Through a window, brightly:
MODULATING DAYLIGHT AND SOLAR RADIATION IN COMMERCIAL AND
INSTITUTIONAL BUILDINGS THROUGH THE USE OF ARCHITECTURAL ELEMENTS
By
Hans-Joachim Schlereth
Dipl. Ing., Technical University of Munich, 1977
Submitted in Partial Fulfillment of the requirements for the
Degree of Master of Architecture in Advanced Studies'at the
Massachusetts Institute of Technology
June 1982
E
Hans-Joachim Schlereth 1982
The author hereby grants to M.I.T. permission to reproduce and to
distribute publicly copies of this thesis document in whole or in part.
/K71
Signature of Author . ..
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Department of Architecture
May 8, 1982
C
Certified by..
Timothy E. Johnson
Research Associate
Thesis Supervisor
/
Accepted
. . . . . . . . . . . . . . . . . . . . . . . - - - . ..
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. . by...........................~6............................................
Accepted by
N. J. Habraken
Chairman, Departmental Committee
MASSACtIUSETTS IN;ii.;TJ a
OF TECHNOLOGY
JUN 4 1982
LmmvkplEs
on Graduate Students
2
table of contents
abstract. . . .
introduction. .
I
. . .
. . . . . . . . . .
. . . . . . . .
3
. . .. .
daylight design:
analytical methods. . . . .
. . . .51
6
PROPOSED DAYLIGHT INTRODUCTION SYSTEM
THE NATURE OF THE PROBLEM
energy use patterns in commercial
and institutional buildings . . . . 10
commercial versus residential:
different needs . . . . . . . . . .12
54
.
objectives and system components.
daylight model experiments. . . .
data analysis and conclusions .
62
. .
.
integration with dynamic artifici al
lighting system . . . . . . . .
2
FUNDAMENTALS
SOLAR RADIATION AND DAYLIGHTING
solar rythms. . . .
orientation . . .
. . . . . .
.
. . . . . . . .
visual and thermal comfort. .
reflection /diffusion .
. .
-
.
. 20
.
daylight and its distribution
18
.
cost-effective daylighting:
qualitative and quantitative
analysis. . . . . . . . . . . .
78
94
.
98
appendix a
recent projects:
principles applied in praxis.
103
. 35
appendix b
Tl-59 computer program. . ....
121
. 38
appendix c
sun altitude and azimuth graphs
138
. -24
. . . . 27
. .
primary types of glazing and
new technology. . . . . . . . . .
light introduction and control:
side and toplighting. . . . .
45
appendix d
glossary of terms .
.
142
. . . .
145
. . . . . .
bibliography and references .
3
Through a window, brightly:
MODULATING DAYLIGHT AND SOLAR RADIATION IN COMMERCIAL AND INSTITUTIONAL
BUILDINGS THROUGH THE USE OF ARCHITECTURAL ELEMENTS
by Hans-Joachim Schlereth
Submitted to the Department of Architecture on May 7th, 1982 in partial fulfillment of the requirements
for the Degree of Master of Architecture in Advanced Studies.
abstract
Natural lighting serves several important
functions in buildings. The visual power of a
shaft of sunlight penetrating a dark space or
the visual beauty of a stained window has long
been recognized by architects and designers.
The primary focus of this study is a more
pragmatic one. Besides strong concern for the
qualitative aspects of daylight design, methods
of daylight and solar radiation modulation for
commercial structures are explored and evaluated
to offset electric lighting load or heat load
requirements. An investigation into the energy
use patterns of these building types - offices,
schools, hospitals, warehouses and other "commercial" structures lead to the conclusion, that
artificial lighting represents the most significant portion of total electrical energy consumption. This study considers daylight and solar
design in several ways:
First, it documents daylight and solar radiation fundamentals and their visual and ther-
mal impact on human comfort. It reviews a series of traditional design tools and architectural
elements to modulate and control daylight and
solar radiation.
Second, it proposes and evaluates an innovative daylight introduction system - a particular "lightshelf" configuration integrated as an
architectural element - with careful consideration of the following criteria:
- acceptance of the full range of seasonal
sun altitude angles through a curved configuration of the reflecting lightshelfsurface to redirect incident radiation
onto the same "reference-range" of the
interior ceiling without any adjustments
- modulation of daylight introduction and
radiation diffusion for solar storage in
distributed mass
- penetration of daylight into a space beyond traditional limits of 15 to 20 feet
for daylight utilization
4
- design of the light introducing "component" as an architectural element and
its integration into a modular window
wall consisting of prefabricated lightweight concrete wall elements
- evaluation of qualitative and quantitative performance of proposed system
- illumination and solar heat gain tradeoffs
- integration of daylight design with dynamic artificial lighting system
Third, analytical and experimental methods
for daylight design are explored and an entensive daylight model experiment is executed to
enable the qualitative and quantitative assessment of the proposed system.
Finally, a number of case studies with innovative daylight introduction methods applied
in praxis, are documented.
Thesis Supervisor:
Title:
Timothy E. Johnson
Research Associate
5
"We were born of light.
The seasons are felt
through light.
We only know the world as it is evoked by light,
and from this comes the thought that material is
spent light.
To me natural light is the only light, because it
has mood - it provides a ground of common agreement for
man - puts us in touch with the eternal.
Natural light
is the only light that makes architecture architecture."
Louis I. Kahn
6
introduction
It seems so simple:
Let the light in, keep the wea-
ther out, and maintain the view.
The solution to the
problem is often also deceptively simple:
Two or more
sheets of transparent glazing materials, often glass.
In reality, with today's technology, optimizing the
daylight, heat exchange and view through a window presents a problem of great complexity irrevocably intertwined with the total building concept and design.
It
is still a problem, since energy conscious design methodology is only now emerging and the solution generated is
nearly impossible to truly optimize for cost purposes.
Within the last decade the direction towards energy consciousness in buildings has led to a revolution in building design strategies.
I
7
This study began with the hypothesis that the
natural lighting function of a window can be used as
an effective element of design.
Light qualities -
natural, artificial, direct, indirect, specular reflective, diffuse, soft, hard, focused, etc., are an important part of how we experience and judge spaces and environments and can be subtly manipulated in the design of
a space to achieve the desired effect.
Natural daylight-
ing, together with the thermal qualities - warm, cool,
humid, airy radiant, cozy, etc. - of a space,
constitute a truly venerable architectural tradition.
Natural light has always provided a perceptual
dynamic to architectural design.
The man-made
environment has been enhanced by positively engaging the natural and has gained particular vitality by
responding to solar rythms.
The play of natural light
on a building facade and its entry into a building challenges the design and technology of architecture.
Sun-
light is predictable in its direction and cycles of day
and season; natural light is unpredictable in its varying
patterns of weather, reflectances and shadows.
The fas-
cination with sunlight derives from our most fundamental
biological and asethetic needs.
Orientation in time and
8
space is critical to our survival and well being.
Day-
light carries with it this assurance of orientation and
the excitement of diversity.
It was not until recently
that the practical aspects of sunlight were rediscovered
after being neglected for more than 20 years in this
country.
9
"Energy is not an expression of life.
of life like gravity or friction.
expression of life.
It is a fact
Architecture is an
Energy is instructed and controlled
by the arrangement of built form, like wind through a
flute - building should not begin with Energy Conscious
Design, nor should it end there.
Energy Conscious De-
sign is simply a bridge crossed while designing.
The
departure point of the building is shelter, the destination is an inspirational place to be.
It is the use of the building in concert with the
search for form that yield original form.
Richard Rush
The Assimilation of Energy
Conclusion
P.A. 4-81
10
1
the nature of the problem:
energy use in
commercial
and institutional Buildings
The decreasing availability and increasing costs of fossil fuels for production of power
for light as well as for heating and air conditioning
has initiated a reappraisal of daylighting as an illumination strategy.
Artificial lighting represents about
20% of total electrical energy consumption or 420 billion Kwh per year and accounts for 5% of total energy
5
consumption in the United States.
11
Artificial lighting has become a major issue for
electric load reduction in commercial and institutional
buildings with predominant daytime-use, where artificial
1000
lighting usually accounts for more than 50 percent of the
total electrical energy consumption.
Non-Services
13%.
Several investiga750
tions of characteristic commercial structures, their
climate and building thermal loads, have identified artificial lighting as a major energy consumer, both as an
Lifts 2%
Refrigeration
10%
Pumps 11%
5001-
Fans 17%
250 F
Lights 47%
electric load and as a cause of increased cooling requirements.
This is frequently the case for office buildings;
artificial lighting may account for as much as 80 percent
of the energy consumption and is thus a major target for
energy conservation.
To accurately assess a window's energy impact on the
total energy load of a commercial structure, the following factors - daylighting, solar heat gain and heat loss must be addressed.
Criteria are often conflicting to achieve energy efficiency:
daylight must be carefully modulated to con-
trol excessive light level variations and glare, and must
be integrated with a dynamic artificial lighting system
in order to realize potential energy savings.
Solar
heat gain must be limited in order to reduce air conditioning loads and ensure occupants' comfort.
Finally,
Fig. 1.1.
Annual electric energy
2
consumption in MJ/m
for a typical office
building
12
winter heating loads must be reduced by new windows with
highly thermal insulating properties:
new glazing mate-
rials (residential and commercial "heat-mirrors," see
Chapter 2), thermal breaks ...
Current building codes ignore the benefit of daylight and consider windows mainly as a source of winter
heat loss and excessive summer solar heat gain.
As a re-
sult, it encourages small glass areas and low transmission glass, which produces typical office buildings with
3 to 4 feet high strip windows.
It is the basic premise of this thesis, that windows,
if careful consideration is given to all available design
options, can contribute to substantial energy savings in
commercial structures, while contributing greatly to worker satisfaction and productivity and providing improved
visual performance and human comfort.
commercial versus residential:
different needs
Daylight design lends itself particularly well to
buildings with intensive daytime use.
The primary fo-
cus in the commercial and industrial sector is office
buildings, schools, commercial low-rise, and warehouses.
Accounting for 14% of total United States energy consumption (Seri, 1981), these building types are character-
ized by:
13
- daytime use patterns
- long hours of lighting use
- relatively high lighting levels
2
*
- high installed watts/ft
Energy loads of small residential buildings are pri-
RESIDENTIAL
electric
OFFICE
marily composed of infiltration of outdoor air and heat
loss through the building envelope; they are commonly referred to as "skin-dominated" buildings.
For this build-
ing type, heat gain and prevention of heat loss are far
more important than lighting consumption (Fig. 1.2).
The
pqtential savings through introduction of daylight in the
residential sector are therefore minimal.
Energy use pat-
terns of large commercial structures are quite different
from those in residential.
Large internal heat gains from
light, people, and equipment, and a small surface to volume ratio generally create "internal-load dominated"
buildings with significant cooling and lighting loads.
Lighting, thus, is a substantial energy consumption factor
and represents a large fraction of total building utility
costs.
Table1.1
summarizes user pattern characteristics
and design considerations for comm./resid. buildings.
For the purpose of this study, potential daylight
savings in the residential sector are not investigated
and discussion is confined to commercial and institutional buildings.
Fig. 1.2.
Residential versus commercial
energy breakdown for the
United States 18
14
COMMERCIAL AND INDUSTRIAL BUILDINGS
(INTERNAL-LOAD DOMINATED)
RESIDENTIAL BUILDINGS
(SKIN-DOMINATED)
- High occupancy per unit area
-
Direct gain desirable, if managed properly
- No direct solar gain desirable, sun and
glare control
-
Low occupancy rate
-
Low lightlevels (Watt/ft2),
consumption/ft 2
-
Visual tasks are frequently not fixed in one
place
-
Individual user control options, e.g., comfort zone definition more flexible
-
Low internal gains
-
Primary heat loss through building envelope
-
High surface to volume ratio
- High lighting levels, therefore, high
energy consumption/ft 2
- Visual tasks fixed to one location, e.g.,
relative permanent space/location occupation
- No tolerance in light and temperature
fluctuations
- Thermal/illumination trade off considerations
-
Large internal gains
- Small surface to volume ratios
- Necessity of dynamic artificial lighting
system to adjust to fluctuating
lighting levels
Table 1.1. User Pattern Characteristics
and Design Considerations for Daylight and Solar Radiation Utilization
in "INTERNAL-LOAD-DOMINATED" and "SKIN-DOMINATED BUILDINGS"
thus low energy
15
What is the value of preserving and strengthening this
sense of awe and wonder, this recognition of something
beyond the boundaries of human existance?
...
There is
symbolic as well as actual beauty in the migration of
the birds, the ebb and flow of the tides, the folded bud
ready for spring.
There is something infinitely healing
in the repeated refrains of nature -
the assurance, that
dawn comes after night, and spring after the winter.
Rachel Carson
16
2
solar radiation and daylight fundamentals
Although the precise nature of the life cycle remains
a mystery, we exist as part of an intricate network of
rythms, patterns and change.
The motion of our planet around the sun, the accompanying seasons and recurring cycles are the expression
of rythmic movements of energy and matter.
The sun's daily and seasonal rythms as a generator
of form, specifically sunlight and gravity, are clearly
reflected in the growth and patterns of nature.
The sun-
ny side of slopes exhibit different plants and animals
than shady slopes.
Natural structures such as sand dunes,
reflect the forces of wind and gravity.
Buildings are sub-
ject to the same natural forces that have caused differentiations in nature, but rarely acknowledge them through
built expression.
17
It is in recognition of these rythms and forces,
that daylight and passive solar design takes its form.
However, an advantageous use of daylight and a widespread
implementation of daylighting practice requires a thorough
understanding of a number of fundamental principles.
Moreover, several availability factors need to be taken
into account:
- variations in the amount of daylight including
position and intensity of sunlight
- luminance and luminance distribution of clear,
partly cloudy, and overcast skies
- effects of local terrain, landscaping and nearby
buildings on the daylight available for use
- glare from various sources of light and luminance
patterns within the field of view
- the color of daylight as combined with other sources of daylight
This chapter describes solar rythms, solar radiation
characteristics, and daylight fundamentals and defines important aspects of light quality and quantity.
It ex-
plores important issues of daylight design such as visual
comfort, thermal/illumination trade offs, diffusion and
reflection, building orientation, etc.
Furthermore, it
documents a description of primary types of glazing ma-
18
terials as the important interface medium and recent developments in glass coating technology.
Finally, tradi-
tional light introduction methods are summarized and a
variety of techniques for simulating daylighting performance of buildings are described.
solar rythms
The seasonal positions of the sun are universally
known in exact terms.
It is directly over the equator
about March 21, the vernal equinox and thereafter it
appears further north each day until it reaches its zenith above the Tropic of Cancer about June 21 (the summer solstice in northern latitudes).
N
ANGLE
Then the sun ap-
pears a little more southerly each day, rising above the
equator about September 21 (autumnal equinox) and reaching its
most southerly point over the Tropic of Capricon
about December 21 (winter solstice).
However, this general information is insufficient to
determine the sun's effect on a specific structure in a
particular location.
To know how the rays will strike a
building and how far the rays will penetrate through the
-WINDOW
AZIMUTH
ANGLE
W
19
opening and to effectively use daylighting to reduce the
use of artificial lighting, we must have the following
information:
- The angle of the sun above the horizon (altitude)
- The bearing of the sun, e.g., the angle of the sun
from true south (azimuth)
- The angle of incidence of the sun relative to the
H
surface being considered
- The "profile angle," the sun's rays make with the
A
horizontal, when projected on a plane normal. to the
window
Appendix c
J*
provides some quick reference data of
.
the sun's altitude and azimuth for different latitudes
(24*-44*).
