve the internal environment. Whatever daylight system
is chosen, it should cope with the sun's movement. Therefore, to
understand how does daylight perform and how it is introduced toward
the buildings is necessaiy, the next paragraphs will attempt to bring
together some previous research on daylighting systems and their
theories. The previous research fall into several categories. The first is
research focusing on different kinds of daylighting systems in order to
understand how they work and how effective they are. The next is on
light shelf to grasp its general application and performance, as it is the
original concept of light plenum. The last is on the light plenum itself to
develop a more clear idea and also to design a scale model office. The
projects under consideration use different research methods and make
varying assumptions based on individual priorities.
14
3.2 The Development of Daylighting Systems
Light Pipe
The light pipe as Paul J. Littlefair mentioned: " is perhaps the most
technologically exciting innovative daylighting systems because of the
I ! long distances over which it can operate". In general, light pipe system
j consists of three components: an outside heliostat, the light pipe itself,
1 and an emitter or luminaries (Figure 3-1 ).
( Heliostat)
C oncentratin g m irro r
| C o llim atin g len s
Tracking m irror > «
L ig h t coloured c eilin g
---------------------------
P lp ed lig ht to interior
— ........
m irror
( Light Pipe)
o
Emitter
M etal h alid e la m p
with reflector
D uct to H V A C system
Figure 3-1 Light pipe
The heliostats are usually on the roof to track, collect and concentrate
sunlight. They are costly and require complex control and
15
maintenance as they have to track the sun all the time. The space
consumed is another problem for building a heliostat. Before the
sunlight enters the pipe, it needs to be concentrated using lens or
mirrors. Smith SCJ claimed that the diffuse daylight is much less
suitable as the primary light source, because of its quantity limits.
Various types of light pipe have been proposed in order to transport the
collimated beam of light, such as reflective metal tube, optical fibres,
solid acrylic rod, and prismatic sides of tube. Reflective metal tubes
were designed to keep the beam concentrated. Fibre optical bundles
are good transitive materials but expensive. Acrylic rods are
comparative inefficient but cheaper. Each one has its merit and defect.
However, the extra costs in each case and the significant volume
occupancy in the building need to be concerned as proposed.
An emitter was used to distribute the exiting light throughout the space,
and some sort of backup lamp is developed to prevent the whole
building being almost completely unlit. A rotating mirror enables
sunlight or artificial light to be selectively beamed into the interior. It
would have to operate instantly when the sun went behind a cloud. In
fact, a sunlighting system is best suited to climates where partly cloudy
conditions are rare. To sum up, light pipe systems deeply depend upon
sunlight may be suitable for North American sunny region, such as in
LA, the sunlight is available for some 75% of the working year.
However, the large space consuming and extra expense may descries
the interest of their applications.
16
Mirror Systems
Unlike light pipe systems, mirror systems are simpler forms which
represent a reduction both in scale and in complexity. Reflective louver
is a typical example of these systems (Figure 3-2). Smaller mirrors are
employed in each window with louvre to stop direct sunlight falling on
the occupants and instead redirect sunlight into the room to form a
large light source on the ceiling. The surfaces of the room are then used
to spread and diffuse the light without a complicated distribution
system with pipes and emitters. The aim is to improve penetration of
light deep within the space.
W hite cellin g acts a s secondary diffuser
M irror lo u v e i
C S 5 K S S 3 2 S S X S 3 w ork p lan e
Figure 3-2 Mirror system — reflective louver
Louvers in general have two main drawbacks. The first is that they tend
to block views out; generally, then louvers will be installed only on top
part of the glazing. The other problem is maintenance, especially where
silvered surfaces are used.
Some other different kinds of mirror systems, such as fixed louvre
systems, moveable louvre systems, reflective sills and scoops, and
rooflight systems have been investigated.
w indow
m irrored light
scoop
©fleeted light
from scoop
sloping m irror
Figure 3-3 (a) Light scoop and (b) Rooflight system
| | Light Scoop is another relative inexpensive daylighting proposal
j | '
| (Figure 3-3a). Here the mirror is used as a "light scoop" actually
increasing the amount of daylight entering the space as well as
l directing light deeper within the interior. The technique is also
j ;
I appropriate for rooms leading off an atrium; generally these are seldom
18
I
; adequately daylit in current practice as they receive little direct sky
light. In fact, the "light scoop" concept can also apply to diffuse light.
Mirrors of this type were used in narrow streets in the City of London
; over fifty years ago. Like "light scoop", a reflective window sill is
i
| another simple application of mirror systems. Sunlight striking the sill
: is bounced onto the ceiling to be reflected onto working area. For these
kinds of applications, glare is however a major difficulty, in that under
! certain circumstances sunlight can reflect straight into the eyes of
occupants. Therefore, any reflector should not be placed below the
occupants' seated eye level in order to avoid the problem of reflected
glare. Maintenance is another problem for these kind of applications.
Mirror systems can also be used in rooflit buildings where the daylight
distribution needs improving, or where sunlight is required in a space.
Such mirrors can be used for diffuse light too. A common problem in
spaces with northlight glazing is that the interior daylight is heavily
directional, with poor daylighting at the north end of the room. Figure
3-3b shows the concept of north skylight. This contains a northlight
fitted with a mirror, the purpose of which is to reflect diffuse light into
the area immediately to the left of the rooflight, which otherwise
receives no direct light. For diffuse light the mirror need not be curved;
plane mirrors can be used depending on type of light distribution
required.
19
Prismatic Systems
In heavily obstructed rooms, prismatic glass systems are introduced to
redirect light from near the sky zenith towards the back of the room,
which would otherwise receive no direct skylight. The principle of the
prismatic glazing systems is based on that refracting the incoming light
to the desired location may act as well as reflecting (Figure 3-4).
Figure 3-4 Prismatic glass redirects light from the sky above an obstructing
building to points near the back o f the room from which no sky would normally be
visible.
Prismatic glass blocks were used in the 1940s and 1950s in American
schools. Note that in this case the prism system is employed solely to
redirect diffuse light, and relies on a white ceiling to act as a diffuser
and spread the light over the working plane. The resurgence of interest
in prismatic glazing has partly arisen from the idea that it can have an
impact on sunlight use as well. Two forms of prismatic glazing have
20
' been employed to redirect light: sunlight direct prisms, and sunlight
excluding prisms.
l !
I Some problems should be noted in these applications. Although
! | maintenance for prismatic glass is much less of a problem than for
mirrors as the prism faces will not need to be cleaned. However,
transmission should be less than for clean mirrors, because of
misdirected light loss through the prism vertices. Ruck quotes
transmission factors varying from 75-85% down to 50-70% (Ruck N
C, 1982). Like mirrored louvers, prismatic glazing will obscure view
out and so it is best placed at the top of the window, above a viewing
strip of clear glass. Color dispersion is sometimes a problem with
prisms.
i
Lens Systems
Lens systems have been proposed to make the refracted rays converge
or diverge, unlike refracted parallel rays from prismatic glasses,
especially in rooflighting application. The principle behind the lens
systems is to incorporate a lens in the rooflight glazing which can
spread the concentrated beam of sunlight over a wider area. Nelson D
T has suggested of fresnel lenses which composed of small prismatic
lens segments. Others like short focal length positive lens, negative
lens, and linear lens have been suggested. Generally the lens had
21
reasonably high transmission factors, around 85% that of a clear
rooflight. In practice, lenses more than a meter wide are not cheap, and
so an array of small lenses would be used.
Holographic Diffracting Systems
Light can also be bent by diffraction. A conventional two-dimensional
diffraction grating will deflect light; but most of the incident light
passes straight through, and the exit angles of diffracted light depend
on the angles of incidence. The holographic diffracting systems,
however, use three-dimensional gratings. The resulting diffraction
pattern is like the x-ray diffraction pattern of a crystal; light emerges at
set exit angles, but only if the angle of incidence and wavelength of
incident light satisfy a particular relationship (Bragg's Law). The
systems can deflect light through varying angles without expensive
tracking equipment. However, movement of the sun during the day
remains a problem, and so does the color dispersion of the output light.
Efficiencies of 30-70% have been quoted.
Light Shelves
Research into light shelves was carried out in the early 1950s at the
Building Research Station. Essentially the light shelf is an old idea
which has recently come back into fashion. The light shelf is only a
22
horizontal, or nearly horizontal, baffle which is intended to provide
j
, shade below it, and also to reflect light into the building off its top
surface. Normally a light shelf would be installed some way up a
window, dividing the glazing into two parts: a view window below the
shelf, and a clearstory window above it. It can be either exterior,
interior or both. An alternative system has the light shelf below a
i clearstory window, with an opaque wall below it (Figure 3-5).
t:
Interior s hie if
) Figure 3-5 Light shelf
I
! (
| The purpose of a light shelf is twofold; first, to improve light quality by
j preventing direct sun from striking work surfaces, and second, to
increase the quantity of light deep in the space by reflecting direct
sunlight up onto the ceiling and down further back in the space. As
i
I Figure 3-5 shows, a south facing light shelf will be able to shade
occupants near the window from the direct sun light, and reflect some
of that sunlight onto the ceiling from where it can be diffused
throughout the room. We also note that sunlight penetration is greatest
in winter and least in summer.
In order to avoid reflected glare, the light shelf should be above eye
level, but otherwise low enough to achieve a good spread of reflected
light over the ceiling. Just over 2m above the floor was recommended
(Lam W, 1986). Another important factor for designing this system is
the depth of the light shelf. Obviously the deeper light shelves will
block direct sun coming through the clearstory window, but they also
allow less daylight through into the interior. Therefore, some form of
blind may be required on the clearstory to block this winter sun. Light
shelves do not have to be horizontal; however, Lam suggests that a
horizontal shelf is the best compromise. A horizontal shelf with a
sloping ceiling has been proposed, with the aim of improving light
distribution within the interior (Figure 3-6).
HVAC ducts
o o
Clerestory window
Sloping celling
Light shelf
Figure 3-6 Light shelf with sloping ceiling
Even though the sloping ceiling only has little effect on internal
j daylight availability, it allows HVAC ducts to be concealed above it,
while retaining a high window and reasonable floor-floor distances.
Compared with a normal ceiling height, one of the major problems with
light shelves is that they required a high ceiling in order to work
effectively. Maintenance in general can be a problem with light
i
| shelves. The deeper the light shelf the more difficult cleaning will be.
I
»
J Light Plenum
Recently, it was conceived that the light shelf could be extended to the
back of the room to create a highly reflective "plenum" which would
control more of the daylight into the interior space of a room, allowing
i •
the designer to put the daylight closer to where it is desired.
Figure 3-7 Light plenum concept in office building with integrated daylighting,
electric lighting and ventilation at ceiling by Don Mirkovich
Ah Exchange
sunlight
PLENUM
■ f \
'Electrical
- Lighting
'aylighting
25
Don Mirkovich first proposed the "light plenum" concept under the
1
| project of a four-story office building in Pullman, Washington, 1983
j j
] (Figure 3-7). Unlike other daylighting schemes, light plenum needs not
u
utilize complex configurations and high-tech materials in an attempt to
enhance daylight contribution. The concept is to form a light trap by an
enlargement of the conventional mechanical plenum, with proper
j spacing and alignment of the structure, and with placement of the
| mechanical network within the plenum (Figure 3-8). From a point of
j view, it is simply an extension of the light shelf application. The
daylight is reflected throughout the plenum by means of flat reflective
surfaces . Because of entering light from above at ceiling level through
diffusing lenses, the glare problems will be reduced . By physical
j model tests under real sky condition, for all seasons, the light level at
i
the back of the rooms was effectively enhanced.
Hi8hly reflectiv* aurface
Unilateral sidelighting
Figure 3-8 Light plenum concept
According to Don the solar altitude and the sky conditions had the
most dramatic effects on the uniformity of the light distribution.
26
In addition, the openings of the plenum are important for this
application. Glenn suggested that different plenum opening
configurations should be considered to optimize the light plenum to the
specific demands of the day, month and time of the peak energy
demand and consumption charges (Glenn, 1986).
! I
..... 1
View window & Clearstory window => Light plenum
Figure 3-9 Light plenum, illumination gradient curves
Figure 3-9 shows the basical idea of using light plenum as second light
source to balance the illumination gradient of the sidelight (window) to
create a more qualitative brightness ratio.
