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7/29/2019 Daylighting Strategies That Maximize Benefits
1/12
H i g H P e r o r m i n g B u i l d i n g s sp 20 083 0
Daylighting
p a r t o n e o f a t h r e e - p a r t s e r i e s
Low energy bills, high quality indoor environment, low construction costs
daylighting is one sustainable building strategy that can help achieve all these goals.
Based on a calculation I did or the National Renewable Energy Laboratory (NREL),
daylighting strategies can potentially reduce our nations total energy consumption
by 1% with a one- to three-year simple payback. When approaching daylighting
design, the project design team needs to understand and consider the various ele-ments that can help maximize daylighting benefts. This is part one o a three-part
series on sustainable strategies. The frst part ocuses on daylighting; subsequent
parts discuss water and integrated design.
stat That maxz BtB y M i c h a e l n i c k l a s , fa i a
The following article was published in High Performing Buildings, Spring
2008. Copyright 2008 American Society of Heating, Refrigerating andAir-Conditioning Engineers, Inc. It is presented for educational purposes
only. This article may not be copied and/or distributed electronically orin paper form without permission of ASHRAE.
7/29/2019 Daylighting Strategies That Maximize Benefits
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s p 2008 H i g H P e r o r m i n g B u i l d i n g s 3 1
s Mxm
The most obvious site consideration
is orientation. Elongating the building
on an east-west axis and locating high
priority spaces on the north and south
exposures can enhance cost-eective
daylighting. Account or shading rom
adjacent buildings and trees and con-
sider the reectance o the materials
in ront o glazing areas.
id D
The most cost-eective, energy-
efcient daylighting strategies are
integrated into the overall design and
take into account all impacts, not just
lighting. They consider the structural,
mechanical and electrical systems,
as well as the landscaping and archi-
tectural design. To ully integrate
daylighting strategies, they cannot be
regarded as alternative strategies.
r M d l
Roo monitors or side lighting with
south-acing lightshelves or high,
north transoms can reduce lighting
and cooling loads.
sth-ac r mt
Roo monitors with vertical south
glazing, interior baes and properly
sized overhangs can create uniorm
lighting having less contrast,
provide daylight in spaces ar
rom the perimeter o the building,
provide passive heating benefts,
and eectively diuse and flter
lighting. Unortunately, roo moni-
tors can only be used in single-
story designs or on the top oor
o multistory designs.
With south-acing roo monitors:
Use light-colored roofng material
to reect sunlight into the glazing.
When placed in ront and to the
sides o the south-acing roo mon-
itors, the glazing area in the moni-
tors can be reduced by up to 30%,
according to a study o my projects
by North Carolina State University
graduate students.
The south-acing roo monitor with baes blocks direct beams.The lightshel reects daylight deep into the
space and shades the lower view window.
For Chattanooga Convention Center, south-acing roo monitors provide natural lighting into the 100,000 t2 main exhibit
area. The daylighting strategy and color selection reduced the load by 40 tons in just this one space.
7/29/2019 Daylighting Strategies That Maximize Benefits
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H i g H P e r o r m i n g B u i l d i n g s sp 20 083 2
bottom o the light well, contrast is
greatly lessened i there is a transi-
tion between the vertical and hori-
zontal plane suraces. A 45-degree
angled plane is good, but a curved
transition is better.
Make sure the colors used within
the monitor well are very light with
high reectance. I acoustical ceil-
ing material is used, ensure that
the total assemblys reectance and
acoustical properties are high.
Use fre-retardant and ultraviolet-
resistant baes to diuse light.
Space white baes, hanging par-
allel to the glass, to block direct
beams rom entering the space.
Design the south-acing monitor to
capture passive heating in the winter
months. This helps to replace the heat
usually provided by electric lights.
Minimize contrast at the intersec-
tion o the well and ceiling. At the
Rely on stratifcation o heat within
the monitor itsel to help reduce
cooling loads. Do not place sup-
ply and return grilles in this area;
instead, let the heat stratiy.
Minimize the depth o the ceiling
cavity. The depth o the well is
important. The deeper the well, the
harder it is or light to reect down
into the space. Figure at let shows
the theoretical decrease in ef-
ciency resulting rom deep wells.