If more accurate information is needed the
C
LOF - Sun Angle Calculator, Libby-Owens-Ford-Co., Toledo,
Ohio, has proven to be an extremely valuable quick and
accurate, yet simple to use and rather inexpensive ($6)
design tool.
In addition, Appendix b
documents a TI-59 (Texas
Instrument) programmable-hand-calculator program, which
provided with the basic data of pertaining location longtitude, latitude, time meridian - will print the
altitude and azimuth of the sun for your location for
every hour the sun is above the horizon for the 21st
Fig. 2.1
Definition of profile
angle ABC
20
day of every month.
orientation
The most fundamental part of window design - its
orientation and the corresponding effects - are often
overlooked or ignored.
5
There is no rational (symmetry,
economy, aesthetics) justification for the presence of
NORTH
7
NOON
11
1
9
3
5
7
Winter
Sorinq/Fall
four (or even two) identical facades on a building.
Summer
Sunlight at different times of the day, produces different qualities, colors and angles of light.
As it moves
through the seasons, the solar load on each face changes,
Winter
SOUTH
I
I7
Spring/Fall
Summer
as does the penetration of sunlight to the back of the
Diffuse only
room, related to solar altitude.
Beam, solar altitude > 20
Beam, solar altitude < 20
At Boston Latitude (42*) hardly any direct sun reaches the
north side of a building.
Instead, north windows make
use of an increased proportion of natural light in diffuse
mode (Fig. 2.2).
A clear glass window on a north facade
may see 5000 footlamberts on a cloudy day.
Windows that
face east or west must be shaded in the summer at certain
times for the purpose of illumination and thermal control
to stop excessive penetration.
Fig. 2.2.
Seasonal and hourly distribution of diffuse and
beam daylighting opportunities for different
building elevations at
40N 1 6
I7777]
21
Since the sun is low in the sky in the morning and afternoon, the introduction of vertical shading elements in
combination with overhangs must be considered for these
orientations.
Any attempt to control direct radia-
tion with the sole use of low-transmission reflective or
heat absorbing glazings will reduce the opportunity to
use natural light or optional solar gain, besides adversely affecting the view outdoors.
An extremely elegant example of recent, energyconscious, responsive design is the 14-story office building for IBM in Southfield, Michigan, designed by Gunnar
Birkarts & Assoc. (for detailed description of the building see Appendix a3, pagell).
It combines a highly in-
novative, patented light introduction system with a twocolor treatment of the exterior wall.
A metallic silver
on the southern and western elevations reflects the light
and heat; a charcoal black on the northerly and easterly
elevations absorbs them.
More than this color control
does effect energy savings all that dramatic, it symbolizes with a "poetic image," the importance of orientation and the response to nature's cyclic rythms and patterns.
Ideal orientation of a building to true south is
desirable, but cannot always be achieved.
Fig. 2.2.1
The ways in which daylight
10
reaches a point in a room.
22
Even with small variations from true south, both
radiation and daylight control becomes increasingly difficult.
For example, with a window plane 200 off south,
the profile angle ABC (see Fig. 2.1 pagel9 ) varies significantly.
It is necessary to know the profile angles
of the sun on many specific dates and hours to be able to
intercept direct radiation when unwanted and its penetration into a room, when wanted.
The development of new
selective transmission glasses hold great promise for innovative design application and has increased the number
of options for radiation and daylight modulation in these
critical orientations through combination of different
types of glass, with specific properties, in multiple
glazing strategies.
A newly developed glass coating, "Commercial Heat
Mirror," is described in section 2f.
With a relatively
low solar gain factor ( 30%), high transmission of visible light (45%), and high reflectivity in the infrared
spectrum it maximizes the potential of daylight for illumination while minimizing solar heat gain.
These tech-
nologies, together with a combination of exterior and interior architectural elements offer the best solution for
effective energy-efficient daylighting.
Fig. 2.3.
The optical air mass in
creases for low solar altitudes thus decreasing
the intensity of direct
sunlight
23
2.000
1.800
1.600
1.400
1.200
1.000
600
~
00
400
200
0
0.2
0.4
0.6
0.7
0.8
1.0
1.2
1.4
1.6
wavelength (micrometers)
Fig. 2.4.
5
Spectral distribution of sunlight1
1.8
2.0
2.2
2.4
2.6
24
solar radiation
While the sun is an abundant source of radiant en-
9000
ergy, only approximately 50% of total incident radiation
8000
fall within the visible spectrum (Fig. 2.4).
The illu7000
mination received from the sun in a sunny climate is in
the range of 6000 to 10000 Lm/ft 2 .
The proportions of
this visible energy, or light, in the solar spectrum varies, depending on the depth of atmosphere the light has
to travel.
C
6000
0
0
U-
5000
E
4000
As Fig.2.3 indicates, the optical air mass
increases with lower solar altitudes.
This results in
lower values for direct solar illumination.
For example,
3000
__
__
-
2000
at a solar altitude of 200 the illumination is of the order of 6.500 Lm/ft 2 .
Average values of direct solar illu-
mination on a plane normal to the sun's rays for various
0
Fig. 2.5.
Although, the ultimate source of daylight is the sun,
the light reaching a building comes from 3 different
sources.
The first is direct sunlight travelling in an
20
30
40
60
63
TO
Solar Altitude Degrees
solar altitudes can be seen in Fig. 2.5.
daylight
10
Illumination from direct
sunlight as a function of
solar altitude (from IES-
Handbook)
£0
25
N
N
E
w
W
E
S
Fig. 2.6.
Luminance distribution of a blue clear sky.
* Position of Sun
S
Fig. 2.7.
Luminance distribution of a fully over10
cast sky (from Hopkinson
26
uninterrupted course.
Diffuse light from the sky vault,
skylight,which, unlike sunlight, comes from all parts
of the sky is the second component and is available in
(lumens)
visible
radiant/
energy/
diffuse
luminance
ft. lambert)
significant quantity under both clear and cloudy conditions
(Fig. 2.8).
irect
Additional skylight is reflected to
some point from the ground and nearby structures (E.R.C.).
\
reflec ted
,I ref lec
Finally, light from the first two sources reflects off the
illumination (fc)
room's interior surfaces to illuminate the point indirectly (I.R.C.).
Besides the directional characteristic of sunlight,
/
which is primarily dependant on dynamic solar location,
/
the intensity of light varies both with solar location
and changing weather conditions.
The amount of light
/
/
/
"0150
/
I
\
received from an overcast sky and the direction, from
~~~~~1
which this light reaches a space, depends on the luminance pattern of the sky.
The luminance distribution of
an overcast sky varies with the location, time, density
and uniformity of the overcast.
A uniformly overcast sky
is normally 2-1/2 to 3 times as bright overhead as near
the horizon (Fig. 2.8).
tant design criteria:
This establishes a very imporFor overcast conditions, an ap-
proximate angle of 60% can be assumed for defining the
direction of a major light source.
The clear sky, or
Fig. 2.8.
partly cloudy (30% or less cloud cover) has a more com-
Luminous distribution of clear
and overcast sky 18
27
plex brightness pattern, being brightest in the vicinity
of the sun with the darker spot approximately 90* across
the sun from the sun's position and then generally brightest at the horizon.
There are sharp differences in the
illumination available on north, south, east, and west
surfaces with clear sky conditions.
visual and thermal comfort
Visual and/or thermal comfort is defined as "a condition of mind that expresses satisfaction with its visual/thermal environment."
This statement conveys the
difficulty of setting definite standards.
Although it is
an accurate statement, it expresses the range of subjec12
tive interpretation of the human condition.
... we are comfortable, when we are free to focus
our attention on what we want or need to see,
when the information we seek is clearly visible
and confirms our desires and our expectations,
and when the background does not compete for
our attention in a distracting way."
Sensory monitors in the human body continuously provide necessary environmental information to fulfill its
need for orientation - an awareness of its location,
movement and state at all times.
Time orientation is an-
28
other important biological need.
Human beings, like most
other organisms, possess inherent biological mechanisms,
which act as clocks of different sorts, to keep track of
the rythm of day and night as well as other biologically
important cycles.
As the seasons lengthen and shorten the
hours of daylight, our internal clocks respond accordingly.
This continually recallibrated time orientation
gives us definite expectations of how light or dark it
should be outside, and these expectations play a major
12
role in our evaluation of any luminour environment.
Implicit in daylight design is the opportunity for
views and experiential contact with the outdoors.
Richard F. Brown, director of Fort Worth's Kimbell
Art Museum, one of the finest daylit buildings in this
country (see Appendix 'a2, p.10 8 ) writes:
"Natural light should play a vital part in
illumination... The visitor must be able to
relate to nature momentarily... to actually
see at least a small slice of foliage, sky,
sun, water. And the effects of changes in
weather, position of the sun, seasons, must
penetrate the building and participate in
illuminating both art and observer... We are
after a psychological effect through which the
museum visitor feels that both he and the art
he came to see are still part of the real,
rotating, changeable world."
Fig. 2.9
Kimball Art Museum, Fort Worth,
Texas
29
Daylight, through its variable nature, creates a
highly dynamic character within a space,
The adapta-
bility of the human eye to these variations is surprisingly great.
Bright sunlight may be 250,000 times
more intense than moonlight and yet we can see the same
forms in the light of the moon as we can in broad daylight.
There is evidence to suggest, that people value and
even prefer the changes and variability introduced by daylight in
a room over uniform lighting conditions.
Stud-
ies have shown that variations in light level have a relaxing effect on the eyes and produce advantageous psychological reactions -in people.
In another survey of
British office personnel by Manning
about lighting pref-
erences, 65% to 95% of the subjects surveyed expressed a
strong preference for daylight in their offices.
Today,
perhaps as many as four-fifths of all Americans work in
a largely 'synthetic'luminous environment because neither
the quality nor quantity of daylight is adequate for the
tasks at hand.
photobi ology
It has only been in recent years, that these stud-
30
ies and surveys have found strong scientific support
through a number of new and unexpected findings in the
field of photobiology (the study of how light affects
animals and plants) about the connections between light
and health.
According to the latest research,
scientists are
becoming increasingly convinced, that all aspects of our
health - mental and emotional as well as physical - are
indeed affected by the intensity of light to which we are
exposed, by the length of the exposure, and by the color
(spectral make-up) of light.
We now spend most of our
time under artificial light - which differs drastically
from sunlight in both character and intensity - with
results that scientists are just beginning to understand.
Experiments have shown strong opposition against lengthened exposure to fluorescent lighting because of its limited spectral distribution (color), mainly its particular
deficiency in the ultraviolet range.
established facts:
Based on two well-
ultraviolet light helps the body man-
ufacture vitamin D and vitamin D helps it absorb calcium.
Richard J. Wurtman, director of the endocrine laboratory
at the Massachusetts Institute of Technology concludes
after several studies:
31
"It seems likely, that properly designed indoor
lighting could serve as an important publichealth measure to prevent the under minenalization of bones among the elderly and others with
limited access to natural light."
task need
quality versus quantity
Unlike biological needs, activity or task needs
have always been recognized as objectives for lighting
too often, unfortunately, as the only objectives.
-
Even
so, optimum lighting conditions for tasks are seldom
achieved, because quantity rather than quality of light
is the common method of specification.
Increasing the
illumination - natural or artificial - on a task or an
object can increase its visibility or it can decrease it,
depending on the qualities of the illumination far more
than on the quality of light provided.
The direction of
the light, its source concentration, its color and its
Fig.
other qualities must be appropriate to the specific nature'
12
of the information required.
Expectation
based on the time of day influences the
evaluation of the color temperature of artificial lighting as appropriate or inappropriate.
We expect illumi-
2.10
Chapel, MIT, Cambridge,
Massachusetts, E.Saarinen
32
nation to be of a high color temperature (relatively
blue) when luminance levels are high, because we refer
them unconsciously to daylight, which has a relatively
high color temperature.
We expect low color temperatures
(i.e., a warmer quality of light) when luminance levels
outdoors are low.
The color temperature of daylight lies
in the range of 4000 to about 10000 K (Kelvin).
Overcast
skies are generally associated with low color temperatures (4500-7000K) and clear skies with high color temperatures
(10,000 K upwards) sunlight has a color tem-
perature in the range of 4000-5000K, depending on solar
altitude.
After the quality and quantity of light needed to
perform necessory tasks in a space has been determined,
the artificial and daylighting needs for this space can
be defined.
better light.
Yet, more light does not necessarily mean
Current recommendations for illumination
levels and luminances for various types of visual tasks
are generally too high (50-100 footcandles and a power
consumption of 5 Watt/ft 2)
and have risen (Fig.2.10) in
the United States over the last years, more rapidly than
European lighting standards (Fig.2.11).
Average reasona-
ble light levels for ambient lighting (biological needs)
are approximately 30 fe, while acceptable task lighting
33
requirements for an office space are in the range of 70 fc.
Stronger economical reasons for energy conservation, more data about daylight availability, and a great
deal of empirical research on visual comfort as it relates to illumination levels exists in Europe.
Thus,
daylighting is still considered a primary source of light
for buildings in Europe, while electrical lighting systems are often considered as supplemental lighting during
the daylight hours.
Ultimately, a complimentary integration of natural
and artificial lighting should produce optimum results
and will prove the most cost-effective and qualitative
acceptable design solution.
discomfort glare
Daylight is an important element in establishing
visual comfort in a space.
The volume of valuable work done by Hopkinson and
others on discomfort glare suggests a stronger relationship between feelings of comfort and the overall design
of an environment than between comfort and the absolute
34
quantity of light in it.
One of the basic problems inher-
ent with the use of natural illumination is glare.
It is
related to the contrast present in one's visual field at
a particular moment.
Any intense light source in an ob-
server's direct field of view can cause this visual disability, or discomfort or both.
If an object in a room
is seen against a background of much higher luminance,
its details will be difficult to detect, because the
adaptation level of the eye is raised considerably by the
relatively bright adjacent areas.
With the introduction of direct daylight/solar radi-
Fig. 2.12
ation into a space, this issue needs particular, careful
consideration.
this problem.
There are a number of ways to deal with
The M.I.T.
Solar Building (Fig. 2.12) has
successfully demonstrated one way of avoiding direct radiation and excessive glare by redirecting sunlight overhead to the ceiling with mirrored louvers at the window
plane - although, in this case for the purpose of heat
gain and storage.
One can soften the contrast at a win-
dow by having a surface adjacent to it.
The light from
the window brightens the surface right next to it and
eases the contrast.
In other words:
the "glare" of the
exterior is related to the brightness of the interior.
If the interior is all dark surfaces, the view to the
-.----
77
MIT Solar Building 5,
Cambridge, Massachusetts
35
exterior through clear glass may be quite undesirable.
A more traditional way is to use the splayed reveal (Fig.
213 ) to ease the transition from'the bright outdoors to
the darker indoors.
The window well should always be
light colored, to reduce contrast with the window.
With the use of indirect daylighting or indirect
artificial lighting, the ceiling becomes the principal
Thus, through the selection of proper re-
light source.
flectances (recommended reflectance for ceiling, 70%
-
see Section 2e) and the elimination of the particular
light source
-
natural or artificial
-
out of ones visual
field, the ceiling acts as a diffuser, light bounces around
in the room, and contrast levels are reduced significantly.
An elegant example of adjusting high outdoor light
levels to lower interior luminance is the Kimbell Art Museum at Fort Worth, Texas (see App. a
case study a2).
Here, besides interior applications delicate elm trees in
the courtyard and entrance areas filter the daylight and
provide a visual transition from the bright exterior to
the less severe interior.
reflection/diffusion
The important contribution of reflected components
36
of daylight to an interior space has been discussed earlier in Section
2c.