27
CHAPTER 4
DAYLIGHT TESTS
4.1 Hypotheses
In addition to providing information regarding the use of light plena for
architectural daylighting through physical model testing in daylight, the
primary goal of this project is to test certain assumptions about light
plena and to answer some questions about their performance. The
hypotheses that I will investigate are as follows:
1) A light plenum can be used to bring daylight deeper into an
office space than identical windows without sun controls.
2) A light plenum improve the quality of light in a space by
blocking direct sunlight and giving more even light distribution
throughout the space.
3) Some light plenum / control devices ( overhang, mirror )
combinations will give better results ( that is, more light deep in
the space, more even light distribution) than others.
4) With proper placement, a light plenum can be effectively
integrated with duct work and applied in an office.
5) The following variables will influence light levels within the
room : — Height of the clear story
— Characteristics of light plenum rear openings
— Light plenum / control devices
To test these hypotheses and to discover more specific information
during processing, the following experiment was designed and carried
out.
29
4.2 Description of Experiment
The tests were done under natural sky conditions, including clear and
overcast sky, at 34 degrees north latitude ( Los Angeles ) over a period
of several weeks. The general format of the tests was to build scale
models of the different light plenum openings and sunshade control
devices and then to measure the interior illumination in foot-candles at
the work surface (2 ' 6") at five feet intervals down the space starting 5
feet from the window wall. Both total and diffuse outdoor illuminance
were measured under clear sky conditions. In order to compare data
from different days the foot-candle values were converted to Daylight
Factors.
The Daylight Factor is the ratio between indoor the illumination and the
outdoor illumination. In this research, under overcast sky conditions,
the Daylight Factor is simply to compare indoor light levels on a
horizontal work plane with outdoor illuminance on a horizontal surface.
In the clear sky conditions, it was calculated using both diffuse and
total outdoor illuminance measured on a horizontal surface. The basic
module for the experiment is a 30' by 30' office bay with a 12' floor to
ceiling height (Figure 4-1). The south wall of this module is a window
wall with a 2' 6" sill, and the rest of the wall is intentionally left empty.
The interior surface reflectance remain constant throughout the
experiment, and are chosen to simulate standard office conditions as
much as possible.
30
SECTION
PLAN
SE N SO R S’ LOCATIONS
Figure 4-1 Basic office module
All light plenums are placed 9' above the floor (resulting in
unobstructed view window) and are fixed in a horizontal position as the
normal office drop ceilings are. The base light plenum has a reflective
upper surface and a white diffusing lower surface. For shading cases,
an overhang is designed to block all direct sun at noon on the
equinoxes at 34 degrees north latitude, thus eliminating all direct sun
within the space during the summer months.
The variables being studied are: (1) base office module with / without
plenum (2) clerestory height (3) light plenum inner depth (4) control
device applications (5) integration of duct work. In order to test and
record easily, sixteen cases were designed to meet these variables. The
details for each test are as follows:
(1) Base office module with/without plenum
An office module with a 12' ceiling and 3' clerestory was chosen as the
; base case. The plenum had a specular reflective surface with a depth of
| about 20'. One conventional office had no plenum with a 12' true
height, and the other had a plenum from the window wall to the back of
the room with 9' height (Figure 4-2).
(2) Clerestory height
The ceiling heights remained constant at 12 feet, and the plenum
height was adjustable to 8', 9', and 10', making the corresponding
clearstories 4’ , 3', and 2'. The inner depth of each light plenum
remained the same in order to find the optimal height (Figure 4-3).
(3) Light plenum inner depth
By keeping the plenum's height constant at 9 feet, this test varied the
plenum inner depth from 5', 10', 15', 20' to 25'. For each plenum depth
even the very deep plenum should allow natural lighting for both
perimeter and interior offices (Figure 4-4).
32
l j g
^ J
. T T F V f
CASE. 1 OFFICE/ceiling=12' CASE. 8 CLEARSTORY/ height=2’
i im t
- i M „ ... . . . . . . . . . . ..i t .... . . - . , ..... .... a,...... f t
* * 1
Jffi,— * * » « .
x ~ ‘ ’ Z
CASE. 2 OFFICE/ceiling=9’
CASE. 9 CLEARSTORY/ height=3’
* " % | P
1 L I B 0 C
CASE. 6 OFFICE / PLENUM
Fig 4 -2 Light plenum vs.base eases
CASE. 10 CLEARSTORY/ height=4’
Fig 4 -3 Clearstory height
33
CASE. 3 PLENUM/depth=5’
fe&r Nw&frfe&y ■ J -0 ? % w L. * * • * ^ • 1 1
M - l i ^ B
CASE. 4 PLENUM/ depth=1 O’
CASE. 5 PLENUM/ depth=15’ CASE. 6 PLENUM/ depth=20’
CASE. 7 PLENUM/ depth=25’
Fig 4 -4 light plenum inner depth
34
CASE. 11 PLENUM wo/
control device
CASE. 12 PLENUM/ mirror
■ H I
CASE. 13 PLENUM/ mirror,
overhang
Fig 4 -5 Control device applications
CASE. 14 PLENUM/DUCT SYSTEM
(corridor mechanical duct system)
CASE. 15 PLENUM / DUCT SYSTEM
(perimeter supply duct system)
L Z j
L
CASE. 16 PLENUM / LIGHT SHELF
Fig 4-6 Integration of duct work
35
(4) Control device applications
In order to achieve even light level distribution, two devices were
designed and examined. They are an overhang and a rear mirror. The
overhang was designed to block the glare caused by direct sun, and
then to reduce the front illuminance. The rear mirror was used to
enhance the illuminance at the back of the room (Figure 4-5).
(5) Integration of duct work
This test is try to integrate the duct work which were generally located
in two positions:
(a) plenum with corridor mechanical duct systems
(b) plenum with perimeter supply duct systems (Figure 4-6)
In perimeter supply systems , two different configurations were tested.
One is the plenum with constant 9' height. The other one has 8' plenum
height at the first 5' depth, the rest of the space retains the 9' height.
All variables were compared with two plenum opening characteristics,
and all tested under both clear and overcast sky conditions. The first
was the basic office module with a clear plenum rear opening. The
second was the basic office module with diffuse plenum rear opening.
It is important to test both cases, because in a real office application,
duct works prefer not to be seen. However, the clear opening cases are
obvious experimental tests to understand how the light works through
the plenum. Moreover, the window wall with no sun controls is also an
experimental control, except for the fact that it allows unhindered
direct sun on the work surface. All tests were done with combined
36
view and clear story openings, and both of them are intentionally left
empty for the purpose of model manipulation. In an actual office
building, the view glazing is often tinted to reduced glare, and the clear
story could be clear glass with about 90 % transmittance. As a result,
the Daylight Factor from the measured data will be higher than final
values in typical applications (see section 5.1).
All tests were also done at sun angles representing the vernal equinox
conditions in Los Angeles. The average profile angle for these tests
was about 57 degrees.
4.3 Model Description
The models were constructed to simulate light levels from daylight in a
comparable office space. Hence, they were abstractions of reality, only
dealing with the grosser elements of an office environment that
influence light levels and ignoring everything else. The models were
simple rectangular volumes built at 1"— 1' scale out of white foam core
board. The outside of the box was carefully covered with black
construction paper and sealed at the edges with black tape to prevent
light leakage through the translucent foam core. The inside of the
model was carefully treated to simulate appropriate surface reflectance.
The floor of the model was covered with medium grey felt with about
30% reflectance to simulate carpet. The walls were covered with cream
colored drawing paper with about 70-80 % reflectance, and the ceiling
37
! was covered with light weight silver board with about 90% reflectance
I
to simulate high reflectance plenum surface. The light weight, silver
i board was glued to the foam core for the specular reflective surfaces
needed for this test, such as light plenum and overhang upper surface,
ducts, and mirror. One base model was built at 12' ceiling height, and
| was used for all the tests at this height by changing only plenum
! configurations. On both side walls, there are three slots to adjust the
j plenum height. The removable light plenum was made from white foam
' core with precautions taken to prevent light passing through the
j material. Two sets of plenums were built. One is with clear openings,
I another is with diffuse openings which was covered with tracing paper
i with the transmittance of 70%. The overhang was attached at plenum
' height.
I
i
4.4 Instrumentation
i
1
I The equipment used to take all the footcandle measurements
| throughout the experiment consist of a portable COMPAQ 286
computer, a Serial Analog Module (SAM) connected to Licor 210A
! light sensors, and the DATALIT program ( DATALIT user's manual,
! Murray Milne, 1987 ).
| During the whole series of tests, a set of 6 sensors , including one
i
| outside sensor and five inside sensors, was used to measure light i
i
i
levels. The size of the sensor is important in determining the scale of i
l
I
38 ,
i .
the test model. The Licor light sensor is about 1" tall. In order to
simulate a typical work surface in a 1" -1 ' scale model with the original
sensor, a house was built for the sensors which was the proper height
of 2'6". These sensors, therefore, were set on a level surface, and
could be moved to the desired locations easily. The sensor is designed
to measure illumination in terms of lux (1 foot-candle = 10.764 lux ).
This is radiation as the human eye sees it. The sensors' output is given
in micro am ps/1* 105 lux and is calibrated at the factory.
The analog input module that is used to collect and multiplex the
incoming data signals is a Serial Analog Module ( SAM Model No.
8.12.4 ) developed and manufactured by Fowlkes Engineering,
Bozeman, Montana. The module can measure voltages in the +/- 200
millivolt range. Incoming analog voltages are integrated for 1/60 of a
second to permit excellent noise rejection. Up to 15 signals can be read
in a second. When connected to the microcomputer, the module
operates as follows:
(1) the computer outputs an 8 bit command to the serial port which
is connected to the SAM
(2) each module decodes this command into the module address,
analog channel to be converted, and output port information. If a
module decodes its address, then the following will occur. Otherwise,
the command is ignored.
(3) the module accepts the output data and performs a 12-bit analog-
to-digital conversion on the selected analog channel, and
39
| i (4) the module transmits two response data bytes back to the serial
: j
port on the computer.
i j
The module is battery operated and also includes a AC charging unit.
| The DATALIT program is hardware dependent due to the fact that it is
performing data acquisition. The purpose of the program is to gather
incoming data from the light sensors and to present this information in
table and graphic forms that are easily understood by the professional
i !
and client alike.
i j
I ;
i ;
i i
4.5 Data Collection Procedures
| The daylight model testing site was chosen at the roof of Watt Hall on
! the USC campus where there is a large open area raised above some
ground level obstructions. Thus, a clear view of the sky is met for the
| | required environment. It was also conveniently located for working
i with the physical model. The entire series of tests were basically done
with the models facing south on a fixed stand. Some tests were
measured in four orientations.
The DATALIT program will record data that is needed for the tests,
including date, time, sky condition, model test variable descriptions,
j j The measurement sequence itself went as follows. Before each test, I
designed the order of different cases to be tested. I also noted the date,
time ,and sky conditions that I will use for later computer data input.
Next, I put all six sensors together to calibrate them first in order to get
40
equal readings of the sensors. This is a very important step, because we
can find whether these sensors are working correctly by looking at the
correction factor. I have the option to accept the shown calibrations, re
acquire calibration data, remove a bad sensor from calibration
averaging, restore a removed sensor, or employ factory calibrations.
Then I placed a sensor on the top of the model to measure outside
illumination. At the same time, I put the rest of the sensors into the
model, and placed them in right, middle and left rows. Diffuse outdoor
illumination was measured by shading the sensor with one 1' by 1/2'
poster held about 10" to 12" above it, blocking all direct sun. After
inputting all the data asked by the sequence screens, such as the room
dimension, window information, surface reflectance, the DATALIT
program was designed to record all the sensors' illumination in order. A
second run was performed, without the shading device, producing total
outdoor illuminance on the exterior sensor. A serial of forms were
designed to translate the data from computer output (Figure 4-7).