According to an IESNA workshop,
a 7 t deep, square sky well with
70% reectance loses 50% eec-
tiveness because o well depth.
nth-ac r mt
North-acing monitors, although
eective in providing natural light,
typically require at least 25% more
glazing than south-acing monitors
to achieve the same annual daylight-
ing contribution. Because o the
additional glazing needed and the
lack o passive heat benefts in win-ter, they are not as cost-eective
as south-acing monitors.
In many spaces, baes can be
eliminated when using north-acing
roo monitors because direct beam
Smith Middle School was constructed at $750,000 under budget. The Lighting
Research Center at Rensselaer Polytechnic Institute analyzed the daylighting
perormance and ound that electric lighting was reduced by 64% and 78 tons o
cooling were saved. The acility is 128,000 t2 and the area daylit is 63,000 t2.
Lightshelves can shade lower view glass.
i M p a c t o f c e i l i n g c a v i t y
Light lost when depth o ceiling cavity increases.
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Adverti sement formerly in this space.
7/29/2019 Daylighting Strategies That Maximize Benefits
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H i g H P e r o r m i n g B u i l d i n g s sp 20 083 4
light enters early or late in the day
during the summer. I baes are
needed, consider vertically sus-
pended baes, such as banners,
that can intercept the light during
these key times.
sth-ac lhthv
Lightshelves are typically the system
o choice or multistory buildings
because they can bounce sunlight
deep into moderately sized rooms
through high glazing areas on the
south side o buildings. Typically,
lightshelves cost less than moni-
tors. The downside o this approach
is that the light comes rom one
side o the room, making it harder
to achieve uniorm lighting. Also,
contrast between the brighter glazed
wall and the opposite side o the
room must be addressed.
When optimizing lightshel design:
Recognize the limitations o side
daylighting. In typical windows,
light levels drop considerably mov-ing away rom low view windows.
It is common or the light level to
t h e r M a l g a i n s B y W i n D o W o r i e n t a t i o n
Btu/t2 o unprotected glass/day at 35N Latitude. Btu/t2 o unprotected glass/day at 48N Latitude.
Baes inside south-acing monitor.
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HPB.ht.c/18426-5
Adverti sement formerly in this space.
7/29/2019 Daylighting Strategies That Maximize Benefits
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H i g H P e r o r m i n g B u i l d i n g s sp 20 083 6
lighting strategy in rooms with 10t ceilings and no more than 15 to
20 t deep rom the window. The
deeper the room, the higher the
ceiling must be. The daylightingwindows should be placed as close
to the ceiling as possible.
Select durable but reective lightshel
material. Aluminum is a good option.
Shade low view glass. The exterior
lightshelves can shade the windows
below. I using window treatments,
do not install one continuous blind
that covers the top lightshel glass
and the low view glass.
Stop direct beam light with blinds
between the glass. An interior
lightshel usually cannot stop
direct beam light rom entering
the top section o glazing when the
sun has a low altitude. One option
is to incorporate an extended inte-
rior lightshel, but this requires a
be 120 ootcandles at a low windowand 20 ootcandles at a distance 8
t away. However, with lightshelves,
this is an eective multistory day-
Architectural detail intentionally darkens the projection screen while still allowing daylight to the rest o the classroom.
g l a s s - t o - f l o o r a r e a g u i D e l i n e s
sa t mz la V
spac (Ca) spac (gya)
sth-ac r mt 8% t 11% 5% t 8%
sth lhth 8% t 11%
sth lhth Wth B Btw gaz 10% t 18%
nth-ac r mt 12% t 15% 7% t 10%
Hh nth-ac Ta gaz 15% t 20%
Until detailed daylighting analysis is conducted, these guidelines, developed
based on my experience, can be useul in estimating daylighting glazing amounts
or particular approaches.
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s p 2008 H i g H P e r o r m i n g B u i l d i n g s 3 7
deep shel. Another option is to
incorporate blinds between the
glass to intercept this problematic
light and reect it up to the ceil-
ing. When sizing the amount o
glazing required, account or theloss in transmission due to blinds
between the glass. Most blinds
between the glass can be closed i
desired. However, i the space does
not need this option, the blinds
position can be permanently set to
angle up to the ceiling.