In addition, the use of reflective -
specular, semi-specular, diffuse - surfaces to redirect
or diffuse daylight, to modulate the amount of light
gathered and the depth of its penetration into a room
specular
plays a significant role in daylight design.
The reflective characteristics of a material are determined by two physical properties, reflectance and finish.
Light is reflected from a surface in one of several
ways.
Specular reflections are those in which the light
leaving the surface has the same angle as the incident
light.
semi-specular
Specular reflective surfaces can direct a very
controlled beam into the room.
Diffuse reflection are
those in which the light leaves the surface in a multitude of directions, and its distribution is the same
regardless of the angle of incidence.
Mirrors, polished
diffuse
aluminum and stainless steel give specular reflections;
matte surfaces - flat wall paint, plaster, and other
materials - produce a diffuse reflection.
Specular and
diffuse finishes represent the two extreme cases.
Most
materials encountered will be neither perfectly specular
nor matte.
of both.
Instead, they will exhibit some properties
The finish of a material, as the second physi-
cal property, also determines the direction of
Fig. 2.14
Schematics of reflection
37
Typical specular materials
Luminaire reflector materials:
Chromium
Aluminum: Polished
Alzak polished
Stainless steel
90-92%
63-66%
60-70%
75-85%
50-60%
Clear glass or plastic
Stainless steel
8-10%
50-60%
Luminaire reflector materials:
White paint
White porcelain enamel
70-90%
60-83%
Masonry and structural materials:
White plaster
White terra-cotta
White porcelain enamel
Limestone
Sandstone
Marble
Gray cement
Granite
90-92%
65-80%
Building materials:
Silver
Typical diffusing materials
Brick: Red.
Light buff
Dark buff
Wood:
Light birch
Light oak
Dark oak
Mahogany
Walnut
Paint:
New white tnaint
Old white paint
60-83%
35-60%
20-40%
30-70%
20-30%
20-25%
10-20%
40-45%
35-40%
35-50%
25-35%
10-15%
6-12%
5-10%
75-90%
50-70%
Fig. 2.15 Percentage of incident
solar radiation specularely or diffuseley
reflected (from 'Arch.
Inter. Systems', Flynn,J.)
I
38
reflected light.
It is usually possible, to establish the
/
predominant characteristics of a given material with the
help of established tabular data (Fig. 2.15) or by visual
inspection.
direct
light
Any visual roughness will indicate, the the
surface has some diffusing properties.
Fig.2.16 shows a
way to determine the reflectance of a material with the
help of a lightmeter:
REFLECTANCE of surface
=
REFLECTED
INCIDENT
%
In both kinds of reflection - specular or diffuse - some
of the radiant energy is absorbed and transformed into
heat.
The darker the color, the less is reflected and the
more is absorbed and converted.
This property is partic-
ularly important, since together with the selective use
of specific glazing options (see section on glazing) it
provides a very subtle means of modulating the daylight
solar gain ratio by selectively determining the reflection
characteristics of the light introducing surface and ceilings and walls for a particular design application.
glazing materials
This section briefly describes the primary types of
Fig. 2.16 Approximate reflectance measurements of a given material with a
hindheld lightmeter
39
glass products currently available to the architect and
how they can be applied.
In addition, it introduces two
new, highly innovative glazing products - optically transparent, selective transmitting glass coatings, referred
to as "Commercial Heat Mirror" and "Residential Heat Mirror.
A window acts as the interface element between adjoining environments, glazing materials act as the interface medium.
In early history, until the Romans intro-
duced transparent glazing materials, commonly used materials were alabaster, mica, oiled linen and shell.
Even
recently, American colonists used parchment and oiled paper before glass became available.
Ideally, a window serves to keep out undesirable external elements while admitting those elements which are
desirable (Fig. 2.17).It moderates view, heat and light in
an interior space.
These moderations are achieved
through four primary types of glazing materials:
- transparent
- diffussing
Elevat ion
-
Fig.
directionally transmitting
- selectively transmitting, including:
directionally selective
spectrally selective
2.17
Sec t ion
Traditional window detail from
Najwani house, India.
40
Light can either pass directly through the glazing
Approximate
Material
material, as in transparent glazings, or it can be redirected in translucent or optical glazings.
A transparent
glazing material preserves the image, since light passes
through with little or no directional change.
Trans-
parent glass is clearly the most common type of glazing
material in use today.
It is available with varying de-
grees of strength, breakage resistance and thickness,
clear, reflective or absorptive.
Transmittance factors
(Fig.2.19)indicate the proportion of incoming light that
is allowed to pass through a specific type of glazing material.
portions.
Transmittance
(per cent)
Polished Plate/Float Glass
Sheet Glass
Heat Absorbing Plate Glass
Heat Absorbing Sheet Glass
Tinted Polished Plate
80-90
85-91
70-80
70-85
40-50
Reflective Glass
23-40
Figure Glass
Corrugated Glass
Glass Block
Clear Plastic Sheet
Tinted Plastic Sheet
Colorless Patterned Plastic
White Translucent Plastic
70-90
80-85
60-80
80-92
90-42
80-90
10-80
Glass Fiber Reinforced Plastic
5-80
Double Glazed-2Lights Clear Glass
77
The remaining light is reflected in varying proA translucent glazing material creates a non-
selective diffusion of transmitted light.
As the diffu-
sion level increases, the transmittance decreases.
Typi-
cal translucent glazing materials include opal glass,
coated and "frosted" glasses, various types of patterned,
hammered and textured glass, fabrics, fiberglass and
plastics.
An example of the use of diffusing glazing material
for a Passive Solar design application is the St. Georges
School in England (Fig.2.20).
used to break up the light.
Includes single glass. double glazed units and laminated assemblies.
specific values.
,o
Consult manufacturer's mateia
Here, patterned glass is
Sunlight enters the room
diffusely, rather than specularly, so solar energy is
Fig. 2.19
Typical transmittance
values for common glazing
materials.
41
distributed uniformly over the building mass.
This is
advantageous for solar heat gain purposes; however, it
causes significant glare problems on sunny days and does
not provide important "visual connection" (see Section
2d
,
page 27) with the outdoors.
Directional Transmittance.
Optical glazings, such
as prismatic glass, fresnel lenses, plastics and glass
block produce a definite controlled change in the direction of transmitted light by refraction.
The most widely
used type of directional transmitting glazings is lightdirecting glass block.
1S
Prismatic glass has one smooth
face and one surface made up of parallel prisms, which
refract the light in a certain direction according to
the angle of incidence of the light (directionally selective), and the angle of the prism.
Prismatic glass is
available in three angles, each of which is specifically
designed for a particular angle of incidence.
One important application of prismatic glass is to counteract, in dense urban locations, for example, the effect of sky obstruction through opposite tall structures.
By refracting skylight which reaches the window plane at
particular incident angles, it increases the daylight
levels in the deep zone of a room significantly
Fig. 2.20
Saint George School,
Wallasey, England
42
Since this material is translucent, and therefore
does not provide view to the exterior, one possible application might be to use prismatic glass for the upper third
of the window and clear glass for the lower part.
Selective Transmittance.
Tinted, heat-absorbing and
heat-reflecting glasses are spectrally selective materials (Fig.2.19).
These low transmission glasses are exten-
sively used in commercial buildings (Fig.2.21) to control
solar radiation and reduce sky brightness.
However, they
have an inhibiting affect on the amount of daylight admitted into the room.
This decreased level of sky and
outdoor luminance seen from the interior creates a dreary
impression.
The contradiction from incoming sensory data
(Chapter 2, page 27) of expectations based on time orientation and not the low level of luminance causes this sensation of gloom.
new glas technology
Fig. 2.21
The M.I.T. "Solar Five," a passive solar heated experimental structure, (Fig.2.12) designed by Timothy
Johnson (1978), and its most recent addition, the "Crys-
John Hancock Building,
Boston, Massachusetts,
1.1.
Pei and Partners
43
Residential Heat Mirror
7
3
Solar
spectrum
7
Commercial Heat Mirror
WAVELENGTH (mincrometore)
Fig.2.22. Ideal Heat Mirror trans- 5
mission characteristics
Visible
Short Wave Infrared
Thermal, Long Wave Infrared
44
tal Pavilion" (1982) successfully demonstrate the use of
new, innovative heat-reflecting glazing products known as
"Heat-Mirrors."
Coating technology has produced this low
emissivity selective transmitting film which is applied
to the inner layer of a double-glazed window unit.
This
Transmittance
%Inch
0/(3 cm)
Glass
Clear
Gray
Bronze
Rellective
Reflectance
Total
Total
energy
Ultraviolet
(percent)
VIsible
(percent)
Infrared
(percenty
(percent)
78
51
43
10-60
90
62
6114
0-60
79
64
62
.10-60
85
65
66
10-60
Reflectance
total
energy
(percent)
8
6
7
8-80
chemical coating is referred to as a "Heat-Mirror," because it reduces heat loss by reflecting 75% of the long
wave infrared radiation emitted by all room surfaces back
into the space, while remaining transparent to visible
and solar radiation transmission (63-71% for double
glazed application, 72-81% for single glazing.
This coating, developed for residential buildings, has been specifically designed for
"skin-dominated" buildings (Chapter 1, page 14).
in order to maximize passive solar heating.
In most com-
mercial buildings, however, this heat gain is undesirable.
A "heat-mirror" coating for this building type must
balance the needs to transmit visible light while reducing solar heat gain.
Research into glass coatings for
these "internal-load dominated" buildings with this particular objective of low solar heat and high daylight
transmission has led to the development of a different
type of film, the "commercial heat mirror."
Jim Rosen
(M.I.T. Masters Thesis, February 1982) presents a thor-
Fig., 2.23
Transmission and reflectance
characteristics of low transmission glasses
45
ough investigation of performance and application of this
coating material, which can combine the benefits of clear
glass and low transmission glass.
The principle of this new selective transmitter is
based on the fact that the visible portions of the solar
spectrum contain less than 50% of the sun's energy.
The
remaining solar energy is contained in the near-infrared
region which is invisible to the human eye.
Therefore,
a selective coating with high transmission of visible
light and high reflectivity ofnear-infrared energy can
combine the benefits of both clear glass and reflective
glass with few of their drawbacks.
light introduction methods
There are a number of light controlling design considerations which significantly affect the shape, form and
details of a building.
An understanding of the two basic light introduction
strategies - sidelighting and toplighting - and the effects of various building elements on daylighting provides
the basis for manipulating form to achieve adequate lighting levels.
This section documents some of the most com-
46
mon types of light introduction and control methods and
presents an overview of the most important analysis techniques available to the designer today.
Unilateral Daylighting.
Most of the "classic" room
sections have been derived directly from daylighting considerations.
The high ceiling and window wall, with a
minimum room depth, is one such example developed specifically to provide daylight to all parts of the room.
The skylight, the clerestory, the sawtooth roof and the
multilaterally lighted room were all designs intended to
bring daylight deeper into a space.
Considering the na-
ture of contemporary buildings and the proliferation of
multistory buildings, the introduction of daylight through
the side of a room, i.e., side lighting, represents the
most common form of window configuration.
In fact, the
majority of interior spaces are unilaterally lighted.
The investigation presented in this thesis is exclusively limited to this type of light introduction.
There are a number of characteristics that should be
recognized in studying methods of sidelightingt
- A typical limit of daylight penetration into a
space is 15 to 20 feet from the window wall
- With a normal window wall (that means no specific
47
light introduction elements), the effective depth
--
S-
of a room should be limited to the range of 2 to
12%
8%
2-1/2 times the window height (from floor to win-
D.F.
4%
0%
dow head) for daylighting purposes
- Windows should extend as close to the ceiling as
possible, since this is the most valuable area of
.the window wall to pick up greater amount of skylight (sky component, see Section
2
c
--
12%
8%
%
--
)
possible, e.g., "task" layout must be based on
~-4~~
----
- Avoid orienting tasks towards a window whenever
-
-~~--
-
D.F.
0%
this (side-lit) conditions
Depth
The monodirectional qualities of light introduced
through side-lighting are critical:
the problem of light
distribution and glare.
Lighting from more than one side
is much more desirable.
Contrast levels - light from one
window wall falls on the other window wall - are reduced, relative illumination levels are increased and
room size perceptions are positively influenced by increasing the number of window walls.
If it is possible
to provide windows on two opposing walls, bi-directional
light will be provided, task layout will have more flexibility and a space twice as wide can be illuminated with
daylight (Fig. 2.24).
Fig. 2.24
The effect of bilateral
daylighting compared
with unilateral daylighting
48
Toplighting has been an important part of the design of public and religious buildings for thousands of
years.
Within the last decade, it is most commonly ap-
plied to manufacturing facilities, warehouses and other
commercial structures.
Direct downlight skylights are
very efficient for introducing diffussed light which is
incident from all directions of the sky.
Although less
appropriate for task lighting, they supply more uniform
light for ambient illumination.
Historically designed to exclude direct sun, the
range of application through today's technologies - diffusing glazing materials, control devices such as freon
operated power systems, etc. - has been significantly
broadened.
Glazing materials are available in a variety
of transmittances to aid in balancing total light transmission with toplight surface luminance.
Again, several
rules-of-thumb can be applied regarding the use of rooflights:
- to ensure acceptable uniformity over a reference
plane, the distance between adjacent areas of
rooflights (skylights, clerestories, etc.) should
not exceed twice the height of the rooflights above
the work plane (Hopkinson)
- give careful consideration to the excessive heat
49
I
D/a
I FA' 0/d
pro~
- ---I
rwri
r
r77
rLriinl
A~
-T
I
I
-on
LJ
LII El] (I]Liii Li]
It~\]~~iI
Fig.2.24.1 Sidelighting, rooflighting, and multiple source
lighting: design examples - room and building sections in various orientations.
I
Li
50
input, which results with improper use of skylights,
particularly when they are exposed to high levels
of illumination from direct solar radiation
-
use bouncing surfaces (e.g., splayed reveal) adjacent to any roof opening to reduce contrast and
further diffuse entering light.
Maximize the in-
terreflection of light that enters a space by using
light colors on the undersides of any roof area
-
40
consider maintenance problems, accumulation of
dirt, snow, etc.
Fig. 2.25 shows a good example of top lighting in
the
study of a General Electric plant, 340 feet long with a
sawtooth span of 25 feet, which gained high illumination
and uniformity.
Conventional skylights are limited to
providing daylight in one story or multi-atrium spaces,
but several concepts recently have been explored that use
direct sunlight through a roof aperture and then distribute that light through the building by using mirrors, lenses and other optical controls.
Such schemes are feasi-
ble, but their optical performance requirements and complexity limit their practical use in most building applications (see TVA-building, Appendix al ).
Fig. 2.25 Natural lighting
of a General Electric plant with
high illumination
and uniformity.
51
analytical methods
A major obstacle to efficient daylight design and its
implementation through the planning and design process is
the continuous lack of simple and accurate analytical
methods.
For an architect to include natural daylight
effectively into the building design, it is necessary
that the skin analysis and the building plan development
take place simultaneously.
There are a variety of techniques available to the
architect for simulating the daylighting performance of
buildings:
- graphical methods (protractor, etc.)
- mathematical calculations in form of computer
programs ...
and programmable hand calculator
programs (Texas Instrument T1-59, etc.)
- physical scale models
- full scale mock-up
For large buildings a combination of these methods
are the most likely solution.
Calculations are at best
a representation, or simplification of reality.
All com-
puter programs are a model of reality; what they do and
do not measure is frequently more important than how well
52
they measure a given element.