4.6 Problems
A lot of problems arose during the tests, some as a result of working
outdoors and some simply operating difficulties with taking
measurements. The biggest problem with depending on the sun as a
light source for a study of this kind was getting consistently sky
41
(S E N S O R S ’ L O C A T I O N ) O U T
\ \
3
CASE .1
> * b f l m n : t
CASE.2
E t= O U T D O O R T O T A L I L L U M I N A T I O N
Ed= O U T D O O R D IF F U S E I L L U M I N A T I O N
CASE.3
CASE.4
CASE.S
CASE.6
CASE.7
CASE. 8
Fig 4 -7 Testing Record Form (F O O T C A N D L E S )
42
conditions at the right time of day. I sometimes had to delay tests for as
long as a week in order to get really clear or overcast sky conditions.
Sunstroke was a surprise side effect of standing out on the roof for
hours at a time. Wind was also an occasional problem. Sometimes the
blowing sheet make the sensor's calibration impossible. Sometimes the
scattering sheets of data or blowing the attached overhang out of their
proper horizontal position delayed the experiment. Computer operation
sometimes caused unnecessary harassment. Unexpected program jams
or the low level battery power also made havoc of the results.
43
CHAPTER 5
DATA ANALYSIS
This section analyzes the results of the daylight tests on specific
variables in light of the initial assumptions on light plenum
performance. To review, the variables tested were:
(1) clerestory height (2) light plenum inner depth
(3) control device application (4) duct work integration.
The starting assumptions were that the light plenum could improve the
quantity and quality of light in a space and that the above variables
would make a difference. Systems were tested under both clear and
overcast sky conditions at the equinox sun angle. The analysis
compares daylight factors measured throughout the space, average
values under real sky conditions with both clear and diffuse plenum
openings, and the evenness of the light distribution as measured by the
difference between maximum and minimum daylight factors. Assuming
lighting requirement for most office work is 50-100 footcandles, and an
average outdoor clear sky illumination at 4 PM on the equinox is
4300 footcandles, ( it is 900 footcandles for overcast sky illumination
at the same time, but this condition is inappropriate for areas with
predominantly clear skies like Los Angeles.) the minimum daylight
factors in this case should be between 1.16 ~ 2.3 [Marc Schiler, 1992:
p.99]. If we count the glazing /window ratio (subtracting mullion parts)
at about 80% and the transmittance factor about 65% ( clerestory
glazing 90%, view glazing 40%) into the real office situation, we
should apply a factor of 70% to interior illuminations of the testing
45
model. That is, the imnimum daylight factors to aim for are between
1.6 ~ 3.2 in this tests.
i;
5.1 Base Light Plenum vs. Conventional Offices
a
j !
The first area to investigate was the relationship between the base light
I plenum and two conventional office cases (Figure 4-2). The office
| module with a 12' ceiling and 3' clerestory was chosen as the base light
plenum case. The light plenum had a specular reflective surface and
| had a depth of about 20'. One conventional office had no plenum with a
12' ceiling height, the other had a plenum from the window wall to the
| back of the room with 9' ceiling height.
| i
| In the clear sky tests, the average daylight factor for 12' ceiling case
j i
! was 11.47, for 9' ceiling case was 6.12, and 9.56 for plenum with clear
rear opening, 7.97 for plenum with diffuse rear opening. At 25' from
window, the daylight factors for both clear and diffuse light plenum
i j
| opening case were almost identical at 3.2 and 3.17 versus 4.15 for 12'
j ceiling case and 1.39 for 9' ceiling case (Figure 5-1). Table 5-1 is a
i f
summary of daylight factors' comparison. Both averages and values at
; | 25' from window for system with light plenum exceed the daylight
factor specified earlier as needed for adequate illumination assuming
average outdoor illumination for equinox.
Under overcast sky conditions (Figure 5-2), the average daylight
INTERIOR ILLUMINATION COMPARISON IN DF
CLEAR SKY
40
35
6 ? 30
F 25
20
q 10
25 20
S E N S O R S P O S I T I O N (Ft)
-m - CASE1-C - + - CASE2-C H*r- CASE6-C S - CASE6d-C
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY
20----------------------------------------------------------
8 ----------------------------------------------------------------------------------
16
R ( OUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 1 0 1
DF(25’) DF(AVG)
88888 CASE.1-C H CASE.2-C § | ^ CASE.6-C [Tfq CASE.6d-C
Figure 5-1 Light plenum vs. base cases, illumination comparison, clear sky
DAYLIGHT FACTOR %
INTERIOR ILLUMINATION COMPARISON IN DF
OVERCAST SKY
40
35
h 25
20
a 10
20 25
S E N S O R S ’ L O C A T I O N (Ft)
CASE.1 -O — CASE.2-0 CASE.6-Q - e - CASE.6d O
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY
EQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 1 K
A
DF(25’ ) DF(AVG)
CASE.1 -O CASE.2-0 ^ 3 CASE.6-0 FEB CASE.6d-0
Figure 5-2 Light plenum vs. base cases, illumination comparison, overcast
factors for the 12' ceiling case was 13.21,9' ceiling was 8.77, versus
9.98 for plenum with clear opening case and 8.44 for diffuse one. At
25' from window, the daylight factor for 12' was 4.69,1.87 for 9 ', 2.57
for the clear case, and 2.52 for the diffuse case (Table 5-2).
CASE
IN
COM PARISON
kYLIGHT FACTOR
Average
DF.
25'
DF.
M ax/M in
DF.
C .I 12' ceiling height case 11.47 4.16 5.73
C.2 9' ceiling height case 6.12 1.39 11.38
C.6 Plenum /clear opening 9.56 3.17 6.84
C.6d Plenum /diffuse opening 7.97 3.2 5.66
Table 5-1 Base light plenum VS. conventional office cases under clear sky
CASE
IN D^
COM PARISON
l YLIG H T FACTO R
Average
DF.
25’
DF.
M ax/M in
DF.
C.1 12' ceiling height case 13.21 4.69 6.06
C.2 9' ceiling height case 8.77 1.87 12.86
C.6 Plenum /clear opening 9.98 2.57 10.86
C.6d Plenum /diffuse opening 8.44 2.52 9.37
Table 5-2 Base light plenum VS. conventional office cases under overcast sky
Although the reflective plenum under overcast sky seemed not work as
good as clear sky, the average daylight factor throughout the plenum
49
again exceeded the needed value for adequate illumination. The diffuse
rear plenum opening also worked better than clear case under overcast
sky condition. As we look at the gradient of these plots, the smaller the
gradient is, the evenner the light distribution. "Contrast ratio" was used
to decide the evenness of light distribution. The contrast ratio is a value
by dividing the minimum daylight factor with the maximum daylight
factor. The smaller the contrast ratio, the better the light distribution.
Under clear sky, the light plenum with diffuse rear opening and 12'
ceiling case have the most even light distribution of 5.66 and 5.73
respectively versus 6.84 for plenum with clear opening, and the 9'
ceiling case had the worst light distribution of 11.38 contrast ratio.
OVERCAST
B CASE.1 B C A SE .2 B CASE.6 □ CASE.6d
Figure 5-3 Light plenum VS. base office case in contrast ratio
Likewise, in overcast sky condition, the contrast ratio showed that the
50
DAYLIGHT FA C TO R %
DAYLIGHT THROUGHOUT LIGHT PLENUM
CLEAR SKY
4
3
2
1
0
-1
-2
-3
-4-
3.44
JQHT GAIN FROM PLENUM
LIGHT LOST DUE TO PLENUM
_________-3.5
D F(25’ ) DF(AVG)
B S S 9 CLEAR d iffu se
LIGHT THROUGHOUT LIGHT PLENUM
OVERCAST SKY
LIGHT GAIN FROM PLENUM
0
<
O
-2.122.17
LIGHT LOST DUE TO PLENUM
DF(25’ )
RSSS CLEAR GLAZING DIFFUSE GLAZING
Figure 5-4 Light gain and light lost through light plenum
9’ ceiling case, again, was the worst in light distribution. For the 9'
ceiling case the ratio was 12.86, clear plenum opening was 10.86,
diffuse case was 9.37, and 12' ceiling case was 6.06 (Figure 5-3).
Looking at clerestory glazing alone, we wonder how much light comes
through it ? For average daylight factors, we got 3.44 difference
between plenum with clear opening and 9' ceiling case, 1.85 for plenum
with diffuse opening and 9’ ceiling. On the other hand, we only lost
daylight factor of 1.91 by using light plenum with clear opening, 3.5
from diffuse plenum opening comparing to 12' ceiling case. At 25' from
window, daylight factor arose 1.78 through clear plenum opening, and
1.81 by diffuse plenum opening. It is interesting that the daylight factor
dropped 0.98 from clear plenum opening and 0.95 for diffuse plenum
opening (Figure 5-4). It was a surprise that the diffuse rear plenum
opening worked better than the clear one.
5.2 Impact of Inner Light Plenum Depth
The next variable to consider is inner light plenum depth for both clear
and diffuse plenum opening characteristic. Floor height was kept at 12',
the plenum height at 9', and the inner light plena were tested at 5’ , 10',
15', 20’ , and 25' deep (Figure 4-4). Figure 5-5 and Figure 5-7 show
comparisons of daylight factors through the room for each light plenum
depth, Figure 5-6 and Figure 5-8 plot average daylight factor and
daylight factor at 25' from the window wall against inner plenum
52
DAYLIGHT FACTO R % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY /DIFFUSE GLAZING
40
35
30
25
20
15
10 15
S E N S O R S ’ L O C A T I O N (Ft)
20 25
-m - CASE.3-C - + - CASE.4-C CASE.5-C
- e - CASE.6-C CASE 7-C
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY/ CLEAR GLAZING
40
35
30
25
20
20 25 15
S E N S O R S ’ L O C A T I O N (Ft)
|
CASE.3-C —I — CASE.4-C CASE.5-C
- e - CASE.6-C - X - CASE.7-C
Fig 5-5 Impact of light plenum inner depth, illumination comparison, clear sky
53
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY /DIFFUSE GLAZING
fc ?
K
O
H
fc
O
P
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
12.16
1
....II
tm m m tZ >>>
DF(25’ ) DF(AVG)
CASE.3d-C
FFffl CASE.6d-C
CASE.4d-C |
CASE.7d-C
CASE.5d-C
20
18
16
14-
12 -
10
8
6
4-
2
0
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/ CLEAR GLAZING
1 2 9 4
■ ■ ■ ■ ) ! » > > >
iini>>>>
« ■ ■ ■ ! > > > >
6 ?
O S
e
§ fc
H
ffi
O
p
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
4 4 ,3 3
-5:10"
DF(AVG)
CASE.3-C
CASE.6-C
CASE.4-C |
CASE.7-C
CASE.5-C
Fig 5-6 Impact of light plenum inner depth, DF(25’ )& D F(A vg) comparison, clear sky
54
2036^8308837
DAYLIGHT FACTO R % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON
OVERCAST SKY/CLEAR GLAZING
40
35
30
25
20
10
25 10 20
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE-3-O - + - CASE.4-0 CASE.5-0
- S - CASE.6-0 CASE.7-0
[ i
INTERIOR ILLUMINATION COMPARISON
OVERCAST SKY/DIFFUSE GLAZING
40
35
30
25
20
25 20 15
S E N S O R S ’ L O C A T I O N (Ft)
CASE.3-0 — CASE.4-0 CASE.5-0
- e - CASE.6-0 -*S- CASE.7-0
Fig 5-7 Impact of light plenum inner depth, illumination comparison, overcast
55
DAYLIGHT FACTO R % DAYLIGHT FA C TO R %
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/CLEAR GLAZING
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
1
R
DF(25’ ) DF(AVG)
BS S 8 CASE.3-0 CASE.4-0 |H § CASE.5-0
HTffl CASE.6-0 ^ CASE.7-0
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/DIFFUSE GLAZING
20
18
16
14-
12
10
8
6
4-
2
0
■ ■ » ► > > >
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
9.84
3:09
D F(25’ ) DF(AVG)
888S CASE.3-0 H | CASE.4-0 ^ 3 CASE.5-0
CASE.6-0 CASE.7-0
5-8 Impact of light plenum inner depth, DF(25’ )& D F(A vg) comparison, overcast
56
DAYLIGHT FA C TO R % DAYLIGHT FACTO R %
CONTRAST RATIO COMPARISON
CLEAR SKY/DIFFUSE ILLUMINATION
12.50
6.04 5.99 6.33
CLEAR/GLAZING DIFFUSE/GLAZING
CASE.3-C H i CASE.4-C |
EEEB CASE.6-C E g ) CASE.7-C
CASE.5-C
IMPACT OF LIGHT PLENUM INNER DEPTH
OVERCAST SKY
11,33
J
nir>>>
I l l r S / /
■ l l r / / / i
I ll y //
l i ar> > > {
iia » > > > ;
lllr//>
! ■ » ► > > ?