Increase the perormance o the
lightshel by implementing a
sloped ceiling rom the top o thelightshel glass downward to the
back, north wall. In my experience,
this improves reectance and can
reduce glazing up to 10%. By slop-
ing the ceiling rom the outside wall
to the back o the space, it is oten
possible to encroach into the ceiling
cavity above the window area and
gain needed space or mechanical
systems on the north side without
increasing oor-to-oor dimensions.
The benefts o the sloped ceiling
are apparent when comparing a
room with a at, 10 t ceiling to
one with a ceiling that is 11 t 4
in. at the lightshel and 9 t at the
back o the space.
nth-ac Ta gaz
In spaces located on the north side
o the building, high transom glaz-
ing can be an eective strategy,
specifcally in narrow rooms or large
spaces, when used in combination
with south-side lightshelves or roo
monitors. High north-acing transom
glazing can provide good daylight-
ing in spaces that are not too deep
without the problem o direct beam
e n e r g y r a M i f i c a t i o n s
A ayht taty that t typcay
p t ctc ht w cat a
atv y tat. ict ay-
ht t th ht b t ,
a hat pc th ht
a w a th ht. i
ccty, a ayht taty ca c
ctcty ht a pak ctca
a, c y a pak c
a, atac ct acat wth
ap pact, a ctca vc
t th b.
Mxm d mm -
d w- . Th accpay
chat cat th at tha a
t fat ac wtht a th
vha. T axz wt hat a a
z hat a, th-
ac apt. it ay t a az
a achv a hh ayht ctb-
t. Th ky pt az that
pv p ayht 60% t
70% th t wtht ca c
a pak. Th bt ca b
t by at th vay az
at a vha th pak
c t. Bca th w
aztha a that ht th at a wt
vat, t ct a ca b xp-
v t pc a ct ayht -
t at- a wt-ac az.
ad d .
skyht pv th at ayht
bt a y ppctv. m
tha twc th hat w t t a b
thh a fat kyht th tha
th wt, jt th ppt what
. i th z a fat kyht pt-
z t c hat th ,
t w t pv th cay ayht
th t th ya a ca bc
pbatc a ct ba tapt.
Athh kyht ca b wth
ta tack v a pc
qaty ayht, t ct t jty
th wh c c pak
a. oy a w aa th cty,
wh th cat a ky ct
a pta, h kyht b c
a btt y chc tha t
hthv.
rd d. i th wa
th, c a ca b c by
pv jt th ht at ayht
t t th tca bjctv. Wh
th ctc ht a , th c a
bca ayht ca pc th
a a fct xt bt
wth y ha th hat. T achv th
c ct, th- a th-ac-
tat wth atat .
cd
w dd b .
g ayht tat t th
ht b t th ajty th t
ya-. Th a that th wt hat
typcay pc by ht caty
. sth-ac, vtcay pac ayht-
tat atay ca hat t-
t th pac th wt th
a ca cpat th hat that wa
pv by ht.
s . it ptat t
z th z a axz th vb
ht ta ayht apt.
Ww h b a hh-qaty
ctct, cpat tha bak,
a c th apppat az
th appcat. mak a ca tct
btw az vw a/ vtat
a az ayht. ayht-
ww, ca a typcay ha a
avata v az wth a w- cat-
. Bca a 10% t 40% ct
vb ht ta chaacttc
t w- cat xt, 10% t 40%
a q t atta th a
ayht bt. Wh cpa th
tha bt w- cat t th
bt vb ht ta, c-
th ct hth t
cpt that w b a
az q. Hwv, whv w
vw a ww a cpat, w-
cat h b t pv ct
a av y.
7/29/2019 Daylighting Strategies That Maximize Benefits
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3 8
light. However, like north-acing
roo monitors, it is necessary to
increase the glass area to achieve the
same contribution as south-acing
lightshelves.
When optimizing north-acing
transom glazing:
Dont use lightshelves. Because
o the lack o direct beam light on
the north side, lightshelves do not
provide any beneft and should not
be used.
Use high, sloped ceilings. Place the
glazing high in the room, with the
ceiling plane starting at the windowhead and sloping to the opposite
wall, to enhance perormance.
Use high glass instead o view
windows. High, horizontally placed
glass is, rom a daylighting per-
spective, superior to low view
windows.