The daylight designs must,
therefore, approach all such programs and calculations as
useful, but not conclusive, information.
It is advisable
to use such programs parametrically, to investigate, rather than solve a particular question.
A physical scale model of the investigated space is,
therefore, the most simple and versatile design tool,
since it is the only one enhancing the opportunity for
qualitative evaluation through visual observation and
photography.
Daylight is a visual, dynamic phenomenon.
One should
believe one's common sense and eyes and use them to challenge calculations.
Hopkinson states, that
"whenever we treat lighting in purely physical,
quantitative terms... we must constantly sit
back and think where our calculations are leading us. If they lead us to a design, that common sense and experience tell us will be disliked,
there is no choice but to examine the design on
those grounds and to reject it if it is clearly
at fault."
53 .
THERE IS MORE LIGHT HERE
Someone saw Nasrudin searching for something on the
ground.
"What have yoti lost, Mulla?" he asked.
key," said the Mulla.
"My
So they both went down on their
knees and looked for it.
After a time the other man asked:
"Where exactly
did you drop it?"
"In
my own house."
"Then why are you looking here?"
"There is
more light here than inside my own house."
- The Exploits of the
Incomparable Mulla
Nasrudin
54
3
proposed
daylight introduction system
The limit of daylight utilization in a typical space
has been traditionally in the range of 15 to 20 feet from
the window wall.
The proposed daylighting introduction
system described in this chapter tries to maximize possible penetration in unilaterally side-lit rooms to a
maximum depth of 48 feet.
Through a particular light-
shelf configuration integrated as an architectural element, it attempts to meet all important criteria - quality, quantity, contrast reduction, low maintenance, etc. which were described in previous sections.
In addition,
it offers, together with various other components
ing materials like commercial "heat-mirror" - a key role
in modulating solar radiation entering the space for heat
gain diffusion on distributed thermal building mass.
An extensive daylight model experiment is executed
55
and documented to evaluate through quantitative data and
qualitative impressions through observation - the proposed
design in direct comparison with traditional window wall
concepts.
Its integration with dynamic artificial light-
ing system - "software" and "hardware" (see Section 3d)is studied.
Finally, an argument is made for the addi-
tional effort of daylighting not only on the basis of
energy conservation in a one-sided economic cost-benefit
analysis, but also in the context of humane as well as
efficient environments.
Building configuration - compact versus extended
building forms - is the first parameter influencing daylight utilization in an interior space.
While the ther-
mal requirements of a building call for a low surface to
volume ratio, the need for natural illumination is just
the opposite.
Massive, centralized, compact forms have
been generated by the pressures of high urban land costs,
increasing building material costs, business organizational requirements and, in part, by overly simplistic energy
conservation means to minimize external envelope area.
The second, most important set of parameters is the
location, shape and arrangement of the window component.
Appendix a
describes various light introduction schemes
using highly innovative components.
56
Original investigations for this thesis began with
the search for the design of a "diffuser-element" for
solar heat gain applications.
In order to passively so-
lar heat a space efficiently, and distribute radiation
uniformly onto distributed building mass, sunlight would
have to enter this space diffusely rather than specularly
(see Section 2f , p.
41, St Georges School).
To do this
successfully, this "diffuser-element" has to meet the following important criteria:
- view to outside cannot be obscured
- the diffuser cannot become a bright light source
(visual comfort)
- light must be broken up and distributed uniformly
- solar gain must be maintained
- ventilation must be possible
If the diffusion takes place in the window plane, all
of the listed requirements cannot possibly be met.
If,
for example, the diffusion is increased through application of a translucent glazing material, the windows become an intolerable source of glare.
In the course of this investigation, interest in daylight application grew and a moderate shift took place towards integration of both design objectives - daylight for
illumination and solar radiation for heat gains - in one
57
element, with equal priorities, but optional characteristics.
After defining all important requirements, the
approach became clear:
separation of fenestration into
two levels through the introduction of a light-shelf.
The division into an upper and lower part above eye-level
allows different treatment and control of each section,
according to specific applications.
Direct sunlight is
specularly reflected from the top of the
lightshelf (Fig. 3.1)
traditional
and redirected into the space onto
the ceiling, without obscuring and impairing view and
visual comfort below.
The "diffusing-element" has moved from the window
plane into the space:
the ceiling now acts as the inter-
mediate diffuser, eliminating potential glare problems at
the window.
Through careful selection of reflectivity
and of ceiling and wall finishes, this can be efficiently
optimized, bouncing light around the room for good lighting
levels and optional heat.
while this heat gain is general-
ly desirable in passive solar designs (residential, etc.),
it is mostly undesirable in internal-load-dominated commercial structures.
In order to control and modulate thermal
requirements and illumination objectives most effectively
for this building type, selective glazing options are
applied.
In order to assess the overall utility of solar
Fig. 3.1
12
Traditional lightshelf
58
gain, an examination of the entire building must occur:
glazing cannot be treated in isolation.
For example, if
solar heat gain is to be minimized year-round for a specific design application - high internal load or climatic
reasons - "commercial heat-mirror" (see Section 2f page 38
)
should be applied above the lightshelf level, thus reducing it by approximately half, while daylight transmission
is hardly affected.
If the additional heat gain through
solar radiation is desired and measures of heat loss prevention are advisable - low internal load and severe climatical constraints - "residential-heat mirror" (see Section 2f
page 38 ) can be used.
In addition, through man-
ipulation of the lightshelf surface's reflection/diffusion
characteristics (high specular, semi-specular, glossy,
etc.) the ratio of daylight versus radiation distribution
can be subtly altered to complement above mentioned options.
Various light introduction methods and traditional
lightshelf configurations have been investigated and have
led to the following conclusion:
- light introduction components, external or internal
hardware did not integrate generally into an overall architectural form and design concept, but
mostly were added on elements (louvers, etc.) with
59
a negative aesthetic impact
- continuous adjustments to varying sun angles had
to be made to continuously optimize system performance.
'ppuppu
~
'E
Or, in the case of the traditional, flat
lightshelf, accept a constantly varying referencerange, to which sunlight is being redirected, and
therefore a limited penetration of natural light
- maintenance problems (accumulation of dirt, etc.)
VjFPUWIUN~~
Yr~Fu"
of exterior components exposed to weather elements
architectural integration
The proposed daylight introduction system overcomes
these drawbacks and establishes new options.
Figure
shows a section through a typical 48 feet deep space with
the proposed lightshelf configuration integrated into the
window wall.
The facade design is based on a modular sys-
tem, using prefabricated lightweight concrete wall elements (Fig. 3.2).
Thus,the lightshelf, as an integrated
component of this system, provides a natural architectural break to define different functions.
Fig. 3.2
Prefabricated window wall
60
In addition, it incorporates a cove (Fig.3.3 ) for
artificial lighting hardware for indirect illumination in
the perimeter zone (the overall artificial lighting system and its
integration is
explained in
Chapter 3d
).
Ceiling
The exclusion of any possible glare through direct beam
radiation originating from the specular surface of the
artificial
lighting
cove
lightshelf, at any point at eye-level in a daylit room,
is another important function of this cove.
reflect:
surface
Finally, the criterion to eliminate any necessary
seasonal adjustments for higher or lower sunangles, determined the final geometric configuration of the element:
The receiving reflective surface is geometrically shaped
in such a way that it accepts a maximum of incident sunangles (assumed for this study - maximum 720, minimum 260
for Boston 42* latitude) yet without adjustments, redirects this incident radiation and light onto the same
reference range (for this study approximately 48 feet
into the space) independent of the sun's altitude.
In order to accept high sunangles, the lightshelf
element had to be extended beyond the window wall plane
to the exterior.
Through a 58* inclination of the upper
level glazing component, an exposure of the reflecting
surfaces of the shelf to weather and increased dirt accumulation was avoided.
In addition, glazing placement
Fig. 3.3
Lightshelf component with
integrated lighting cove
I
61
angles play an important role in determining the quantity
of light transmitted.
Low incident angles of the sun's
rays relative to the glazing surface increase reflection
losses and decrease transmission.
Through interpolation
of highest and lowest incident angle of the sun's rays on
a south facing vertical surface, "Normal to window" (see
Appendix
d
for definition) was identified, and, with a
minimal correction towards lower altitudes, the tilt of
the glazing component was determined (58* to the horizontal).
Finally, the precast concrete framing system developed for this study, its angular principle and the extension beyond the office space to the outdoors provide opportunity for sun shading
ements
-
-
horizontal and vertical el-
and additional surfaces for bouncing daylight
into interior spaces.
Fig. 3,4
daylight model experiments
Out of the variety of analytical methods described
in Chapter 3.h the use of a physical scale model has been
selected to test and evaluate performance of the proposed
light introduction system.
With an equal emphasis on
Daylighting model: facade
elementa.
62
Sun
Ceiling
Sun
angle
260
Artificial
Lighting
Cove
Lightshelf
component
Office Space Interior
Fig.
3.4.1
Integrated
Lightshelfcomponent,
section
scale 1/2"= 1'
63
both qualitative and quantitative aspects, a model simulation still provides the most valuable means of visual
assessment.
It is specifically important for this study,
where a sophisticated lightshelf configuration is tested
to redistribute sunlight and to find out where it is
beamed at and what the qualitative, visual distribution
looks like.
This section documents construction and use of the
scale model (Fig. 3.4),model and external condition parameters, comparative tests of traditional window walls
with the proposed configuration and the general test setup and procedure.
Results are analyzed and discussed
and design graphs are presented to increase the usefulness of obtained tabular data.
model:
scale and construction
A model, duplicating a full scale space in geometry
and reflectivity of surfaces, will accurately yield identical light levels under identical skies.
To ensure maxi-
mum flexibility, it was built in a modular fashion (Figs.
3.5-3.9
).
Facade components, walls, ceiling and floor
are easily interchangeable to test different surface reflectivities and finishes.
The scale selected was one
Fig. 3.5-3.9 Daylighting model: modular
assembly (following pages)-
I
64
40 A,
...... . .
Lrn
66
67
4
I
'4,
00I
i
I
I
i
I
68
69
inch equals one foot, a minimum recommended for daylight
models.
It facilitates visual inspection and reduces po-
tential modeling errors attributed to the small scale.
To ensure compatibility with a full scale, typical office
space as closely as possible and simulate real space
conditions in terms of surrounding reflecting surfaces,
scale furniture was installed.
Full scale, daylight test
model and location parameters are summarized in Fig. 3.14.
Three different window walls were tested.
The pro-
posed "splayed" window wall (Fig.3.10) with integrated lightshelf configuration was compared to a conventional curtain wall without any light introducing elements (Fig.3.11) and a facade with a traditional, flat
lightshelf (Fig.3.12).
Further, four different reflec-
tive/diffusive lightshelf surfaces (Fig.3.13) were tested.
The "splayed" window wall was built adjustable to accomodate these varying surfaces.
In order to establish
different reflection/diffusion characteristics, the following materials were selected:
I
- high-specular aluminum mylar .. 91% reflectance........
- semi-specular chrome foil.....82% reflectance......
- semi-gloss aluminum tape......43% reflectance....
- semi-gloss white spray-paint
..
55% reflectance..
Fig.
3.13 Tested reflectances
70
Traditional window wall:
Overall dimension and reflectances of modeled space:
Room width. . .
Room depth . .
Ceiling height .
-
-.
-.
. . . -.
Wall reflectance. . . . . .
. . . . . . . . .
Ceiling reflectance . . .
Floor reflectance . .
. .
. . . . . . . .
. . . . . . . ..
. . . . . . . . . .
-.
. .
.
6"
6"
10' 0"
-
.. .. ... .
. . . *.
Sill height . . . . . . . .
Scale of model
25'
48'
. . -.
. . . . . . . . . .. .
. . . . . . . . . . . . . . -
2' 0"
.
5"-6"
. . .
2'-0"
. . . .
Window height . . . . .
Proposed configuration:
Sill height. . . . .
Window height . .
. . . .
. .
. . . . .
. . .
58%
Lightshelf to ceiling. .
.
65%
Lightshelf surface reflectance:
.
4'-6
.
'-0"
. . . . .
41%
. . .
Room dimensions and sensor locationplan:
.
91%
b. semi-specular chrome foil . . . .
82%
c. semi-gloss aluminum tape. . . . .
43%
. . . .
55%
. . . . .
20%
a. high-specular aluminized mylar.
d. semi-gloss white paint. .
Ground reflectance . . . .
Location test site:
M.I.T. - Campus,
Cambridge, Massachusetts
Latitude . . . . . .
Area condition .
. . . .
. . . . .
Climate condition. . . .
Obstructions
Fig. 3.14
Daylight test model, test site and sensor location parameters.
. .
. . . .
. . . . 420 L
. . . . .urban
. . . .temperate
. . .
. . . none
71
photometric
sensor
equipment
Six photometric sensors and a "Vactec" photometer
unit, with a range of 0 to
10000
footcandles, were used
to record interior and exterior lighting levels.
The equipment was generously made available by William Lam Assoc., Lighting Consultants, Cambridge,
Massachusetts.
For a more accurate distinction of day-
light conditions in the space and to define sensor locations in the tested model, the room was divided into three
zones:
- PERIMETER ZONE
The zone where direct daylight penetration is
effective.
-
INTERMEDIATE ZONE
The zone beyond the perimeter, where daylight
can be directed utilizing simple, stationary,
non-concentrating means.
- DEEP ZONE
The core area, where daylight is diminished by
distance and concentrating and bouncing methods
are required.
72
Sensors were located in the center of each zone along
the rooms centerline
(Figs.3.6
,
3.7 ,3.8)
feet from the window wall; Sensor
42 feet
-
-
Sensor,
8
, 24 feet; Sensor
and two additional ones on both sides of Sensor
One
III to obtain additional readings in the deep zone.
sensor was
placed outside on top of the model to simul-
taneously record exterior illumination levels on a horizontal plane whenever interior light levels were measured.
All five interior photometric sensors were raised to a
level to correspond to desk height (3 feet).
Locations
of sensors were unchanged throughout the test period.
model testing
The model experiments were carried out in Cambridge,
M.I.T. West Campus, in front of the M.I.T. Solar 5 Building (see location parameters, Fig.3.14).
The site, a
large open field with no obstructions and reflections
from surrounding buildings, offered good outdoor conditions with average ground reflection of approximately 25%
Final test data was recorded over the period of two
days, one overcast
-
April 25, 1982
-
and one clear
-
April 29, 1982.
Fig. 3.10-3.12 Window wall configurations
tested
73
The scale model was used to test the proposed light
introduction strategy, to varify its performance under different sun altitudes and relative azimuths and to compare
the daylight levels to conventional window configurations.
With emphasis on comparative values, I also wanted
to obtain illumination data for most of the year for both
To achieve this, the following steps
overcast and clear.
A range of representative sun altitude angles
were taken:
were selected
63*--- 42*---21*---
and the corresponding
time for this latitude (42*L) and days of testing (April
This was sufficient for cloudy day
25, 29) calculated.
testing, since the distribution of light from an overcast
day is independant of the sun's azimuth (see Fig.2.7 p.25).
For clear day testing, this is more complex.
In ad-
dition to reorienting the model to selected sun altitudes
to simulate solar noon, a number of relative solar szimuth had to be tested - 0*,
2 0 *,
45* - since interior il-
lumination levels for a clear sky depend both on the sun's
altitude and azimuth.
The optimal way to test a model would be to monitor
it continuously over a period of six months or a year.
