daylighting strategies that maximize benefits

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 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.


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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.


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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.


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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



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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

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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.


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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

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Vw Ww

Vw Ww

Vw Ww

Vw Ww

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nth

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r mt ga

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sth

nth

sth nth

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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.


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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.


daylighting strategies that maximize benefits

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