Provide proper glass-to-oor
area ratios.
hm f
Understanding human nature is
essential to designing good day-
lighting solutions. Quality, energy-
efcient daylighting cannot be
accomplished by installing many
uncontrolled windows. For example,
i direct beam light enters a space,
it quickly will irritate occupants,
leading them to block the light,
negating the daylighting strategy.
Eliminate direct beam light.
A key component o good daylight-
ing, which essentially eliminates
commonly used view windows, is
the elimination o uncontrolled,
direct beam light. In all spaces
where light quality is critical, the
Eliminate direct beam light by bouncing, redirecting and fltering sunlight.
The south-acing monitors with baes provide daylight to the gymnasium.
7/29/2019 Daylighting Strategies That Maximize Benefits
10/12
Adverti sement formerly in this space.
7/29/2019 Daylighting Strategies That Maximize Benefits
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H i g H P e r o r m i n g B u i l d i n g s sp 20 084 0
strategies used should bounce,
redirect or flter the sunlight so that
direct beam light does not enter.
Develop daylighting strategies
to provide superior lighting or
two-thirds o the daylit hours.
Daylighting must be superior toelectrical lighting the majority o
the time the space is occupied.
I not, the habit o walking into a
Appcat exp gaz Typ
n-D
Vw Ww
Vw Ww
Vw Ww
Vw Ww
sth
nth
eat Wt, uha
eat Wt, sha
Ca db ( Tt), lw-
Ca db, lw-
Tt db, lw-
Ca db, lw-
D a
ga Abv lhthv
Hh ga Abv Vw Ww
r mt ga
B Btw th ga
sth
nth
sth nth
sth
Ca db
Ca db
Ca db
Ca db
This chart does not apply to the coldest climates, which may require triple glazing.
g l a z i n g f o r D i f f e r e n t a p p l i c a t i o n s
space and turning on the lights
will never be broken.
Consider the need to darken indi-
vidual spaces. The success o
daylighting strategies is greatly
inuenced by how the occupants
interact with the components othe strategy, especially blinds or
shades. I periodic darkening o a
space is not required, do not install
shades or blinds. Using blinds
results in decreased perormance,
increased frst costs, and greater
long-term maintenance expenses.
Try designing the space so that
areas that need to be dark, suchas a projection screen, television
monitor and computer monitor,
are in a shaded area, while the
majority o the space remains lit.
Televisions can be located in a
corner, not adjacent to a window, to
avoid glare.
g rmmd
Minimize contrast between brightsuraces and dark suraces. Avoid
bright, visually exposed windows.
Select light colors or interior
fnishes. The color o the ceiling,
walls, oor, and urniture has a
major impact on the eectiveness
o a daylighting strategy. Finishes
should be white or light colored
with good reectance. Color is
not the only actor to consider.Account or fssures or holes
within acoustical tiles that will
absorb light.
A south-acing lightshel with blinds between the glass can
reect problematic light to the ceiling and back into the space.
Sloping the ceiling downward rom the head o the win-
dow to the back o the room improves reectance.
7/29/2019 Daylighting Strategies That Maximize Benefits
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patibility between ballast, lamps and
controls. Mount the photosensors in
a location that closely simulates the
light level (or can be set by being
proportional to the light level) at the
work plane.
Use dimming controls. To enhance
the economic benefts and provide
or a smoother transition between
light conditions, use dimmable or
multistepped lighting controlled by
photosensors. There should be com-
mcha ncka, AiA, pt, ca pcpa at ivatv d,
ic., rah, n.C. H pat pt
th itata sa ey scty.
rcty, h v th pjct ct-
t AsHrAe pbcat,Advanced Energy
Design Guide for K12 School Buildings:
Achieving 30% Energy Savings Toward a Net
Zero Energy Building.
a B o u t t h e a u t h o r
Select compatible electric light fx-
tures. Use indirect lighting fxtures
that more closely represent daylight.
Consider the urniture and space
layout. Notice the light directionand the potential or glare. This is
particularly important when decid-
ing the location o computers.
Subsequent articles by the author,
discussing water and integrated design,
will be published in future issues.
Durant Road Middle School was constructed under budget. The frst year
savings attributed to the daylighting and roo assembly were over $0.50/t2.
The additional cost or the 150,000 t2 acility was $115,000, and the simple
payback was less than two years.
Adverti sement formerly in this space.