DIFFUSE/GLAZING CLEAR/GLAZING
CASE.3-0 ■ ■ CASE.4-0 |
ETffl CASE.6-0 ^ CASE.7-0
CASE.5-0
Fig 5-9 Impact of light plenum inner depth, contrast ratio comparison
57
7029691
depth. Figure 5-9 shows the contrast ratio of different inner plenum
depth comparison under both clear and overcast sky conditions. Table
5-3 and 5-4 are the summary of the comparisons.
CASE COM PARISO N DF (Avg.) DF at 25' DF(max/min)
IN BDAYLIGHT FACTO R Clear Diffu Clear Diffu Clear Diffu
C.3 5' inner plenum depth 11.3 12.1 5.1 4.18 2.65 6.04
C.4 10* inner plenum depth 9.88 10.0 4.6 3.85 2.97 5.56
C.5 15' inner plenum depth 7.56 8.88 3.14 3.49 5.0 5.99
C .6 20* inner plenum depth 9.55 7.97 3.17 3.2 6.85 5.67
C.7 25* inner plenum depth 13.0 7.55 2.98 2.67 12.5 6.33
Table 5-3 Light plenum inner depth comparison under clear sky
CASE COM PARISON DF (Avg.) DF at 25’ DF(max/min)
IN EIAYLIGHT FACTO R Clear Diffu Clear Diffu Clear Diffu
C.3 5' inner plenum depth 10.0 9.84 3.91 2.73 5.6 8.6
C.4 10' inner plenum depth 8.75 9.38 3.33 3.12 6.62 7.39
C.5 15' inner plenum depth 7.9 8.76 2.86 3.09 7.67 7.42
C.6 20' inner plenum depth 8.14 8.30 2.01 2.61 11.3 8.73
C.7 25' inner plenum depth 7.98 8.03 1.48 1.97 15.3 11.3
Table 5-4 Light plenum inner depth comparison under overcast sky
The test results show that changing the inner light plenum depth do
58
have some influence on daylight factors inside the room. The daylight
factor at 25' from window decreased 36% from 5’ inner plenum depth
case to 25’ case under clear sky clear rear plenum opening. When only
considering with the light quantities, that is, the value of daylight
factor, the cases with clear plenum rear opening work better than
diffuse cases. However, the former cases usually caused unwanted
glare or at least very high contrast for certain distance respective to
different plenum depth. For instance, in the 5’ inner plenum depth case,
the daylight factor at the 10' location was much higher than at 5' from
the window. The same situation happened in the 10' depth case. It
meant that direct sun light causing the glare was a big problem for
those narrow plenum cases, even though they might have higher light
level. On the other hand, under overcast sky condition, there is a 62%
of DF value decrease at 25' from the window wall between the 5’ and
25' inner plenum depth for clear rear plenum opening, and a 27.8%
decrease for diffuse case. The results show that under overcast sky
condition, the characteristic of the inner plenum opening is more
critical factor for light distribution than under clear sky. For
considering an even distribution, we might look at the contrast ratio
(Figure 5-9). It is quite clear when the plenum rear opening is clear, the
wider the light plenum, the more uneven the light distribution, no
matter under clear sky or overcast sky conditions. The diffuse opening
gives less difference in contrast ratio comparison for all of the cases.
! ! Overall, the results suggest that one should choose the proper light
plenum inner opening to light inner offices. It is difficult to give a
optimal plenum inner depth to suit for all situations. However, the 20'
i i
i ,
I inner depth light plenum with diffuse rear plenum opening case, under
! j clear sky, had daylight factor of 3.2 at 25' from window, and average
l | .
daylight factor of 7.97. These values are enough to provide at lease 100
FC throughout the space assuming typical outdoor illumination for the
| equinox. For considering both light level and contrast ratio, it seems to
i be the best case among these 5 different inner depth cases comparison.
More tests need to be done to ascertain the effect of the change of the
sun angle in different season, and varying the light plenum inner depth
only without combining with a view window.
i j
5.3 Impact of Clerestory Height
i The next variable to consider is the impact of clerestory height on
i j
indoor illumination. Tests were done on constant 12' floor to floor
height with 8', 9', and 10' ceiling having 4', 3', and 2' clerestories
respectively (Figure 4-3). Figure 5-10 through 5-13 compared daylight
factors for each ceiling height under both clear and overcast sky
conditions. In all cases, there is not a constant increase in light level
throughout most of the space with increasing the clerestory height. This
result told us that the daylight factor at the back of the room was
influenced by the light coming from both clerestory and view window.
60
DAYLIGHT FACTOR % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY/CLEAR GLAZING
100
90
80
70
60
50
40
30
20
10
*
15 20 25 5
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE.8-C CASE.9-C - x - CASE.10-C
- B - CASE.8T-C — X - CASE.9T-C - A r CASE.1 OT-C
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY/DIFFUSE GLAZING
40
35
30
2 5
20
10
10 20 25 5 15
S E N S O R S ’ L O C A T I O N (Ft)
- * • CASE.8-C - + - CASE.9-C -»*- CASE.10-C
Fig 5-10 Impact of clearstory height, illumination comparison, clear sky
6 1
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/CLEAR GLAZING
2 4 .® .® 7
REQUIRED DAYLIGHT FACTOR FDR 1 0 0 fc
1 1 . 6 1
DF(25’ ) DF(AVG/DIFFUSE)DF(AVG/TOTAL)
CASE.8-C CASE.9-C CASE.10-C
20-
18-
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/DIFFUSE GLAZING
16-
14-
12-
REQUIRED DAYLIGHT FACTOR FOR ILLU M IN A TIO N OF 100 fc
DF(25’ ) DF(AVG/DIFFUSE)
CASE.8-C CASE.9-C CASE.10-C
Fig 5-11 Impact of clearstory height, DF(25’ )& D F(A vg) comparison, clear sky
62
^5201^7879882746
^87556890200489620^61
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON
OVERCAST SKY/CLEAR GLAZING
40
35
30
25
20
10
20 25
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE.8-0 —1 — CASE.9-0 -*«- CASE.10-0
INTERIOR ILLUMINATION COMPARISON
OVERCAST SKY/DIFFUSE GLAZING
40
35
30
25
20
10 20 15
S E N S O R S ’ L O C A T I O N (Ft)
25
-m - CASE.8-0 - + - CASE.9-0 CASE.10-0
Fig 5-12 Impact of clerestory height, illumination comparison, overcast
20 -
18 -
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/CLEAR GLAZING
16-
14-
O S
e
fc
a
o
3
<
Q
IIEQUIREO DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
DF(25’ )
9,55-
DF(AVG)
CASE.8-0 CASE.9-0 CASE.10-0
20
18
16
14
12
10
8
6
4
2
0
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/DIFFUSE GLAZING
O S
o
< <
fc
E h
£
p
REQUIRED DAYLIGHT FACTOR FOR ILLU M IN A TIO N OF 1
DF(25’ ) DF(AVG)
CASE.8-0 CASE.9-0 CASE.10-0
Fig 5-13 Impact of clerestory height, DF(25’ )& D F(A vg) comparison, overcast
DAYLIGHT FA C TO R % DAYLIGHT FACTO R %
CONTRAST RATIO COMPARISON
26.1128.9432.7fL E A R S K Y
10.5810.39
CLEAR GLAZING DIFFUSE GLAZING
CASE.8-C CASE.9-C CASE.10-C
CONTRAST RATIO COMPARISON
OVERCAST SKY
14:47
10.68
CLEAR GLAZING DIFFUSE GLAZING
CASE.8-0 CASE.9-0 CASE.10-O
Fig 5-14 Impact of clerestory height, contrast ratio comparison
65
82
1954429554
In fact, without plenum, light from the view window was much more
than it from the clerestory. As expected, I again found that the light
plenum did help to increase the illumination at the back of the room
from this testings, especially in the diffuse plenum rear opening case..
For the light distribution comparison, under clear sky condition, the
characteristic of light plenum rear opening caused totally different
results. Under overcast sky condition, neither larger clerestory nor
smaller clerestory would get good distribution. The detail is following.
CASE COM PARISO N DF (Avg.) DF at 25’ DF(Max/Min)
IN iYLIG H T FACTOR Clear Diflu Clear Diflu Clear Diffu
C.8 2 ' clerestory height 11.6 8.78 3.47 2.1 26.1 10.5
C.9 3' clerestory height 9.64 7.28 3.17 1.72 28.9 10.3
C.10 4' clerestory height 8.48 6.43 2.62 2.48 32.7 6.35
Table 5-5 Clerestory height comparison under clear sky
Under clear sky, see Table 5-5, in clear rear plenum opening case, the
daylight factor at 25' from window was 3.47 for 2' clerestory , 3.17 for
3' clerestory, and 2.62 for 4' clerestory case. On the other hand, by
using a diffuse rear plenum opening, it was 2.1 for 2' clerestory, 1.72
for 3' clerestory, and 2.48 for 4' clerestory case. It meant that diffuse
plenum characteristic help balance the inner illumination, even though
the average daylight factor was lower than clear opening case.
6 6
CASE CO M PARISO N DF (Avg.) DF at 25’ DF(Max/Min)
IN iYLIG H T FACTO R Clear Diffu Clear Diffu Clear Diffu
C.8 2 ’ clerestory height 7.55 10.0 1.89 2.52 11.5 10.7
C.9 3' clerestory height 6.52 6.77 2.23 3.16 8 5.83
C.10 4' clerestory height 9.55 7.47 1.51 2.54 17.6 8.05
Table 5-6 Clerestory height comparison under overcast sky
Table 5-6 shows the daylight factor ,under overcast sky, at 25' from the
window was 1.89 for 2' clerestory, 2.23 for 3' clerestory, and 1.51 for
4' clerestory case with clear rear plenum opening. For the diffuse case,
it was 2.52 for 2' clerestory, 3.16 for 3' clerestory, and 2.54 for 4'
clerestory case. The average daylight factors in clear rear plenum
opening were 7.55, 6.52, and 9.55 related to 2', 3' and 4' clerestory
height. In diffuse case, they were 10.05, 6.77, and 7.47 respectively.
That is, under overcast sky condition, clerestory heights of 2' and 4'
had higher average light distribution. However, the 3' clerestory case
had a higher value at the back of the room. Figure 5-14 shows the
contrast ratio of different clerestory height comparison under both clear
and overcast sky condition. It is quite interesting that under clear sky
condition, the 2' clerestory case had better light distribution than the
others in the clear rear plenum opening tests, while 4' clerestory case
did a better distribution in diffuse rear plenum opening. On the
contrary, 3' clerestory height had better light distribution in overcast
67
sky tests. This again tells us that light comes from both view window
and clerestory window. When the floor height is set to a constant, the
variation of interior light level will not necessarily be of proportional to
the change of clerestory height. Therefore, the proportion of clerestory
and view window need to consider both light quality and quantity. The
fact is that a smaller clerestory has higher interior light level, but worse
light distribution. A large clerestory results in lower light level, but
better light distribution.
5.4 Light plenum with control device
In this section, a base light plenum case was chosen to compare with
two control devices (Figure 4-5). A rear mirror was used on the rear
part of the plenum, and was expected to enhance the illumination at the
back of the room. An overhang with a reflective surface was designed
to block all direct sun on the equinox at 34 degrees latitude. In all tests
under both clear and overcast sky conditions, the plenum with rear
mirror case, DF values were very close to those with base light plenum
case. Direct sun admitted with these two cases (no sun control) caused
an abrupt increase in daylight factor near the window. By contrast, the
overhang blocked direct sun and consequently the light levels near the
window were fairly even. DF values for the overhang were consistently
lower than for the other two designs throughout the room (Figure 5-15
to Figure 5-18).
