The Energy Impact of Daylighting

and Your Impact on Building Design

Jon McHugh, MSME

Heschong Mahone GroupASHRAE/AIA Meeting April 20, 1999

What is Daylighting

Daylighting is the illumination of building interiors with:

Direct beam Sunlight

Sky Diffuse Light

Reflected light from the sun or sky

Effective Daylit Buildings Need an Integrated Design

• Orientation and Shape

• Glazing

• Mechanical System

• Lighting Controls

Need to Work Together

Motivation for Daylighting People are Important

Correlation studies of daylighting and productivity

HMG Analysis of 108 Stores (2/3s daylit)

HMG Analysis of 21,000 elementary student test scoresOperable windows also a benefit

Daylighting Motivation - Energy Savings

FractionDaylitArea50%

FractionLighting Energy

Savings inDaylit Area

30%

PrimaryLightingEnergy

3.73 Quad10 6 GWH

MarketPenetration

16%X X X =

26,000GWH

Savings

• 30% to 70% savings in daylit zone

• 60% of commercial space directly under a roof– Single story buildings 41% of area

• 18% could be daylit over next 10 years

US Primary Energy Consumption

Residential20%

Commercial16%

Industry38%

Transportation26%

US Carbon EmissionsProjected Carbon Emissions by Region 1990 - 2010

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

Uni

ted

Stat

es

Oth

er N

Amer

ica

Japa

n

Wes

tern

Euro

pe

EE/F

SU

Chi

na

Oth

erAs

ia

Mid

dle

East

Afric

a

C. &

S.

Amer

ica

Ann

ual M

illio

n M

etri

c To

nnes 1990

1992

2000

2005

2010

Design Goals: Visual Quality–Provide appropriate illuminance levels

(task and ambient)–Control luminance contrast (highlight

or uniformity)–Integrate electric lighting and daylight–Provide a view–Create a pleasing environment

Design Goals: Energy Savings

• Electric lighting reduction

• Cooling load avoidance

• Passive solar heat gain

Design Goals: Cost Containment

–Use standard building elements–Use building form and orientation

to admit light and reject heat–Reduce mechanical equipment

size–Reduce connected lighting load–Simplify controls

Orientation - Solar Gain

0

1000

2000

3000

4000

5000

6000

7000

8000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

North East/West South Horiz

Source: ASHRAE 1997 Handbook of Fundamentals, SHGF

Geometry

Overhangs - Sun Path Diagram

Shading 4’ below2’ overhang

Ref: Fuller Moore - Architectural Daylighting

15

Quick Estimate of Solar Altitude, at at Solar Noon

At Latitude, L, and a declination, :

at=90° - L + (degrees)

= 0, during equinoxes (3/21, 9/22)

= 23.45°, summer solstice (6/21)

= -23.45°, winter solstice (6/21)

Albuquerque L = 35°

Glazing Specifications

Solar Heat Gain Coefficient (SHGC) - how much heat gain is transmitted

SC = SHGC x 0.87

15.1tCoefficien Shading

nceTransmittaVisible

0.1SHGC

nceTransmittaVisible

Zero Energy Building

• Ultra Efficient Small Office

• R-19 Walls, R-32 Ceiling

• R-8 Glazing R-5.5 overall window

• Photocontrols on dimmable electronic fluorescent ballasts

• Direct/indirect evaporative cooling

18

Daylighting Design Constraints

• Multi-Story Design

• No Moving Parts (Passive)

• Inexpensive Components

• Make use of Direct Beam Sunlight

20

Simulation Steps

DAY3DProgram

Geometry and Surface Props

ExchangeFractions

TMYData

Irradiance PerezEfficacyModel

Electric Lighting Savings

Illuminance

BuildingDescription BLAST Energ

y Results

21

Parametric Runs

a) Chiller no daylighting

b) Evap cooling no daylighting

c) Chiller w/ daylighting

d) Evap w/ daylighting

e) “c” w/o daylighting controls

f) “c” w/o clerestory

Annual Energy End Uses

0

10

20

30

40

50

60

( a ) ( b ) ( c ) ( d ) ( e ) ( f )

kB

tu/S

F

BoilerChillerHW PumpFansPlugLights

23

Skylighting Guidelines

Skylighting design manual

Can be downloaded from www.energydesignresources.com

Funded by public interest energy research grant

24

SkyCalc - Skylighting Design Software

MS Excel application (spreadsheet)

Simple inputsType of building

Type of skylights

Number of skylights

Lighting control type

25

Outputs

Total Energy Cost Savings from Skylightsfor Lighting, Cooling and Heating

Design

-$2,000

$0

$2,000

$4,000

$6,000

$8,000

$10,000

0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0%

Skylight to Floor Ratio (SFR)

Ann

ual C

ost

Savi

ngs

($/y

r)

26

Components of Energy Savings

-400,000

-300,000

-200,000

-100,000

0

100,000

200,000

0% 2% 4% 6% 8% 10% 12%

Skylight to Floor Ratio

kWh/

yr

Lighting

Cooling

Heating

Total Energy

Efficacy of Light Sources

0

20

40

60

80

100

120

140In

can

d

EE

Ma

g

Ele

ctro

nic

Met

alH

alid

e

HP

S

Su

nli

gh

t

Cle

ar

Sky

Ove

rcas

tS

ky

Lu

men

s/W

att

28

Cost-effectiveness of skylights

Optimum Sizing of Skylights for Cost Savings

$-

$1.00

$2.00

$3.00

$4.00

$5.00

$6.00

$7.00

1 2 3 4 5 6 7 8 9

Cos

t Sav

ings

per

SF

of G

lazi

ng A

rea

Daytona

Albuquerque

Albany

Nashville

Madison

Seattle

29

Conclusions

Daylighting is a highly desired building feature

It can save energy if applied correctly

Guidelines and tools are available to assist designers