To restrict it, as a practical alternative, to two days
of testing - clear and overcast - has created,during this
model experiment, only one important limitation:
the sun's
74
peak altitude of 640 at solar noon on the clear day tested
(April 29) had to be accepted as the highest angle for
this model simulation.
To tilt the model downwards to
simulate higher summer sun angles, strongly influences
interior light levels, since the model suddenly "sees" a
different portion of ground and sky.
Further, the inten-
sity of sunlight varies with the solar altitude because
of the thickness of the atmosphere through which it must
travel.
Tables 3.1 to 3.3 represent the data collected during both of these test days.
75
EXTERIOR
traditLonat window wall,
no daylight
Introduction system
w2idow
wall1
with traditional
'lightshelf'
RELATIVE
SOLAR
AZIMUTH
SOLAR
ALTITUDE
6*
63*
63*
61*
42'
42*
42*
21'
21*
21*
0*
20
450
18fl
0'
20*
45*
0'
20*
4S*
63*_
63*
63
63*
42'
42i0
42*
21*
*
709
45*
180*
0'
45*
0*
70
21"
45"
21'
'splayed' window wall
hatograted lightshelf
sigit
conI
gusrata.n, surface42*
surface
reflctance. . . . . i.hspecu.
.1*
3
63*
63
61*
63*
42"
42*
21*
21'
Table 3.1.
Clear Day:
0
0*
*0
45*
180'
0*
20*
450
0
20*
45*
I.I.tUMINATION
ON A HbORIZONTAL
SURFACE
6750
6580
6720
400
5600
31005
4950
3620
3100
30R0
6650
PlERIHETER
ZONE
-530
505
410
165
779
7
60
3280
2450
1625
445
430
330
160
742
730
540
838
710
-
A6n
6
6590
6400
5480
5180
4800
3800
3100
o0o0545
6600
6980650n
6400
5250
5600
4620
3720
3320
2955
--
620
570
440
140
930
895
623
920
772
532
INTERIOR
ILLUMINATION
MEASURED
INTERMEDIATE
DEEP
ZONE
ZONE
15
___60 57
140 - -55 48
115
45 40
59
26 -2
75 67
212
-_ 178
6460576
148 5 7
240
91 75
75 67
212
43 39
129
128
120
9
60
205
185
140
258
239
135
168
15
11.2
50
265
232
150
268
235
128
-
58
52
40
29
77
68
51
99
85
52
44
-35
25
67
62
45
82
26
60
44
41
23
69
49
79
63
39
57
46
37
26
70
60
48
88
71
INTERIOR
ILLUMINATION
CORRECTED 85% TRANSM.
PERIMETER
INTERIMEDIATE
DEEP
ZONE
ZONE
ZONE
127
51
48 51
A 50
46 40 37
119
429
97
38 34 34
348
140
50
22 18 19
180
63 56 58
662
637
151
54 51A8
56
125
45 39 41
2788
204
77 63 67
63 56 53
180
2082
1381
106
36 33 33
108
102
84
51
174
157
119
219
201
49 44 48
44 L7 39
34-29 3L
24 21 2
65 56 59
57 52 51
43 38 40
84 69 74
72 22 60
-
114
41
1
180452
2
127
95
42
225
197
127
227
199
108
71
59
40
21
93
73
378
365
280
136
630
620
459
712
603
494243
463
710 72 56
48 51 40
25 21 22
110 103 100
87 87 71
55 49 48
110 91 96
86 81 71
46 39 39
484
74
119
790
760
592
782
656
452
35
68
61
43
17
87
73
i4T6
93 77
73 68
39 33
36
62
47
34
18
85
60
40
81
60
33
daylight model data recorded for selected test configurations (cont'd. Table 3.2).
76
INTERIOR
ILLUMINATION
CORRECTED 85% TRANSM.
PERIMETER
INTERMEDIATE
DEEP
ZONE
ZONE
ZONE
INTERIOR
SOLAR
ALTITUDE
'tipiyed' window wall
Intenrated 1ightshelf
configuration, surface
reflectance. . . . . . . .
821
semi-specular
'splayed' window wall
Integrated llghtshelf
configuration., surface
43%
reflectance. . . . . . . .
semi-gloss
63*
63*
63*
630
-120
42
42*
210
210
21*
0*
?0*
45*
180*
00
200
450
0*
200
45*
630
630
63"
63*
490
42"
42*
21*
21
21*
'splayed'window wall
integrated lightshelf
confIguration, surface
552
reflectance. . . . . . . .
semi-gloss white
63*
fl
63
630
42_
42*
474*
210
PERIMETER
ZONE
6850
90
6480
6400
5370
5480
4750
3600
3350
MFASURED
INTERMEDIATE
ZONE
290
587
548
412
139
928
875
595
870
770
505
153
149
110
50
260
250
145
272
232
124
00
20*
45*
180*
0*
20*
450
0*
2
45*
6500
_6620
6580
6450
5370
5520
4650
3400
3300
2710
345
310
248
125
635
580
390
550
545
362
98
92
76
51
180
160
105
205
185
98
0*
*
451
180*
0*
20*
6580
66?1
658
6450
5400
5550
15?0
3600
3580
2650
420
380
310
135
780
708
468
718
692
437
115
109
89
51
210
165
118
235
208
109
2
0
21*
21
Table 3.2.
RELATIVE
SOLAR
AZIMUTH
ILLUMINATION
EXTERIOR
ILLUMINATION
ON A HbORIZONTAL
SURFACK
0
450
-
-
Clear Day data for selected test configurations.
DEEP
ZONE
75
70
69
69
45
44
24
21
110 100
~6787
53
47
108
92
84
79
45
39
45
9
498
465
350
118
88
7
4 3
505
739
654
429
70
36
3
37
30
21
62
57
34
69
68
31
36
29
22
65
53
34
74
58
31
293
263
210
106
539
493
331
467
463
307
50
47
37
25
82
71
45
95
78
40
43
41
33
20
72
64
40
79
69
34
44
42
33
21
75
62
40
84
65
34
357
323
263
114
663
601
397
610
588
371
42
33
25
71
62
39
,
69
55
39
22
100
71
46
98
69
39
64
i
130
126
93
42
221
212
123
231
197
10
63
58
38
20
93
73
45
91
1
38
58
46
33
18
85
73 6d
39 39
78 83
6T 58
3 3
83
78
64
43
153
136
89
174
157
83
38
35
28
21
60
52
33
71
59
30
33 34
31 30
25 24
17 18
52 55
48 45
28 28
58 62
57 49
26 26
97
92
75
43
178
140
100
199
176
92
42
39
31
21
69
60
3&
80
66
34
36
34
28
17
61
54
34
67
58
59
58
37
17
85
28
37
35
28
17
63
52
34
71
55
28
77
63*
RELATIVE
SOLAR
AZIMUTH
00
180*
40
42*
27"
27*
630
630
42
420
270
1A0*
O*
190*00
1800
0
1800
00
27*
1800
SOLAR
ALTITUDE
61*
traditional window wall,
daylight
introduction system
1no
wIndow wall
with traditional
'ghstshelf'
3
I
63"
630
-4.20
420
27*
27*
'splayed' window wall
integtrated lightshelf
configuratlon, surface
refectance
semispecular
630
630
42*
420
0*
1800
02
180**
27*
180
482%
Integrated lightshelf
conflgtiration, surface
reflectancee.
. . --
63*
-
630
420
-.
43%
.
27*
2763a
'splayed'window w630
Integrated 1lgltslself
eaconfieratio, surface
semi-gloss white
(.10
3820
2820
2200
00
180*
00
1800
9splayed' widow wall
itegrated lightshelf
conifiguiration, surface
reflectance. . . . . . . .
91%
high-apecular
'splayed' window wall
5
o*
EXTERIOR
ILLUMINATION
ON A HORIZONTAL
SIRFACE
3620
-3800
1980
2040
1430
600
3860
3400
1985
2200
1580
180*
0*
__
168
138
152
89
2408
51
800
__
_
180*
???0
180
2180
00
180*
0"
1800
1595
1000
3700
3050
170
145
140
92?
4Q
285
3900
2800
2180
__
64
305
187
340
138
91
17
28
-
2320
1400
620
PERIMETER
ZONE
405
250
170
162
1.1.2 -
..
_20
115
991
60
47
260
146
INTERIOR
ILLUMINATION
MIMSURED
INTERMEDIATE
ZONE
89
50
37
35
28IQ10 _
87
48
47
1
40
29
11
75
44
4..0
40
.. 25
1n
76
46
43
42
301.J2
13
6733
21
19
13
77
41
32
17
13.
15
10
4
33
16
5
17
11
5
34
15
17
17
11
4
DEEP
ZONE
29 30
15 16
12 13
12 13
9)
9
4
3
28 31
14 15
314
14 15
9 10
4
3
9
_n
14 14
15 16
14 16
9 10
3
4
33
16
16
28
10
6
28
14
14
14
8
4
20
11
10
18
13I
7
6
31
14
27
15
15
16
9
5
23
1
11 1
6
7
.
4
25 29
12 13
?7"
1800
0 *
180*
I
DEEP
ZONE
21
6
9
8
8
7
8
5
7
1
1
1
2
2
1
1
1
1 L_
1
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
_
1
?
6
1
1
1
1
6
6
7
6
7
?
2
2
2
2
2
1
1
1
1
1
1
1
1
1
1
6
2
1
1
1
?
-L-
L
L_7
___
6
9
7
6
6
6
5
6
6
2
2
2
2
2
.4.
51
4
5
7
5
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
_-
_
1
1
2
T
1
1
1
I
1
1
1
1
1
1
1
1
1
1
1
1
1
5
4200_2_2-______2--
42"
27 *
PERIMETER
ZONE
INTERIOR
ILLUMINATION
D.F. %*
INTERMEDIATE
ZONE
2450
1250
1?00
128
__.
65
28
19
17 13
6
8
6
8
15
5
1
7
5
1
7
5
1
divided by the illumination
*D.F. = Daylight factor expressed as the illumination at a point indoors
received silultaneously outdoors on an unobstructed horizontal surface.
Table 3.3.
Daylight model data taken under overcast day (April 25th, 1982).
77.
MORE USEFUL
Nashrudin entered the teahouse and declaimed:
moon is more useful than the sun."
"Why Mulla?"
"We need the light more during the night than
during the day."
The Pleasantries of
the Incredible Mulla
Nasrudin
"The
78
analysis of data
In order to gain familiarity with test site and conditions, data recording procedure and equipment, and to
exclude any possible modelling and data collecting errors
during the final 2 days of testing, an informal preliminary test was carried out under clear sky condition at location.
During this stage, several refinements were made
and some comparitive measurements were taken to define the
performance range.
It
was found that,
in
order to objectively compare
different configurations and strategies, measurements
had to be taken as closely spaced as possible because of
daylight level fluctuations.
Furthermore, by comparing
an overall room wall reflectance of 40% to a reflectivity
of 60%, the lightlevel
in the perimeter zone showed a
significant increase of approximately 15%, while the
lightlevel in the deep zone remained the same, thereby
contributing to a higher contrast level between the two
zones.
A possible implementation of this finding could
be a light gradation of wall tones, i.e., decreasing
Fig. 3.13
Visual effects of light diffusion from a bright surface
/79
reflectivity towards the window wall in predominantly
sunny climates with high exterior luminance.
Figure 1
visualizes this effect and the amount of diffused daylight reflected from a wall receiving direct sunlight.
Note the fading shadow (due to the diffused light received from the white wall) on the bottom of the picture
compared to the dark shadow in the center.
A mirror replacing an opaque side wall in the scale
model was used to simulate a space double the width of
the original model and to evaluate its effect on light
distribution as a function of room width.
Informal tests
showed that lightlevels in perimeter and intermediate
zones fluctuated significantly with or without direct
beam exposure and the mirror wall was eliminated from
final testing.
Final data was recorded on April 25 (overcast) and
April 29th (clear sky).
Tables
3.1 to 3.3
show the
measured interior and exterior illumination values and
data for all 6 options.
In order to compare the different window strategies,
the raw data had to be corrected, accounting for various
parameters such as daylight fluctuations, dirt accumulation and the type of glazing used for the various applications in the real space.
A single glazing with a trans-
Fig. 3.14
Mirror wall experiments
80
mission of 85% was assumed for this experiment.
The re-
corded data from the overcast day (Table 3.3) was expressed in Daylight Factors.
The Daylight Factor is de-
fined as the ratio of the internal illumination to the
illumination simultaneously available outdoors.
This has
the advantage that, even though the daylight outdoors may
increase or decrease, the Daylight Factor will remain
constant because the interior illumination is also changing with the exterior daylight.
The clear day data with
a blue sky of fairly constant luminance, was corrected
for the transmission losses and expressed in footcandles
(fc).
Any account of the proposed system's realistic
maintenance is still conjecture.
Studies on the effect
of dirt on light transmission and reflection indicate
that surface dirt will, to a certain extent impair the
specular reflection of direct beam and to a lesser degree,
diffusion.
Design graphs were prepared to increase the usefulness of the tabular data and to provide a quick visual
impression of comparative performance
(Figs. 3.15 to 3 .1
8
).
All six options tested were evaluated under two equally
important considerations:
distribution.
issues:
quality and quantity of light
Included in this assessment were several
Figs. 3.15 to 3.18 (following pages) Data
graphs for clear and
overcast sky
81
Sun
Altitude 630
U
4.4
Sun
Altitude 420
0
0'A
0
0
0~
0
-t
0
0
.4
Sun
Altitude 210
0
0
U,
I
In
11
0
0
I.
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U
4.'
00
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00
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in,
IA
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0
8
I
24
FEET
40
48
0
8
24
40
48
0
I
I
8
24
- traditional window wall, no lightshelf ....................
- window wall, with traditional flat lightshelf..............
- 'splayed' window wall, with integrated lightshelf
ation, surface reletac:
uuigur
Fig. 3.15. CLEAR DAY:
comparative light distribution in modeled space
(depth of penetration) as a function of various sun altitudes.
40
48
FEET
FEET
- high specular
( 91%
- semi-specular
( 82%
- semi-gloss white ( 55%
- semi-gloss
( 43%
) .........
>.......
).......
).........
-0-0-e-
a-*-
82
traditional
window wall,
no lightshelf
r4
0-
('
'splayed'
window wall
-
o-
high specular
0
0
U
1%%%
*%.
%%.
1%N..
'44
H
window wall,
traditional
lightshelf
'
Ii
"4
'-4
H
C%.
H
IA4
4
'-4
M
'4
'4
'-4
1
20
0
1
45
0
180
RELATIVE AZIMUTH ( degrees )
0
('4-4
20
RELATIVE AZIMUTH ( degrees
0
C4.
'splayed'
window wall,
0
180
45
a
1
20
45
RELATIVE AZIMUTH ( degrqes
)
0
(-4-4
'splayed'
window wall,
U
semi-gloss
semi-gloss white
semi-specular
'4%....
0-
"'4..
'4%..
0'
)
'splayed'
window wall.,
eq
0-
180
0~
0
'44
""C-
'-4
44
-4
0
0~
0d
H
H
1-4
'0
4
0~
'C
H
'-4
'-4
H
0-
C',
I
0
20
I
45
RELATIVE AZIMUTH ( degrees
180
)
0
20
45
RELATIVE AZIMUTH ( degrees
Fig. 316. CLEAR SKY:
Interior Illumination in (fc) for Deep Zone
as a function of the sun's azimuth.
180
)
0
I
1
20
45
180
RELATIVE AZIMUTH ( degrees
sun
altitude:
630
'-'---.42*
------
21*0
83
U
Relative
Azimuth 45*
Relative
Azimuth 20*
Relative
Azimuth 0*
0
('4
'-4
'4
0.