6 8
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON IN DF
CLEAR SKY/CLEAR PLENUM GLAZING
40
35
30
25
20
20 15
S E N S O R S ’ L O C A T I O N (Ft)
25
-m - CASE.11-C - + - CASE.12-C CASE.13-C
INTERIOR ILLUMINATION COMPARISON IN DF
CLEAR SKY/DIFFUSE PLENUM GLAZING
40
35
30
25
20
10
20 25
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE.11-C —I — CASE.12-C H*r- CASE.13-C
Fig 5-15 light plenum vs. control devices, illumination comparison, clear sky
69
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/CLEAR PLENUM GLAZING
20
18
16
14
12
10j
8
6
4-
2
0
EQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
-------------------------------------------------7.35
ST.06 2 .2 0
DF(25’ ) DF(AVG)
CASE.11-C CASE.12-C ^ 3 CASE.13-C
20
18
16
14
12
10
8
6
4
2
0
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/DIFFUSE PLENUM GLAZING
F EQUIRED DAYLIGHT FACTOR FOR ILLUM INATION OF 100 fc
6.37 6.41
DF(25') DF(AVG)
CASE.11-C ■ ■ CASE.12-C CASE.13-C
Fig5-16 Light plenum vs. control devices, DF(25’ )&DF(avg) comparison, clear sky
70
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
INTERIOR ILLUMINATION COMPARISON IN DF
OVERCAST SKY/CLEAR GLAZING
40
35
30
25
20
15
10
20 25 10
S E N S O R S ’ L O C A T I O N (F iO
CASE.11-0 -+ — CASE.12-0 -**- CASE.13-0
INTERIOR ILLUMINATION COMPARISON IN DF
OVERCAST SKY/DIFFUSE GLAZING
40
35
30
25
20
20 25
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE.11-0 - t — CASE.12-0 CASE.13-0
Fig5-17 light plenum vs.control devices, illumination comparison, overcast
71
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/CLEAR GLAZING
20-
o s
fa
H
C5
<
Q
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100 fc
9.98 9 7 9
DF(25’ ) DF(AVG)
CASE.11-0 I CASE.12-0 I CASE.13-0
2 0 -
18-
DF(25’) & DF(Avg) COMPARISON
OVERCAST SKY/DIFFUSE GLAZING
16-
14-
f c \ °
12-
REQUIRED DAYLIGHT FACTOR FOR ILLUM INA TION OF 100fc
2.52 2 71
DF(25’) DF(AVG)
CASE.11-0 Wm CASE.12-0 S 3 CASE.13-0
Fig5-18 light plenum vs.control devices, DF(25’ )& D F(A vg) comparison, overcast
72
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
CONTRAST RATIO COMPARISON
CLEAR SKY
20
18
16
14
12
CLEAR/GLAZING DIFFUSE/GLAZING
B S 8 CASE.11-C CASE.12-C CASE.13-C
CONTRAST RATIO COMPARISON
OVERCAST SKY
10.86
s s
CLEAR/GLAZING DIFFUSE/GLAZING
8888 CASE.11-0 CASE.12-0 CASE.13-0
Figure 5-19 Light plenum vs.control devices, contrast ratio comparison
Average daylight factor under the clear sky test with clear rear opening
was 7.35 for base case versus 6.98 for the plenum with rear mirror case
and 3.78 for the overhang. With diffuse case, it was 6.37 for base case
versus 6.41 for rear mirror and 3.51 for overhang. At 25' from the
window, the rear mirror had the highest value of 2.2, and overhang had
the lowest of 1.67, versus base plenum case of 2.06 in clear rear
opening tests. In diffuse rear opening test, rear mirror case again had
the highest value of 2.21. It was a surprise that even the overhang got
higher value than base plenum case (Table 5-7). It should noted that all
three values came close together at the back of the room where the
influence of the direct sun is the least.
CASE COM PARISON DF (Avg.) DF at 25’ DF(Max/Min)
IN kYLIGHT FA CTO R Clear Diffu Clear Diffu Clear Diffu
C .ll base light plenum 7.35 6.37 2.06 1.65 8.65 9.73
C.12 plenum / rear mirror 6.98 6.41 2.20 2.21 7.7 7.21
C.13 plenum / overhang 3.78 3.51 1.67 1.73 5.14 4.73
Table 5-7 Light plenum VS. control device DF comparison under clear sky
The overhang gives the most even light distribution of the three
applications with the contrast ratio of 5.14 in clear rear opening test.
The rear mirror case is next with the contrast ratio of 7.21, and base
case is a distant third with that of 9.73 due to direct sun (Figure 5-19).
74
Testing under overcast sky condition, average daylight factors with
clear rear opening are 9.98 for base case, 9.79 for rear mirror case
and5.38 for overhang. The values at 25' from window are 2.57 with
base plenum, 3.16 with rear mirror and 2.86 with overhang (Table 5-8).
As before, the three systems are closest together at the back of the
room. Even under overcast sky condition, the daylight factor at 25' and
the averages for all systems are at least as high as required. The
contrast ratio is 10.8 with base plenum case, 8.85 with rear mirror and
4.5 with overhang. Obviously the overhang again gave the most even
light distribution, but the least daylighting. The rear mirror case did
help to enhance light level at the back of the room; nevertheless, it did
not help to balance light distribution as much as overhang does.
CASE COM PARISO N DF (Avg.) DF at 25* DF(Max/Min)
IN l YLIG H T FACTOR Clear Diffu Clear Diffu Clear Diffu
C .l l base light plenum 9.98 8.44 2.57 2.52 10.8 9.37
C.12 plenum / rear mirror 9.79 8.07 3.16 2.71 8.85 8.22
C.13 plenum / overhang 5.38 6.98 2.86 3.87 4.5 4.43
Table 5-8 Light plenum VS. control device DF comparison under overcast sky
5.5 Duct work integration
The last variable to consider is the duct work integration. Two systems
have been examined: one is a plenum with a corridor mechanical duct
system; the other is a plenum with a perimeter supply duct system
(Figure 4-6). Figure 5-20 through 5-23 show comparisons of daylight
factors through the room with different duct systems, and Figure 5-24
shows the contrast ratio of systems under both clear and overcast sky.
Since one reason for considering duct work integration was to test the
feasibility of daylighting inner offices as well as perimeter offices
through the plenum, the plenum with duct which parallel to window
wall is of particular important here.
From the test results, the system with ducts perpendicular to the
window wall did have some effect on the function of the light plenum.
In the perimeter supply duct system, the duct parallel to window wall
blocked significantly more daylight into the interior than the base case,
and therefore, reduced the performance of the light plenum. By
installing a light shelf in the front of the room, the problem of daylight
blocking from the duct parallel to the window wall could be
moderated. The graphs of both duct systems' daylight factor near the
window wall were very close in all testing. However, they were
clearly different at the back of the room, such as at 25' from the
window wall where the clerestory affect the inside light level most. The
case with light shelf having clear openings peaked at 10' from
76
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY/CLEAR GLAZING
40
35
f c ? 30
O S
S 25
« :
t 20
B
£ 3 15
c
Q
20 25 15
S E N S O R S ’ L O C A T I O N (Ft)
-m - CASE.14-C —I — CASE.1 S-C -a s - CASE.16-C
INTERIOR ILLUMINATION COMPARISON
CLEAR SKY/DIFFUSE GLAZING
40
35
f e ? 30
O S
° 25
£ 20
a s
M 15'
Q 10
25 20
S E N S O R S ’ L O C A T I O N (Ft)
-m~ CASE.14-C — 1 — CASE.15-C CASE.16-C
Fig 5-20 Light plenum vs. duct work, illumination comparison, clear sky
DAYLIGHT F A C T O R % DAY LIG H T F A C T O R %
DF(25’) VS. DF(Avg) COMPARISON
CLEAR SKY/CLEAR GLAZING
20 -
18-
16-
14-
12-
REQUIRED DAYLIGHT FACTOR FOR ILLUMINATION OF 100 fc
3.58 - 3-43
DF(25’ ) DF(AVG)
CASE.14-C I B CASE.15-C l==^ CASE.16-C
20
18
16
14
12
10
8
6
4
2
0
DF(25’) & DF(Avg) COMPARISON
CLEAR SKY/DIFFUSE GLAZING
REQUIRED DAYLIGHT FACTOR FOR ILLUMINATION OF 100 fc
-5 3 4
3,70 3.62
DF(25’ ) DF(AVG)
CASE.14-C ■ ■ CASE.15-C E S CASE.16-C
Fig 5-21 Light plenum t o . duct work, DF(25’ )& D F(A vg) comparison, clear sky
7 8
4
^28690
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
LIGHT PLENUM VS.DUCT SYSTEM
OVERCAST SKY/CLEAR GLAZING
40
35
30
25
20
15
10 20 25 15 5
S E N S O R S ’ L O C A T I O N
HBK CASE.14-0 — + — CASE.15-0 CASE.16-0
LIGHT PLENUM VS.DUCT SYSTEM
OVERCAST SKY/DIFFUSE GLAZING
40
35
30
25
20
15
20 25
S E N S O R S ’ L O C A T I O N
-m - CASE.14-0 - + - CASE.15-0 -* e- CASE.16-0
Fig 5-22 light plenum vs.duct work, illumination comparison, overcast
DAYLIGHT FA C TO R % DAYLIGHT FA C TO R %
LIGHT PLENUM VS.DUCT SYSTEM
OVERCAST SKY/CLEAR GLAZING
20-
18-
16-
14-
IEQUIRED DAYLIGHT FACTOR FOR ILLU M IN A TIO N OF 100 fc
& . 2 6 "5t 20-& 38
D F(25’ ) DF(AVG)
CASE.14-0 ■ ■ CASE.15-0 i= = l CASE.16-0
20-
18-
16-
14-
LIGHT PLENUM VS.DUCT SYSTEM
OVERCAST SKY/DIFFUSE GLAZING
IIEQUIRED DAYLIGHT FACTOR FOR ILLU M IN A TIO N OF 100 fc
DF(25’ ) DF(AVG)
CASE.14-0 mm CASE.15-0 CASE.16-0
Fig 5-23 Light plenum vs.duct work, DF(25’ )& :D F (A vg) comparison, overcast
8 0
CONTRAST RATIO COMPARISON
CLEAR SKY/DF(MAX)/DF(MIN)
PS
0
H
U
<
k
1
C
Q
20
18
16
14-
12-
10
8
6
4-
2
0
-7.58.
CLEAR/GLAZING
8.32
DIFFUSE/GLAZING
CASE.14-C I CASE.15-C I CASE.16-C
CONTRAST RATIO: PLENUM VS.DUCT SYSTEM
OVERCAST SKY
3.49
6.78
4 . 4 2 .4 ,4 8 ..
3 . 0 8
"3:62
CASE.14-0 CASE.15-0 I CASE.16-0
Fig 5-24 Light plenum vs. duct work, contrast ratio comparison
81
window wall under clear sky. This means that certain solar angles will
cause a glare problem from the split space between light shelf and
plenum. Table 5-9 shows the summary of the base plenum case and
the different ducted daylight factors under clear sky. The average
daylight factor for plenum with the light shelf case was 9.11 close to
that of the base light plenum case at 9.56, and superior to 5.26 for the
perpendicular duct case and 5.2 for the parallel duct system in the clear
rear plenum opening tests. The daylight factor at 25' from the window
wall the plenum with light shelf case was 2.86, the perpendicular duct
case was 2.58, the parallel duct case was 1.83, and the base light
plenum was 3.17. This tells us that ducts, no matter in which locations
inside the plenum, will block daylight, and reduce the interior light
CASE CO M PARISO N DF (Avg.) DF at 25' DF(Max/Min)
IN DAI/L IG H T FACTO R Clear Diflu Clear Diffu Clear Diffu
C .l l base light plenum 9.56 7.97 3.17 3.2 6.84 5.66
C .I4* plenum /perpen duct 5.26 6.66 2.58 3.51 4.98 4.43
C.1S plenum /paralle duct 5.2 6.18 1.83 1.97 7.24 7.67
C.16 plenum / light shelf 9.11 5.34 2.01 1.71 5.25 6.91
Table 5-9 Duct work DF comparison under clear sky
* C. 14 plenum/ perpen duct = plenum with duct perpendicular to window wall
C. 15 plenum/ parallel duct = plenum with duct parallel to window wall
C. 16 plenum/ light shelf = plenum/ parallel duct + light shelf
8 2
level. A light shelf improves the interior light level. In the contrast
ratio comparison, the plenum with a light shelf results in a value of
5.25, and the perpendicular duct results in 4.98, both of which were
better than the plenum with a parallel duct which results in a value of
7.24. Due to no overhang, the base light plenum case of 6.84 was
worse than the others in light distribution except for the plenum with
parallel duct case. In general, daylight factors were smaller in the
diffuse rear plenum opening cases than for the clear cases. Otherwise,
the comparison in diffuse tests are almost the same as in the clear
cases.