0
0%
'-4
U
0
0'
-
0',
Z
-4
0
0
O
0
0
0
C
Z
0
0
Mn
0
an
0
15
30
45
ALTITUDE ( degrees
60
75
0
15
30
60
45
ALTITUDE ( degrees
0
75
15
)
30
ALTITUDE
- traditional window wall, no lightshelf ....................
- window wall, with traditional flat lightshelf..............
- 'splayed' window wall, with integrated lightshelf
configuration, surface reflectance:
-
high specular
semi-specular
semi-gloss white
semi-gloss
Fig. 3.17. CLEAR SKY.
Comparative illumination levels in (fc) for Deep Zone of all
tested window wall systems as a function of
the sun's altitude.
(
(
(
(
91%
82%
55%
43%
)
)
)
)
45
60
75
( degrees )
*"**"*"***"*
-*-*-*-*
@00
-*-
84
PERIMETER ZONE
INTERMEDIATE ZONE
DEEP ZONE
C0
0
CL
Ln.
C'4
mm
-
mimi
0
C'4
0
0
C14
C4
0
'44
0
Hn
0
Hn
0
LH
z
H
H
z
0
0
r__
L0
0
10
21 30
43 50 63
Altitude (degrees)
70
z
C0
0__
0
0__
L0
Ln
0
Fig. 3.l&
OVERCAST SKY:
Interior Illumination in (fc) for Perimeter,
Intermediate and Deep Zone as a function of
the sun's altitude
10
21 30
43
50
Altitude (degrees)
63 70
0
10
21 30
43
50
63 70
Altitude (degrees)
traditional window wall, no lightshelf .....................*****.******
-e-e-*-window wall, with traditional flat lightshelf..............
'splayed' window wall, with integrated lightshelf
configuration, surface reflectance:
----( 91% ).... .. -high specular
semi-specular
( 82% )........
semi-gloss white ( 55% )..........
(43% ).........
semi-gloss
85
I
AI
86
#,
I
-J
I
88
sensitivity to off-south orientation, evenness
of light distribution for solar storage in distributed
mass, glare conditions.
In quantitative terms, the following conclusions may
be drawn:
Under clear sky, both light specular (91% reflectance) and semi-specular (82% reflectance) surfaces on
proposed daylight introduction component clearly outperform all other options.
They result in an improved over-
all daylight distribution and a significantly increased
lightlevel in the deep zone.
The high illumination lev-
els obtained - e.g., semi-specular surface, sun altitude
420,
relative azimuth 0*,
deep zone:
lightlevel at 42 feet in the
93 (fc) - suggest an even deeper daylight
utilization of space.
Most important:
the "lightshelf-component"
through its curved configuration accepts high and low
sun altitude angles with equal consideration and only
minor
lightlevel variations for redistribution into the
deep zone.
As recorded data shows, lightlevels in this
zone remain constant, e.g., 93 footcandles despite a
changing sun altitude from 42* to 21*, compared to significant fluctuations with the tested "traditional"
89
window wall systems.
A comparison of intermediate and
deep zone exhibits a remarkable consistency of lightlevels
through varying sun altitude angles.
The higher light-
level in the zone is explained by the increased amount
of light reflected onto the perimeter ceiling through
the curved high specular surface of the lightshelf and
additional diffused light from the exterior surfaces of
the "splayed" window wall components
(Fig. 3.8
,
page 71).
An analysis of lightlevels in intermediate and deep
zone as a result of an increasing sun azimuth angle (or
off-south orientations) show a relative insensitivity up
to a 30 to 35* bearings from true south.
Beyond that
range, lightlevels in these zones gradually decrease.
Re-
corded data from the daylight model experiment suggests a
limitation of a building's off-south orientation to a maximum of 100 east or west, since the proposed system's sensitivity to a larger bearing off south increases and its
overall efficiency is greatly reduced beyond that range.
Visual comparison of light distribution patterns
from all tested options show that best diffusion (most
even light distribution) for solar storage on distributed
mass is achieved with white semi-gloss or matt surfaces
on either the curved or flat lightshelf, but with serious
limitation of diffusion into the intermediate and
Fig. 3.19.Light distribution pattern on
ceiling: high specular reflection 91% (top), s.emi-gjoss aluminized 43% (bottom)
90
deep zone.
Distribution into the deep zone decreases
sharply compared to high and semi-specular surfaces, resulting in low lighting levels (Fig.3.19).
This suggests
the use of semi-specular surfaces with a reflectance in
the range of 65% to 80% in order to achieve a balanced
modulation of diffusion for solar storage and penetration
for daylighting purposes.
Under clear sky conditions, the proposed system
significantly increases illumination levels in the deep
zone.
However, with no direct beam radiation on the win-
dows, under overcast conditions, the light introducing
"components" have little effect on interior light levels.
There is only a minimal redistribution of diffused light
(Sky Component) in the perimeter zone.
Cloudy condi-
tions were not expected to greatly improve daylight penetration, since the proposed system is primarily designed
to exploit direct beam radiation for redistribution or
diffusion.
Despite this relative insensitivity of the
system to diffused skylight, light levels in the Perimeter and Intermediate Zone (8' and 24') are still sufficient for ambient light (with high and semi-high specular
surfaces) for the sky conditions tested.
(Table 3.3, page 77)
Recorded data
shows a Daylight Factor (D.F.) of 2%
maintained for this zone throughout the entire test peri-
91
od and therefore most of the occupied hours of an office
building.
This is acceptable for average cloudy sky con-
ditions of about 1500 footcandles (design minimum), since
one does not try to design for worst conditions (heavily
overcast approximately 400 - 500 fc).
In quantitative terms, under clear sky conditions,
results are encouraging:
light levels suggested for
ambient lighting (30 fc) are exceeded in all three zones
during most of the working hours for the relative orientations tested.
Enough illumination to make artificial
task light negligible (70 fc) is provided in about 50%
of time occupied.
This is achieved with a ceiling height
of 10 feet (normal office ceiling height approximately
8.6') compared to a height of 12 feet in the TVA-building
(see Appendix al).
In qualitative terms, lightlevel measurements are
subjective in several ways:
They were recorded with sens-
ors placed to simulate a work station, mainly receiving
light from the ceiling.
Consequently, the lightlevels
measured, while indicating the amount of light available
on a task, may understate the ambient lightlevel perceived
by the building's user.
Our perception of the brightness
and quality of the ambient light environment of a space
is influenced as much by light reflected from vertical
92
surfaces as from horizontal ones, since the vertical surfaces generally occupy the majority of the cone of vision
for non-writing task operations.
Since vertical walls
receive light reflected from other surfaces as well as
light from the ceiling, the space may well be perceived
as brighter than measured horizontal values indicate.
Furthermore, these values do not reflect the overall qualitative perception of a space and sources and levels of
glare.
Figure 3.33to 3.21shows the light distribution
patterns of options.
Photos are taken with a sun alti-
tude of approximately 51*.
The high specular surface
Fig. 3.20
creates the most distinct, light pattern, resulting in,
Reflected light pattern on ceiling from high specular surface
as previously discussed, the highest distributed lightlevel among all of the alternatives.
As visual inspec-
tion verified, no direct glare was received from this
highly reflective surface in any point of the room at
eye level.
Although the "light-spot" on the ceiling
close to the lightshelf dominates one's field of vision
looking towards the window wall, this disadvantage is
compensated:
additional light is reflected onto the in-
terior surfaces of the window wall, creating a "splayed"
effect and thus reducing contrast levels.
In addition,
the natural "light-spot" occupies the same area on the
ceiling as the one used for indirect illumination from
Fig. 3,21
Reflected light pattern on ceiling from semi-gloss white surface
93
the artificial lighting cove which is integrated into the
lightshelf element.
Therefore, maintaining the same dom-
inant direction in the flow fo light, the integration of
artificial and natural light is complemented.
The diffusing characteristics of the semi-specular
surface have been discussed earlier.
With a less domi-
nant, more even light pattern, this surface combined with
the proposed lightshelf configuration, represents the optimal synthesis of high penetration, moderate diffusion
and low glare.
94
integration with artificial
lighting system
Electric energy will, of course, continue to be a
major source of light, heat and cooling in buildings.
However, the economic constraints of operation forces
designers into a more careful analysis of environmental
systems, which make use of both electric energy and solar
energy.
It is not the issue of either/or - each has its
own advantages.
Rather, to achieve optimum economical
and qualitative solutions for the integration of natural
lighting, they must be used complementary and coordinated
with the total building concept.
This section documents an overall concept of integrating and optimizing both "software" - automatic control
systems, etc. - and "hardware" - lighting fixtures, their
indirect use, location, etc. - to realize energy savings
and produce a qualitative, aesthetically satisfying environment.
No technology exists in a vacuum.
While building
designers were awakening to the advantages of daylighting,
lighting product manufacturers were inventing ways to
improve task lighting while cutting down electrical consumption from over five Watt per square foot to under
two.
In reducing lighting energy consumption, they were
Tig. 3.22
Artificial lighting hardware components for indirect illumination
95
also cutting down the heat contribution from office lighting.
To reduce this heat contribution from any light-
source - both artificial and natural - and therefore airconditioning loads, is the essential goal for "internalload-dominated" structures.
Through the application of
commercial "heat-mirror" as an important component of the
proposed daylight introduction system, this heat content
of daylight - which nearly equals that of fluorescent
lighting at approximately same lighting levels - is decreased significantly (see Chapter 2 on new glazing products).
The resulting "cool" light becomes especially
attractive and economical for a variety of applications.
Integration of lighting components
into office furniture
Fig. 3.23
A similar revolution in artificial light control
Dayilght L evl
systems were automatic dimming capabilities and energy
optimization in general throughout the building.
The
inconsistency of light level from a natural source makes
150
light dimming and the automatic control capability an
30
ideal match for sophisticated daylight design in commer-
10
cial buildings.
10%
Sso
Unoccupied...
4
S I
They range from the traditional manually op-
erated on/off switches to advanced photoelectric dimming
systems.
Each type of control system has a different
I 1 S Q0 11 t 1 2
Noon
AM
3
4 S 4
PM
7 f
9
NO LIGHTING CONTROLS
A variety of control systems are available to the
designer.
Unoccupied
..
Fig. 3.24
Shaded area represents energy
required for supplementary
lighting (Ternoey et al.,1981)
96
100
effect on the amount of lighting energy which will be used
They can be divided into three general
in the building.
categories:
automatic on/off, stepped and continuous dim-
I
70
go
60
dso
An on/off system (Fig.3.25a)utilizes photo
ming systems.
sensing devices to determine the level of daylight exceed10
ing a preset level in a defined zone to turn off artificial lighting.
A two-stepped system (Fig.3.25b)uses less
ON/OFF SWITCHING
energy since it tracks changing daylight levels more closely.
It works on the same principle as the on/off system.
Fig. 3.25c)shows the profile for a photo cell controlled
100
sgo
Tao
70
sGo
continuous dimming system, which is typically more complex
and costly.
It is analogous to a step switching system
with an infinite number of set points, which allow the
a20
10
4
5 4
electric lights to track the available daylight perfectly.
Since it operates nearly invisibly, build-
ing occupant acceptance is high in opposition to automatic
on/off systems, which have been widely rejected because
of abrupt changes in electric lighting levels.
A 9
.
to
11
12 1 2
Noon
3
4
5 1
PM
STEPPED SWITCHING
(2 Steps:30 and 60 fc)
Understandably, it's the most effective way to reduce
lighting loads.
7
AM
100
Daylight Level
go
so
Multi-
30
Unoccupied
Unoccupie
level step dimming, if the steps are sufficiently small,
should also avoid the user acceptance problem.
4
UncuidAM
011112
6 1 1 4
10
so
Noo
1
12
U68
1
2 3 4 5 6 1
a
Given these options among automatic control systems,
the choice of an appropriate artificial light distribution
concept becomes the next important step towards a comple-
CONTINUOUS DIMMING
Figs. 3.25 a,b,c Generic lighting control
lighting devices
97
mentary synthesis of natural and artificial lighting.
In order to provide adequate ambient and task light
at any point of the room, to eliminate any direct glare
source from one's field of vision, and to allow for maximum flexibility of space layout, all light components
-
are integrated into the office furniture (Fig.3.23).
This concept makes use of the ceiling as a source
of indirect illumination for ambient lighting.
Since
introduced daylight, whenever available, uses the same
surface as an intermediate diffuser, fluctuations of
natural light are evened out by multistep or continuous
dimming systems, offsetting a change in the flow of light
from different dominant directions.
This eliminates the
marked difference in subjective impressions of quality and
character in typically daylighted and electrically lighted
interiors.
This same principle of maintaining some domi-
nant directions of light sources is applied to incorporate
an artificial lighting component into the proposed lightshelf element described in Section 3a .
Task light is pro-
vided as local downlighting from individual light components, wherever needed.
jr_3
----
98
cost-effective daylighting:
an analysis
With all the perceptual subtleties inherent in the
evaluation of alternative luminous and thermal environments, it is truly difficult to present an objective costbenefit analysis, which does not only count for a reduction of lighting, heating and air-conditioning costs in
dollar savings.
There are two principle ways of looking at costs
in relation to design decisions.
used as an absolute constraint:
First, costs can be
what is the best possi-
ble environment to be created for a set amount of spending?
Second, costs can be used as a measure of relative
performance:
to evaluate the relative merits of differ-
ent design solutions, if all solutions meet the design
criteria equally well.
How, for example in the case of
Louis Kahn's Kimbell Art Museum, can the cost of those
elements of the design which introduce and control daylight be attributed exclusively to daylighting expenditures when their costs might be as well attributable to
aesthetic quality or total atmosphere of the environment?
99
The strongest justification for the daylight effort
comes, when economy and energy conservation are understood in the context of humane, as well as efficient
environments.
How do we quantify the psychological in-
volvement with the passage of the sun and season that
How do we place
daylight can provide the indoor user?
numerical values on the conservation of future scarce
resources, the richness of natural light's ambience and
Not valued in the
its inherent bond to the day's cycle?
financial marketplace, these benefits must be given strong
consideration in addition to an overall cost-benefit picture
of daylight design in conjunction with other lighting
costs and benefits, with solar heat gains and losses, and
with energy uses and savings.
It is not within the scope
of this discussion to give a detailed breakdown of first
and life-cycle costs for the proposed light introduction
concept.
Instead, it tries to document all the parametric
values possibly influencing an objective evaluation of
first costs, operating costs, and overall savings of a
space utilizing daylighting techniques.
A study, done
by Stephen Selkowitz from LBL (Lawrence Berkeley Laboratory) gives a general idea of the magnitude of potential
energy savings utilizing daylighting techniques on a dollar-per-square-foot basis.
By assuming 3 Watts/ft2 in-
100
stalled power and 2500 hours per year of use, a consumption of 7.5 kWh/ft 2/yr results.
With a well designed
daylighted system incorporating on/off or dimmable controlls, perhaps 20 to 75 percent savings can be realized.
These savings of 1 to 6 kW hr/ft 2/yr represent an economic value of $0.05 to $0.50/ft 2/yr, which becomes significant in absolute dollar value for large commercial
structures.
In addition, substantial savings of 2, 3 to
3.0 kW hr/ft2 are achievable, if daylighting strategies
are used in conjunction with commercial "heat-mirror."
However, with increasing availability of more efficient
electric lighting systems (1 to 1-1/2 Watts/ft2 installed
power), the potential savings achieved with only daylighting are reduced.