Under overcast sky condition, Table 5-10 shows that plenum with duct
systems let in much less daylight than base light plenum case.
The light level distribution for an overcast sky was similar to that of a
clear sky. The average daylight factor for the base light plenum case
with a clear rear plenum opening was 9.98, for plenum with light shelf
CASES CO M PARISO N D F (Avg.) DF at 25’ DF(Max/Min)
IN DAI(T IG H T FACTO R Clear Diffu Clear Diffu Clear Diffu
C .ll base light plenum 9.98 8.44 2.57 2.52 10.8 9.37
C.14 plenum /perpen duct 3.58 3.70 1.52 1.41 5.55 6.17
C.15 plenum /paralle duct 3.43 3.62 1.10 1.06 7.58 8.32
C.16 plenum / light shelf 5.38 6.98 2.86 3.87 4.5 4.43
Table 5-10 Duct work DF comparison under overcast sky
83
it was 5.38, plenum with perpendicular duct was 3.58, and with
I parallel duct was 3.43. At 25' from the window wall, the value of
| daylight factor shows that light shelf could doubtless increase the light
| level at the back of the room. For a plenum with a perpendicular duct,
the value was only 1.52 ,and with a parallel duct was 1.1. However, it
I was 2.01 for the plenum with a light shelf close to the base plenum
case of 2.57. In the contrast ratio comparison, the base light plenum
case had the worst light distribution. It was interesting that the plenum
I
with light shelf case performed the best, probably because of diffuse
: sky light instead of direct sun light. The value of the contrast ratio for
i the plenum with a light shelf was 5.25, almost the same as the plenum
with a perpendicular duct of 5.55. The plenum with a parallel duct was
7.58, and the base light plenum case of 10.8 was the worst.
| After the tests with the duct system, the results tell us that the light
I plenum undoubtedly is feasible in modem office buildings, though the
| ducts will obstruct some of the incoming light. Trunk, or corridor
systems are preferable to perimeter systems. Especially under a clear
| sky, the average daylight factor or value at 25' from window wall, both
| duct systems exceeded the required light level for the equinox.
CHAPTER 6
CONCLUSION
6.1 Summary
From the scale model test results, certain theories about the light
plenum have been confirmed, such as it undoubtedly provides a means
of reflecting daylight to the interior of an office space. This study has
also tried to broaden the general understanding of the processes
involved in the hope that this would help architects design sun control
devices which fit their particular needs.
| One basic theory which has been confirmed is that light plena do not
I generally give higher average light levels in a space than rooms with no
plena, but they do improve the quality of light by reducing the
discomfort glare of a unilaterally sidelighted office space, and reflect
!
I more light deep into the space. Moreover, an effective combination of
contrast ratio and quantity of light can be obtained from the light
! plenum compared with the conventional unilaterally sidelit office with
! closed drop ceiling. This points out that light plenum is feasible in
today's office buildings wherever the closed drop ceiling was generally
existing.
i f
1
| The area of the light plenum opening influences the overall quantity of
1 light in the space. In fact, larger openings (smaller light plenum inner
I '
j depth) will result in greater quantities of light. However, initial field
i testing indicated that too large an opening can result in high contrast
8 6
ratios which are not conducive to a balanced composite illumination
gradient between the plenum light source and the sidelight. For a good
j daylighting design, not only the light quantity should be considered, but
j also the quality must be taken into account. Therefore, opening
i '
j | configurations should be carefully considered with both factors.
I
j i
| | One of the best ways to increase light levels deep in the space is to
j !
increase the height of the daylight aperture through increased ceiling
| and clerestory. However, increasing ceiling height has the drawback of
!
increasing construction costs significantly. From the test result, by
j keeping the floor to floor height constant, a smaller clerestory has
higher interior light level, but worse light distribution. A large
clerestory results in lower light level, but better light distribution.
Since the glare permitted by unshaded windows is not acceptable, the
more practical question is how do light plena compare with other
control devices. Overhangs can give equal shading, thus blocking
direct sun for striking works' desks. A rear mirror gives considerably
more illumination deep in the space, especially for lower sun angles.
This points out an important improvement of interior light quality by
utilizing the control devices. One major difference is that both windows
with a light plenum and with a rear mirror depend on direct sun for a
large percentage of indoor illumination. By contrast, overhangs are
designed to exclude all direct sun, using only sky light and light
8 7
reflected from the ground and other surfaces for interior daylighting.
Therefore, the light plenum and rear mirror produce higher light levels
than an overhang, and are more sensitive to changes in sun angle.
In general, drop ceilings are installed with ducts, and act as a return air
plenum in most offices. The testing results told us that the ducts did
block some daylight and reduced the performance of the light plenum,
especially with ducts parallel to window wall. However, for those light
plena with ducts parallel to the window wall, the interior illumination is
still improved compared to offices with a closed ceiling, especially
with the addition of a light shelf. While combining with light shelf, the
system would work even better by reducing the glare in the front of the
room and reflecting more light to the back of the room.
The light plenum with a clear opening did not give uniformly better
performance than an opening with diffuse characteristics. The clear
characteristic was much more sensitive to sun angle than the diffuse
opening. There may be glare problems with a clear opening caused by
the bright and concentrated light reflected from the ceiling, and very
high and peak illumination values they give a larger opening. Unlike
the clear opening, a diffuse characteristic helps to balance the interior
illumination, even though it generally produces lower light levels than a
clear one.
88
A light plenum, from the testing results, has better performance under
clear sky condition, and generally reach the required daylight factor for
adequate illumination in the equinox. On the other hand, the light
plenum does not work very well under overcast sky condition, because
there is less daylight and not direct beam sunlight entering the light
plenum.
My personal opinion is that people sometimes do hesitate to utilize
daylighting systems because they not only bring in the light but also
solar heat. Unlike other daylighting systems, the light plenum using
return air plenum as a light trap hopefully can reduce some cooling
load which is produced by the sun light. However, this is an area which
needs further study.
6.2 Design Guidelines
1) Utilizing a light plenum under the clear sky condition:
Since a light plenum does not work well under overcast sky conditions,
the light plenum is recommended primarily for areas with
predominantly clear skies.
2) Choosing a diffuse plenum opening:
If designing a simple light plenum, a diffuse rear opening is probably
89
better than a clear opening because it gives a more even light
distribution.
3) Combining with overhangs:
For south facades where direct sun is an important factor, a light
plenum with an overhang designed to block direct sun will give a better
combination of high light levels and good quality natural light than a
conventional office room ( having a closed drop ceiling) with unshaded
windows.
4) Using higher daylight aperture:
In general, increasing ceiling and clerestory height will raise light levels
deep in the space. Therefore, the higher the daylight aperture is, the
deeper the light will get in. Since the interior light levels are influenced
by both view window and clerestory, in the consideration of economy,
the effect of the different proportions between the view window and
the clerestory, has to be decided with a constant floor to floor height,
5) Selecting appropriate plenum opening:
Improper plenum opening (too big or too small) will degrade the
performance of light plenum. Therefore, the plenum opening
configurations should be considered to optimize the light plenum to the
specific demands of the day, month and time of the peak energy
demand and consumption charges.
APPENDIX
A. FOOTCANDLES MEASUREMENT
B. DAYLIGHT FACTOR
91
CONVENTIONAL OFFICE COMPARISON IN FOOTCANDLES
M ar 30’9 3
Clear
CASE .1-C
CASE .2-C
Et Ed___________________________________ OUT
2590 569 378 223 150 96 2590
2590 1333 1826 378 223 150 96 2590
2552 607 369 223 158 106 2552
2552 1333 1826 369 223 158 106 2552
2527 1321 383 259 163 123 86 2527
2438 1290 416 183 87 49 30 1280
2438 1276 387 182 90 53 34 2438
2400 1267 279 132 66 44 30 2400
Feb 22 93
Overcast OUT O U T
CASE .1-0
CASE .2-0
1 1536 418 239 143 85 65 1548
2 1638 467 276 164 101 77 1643
3 1688 445 234 138 88 67 1688
1 1581 370 143 68 36 26 1578
2 1553 373 157 79 43 29 1553
3 1559 332 132 65 36 26 1559
92
LIGHT PLENUM INNER DEPTH COMPARISON IN FOOTCANDLES
M ar 05’9 3
Clear
CASE .3-C
ram a 2 1
CASE .4-C
CASE .S-C
ram
/
CASE 6-C
CASE .7-C
Et Ed O U T
1 6633 876 4370 687 466 351 6633
6633 1408 6101 4593 687 466 351 6633
2 6615 897 1429 642 427 334 6633
6615 1514 6016 6530 658 432 338 6633
3 6633 291 551 405 319 362 6633
6633 1457 5707 551 405 319 360 6633
1 6410 899 608 1223 449 311 6410
6410 1465 5844 612 1193 449 311 6410
2 6393 874 600 968 415 294 6376
6393 1457 5810 602 945 415 294 6376
3 6376 668 433 315 279 236 6393
6376 1474 5587 433 319 279 238 6393
1 5947 908 568 326 219 176 5947
5947 1508 5347 568 326 219 176 5947
2 5707 895 441 199 155 156 5707
5707 1512 4953 559 310 214 179 5707
3 5604 1457 670 424 219 159 146 5587
1 4867 1155 608 368 213 152 4867
4867 1429 4593 608 368 214 152 4867
2 4833 1048 568 475 198 153 4833
4833 1442 4456 568 343 200 154 4833
3 4833 1435 698 383 242 154 125 4833
1 3890 1692 542 321 191 119 3908
3890 1469 4113 544 321 191 119 3908
2 3959 1463 490 293 177 117 3890
3959 1463 3959 495 293 178 117 3890
3 4113 1463 565 319 202 137 102 4165
93
LIGHT PLENUM INNER DEPTH COMPARISON IN FOOTCANDLES
March 5'9 3
Clear
CASE .3d-C
CASE .4d-C
CASE .Sd-C
CASE .6d-C
CASE .7d-C
Et E d
1 2 3 4 5
O UT
1 2468 655 433 230 134 91 2468
2468 1169 1954 433 229 134 91 2434
s 2 2417 610 394 226 139 101 2417
2417 1176 1851 394 225 139 100 2417
3 2417 1165 377 270 171 115 89 2417
1 2365 605 291 1B0 116 80 2365
2365 1170 1800 293 180 116 81 2365
s 2 2365 506 270 195 127 91 2365
2365 1155 1716 270 195 127 91 2365
3 2365 1140 328 206 160 109 82 2365
I 2279 476 248 135 95 71 2279
2279 1129 1626 248 134 95 71 2262
s
I I S
2262 473 219 133 100 79 2262
2262 1137 1598 219 133 100 79 2262
1 1 1 2211 1129 293 150 99 80 68 2211
1 2159 552 237 122 75 62 2159
2159 1109 1602 237 122 75 62 2159
s
I I S
2159 391 204 117 79 69 2159
2159 1109 1441 204 117 79 69 2159
3 2159 1103 279 140 86 65 61 2159
III 2057 492 223 111 65 47 2057
2057 1086 1463 223 111 65 48 2074
s 2 2057 194 195 109 70 55 2057
2057 1079 1172 195 109 70 55 2057
3 2057 1084 270 134 81 58 50 2057
94
LIGHT PLENUM INNER DEPTH COMPARISON IN FOOTCANDLES
March 23’93
Overcast O U T O U T
259 259
256 256
253 254 CASE .3-0
246 246
240 240
234 235 CASE .4-0
214 215
210 210
206 206 CASE .S-O
200 200
199 200
199 199
CASE .6-0
201 201
203 203
CASE .7-0
205 205
I
I
LIGHT PLENUM INNER DEPTH COMPARISON IN FOOTCANDLES
March 23’93
Overcast O U T O U T
. 1
377 377 84
366 366
360 360 78
377 373 84
386 383
394 394
394 394
388 388
t
379 383
CASE .5 d-0
351 353
347 343
»
338 338
310 310
304 304 27
298 298
CLERESTORY HEIGHT COMPARISON IN FOOTCANDLES
March 30’ 93
Et Ed O U T
CASE .S-C
CASE ,9-C
/
L i
CASE .10-C
1 3390 1600 745 359 185 102 58 3390
2 3390 1600 654 339 179 105 61 3390
3 3390 1600 437 237 130 85 54 3390
1 3314 1574 579 265 132 74 51 3314
2 3276 1562 525 255 131 77 54 1562
3 3263 1562 358 182 97 65 48 3263
1 3162 1536 507 211 104 62 58 3162
2 , 3162 1536 454 202 103 65 61 3162
3 3162 1524 333 149 78 55 52 3162
*S-
^ A
-rt.
CASE .8d-C
CASE .9d-C
A _ai
CASE ,10d-C
1 4114 1752 1306 438 232 137 87 4127
2 4000 1752 890 422 219 140 89 4000
3 4000 1752 541 295 161 111 77 4000
1 4000 1752 783 378 187 115 78 4025
2- 4038 1778 716 368 187 120 83 4012
3 4025 1765 491 251 133 95 72 4025
1 4012 1752 670 303 152 104 96 4012
2 4000 1752 629 298 149 110 99 4000
3 3974 1765 458 207 108 87 82 4000
97
CLERESTORY HEIGHT COMPARISON IN FOOTCANDLES
March 23’93
Overcast O U T
210 210
211 212
CASE .8-0
215 215
221 221
224 224
CASE .9-0
225 225
199 199
199 199
CASE .10-0
198 198
822 822 211 23
872 235 101 872
895 220 895
795 795 142
790 146 792 20
788 136 790
810 158 816
827 169 827
CASE .10d-O
850 850 160
CONTROL DEVICES COMPARISON IN FOOTCANDLES
March 30’93
Clear E d O U T
4000 1752 783 378 187 115 78 4025
4038 1778 716 368 187 120 4012
CASE .11-C
4025 1765 491 251 133 95 4025
3949 1752 720 339 174 108 3949
3911 1752 663 333 174 113 3923
CASE .12-C
3885 1740 473 233 124 90 3885
3797 1740 308 3784
3771 1727 323 3758
CASE .13-C
3733 1714 279 55 3733
3314 1574 579 265 132 74 3314
1562 3276 1562 525 255 131
CASE .11d-C
3263 1562 358 182 97 3263
3085 1511 550 251 123 3085
3073 1511 491 236 120 3085
CASE .12d-C
3047 1486 346 173 91 3047
2895 1447 236 113 59 2895
2882 1447 237 121 65 2895
CASE ,13d-C
2857 1447 208 124 66 2857
CONTROL DEVICES COMPARISON IN FOOTCANDLES
Feb 22’93
Overcast
O U T 1 O U T
CASE .11-0
CASE .12-0
CASE .13-0
1 1621 439 155 78 43 39 1621
2 1632 456 174 92 51 42 1634
3 1683 439 153 77 45 39 1690
1 2159 608 196 98 57 65 2159
2 2142 602 210 110 63 68 2159
3 2159 529 167 84 52 58 2159
1 1114 143 57 30 20 29 1114
2 1120 144 65 37 23 32 1120
3 1142 141 58 32 21 29 1148
1 748 170 55 27 17 16 748
2 754 178 66 34 21 19 754
3 760 164 58 29 19 18 760
I 947 208 67 34 21 20 934
2 996 222 83 43 27 27 996
3 1013 210 74 37 25 25 1013
1 947 157 57 31 26 31 951
2 957 164 67 36 30 37 957
3 923 144 55 30 26 32 917
CASE .11d-0
CASE .12d-0
C A S E .13dO
1 00
j DUCT WORK COMPARISON IN FOOTCANDLES
M ar 30'’ 93
Clear O U T
2857 2857 1435 233 110 56
2832 2819 1447 239 121 64
CASE .14*C
2857 2844 1447 200 98 50
2819 1422 229 105 54 2819
2819 1422 235 119 61 2819
CASE .15-C
27 2806 2819 1409 196 95 48
3205 3188 1306 355 553 110
3188 1306 336 878 106 3188
CASE .16-C
3205 3188 1317 270 212 85
3695 3695 1714 309 147
3695 3695 1714 321 164
CASE 14d-C
3708 3695 1714 271 129
3657 1701 300 145 3644
3593 1676 316 162 3593
CASE .1Sd-C
3581 1676 262 125 3581
2674 2674 1210 347 230
2622 2639 1216 310 197
CASE ,16d-C
2622 2622 1210 226 127
DUCT WORK COMPARISON IN FOOTCANDLES
Feb 22’93
Overcas
O U T 1 2 3 4 5 our
i i i
1649 215 86 44 29 41 1649
. WTTr HTTFTT TX.
i a s
1 1
1705 215 101 55 34 44 1711
C A S E .14-0
3 1851 212 90 48 31 36 1851
111
957 123 46 23 14 15 957
ia
s 2 927 123 55 29 17 17 927
C A S E .15-0
i l l
944 117 48 25 15 15 945
i 1114 143 57 30 20 29 1114
a a ^
SSI
2 1120 144 65 37 23 32 1120
C A S E .16-0
3 1142 141 58 32 21 29 1148
1 602 95 38 20 15 20 602
a » A
i l l
2 598 93 44 24 17 21 598
C A S E .14d-0
3 595 88 38 19 14 15 593
1 310 46 16 8 5 5 310
C C . . J
i n
2 304 46 23 12 7 6 304
C A S E ,15d-0
3 304 45 20 10 6 6 304
1 947 157 57 31 26 31 951
i n
2 957 164 67 36 30 37 957
C A S E .16d-0
3 923 144 55 30 26 32 917
CONVENTIONAL OFFICE COMPARISON IN DAYLIGHT FACTOR
M ar 05'93
Clear
1 2 3 4 5
5’ 10’ 15’ 20’ 25’
1 21.97 14.59 8.61 5.79 3.71
70.50 14.59 8.61 5.79 3.71
2 23.79 14.46 8.74 6.19 4.15
71.55 14.46 8.74 6.19 4.15
3 15.16 10.25 6.45 4.87 3.40
1 32.50 14.30 6.80 3.83 1.61
2 15.87 7.47 3.69 2.17 1.39
3 11.63 5.50 2.75 1.83 1.25
CASE .1-C
CASE .2-C
Feb 22’93
Overcast 10’
2 3
15’ 20’
1 5
25’
CASE .1-0
CASE .2 -0
1 27.00 15.44 9.24 5.49 4.22
2 28.42 16.80 9.98 6.15 4.69
3 26.36 13.86 8.18 5.21 3.97
1 23.45 9.06 4.31 2.28 1.65
2 24.02 10.11 5.09 2.77 1.87
3 21.30 8.47 4.17 2.31 1.67
103
LIGHT PLENUM INNER DEPTH COMPARISON IN DAYLIGHT FACTOR
M ar 05’93
Clear
CASE .3-C
CASE .4-C
CASE .S-C
CASE .6-C
CASE ,7-C
5 ’ 1 0 ’ 1 5 ’ 2 0 ’ 2 5 ’
1 1 3 . 2 1 9 . 9 4 1 0 . 3 6 7 . 0 3 5 . 2 9
9 1 . 9 8 6 9 . 2 4 1 0 . 3 6 7 . 0 3 5 . 2 9
s I f 1 3 . 5 2 2 1 . 5 4 9 . 6 8 6 . 4 4 5 . 0 4
9 0 . 7 0 9 8 . 4 5 9 . 9 2 6 . 5 1 5 . 1 0
3 4 . 3 9 8 . 3 1 6 . 1 1 4 . 8 1 5 . 4 6
8 6 . 0 4 8 . 3 1 6 . 1 1 4 . 8 1 5 . 4 3
1
1 4 . 0 2 9 . 4 9 1 9 . 0 8 7 . 0 0 4 . 8 5
9 1 . 1 7 9 . 5 5 1 8 . 6 1 7 . 0 0 4 . 8 5
s 1 | 1 3 . 7 1 9 . 4 1 1 5 . 1 8 6 . 5 1 4 . 6 0
9 1 . 1 2 9 . 4 4 1 4 . 8 2 6 . 5 1 4 . 6 0
1 1
1 0 . 4 5 6 . 7 7 4 . 9 3 4 . 3 6 3 . 7 0
8 7 . 3 9 6 . 7 7 4 . 9 9 4 . 3 6 3 . 7 3
1 1
1 5 . 2 7 9 . 5 5 5 . 4 8 3 . 6 8 2 . 9 6
8 9 . 9 1 9 . 5 5 5 . 4 8 3 . 6 8 2 . 9 6
s 2 1 5 . 6 8 7 . 7 3 3 . 4 9 2 . 7 2 2 . 7 3
8 6 . 7 9 9 . 7 9 5 . 4 3 3 . 7 5 3 . 1 4
3 1 1 . 9 9 7 . 5 9 3 . 9 2 2 . 8 5 2 . 6 1
. 1 2 3 . 7 3 1 2 . 4 9 7 . 5 6 4 . 3 8 3 . 1 2
9 4 . 3 7 1 2 . 4 9 7 . 5 6 4 . 4 0 3 . 1 2
s 2 2 1 . 6 8 1 1 . 7 5 9 . 8 3 4 . 1 0 3 . 1 7
9 2 . 2 0 1 1 . 7 5 7 . 1 0 4 . 1 4 3 . 1 9
3 1 4 . 4 4 7 . 9 2 5 . 0 1 3 . 1 9 2 . 5 9
1 4 3 . 3 0 1 3 . 8 7 8 . 2 1 4 . 8 9 3 . 0 5
1 0 5 . 2 5 1 3 . 9 2 8 . 2 1 4 . 8 9 3 . 0 5
s 2 3 7 . 6 1 1 2 . 6 0 7 . 5 3 4 . 5 5 2 . 9 8
1 0 1 . 7 7 1 2 . 7 2 7 . 5 3 4 . 5 8 2 . 9 8
3 1 3 . 5 7 7 . 6 6 4 . 8 5 3 . 2 9 2 . 4 6
104
LIGHT PLENUM INNER DEPTH COMPARISON IN DAYLIGHT FACTOR
March .793:
Clear
CASE ,3d-C
CASE .4d-C
CASE .Sd-C
CASE .6d-C
CASE .7d-C
J 2 3 4 5
5’ 10’ 15’ 20’ 25’
1 1
26.54 17.54 9.32 5.43 3.69
80.28 17.79 9.41 5.51 3.71
2 25.24 16.30 9.35 5.75 4.18
76.58 16.30 9.31 5.75 4.14
3 15.60 11.17 7.07 4.76 3.68
l 25.58 12.30 7.61 4.90 3.38
76.11 12.39 7.61 4.90 3.42
2 21.40 11.42 8.25 5.37 3.85
72.56 11.42 8.25 5.37 3.85
3 13.87 8.71 6.77 4.61 3.47
1 20.89 10.88 5.92 4.17 3.12
71.88 10.96 5.92 4.20 3.13
2 20.91 9.68 5.88 4.42 3.49
70.65 9.68 5.88 4.42 3.49
3 13.25 6.78 4.48 3.62 3.08
1 25.57 10.98 5.65 3.47 2.87
74.20 10.98 5.65 3.47 2.87
2 18.11 9.45 5.42 3.66 3.20
66.74 9.45 5.42 3.66 3.20
3 12.92 6.48 3.98 3.01 2.83
1 23.92 10.84 5.40 3.16 2.28
70.54 10.75 5.35 3.13 2.32
2 9.43 9.48 5.30 3.40 2.67
56.98 9.48 5.30 3.40 2.67
3 13.13 6.51 3.94 2.82 2.43
105
LIGHT PLENUM INNER DEPTH COMPARISON IN DAYLIGHT FACTOR
March 23''93
Overcast 5’ 10’
2 3
15’ 20’
4 5
25’
a l
CASE .3-0
CASE .4 -0
t& JL
CASE .S-O
CASE .6-0
fc& j.