It is therefore important to relate the
additional benefits which justify the effort for daylighting a commercial space:
- The reduction of heat gain, where unwanted, by lowering electric lighting loads affects energy intensive air-conditioning systems positively
- In conventional mechanically conditioned buildings,
each Watt of electric lighting load requires onehalf to one watt of air-conditioning load
101
- Solar heat gain for buildings in temperate climates
combined with daylighting, can save substantially
on heating energy usage
- Reduction of the use of energy during peak load
periods, therefore cutting peak power demand, which
is penalized by utilities through time-of-day-pricing policies
- Productivity insurance through daylight availability
in the event of a power failure.
According to
Stephen Selkowitz (LBL), a single hour worth of
productivity time from one worker is equal in value to the annual energy cost of lighting the space,
that the worker occupies
Daylighting in buildings, however, has merit beyond mere
energy savings.
Even if good lighting design and hardware
efficiency improvements reduce the electrical energy consumption to lower effective savings through daylight, the
earlier described potential for use as an aesthetic
tool and its qualitative assets argue for a wide spread
implementation.
102
"Let the sun be your decorator
F.L. Wright
...
"
103
appendix a
recent projects:
daylighting
principles applied in praxis
al
TVA office building, Chattanooga, Tennessee.
a2
Kimbell Art Museum, Fort Worth, Texas.
a3
IBM office building, Southfield, Michigan.
a4
Law Library addition, University of Michigan, Ann Arbor.
a5
Shell-building, Houston, Texas.
a6
Museum of Fine Arts addition, Boston, Massachusetts
a7
Beam daylighting techniques
104
TVA OFFICE BUILDING
Chattanooga, Tennessee
al
Members of the design team of the
Chattanooga building are: Caudill
Rawlett Scott, architects; The
Architects Collaborative, Inc.,
architects; Van de Ryn/Calthorpe &
Partners, architects; William Lam
Associates, Inc., lighting.
To "advance the state of the art in energy conscious
design," while stressing the sensitivity to human needs,
the urban context and environmental quality, a design
team of diverse skills and viewpoints, was assembled by
the Tennessee Valley Authority to design an Office complex for its own use of over 1 million square feet for a
downtown site in Chattanooga, Tennessee.
The emphasis of the design team soon became the integration and synthesis of energy strategies with the
more qualitative functional and architectural goals.
Daylighting emerged as a theme central to both the energy mandate and the architectural and urban character of
the building.
Preliminary energy parameter studies have
105
shown that a double "extruded" building section connected
by a solar court (atrium) would be an energy efficient
response to the climatic and programmatic goals.
The
thermal caveat for this design response is that the
court requires external shading on sunny days during
most of the year, but can benefit from direct solar heat
gains on many cool mornings and during the winter months.
This dynamic requirement led to an external horizontal louver system that could continuously track the
sun, redirecting sunlight into or out of the atrium as
necessary to control heat, while allowing diffuse or reflected daylight to enter.
On demand, the louvers can
be repositioned at set intervals or continuously.
A
light shelf on each floor level houses a large
mirror tilted to the proper angle for reflecting light
from the court roof onto the ceilings of the adjacent
office space.
A variation of a classic light shelf is
used on the south facade (Fig.3.26) with a mirrored
inner
shelf to increase the light reflected onto the
office ceilings.
A modified version of the court's mir-
rored light shelf forms the exterior north face of the
building, reflecting the diffuse north sky light onto
the ceiling of adjacent offices.
Figure 3.25.1 shows the
different operational modes of the atrium's louversystem
106
for various conditions.
Cloudy Day
Preliminary tests have shown, that the combination
of mirrored light shelfes, high ceilinged (12 feet) offices and the operable court shading system will increase
the usable daylight penetration from 200 to 300 percent
over a classic sidelit office daylight design using clear
glass and an eight foot ceiling.
Construction of this
project was scheduled for early 1982.
Yet, a change in
administration at TVA and budget cuts are momentarily
jeopardizing the realization of the atrium courtyard and
13
daylighting features for this project.
Fig. 3.25.1 Different operational
modes of the atrium's
louver system
Summer Sun
TRACKJNG MidtD
+ WHTE Af.LECrtR
4 FIXEP MIRMM
t FIXED MIZae
IPIFFU5E BeAM PAYL4,T"
a+ SoLAR HEAT REJECT
Drac BEAJ-i P4MAWri0
* - SNF 6a*AA 4AJN
107
(
*11
TVI
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r
n C'
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ewm
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IP
'tat
AiM M
Fig. 3.26
NOK~,
-'M
s
n5,crIoM
Typical building section illustrates the differential form responses to daylight
108
KIMBELL ART MUSEUM
a 2
Fort Worth,
Texas
Louis Kahn,
architect
Daylight in art museums has historically been approached with trepidation because of the deteriorating
effect from the ultraviolet in daylight.
Kahn decided
to use daylight at its softest level for ambient lighting to satisfy biological needs.
The Kimbell Art Museum is constructed of a series
of adjoining cycloid concrete vaults 100 feet long and
23 feet wide with a clear skylight continuous along each
vault ridge.
The incoming daylight is bounced and fil-
tered by a curved reflector suspended just below the
skylight.
Louis I. Kahn liked to call it a "natural-
light fixture," that particular "harness-like looking
109
thing" that spreads daylight onto the underside of the
concrete vault.
The first proposal made for the build-
ing in March 1967 by L. I. Kahn already contained the
basic elements he would keep throughout the entire development of the design:
a repetitive series of shed-
like structures with roof-top light aperatures interMany roof shapes and reflector
rupted by open courts.
configurations were investigated and numerous changes and
refinements were made during the design period which
stretched till 1969 (Figs.3.27a,b,c).
The precise details of the reflector configuration,
material used and size of perforation were determined
only after four successive models were studied in place
during construction.
Figure 3.27c shows the final con-
figuration selected:
the cycloid curve chosen as pro-
file for the roof, incorporating the reflector or
"natural-light fixture."
The reflector was made of alu-
minum, the type used for electric light fixture reflectors, a highly specular sheet material chemically polished on one surface and perforated to give the required
degree of transparency.
The curved shape was determined
to mirror the diffuse and scattered light of the open
sky and reflect it onto the surface of the cycloid shell.
The last remaining problem was solved by determining the
Fig.
3.27 a,b,c Various reflector configurations
110
exact size and spacing of the perforation.
If the diam-
eter of the holes was similar to the thickness of the
metal and spaced closely, the reflector itself would be
able to provide a 45-degree cut-off for certain angles
of the sun's rays.
The aluminum sheet was .040 inches
thick, a function of curvature and span, and a .050 hole
on 3/32 inch staggered centers was selected for the final design.
Seen from below, the fineness and frequency
of the perforations presented a diaphanous window to the
sky and, as Kahn had predicted earlier, "bathed" the
concrete cycloid in a translucent glow.
As he said:
"This light will give a glow of silver to the room without touching the objects directly, yet give the comforting feeling of knowing the time of day."
111
IBM OFFICE BUILDING
Southfield,
a3
Michigan
Gunnar Birkerts and Associates architects
Birmingham, Michigan
Located in the Detroit suburb of Southfield, this
14-story steel-framed regional office building of IBM
with 263,000 ft
2
of highly usable, flexible and energy
efficient office space has experienced the implementation of an innovative copy-righted light introduction
component.
The object of this project was to design a
general office building of normal investment quality
standards, utilizing presently available techniques of
energy conservation to balance first-cost building economics with economics of operation.
The key element for daylight introduction and energy
conservation is
the skin of the building (Fig. 3.2.8).
Day-
112
light is introduced through a curved, matte finish reflector of stainless steel, that runs along the lower
edge of the ribbons of glass.
Another curve, placed
above the inside window line, catches the reflected sunlight and diffuses it into the room.
The top of the an-
gled window slopes outward for solar shielding.
The 24"
wall panel system with double glazing (20% glass area)
improves energy efficiency and cuts the lighting load by
50%.
Light interior colors and finishes as well as light
colors of furniture, are utilized, so that, with the
s
WALL ANAIROOT
FLUO ES
AL
%IIEDM
PAEFI
LCTSR
IGTLIEC
R
H
curtain wall light source, general artificial illumina-
tion levels are reduced.
INSULTED
LIVIE'
The second feature, a two-color treatment of the
BR
exterior wall was introduced to reinforce energy conser-
INSLA
vation and to symbolize the importance of careful orien-
RAFCTSR_
tation.
ING
EWL
This visual metaphor is in keeping with the
benefits of heat reflection and absorption as it places
CLE
MEA L
ME
[-CARPET
-
the metallic silver color on the south and west and the
darker grey color on the north and east walls.
The site
location and landscaping maximizes the amount of green
area east, west and south of the building in order to
reduce reflected heat gain.
Fig. 3.28 Window wall section with daylight introduction element
113
LAW LIBRARY
Addition
University of Michigan, Ann Arbor
a
4
Gunnar Birkerts and Associates,
Birmingham, Michiggn
Completed Spring, 1979
Confronted by the need to expand its library and the
desire to preserve valuable open space above ground in a
dense urban location with great site restrictions, the
law school at the University of Michigan and its architect, Gummar Birkerts decided to go underground.
De-
prived of all the familiar external tools of architectural design - massing, facade, structural expression
he turned for help to an old friend:
-
daylight.
The key to underground daylighting here lies in the
penetration through the roof.
(Fig.3.29
A larbe L-shaped trench
defining the inside corner of the new library,
represents the major light source for the building.
The
114
limestone panels that face one sloping wall bounce light
through the reflective glass opposite, thus achieving
the effect of a sidelit space.
This surface is the
"workhorse" of daylight distribution, its texture diffusing illumination received from the skylight deep into the
rooms.
More important psychologically, the bright sunlit
expanse is visible to anyone sitting or standing well inside the building.
mit daylight.
The long skylight does more than ad-
A deceptively simple device - yard deep
mirrors set perpendicular to mullions
-
creats a long
row of "stained glass windows" that capture colorful and
changing images of foliage, sky and the gothic details of
the building next to it.
Functionally, the mirror mul-
lions operate as baffles to reduce the amount of direct
sunlight and glare entering the space.
In this guise,
the mirrors add another decorative dimension - a plaid
pattern formed, as direct and reflected light and shadow
meet on the interior part of the limestone slope.
This 77,000-square-foot building reflects the intention of going underground without degrading the building's users and captivating the effect of light on archi13
tecture in a superior way.
Fig. 3.29 Building Section
115
SHELL-BUILDING
Houston, Texas
a5
architects, planners and
engineers: Caudill Rowlett Scott
Programmatic requiremente, a cooperative client, and
an architectural firm with a long history of interest in
environmental factors made the use of daylight in the new
shell huildings a central determinant within the overall
design strategy.
The key element which stimulated the
daylight approach was Shell's requirement for a maximum
number of private offices with outside views in an energyconscious and efficient complex.
The individual offices are stacked in a multistory
building and the long, narrow wings are folded around a
central, triangular-shaped atrium.
A precast framing
system, that extends beyond the office spaces to the outdoors was developed, which provided opportunity for sun
02550
ji
100
116
shading and bouncing the daylight into interior spaces.
To further enhance the daylight contribution and to achieve significant economies, a perimeter HVAC system
was developed that would extend half inside and half
outside the plane of the window glass, acting as a light
shelf to bounce daylight into interior spaces.
This de-
sign eliminated the need for a hung ceiling, allowing an
increase in effective floor to ceiling height.
Daylight conditions in a full scale mock-up showed
very satisfying results, providing a very pleasan
functional lighting environment.
and
Electric lighting en-
ergy consumption has been estimated at .87 Watts per
square foot of floor space based on a conservative projection of annual use. 4
T
+
T
Typca Offe
Typtcal
Office
+_T__-
117
MUSEUM OF FINE ARTS
Addition
a,6
Boston, Massachusetts
I. M. Pei and Partners,
architects
The 80,000-square-foot West Wing addition to the
Museum of Fine Arts in Boston provides another example
of use of natural light in a sequence of buildings East Building of the National Gallery of Art in Washington,
J. F. Kennedy Library in Boston, etc. - designed
by I. M. Pei.
A 22-foot-long galleria forms the main
axis of the structure, with exhibition galleries, auditorium and restaurant attached to it.
A continuous,
vaulted skylight tops this atrium space, exhibiting the
key architectural feature.
It is a further refinement
Fig. 3.30
East Building of the National
Gallery of Art in Washington,D.C.
118
of I. M. Pei's skylight technology for Washington's East
Building, using polished tubes (of approximately 1" diameter, Fig.3.31) to control and diffuse natural light.
In addition, the effect of low glare, even light distribution on clear days with direct sunlight is achieved
through application of slightly tinted glazing materials
on the sloping faces of the vault, while clear glass on
the vertical face maintains unobstructed visual connection to the exterior.
The resulting light quality with-
in the atrium is extrodinary, even on cloudy days.
Fig. 3.30 Skylight Detail, Section
119
BEAM DAYLIGHTING
Techniques
S. Selkowitz; daylight introduction
b)
experiment
T. Johnson, MIT Solar Building No. 5
Direct beam modulation and introduction into a space
represents the most efficient use of daylight in commercial buildings, if carefully treated, since direct solar
/
External shade
radiation of the sun on a clear day provides approximat-
Silvered Beam Blind
(always down)
9000 FC with a Lumen per Watt output of about 100
ely
Lm/w.
6-
the sun to substantially extend the daylight utilization
of interior spaces.
Figure
3
. 3 lillustrates
light-colored Venetian Blind
(available)
A study done by A. Rosenfeld and S. Selkowitz has
investigated and evaluated the use of beam radiation from
L-white
e._
4'-
Duol mode Shade
2'-
the apparatus
used as part of an overall optimized window design.
Two
different sorts of venetian blinds, both mounted behind
0-
Fig. 3.31
Experimental
Configuration
120
a clear window, provide visual and thermal control:
a
silvered "beam" blind mounted behind the upper window and
a solar control - partially reflective - blind located
behind the lower window.
The beam daylighting blinds
function independently of the solar control blinds.
To
provide optimum illumination at a constant depth in the
room, the upper blinds have to be constantly adjusted.
In practice, this represents a major drawback.
Fixed
blinds instead, would provide adequate, though not optimum, illumination.
solar
5
This principle, though not primarily for daylighting
purposes, has been applied at the M.I.T. SOLAR 5 Building,
designed by Timothy Johnson.
Exceptionally narrow, up-
side down reflectorized venetian blinds are fitted between the south facing double glazing unit.
These blinds
redirect sunlight onto the ceiling for both thermal storage (phase change files) and illumination purposes.
Di-
rect glare is eliminated by limiting the application of
blinds to a certain window height.
I ZOa.
"The striking quantities and simularities of light associations among various people: the uplifting effects of
a sparkling sunny day, the dreary overcast day... , the
passion of color saturated sunsets filling built spacesor the delight of dancing water reflections, suggests the
possibility of a language by which qualities of light
evoke particular intellectual, emotional and physical experiences. If this language could be translated into an
architectural vocabulary, we could begin to again rebuild
into our environment 'the luminous food' which man has
in past ages found essential to his daily nourishment and
sustenance."
H. Plummer, "Built Light"
121
appendix b
T1-59 program
Program to calculate beam diffuse,
and total radiation incident upon
and transmitted through a specified
plane. Output includes values for
solar altitude, azimuth, angle of
incidence, beam and diffuse radiation.
C.Benton
122
TI PROGRAMMABLE
TITLE: SOLAR ANGLES & RADIATION
PROGRAMMER: Charles C.
Benton
Partitioning (Op 17) 559.49_
PROGRAM RECORD
DATE: Jan.
1979
Library Module
Sides
------
PRINTER No
CARDS 1,2,3,4
PROGRAM DESCRIPTION
Given base data, calculates beam, diffuse, and total radiation incident upon and
transmitted through a specified plane. Radiation values are given for clear sky
conditions on the 21st day of the month specified.Optional output includes hourly
values for solar altitude, azimuth, angle of incidence, beam and diffuse (ground
plane and sky vault) radiation. Optionally, these values may be obtained for anv
time and day. Calculations are via ASHRAE procedures for incident radiation values..
User may specify solar. time or standard time. This program does not compensate for
cloudiness or shading.
USER INSTRUCTIONS
STEP
1
2
PROCEDURE
Re-partition
Read card sides 1,2,3,4
ENTER
2
5
0
PRESS
DISPLAY
OP 17
559.49
1,2,3,4
123
Option No. 1
To run a day other than the 21st of the month insert the following input steps
after step no. 13 on the first page.
PROCEDURE
STEP
1
Initialize
2
Enter equation of time
3
ENTER
PRESS
DISPLAY
A'
11
Eq. Time
R/S
12
Enter declination
Decl.
R/S
13
4
Enter A factor
A factor
R/S
14
5
Enter B factor
B factor
R/S
15
6'
Enter C factor
C factor
R/S
0
NOTE: These values may be interpolated from the ASHRAE table included in the
Appendix
Option No. 2
To run a specific time 'other than the standard even hour, insert the following
step after step no. 13 on the first page.
124
STEP
1
PROCEDURE
Enter time in decimal,
24 hr. format
ENTER
Time
PRESS
B'
DISPLAY
0
NOTE: It is recommended that Option No. 4 be exercised when Option No. 2
is used.
Option No. 3.
To run on solar* time rather than standard time,
after step 13 on the first page.
STEP
1
PROCEDURE
Initialize
ENTER
insert the following step
PRESS
C'
DISPLAY
O
NOTE: This conversion is accomplished by setting the equation of time
and longitude.= standard meridian
=
0
125
SAMPLE PROBLEM NO. 1
Find daily total radiation values for direct, diffuse, and total radiation,
both incident and transmitted for a vertical 1/8" thick glass window facing
southeast at 420 N latitude, 71* W longitude during May. Atmospheric clearance
is 0.85 and ground plane reflection is 0.2. Use solar time.
INPUT
Month
Latitude
Longitude
Atmospheric Clearance
T.H.
Orientation
Ground Plane Reflectance
Transmission @ 0-55 0
-Transmission @55-65*
Transmission @65-75*
Transmission @75-90*
Adjust for Solar Time
Enter
Press
Display
5
420
71*
0.85
900
45*
0.2
0.90
A
R/S
R/S
R/S
R/S
R/S
R/S
R/S
1
2
3
4
5
6
7
8
0.82
R/S
9
0.70
0.40
R/S
R/S
10
0
-
RUN*
OUTPUT
Daily
Daily
Daily
Daily
Daily
Daily
total
total
total
total
total
total
transmitted beam radiation
incident beam radiation
transmitted diffuse radia.
incident diffuse radiation
transmitted total radiation
incident total radiation
-
C'
0
B
0
C
R/S
D
R/S
E
R/S
*NOTE: RUN is finished when 21.00 enters the Display
614.95
747.33
310.77
378.98
925.73
1126.31
126
SAMPLE PROBLEM NO.
2
Find hourly angle of incidence, incident beam radiation, and incident diffuse
radiation values for the following conditions. The surface is facing due west
and sloped at 450 during a clear October day (21st). Location is 240 N latitude,
70*W longitude; atmospheric cleraance is 1.0, and ground plane reflectance is
0.25. The surface is opaque. Use standard time.
ENTER
INPUT
Month
Latitude
Longitude
Atmospheric Clearance
Surface Tilt
Surface Orientation
Ground Plane Reflectance
Transmission at 0-55*
Transmission at 55-65*
Transmission at 65-75*
Transmission at 75-90*
Set for hourly Output
RUN
10
24*
700
1.0
450
-90*
0.25
N/A
N/A
N/A
N/A
PRESS
DISPLAY
A
R/S
R/S
R/S
R/S
R/S
R/S
1
2
3
4
5
6
-
D'
1
-
B
4.00
OUTPUT
This is a data summary table. The program also produced hourly values
for solar altitude and azimuth which are not shown
127
SAMPLE PROBLEM NO. 2 (Continued)
NOTE: When D' is used to .change the status of flag #1, a positive
1 in the display indicates the flag is set and a negative 1
indicates the flag is lowered. During OUTPUT, if the angle
of incidence is greater than 90* (i.e., the sun does not "see"
the surface), then 900 will be given as the value. This occurs
from 6AM through 8AM in SAMPLE PROBLEM NO. 2.
Hour
Angle of
Incidence
Beam Radiation
Incidence
Diffuse Radiation
Incidence
0
90
90
90
90
87.19
73.26
59.76
47.05
35.99
28.58
0
0
0
0
0
14.51
88.26
156.58
211.58
246.95
257.10
0
0
2.00
16.38
22.57
26.25
28.48
29.52
29.43
28.19
25.74
3
4
27.89
34.35
235.34
165.01
21.76
14.82
5
44.96
0.28
0.03
4
5
6
7
8
9
10
11
NOON
1
2
6
0
0
0
7
8
0
0
0
0
0
0
1375.61
245.16
TOTAL
128
SAMPLE PROBLE M NO.
3
Find the solar altidude and azimuth for 10:15AM standard time on Januaryr6,
at 38*N latitude, 75*W longitude.
ENTER
PRESS
DISPLAY
1
38
75
A
R/S
R/S
1
2
3
Initialize
Equation of Time
Declination
A Factor
B Factor
C Factor
-4.9
-21.7
390
.142
.057
A'
R/S
R/S
R/S
R/S
R/S
11
12
13
14
15
0
Time
10.25
B'
0
INPUT
Month
Latitude
Longitude
(The remaining standard INPUTS
are not applicable)
1
$et for hourly OUTPUT
RUN
OUTPUT
Altitude
Azimuth
B
10.25
R/S
R/S
24.960
-28.220
129
Option No. 4
Hourly data output is available. In addition to finding daily total radiation
values, this program will provide the user with hourly values for solar position
and radiation. DUring the normal run of the program these values will flash
briefly on the display. However, by setting flag .no. 1, the program will stop
at each value.
The program must then be restarted, by pressing R/S,to continue
After each value. Flag no. l's status may be changed by pressing D'.
Do not
do this after the input section of the program because it will misplace the
program pointer. During the run section, change flag status by using the SFG
key.
When flag no. 1 is set, the program will stop at the following values for each
hour (in the following order).
1.
Hour number
2.
Solar altitude in degrees
3.
Solar azimuth in degrees
4.
Angle of incidence in degrees
5.
Incident beam radiation in BTU/SF
6.
Transmitted beam radiation in BTU/SF
7.
Incident diffuse radiation in BTU/SF
8.
Transmitted diffuse radiation in BTU/SF
This information will be presented for clear day conditions on the 21st of the
month specified, beginning at 4AM and running until 8PM. When an hour is
encountered during which the sun is below the horizon, the program will skip
to the next hour.
130
INPUT
3
4
5
6
7
8
9
10
11
12
13
.Enter no. of month (Jan = 1)
Enter latitude
Enter longitude
Atmospheric Clearance
Enter surface tilt (90*=vertical)
Enter surface orientation(+east, -vest)
Enter ground plane reflectance
Enter average transmission factor
for 0-55* angle of incidence
Enter ave.trans.fact.for 55-65*angle
Enter ave.trans.fact.for 65-75*angle
Enter ave.trans.fact.for 75-9 0 *angle
Month
Lat
Long.
Atmos.Cl.
Tilt
R/S
R/S
R/S
R/S
Orient
GPR
R/S
R/S
6
0-55
55-65
65-75
75-90.
R/S
R/S
R/S
R/S
8
9
10
0
A
1
2
3
4
5
7
RUN
14
Run
B
Display
flashes value
OUTPUT
15
16
17
18
19
20
Daily
Daily
Daily
Daily
Daily
Daily
beam radiation transmitted
beam radiation incident
diffuse radiation transmitted
diffuse radiation incident
total radiation transmitted
total radiation incident
NOTE: See the following page for optional prograr features.
data register assignments, program steps, and labels
C
R/S
D
R/S
E
R/S
beam trans.
beam incident
diff.trans.
diff.incident
total trans.
total incident
See program listing for
131
Storage Register Assignments
00
01
02
03
04
Hour Counter
Latitude
Longitude
Atmospheric Clearance
05
Orientation
Ground Plane Reflectance
Transmission @ 0 *-55* Angle of incidence
",
"t
@ 55-65*
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26-37
38-49
Tilt
@ 65-75*
"I
"
"6
@ 75-90*
Equation of time
Declination
A factor
B factor
C factor
Incident Beam Radiation Total
Incident Diffuse Radiation Total
Transmitted Beam Radiation Total
Transmitted Diffuse Radiation Total
.9999999999
Operational
Operational
operational
Indirect Address for 26-37/Operational
Indirect Address for 38-49/Operational
Eq. of Time/A factor/C factor
Declination/B factor
132
PROGRAM LISTING:
000--1 7' L BL.
'Ei
19
001
002 87 IFF
C3 C 131
42 STI 029
004
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01127
219
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91
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1~13: 01 01
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R./S
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92 RTN
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03 9 76 LBL
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76
LBL
16
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01
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32
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133
I 0l 1
102
104
1 Ct, 4
105
106
107
109
111
112
11 3
114
115
116
117
11 :3:
119
1 3.1
1 2
122 2
123
1 '24
1 125
25
-
75
01
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24
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"The history of Architecture is the century-old struggle
for light, the struggle for the window.
Le Cosbusier
138
appendix c
Solar altitude and azimuth angles,
graphs for various latitudes; 24*
280
320
360
400
440
139
240 LATITIJDE
Catcuita~india-Miami eFioridaDacca,IDangI adesli-Montrry,Mxlco
28*LAITJDE
Las Palmas.Canary IslandsIloustonTexas-flew Delhi, Indla
140
36* LATIJUDE
Tokyo.Jnpan-Tebranfran-Kwang-Jo.Koren
VoyolievilleArkansns-t4onterroyCallf-
141
40' LATITUDE
IMadrIdSpaI n-Peklng,Chlna-Donver,Color
Olympus,Greece-Pbi Iadolphln,Penn.
"More and more, so it seems to me, light is the beautifier of the building."
F.L. Wright
142
appendix
d
glossery of terms
143
glossery of terms
specular
having the reflectance properties of a mirror 1 2
diffusion
to pour in different directions; to spread out
reflectance
specular reflection
diffusive reflection
refract
that percentage of incident light upon a surface which is reradiated in the
visual spectrum 1 2
angle of incident light equals angle of reflection
incident light is reflected in all directions.
regardless of the angle of incidence
Its distribution is the same
to bend a ray of light as it passes from one medium into another (glass refracts light)
light
visual manifestation of radiant energy 10
glare
an interference with visual perception caused by an uncomfortable bright
12
light source or reflection
footcandle
footlambert
LUX
the English unit of light intensity (10.76 LUX = lft-candle) 1 2
the English unit of luminance, or measured surface brightness
metric unit of light intensity (lumen per square meter JLm/m
1)
144
illumination
incident light
indirect lighting
direct lighting
activity needs for
visual information
quantity of light per unit of surface area; the "intensity" or "density" of
12
light falling on a surface (English: Footcandle; metric: LUX)
light falling upon a surface 1 2
12
lighting provided by reflection, usually from wall and ceiling surfaces
12
lighting provided from a source without reflection from room surfaces
12
needs for visual information related to specific conscious activities
Biological needs for
visual information
unceasing needs for visual information; not related to specific conscious
activities; but rather related to the more fundamental aspects of the human
relation to the environment: orientation, defense, stimulation, sustenance
and survival 1 2
daylight factor
illumination at a point indoors divided by the illumination received simultaneously outdoors on an unobstructed horizontal surfacell
side-lighting
top-lighting
sunlight
absorption
contrast
3
the light obtained through windows located in the vertical building envelope
3
refers to the light obtained from skylights (horizontal building envelope)
3
light obtained through direct beam radiation from the sun
transformation of radiant energy to a different form of energy by the intervention of water. When light is neither reflected nor transmitted, it is
3
absorbed by the material and may be transformed into heat
the relationship between the luminance of an object or area of interest and
that of its immediate background 1 2
6..."as the basis for music is the presence of silence,
the world of light is dependent upon darkness to give
it definition and form, and a quiet matrix within which
to come alive."
Henry Plummer, "Built Light."
(Master's Thesis, M.I.T., 1975)
145
bibliography and references
1.
Anderson, G., March 1982, Architecture Beneath the Surface, Architectural Record.
2.
Brunkan, R., 1978, Sun Seeking Architecture, M.Arch. Thesis, M.I.T., Cambridge.
3.
Bryan, H., et. al., Sept. 1980, Daylighting - A Resource Book, Center for Architectural Research, Rensselaer Polytechnic Institute, New York.
4.
Evans, B., 1981, Daylight in Architecture.
5.
Gillette, G., 1981, Daylighting Resource Package., National Fenestration Council.
6.
Goldstein, R., 1976, Natural Light in Architectural Design.
M.I.T., Cambridge.
7.
Hellmann, H., 1982, Guiding Light. 'Psychology-Today', April
8.
Heshory, L., Aug. 1980, An Interview with William Lam.
9.
Heshong, L., 1979, Thermal Delight in Architecture.
McGraw Hill, New York.
M.Arch. Thesis,
Solar Age Magazine.
M.I.T. Press, Cambridge.
Heinemann, London.
10.
Hopkinson, R.G., et. al., 1966, Daylighting.
11.
Johnson, Timothy, 1981, Solar Architecture:
Hill, New York.
The Direct Gain Approach.
McGraw
12.
Lam, W., 1977, Perception and Lighting as Formgivers for Architecture.
Hill, New York.
McGraw
146
September 1979, Daylight as a Central Determinant of Design.
13.
Matthews, S., et. al.,
AIA Journal.
14.
Plummer, H., 1975, "Built-Light."
15.
Rosen, J.,
16.
Rosenfeld, A., et. al., 1977, Beam Daylighting: An Alternative Illumination Technique.
Energy and Building, Elsevier Sequoia S.A., Lansanne.
M.Arch. Thesis, M.I.T., Cambridge.
1982, Daylighting and Energy Conservation, M.Arch. Thesis, M.I.T., Cambridge.
17.- Rush, R., Sept. 1980, Glassoline.
Progressive Architecture Journal.
Solar Age Magazine.
18.
Selkowitz, S., et. al., August 1980, The Daylighting Solution.
19.
Selkowitz, S., et. al., Sept. 1979, Strategies of Daylight Design.
20.
Viladas, P., November 1981, Through a glass, brightly.
Journal.
21.
Villecco, M., September 1979, Natural Light.
AIA Journal.
Progressive Architecture
AIA Journal.
"I remember walking through a fairly new
subsidized housing project in Holland one
morning. The streets are empty. Behind the
facades I see only women wandering around
like fish in glass bowls without much to do.
My presence with a camera is suspect. Who
Suddenly the streets
wants to see all this?
returning from
children
are full of small
school. A routine re-asserts itself. Some
husbands will be home for lunch. Someone has
told me that suicide rates among women are
highest in neighborhoods like this.
Observation is the only source for architects.
What is it that those monuments in the
magazines and text books are standing in?
What are we doing in libraries and classrooms
anyway? Did you see something out there
lately?"
(N. John Habraken)