CASE .7-0
21.24 10.42
21.88 12.50
20.95 10.28
21.14
22.08
20.09
21.03
21.90
20.39
21.50
22.61
20.60
21.89
22.66
21.46
6.50
7.92
6.84
7.01
8.57
7.28
7.50
9.05
7.54
7.46
8.87
7.80
6.18
7.03
5.93
4.07
5.42
4.70
3.27
3.33
2.91
3.50
4.52
3.52
3.48
4.43
3.90
4.25
4.69
4.35
3.66
5.00
4.27
2.34
2.86
2.43
1.50
2.51
2.01
1.99
2.46
2.44
3.47
3.91
3.55
2.85
3.33
3.41
2.33
2.86
2.43
1.00
2.01
1.51
1.49
1.48
1.46
106
LIGHT PLENUM INNER DEPTH COMPARISON IN DAYLIGHT FACTOR
I
March 23’93
Overcast
i
I
2.39 22.28 10.08 5.57 3.18
2.73 23.50 12.02 6.83 4.10
i
I
i
i
3.61 2.50 21.67 10.56 5.83
i
3.71 2.67 22.28 8.49 5.57
4.40 3.12 23.06 9.84 6.48
I
2.54 5.33 3.81 21.07 8.63
3.05 2.54 21.83 7.61 4.06
3.09 9.02 4.90 3.87 22.94
21.90 8.18 3.17 2.62 3.96 CASE 5d -0
2.27 2.28 22.22 7.69 3.70
2.61 22.77 9.22 4.32 2.59
CASE .6d-0
2.37 3.55 2.37 21.01 7.69
1.61 3.55 2.26 21.61 7.74
I
1.97 2.63 22.37 8.88 4.28
1.68 7.72 3.69 2.01 20.81
107
CLERESTORY HEIGHT COMPARISON IN DAYLIGHT FACTOR
March 5’93
Clear 25’ 10’
i
i
5.46 3.01 1.71 21.98 10.59
5.28 3.10 1.44 19.29 10.00
CASE .8-C I
3.83 2.51 1.59 6.99 12.89
2.23 1.05 8.00 3.98 17.47
4.93 1.12 33.61 16.33 8.39
I
CASE .9-C
2.97 1.99 1.47 10.97 5.58
t
i 6.67 3.29 1.96 1.39 16.03
I
3.26 2.06 1.93 14.36 6.39
CASE .10-C
1.74 1.64 10.53 4.71 2.47
3.32 2.11 31.65 10.61 5.62
2.10 3.50 22.25 10.55 5.48
CASE .Sd-C
1.93 2.78 4.03 13.53 7.38
2.86 1.60 4.65 9.39 19.45
1.72 2.99 9.17 4.66 17.85
CASE 9d-C
1.79 3.30 2.36 12.20 6.24
2.30 2.59 3.79 16.70 7.55
2.48 3.73 2.75 15.73 7.45 *
CASE .10d-C I
2.70 2.18 2.06 11.45 5.18
108
CLERESTORY HEIGHT COMPARISON IN DAYLIGHT FACTOR
March 23’93
Overcast 15’ 20’
21.43 7.62 3.81 1.90 1.43
21.70 8.49 3.77 1.89 1.89
CASE .8-0
20.00 6.98 2.79 1.40 1.86
17.19 4.98 2.26 1.36 1.81
17.86 6.70 3.57 2.23 2.23
CASE .9-0
16.44 2.22 1.78 4.89 1.33
25.63 9.55 4.02 2.01 1.01
1.51 26.63 11.06 5.53 3.02
CASE .10-0
9.09 23.74 4.55 2.53 1.52
25.67 10.10 4.99 2.80 2.19
26.95 11.58 5.85 3.33 2.52
24.58 2.79 2.12 9.83 4.69
5.66 2.77 17.86 2.77 2.14
18.43 6.44 3.28 2.53 3.16
2.28 2.92 17.22 5.70 2.78
2.21 19.36 6.62 3.43 2.21
20.44 2.54 2.54 7,86 3.99
CASE .10d-O
2.35 18.82 6.71 3.41 2.24
109
CONTROL DEVICES COMPARISON IN DAYLIGHT FACTOR
25’ 15’
4.65 2.86 19.45 9.39 1.94
17.85 4.66 2.99 1.96 9.17
CASE .11-C
2.36 1.79 12.20 6.24 3.30
2.73 1.68 18.23 8.58 4.41
1.78 16.90 8.49 4.44 2.88
CASE ,12-C
12.18 6.00 3.19 2.32 1.90
2.06 1.51 1.37 8.14 3.88
8.59 4.47 2.42 1.76 1.67
f
CASE ,13-C
3.62 1.85 1.47 1.47 7.47
2.23 1.54 3.98 17.47 8.00
4.93 1.28 33.61 16.33 8.39
CASE .11d-C
1.47 1.99 10.97 5.58 2.97
1.34 17.83 8.14 3.99 2.33
1.41 7.65 3.89 2.40 15.92
2.03 2.00 2.99 11.36 5.68
1.15 1.35 8.15 3.90 2.04
1.73 4.18 2.25 1.49 8.19
1.75 7.28 4.34 2.31 1.51
110
CONTROL DEVICES COMPARISON IN DAYLIGHT FACTOR
Fob 22’93 1 2 3 4 5
Overcast 5’ 10’ 15’ 20’ 25’
1 27.08 9.56 4.81 2.65 2.41
s 2 27.92 10.66 5.63 3.12 2.57
CASE .11-0
3 26.03 9.07 4.57 2.67 2.31
1 28.16 9.08 4.54 2.64 3.01
..........’ ■ * .......
s 2 27.99 9.77 5.12 2.93 3.16
CASE .12-0
3 24.50 7.74 3.89 2.41 2.69
1 12.84 5.12 2.69 1.80 2.60
S5a^fc>Ji b h in i 2 12.86 5.80 3.30 2.05 2.86
CASE .13-0
3 12.31 5.07 2.79 1.83 2.53
1 22.73 7.35 3.61 2.27 2.14
m i 2 23.61 8.75 4.51 2.79 2.52
CASE .11d-0
3 21.58 7.63 3.82 2.50 2.37
1 22.12 7.12 3.62 2.23 2.13
i n 2 22.29 8.33 4.32 2.71 2.71
CASE .12d-0
3 20.73 7.31 3.65 2.47 2.47
111
16.54 6.01 3.27 2.74 3.27
i l i h i 2 17.14 7.00 3.76 3.13 3.87
CASE ,13d-0
3 15.65 5.98 3.26 2.83 3.48
DUCT WORK COMPARISON IN DAYLIGHT FACTOR
M ar 30’93
Clear 25’ 10’ 15’
3.85 1.96 1.26 1.33 8.16
2.26 1.52 8.44 4.27 1.41
CASE .14-C
1.37 7.00 3.43 1.75 1.23
1.03 8.12 3.72 1.92 1.17
4.22 2.16 1.31 1.10 8.34
CASE .15-C
0.96 6.99 3.39 1.71 1.10
11.08 17.25 3.43 2.09 1.91
s ;
10.54 27.54 3.32 2.13 2.01
CASE .16-C
8.42 2.65 1.78 1.78 6.61
1.33 8.36 3.98 2.06 1.41
2.35 1.60 1.41 8.69 4.44
1.30 3.48 1.78 1.35 7.31
8.23 3.98 2.00 1.23 0.96
1.06 2.31 8.79 4.51 1.42
CASE .1Sd-C
0.89 7.32 3.49 1.70 1.14
1.57 12.98 8.60 3.70 2.02
1.71 11.82 7.51 3.55 2.10
CASE .16d-C
8.62 4.84 2.63 1.72 1.49
DUCT WORK COMPARISON IN DAYLIGHT FACTOR
20 ’
1.76 2.49 5.22 2.67 13.04
2.58 3.22 1.99 12.59 5.91
CASE .14-0
11.45 4.86 2.59 1.67 1.94
1.46 1.57 12.85 2.40 4.81
3.13 1.83 1.83 13.27 5.93
CASE .15-0
1.59 2.65 1.59 12.39 5.08
5.12 2.69 1.80 2.60 12.84
3.30 2.05 2.86 12.86 5.80
CASE .16-0
1.83 2.53 2.79 12.31 5.07
3.32 3.32 2.49 15.78 6.31
3.51 2.84 7.36 4.01 15.55
2.36 2.53 6.40 3.20 14.81
1.61 2.58 1.61 14.84 5.16
2.30 1.97 15.13 7.57 3.95
1.97 6.58 3.29 1.97 14.80
2.74 3.27 3.27 16.54 6.01
3.87 7.00 3.76 3.13 17.14
15.65 5.98 3.26 2.83 3.48
REFERENCES
1 Benton, Charles C. "Experiential exercises for environmental control
system courses." Proceedings o f the 10th National Passive Solar
Conference, Boulder, Colorado, American Solar Energy Society,
j 1985.
I Boyd, R.A. "Daylight availability," Illuminating Engineering, Vol. 53,
| No.6, June 1958, p.321.
i
Bryan, Harvey. "Standard 90. IP: Daylighting," Architectural Record,
j June 1988: p. 156.
I
| Dubin, Fred S. "Energy Management for Commercial Buildings: A
; Primer," Energy Conservation Through Building Design, Donald
Watson: Editor, McGraw-Hill Book Company, New York, 1979: pp
204-229.
i
! Egan, David M. Concepts in Architectural Lighting. McGraw-Hill
Book Company, New York. 1983.
Evans, Benjamin H. Daylight in Architecture, Architectural Record
i Books, McGraw-Hill Book Company, New York. 1981.
| Gutherz, James M.; Schiler, Marc. A Passive Solar Heating System fo r
I the Perimeter Zone o f Office Building. Los Angeles, California: School
: of Architecture, University of Southern California, 1990.
Hill, Glenn E. "Daylight Penetration Through a Light Plenum" j
Proceedings o f the 11th National Passive Solar Conference, Boulder, j
Colorado, American Solar Energy Society, 1986. j
1
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EES Daylighting Committee. "Recommended practice of daylighting" i
: Lighting Design & Application, February 1979: pp.25-60. i
Kingsbury, H.F.; Anderson, H.H.; Bizzaro, V.U. "Availability of
i | daylight," Illuminating Engineering, February 1957, p.77.
Lam, William M.C. Sunlighting as Formgiver fo r Architecture, Van
Nostrand Reinhold Company, New York. 1986.
| Littlefair, Paul J. "Innovative daylighting: Review of systems and
evaluation methods," Lighting Research and Technology, Vol.22 No, 1,
j 1990: pp. 1-17.
Milne, Murry; Cook, Andrew; Popovic, Olga. DATAL1Tuser's
| Manual. UCLA Graduate School of Architecture and Urban Planning,
j September 1987.
Mirkovich, Don. "Light Plenum Concepts in Office Building Design."
Proceedings o f the 8th National Passive Solar Conference, Santa Fe,
| New Mexico, American Solar Energy Society, 1983.
! Moore, Fuller. Concepts and practice o f Architectural Daylighting,
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i ;
| | Natural Lighting, Solarvision Publications, Harrisville, New
j l Hampshire, 1982.
i|
| Nelson D T.; Evans D L.; Bansal R K. "Linear Fresnel lens
consentrators," Solar Energy 17, 1975: pp.285-289.
I ;
Rosenfeld, Arthur H.; Selkowitz, Stephen E. "Beam Daylighting: an
Alternative Illumination Technique," Energy and Building, 1(1977):
pp.43-50.
Ruck, N C.; Smith S C J. "Solar beam lighting as an energy
conservation techniqe using a prismatic panel," Proceeding Conference
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Daylighting and energy conservation, University of New South Wales,
Australia, 1982.
) j
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: Schiler, Marc. Simplified Design o f Building Lighting, John Wiley &
j Sons, Inc. 1992.
j Schiler, Marc, Editor. Simulating Daylight with Architectural Models,
j Los Angeles: Daylighting Network of North America, University of
j Southern California, 1986.
] Selkowitz Stephen. "Effective daylighting in buildings — part 1"
| Lighting Design & Application, February 1979: pp. 6-11.
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| Daylighting Conference, Long Beach, 1986: pp. 420-423.
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Asset Metadata
Creator
Wang, Peng-Chih
(author)
Core Title
Office natural lighting effective of a reflective light plenum
Degree
Master of Building Science
Degree Program
Building Science
Publisher
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