NATL INST. OF STAND & TECH 1111111

A11107 BTOlfll

NBSIR

Evaluation of the Daylighting and

Energy Performance of Windows,

Skylights, and Clerestories

Prepared by:

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, DC 20234

Prepared for: National Fenestration Council

3310 Harrison St.

Topeka, KS 66611

Naval Facilities Engineering Command

U.S. Navy

Washington, DC 20390

Directorate of Civil Engineering

U.S. Air Force

Washington, DC 20330

and

Office of Chief of Engineers

U.S. Army

Washington, DC 20314

June 1983

DEPARTMENT OF COMMERCE

V C.2

NATIONAL BUREAU OF STANDARDS

NATIONAL BUREAU OF STANDARDS

LIBRARY JUL 2 1 1983

r\oV GLCC-rOfC

i sJ^sO

t^?

NBSIR 83-2726

* ++ EVALUATION OF THE DAYLIGHTING AND

ENERGY PERFORMANCE OF WINDOWS,

SKYLIGHTS, AND CLERESTORIES

Stephen Treado, Gary Gillette, Tamami Kusuda

Prepared by:

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Washington, DC 20234

Prepared for: National Fenestration Council

3310 Harrison St. Topeka, KS 66611

Naval Facilities Engineering Command

U.S. Navy

Washington, DC 20390

Directorate of Civil Engineering

U.S. Air Force

Washington, DC 20330

and

Office of Chief of Engineers

U.S. Army

Washington, DC 20314

June 1983

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

ABSTRACT

This paper examines the impact of several fenestration options on building

space heating, cooling, and lighting loads. The use of skylights, windows, and

clerestories is evaluated for a single floor commercial building, using the

NBSLD-2 building energy analysis computer program, which posesses a fully

integrated daylight model (DALITE). The evaluation focuses on:

a) the impact of daylighting on heating and cooling energy requirements,

b) the potential reduction in electric lighting energy requirements

through daylight utilization,

c) the relative daylighting/thermal performance of skylights,

clerestories, and windows, and

d) the effect of aperture orientation on fenestration optimization and

selection.

The NBSLD-2 computer procedure performs a dynamic simulation of hour-by-hour

building thermal performance and energy requirements for a one-year period.

The thermal and daylighting characteristics of each fenestration aperture are modeled to enable evaluation of the trade-offs associated with the use of each

fenestration type. The results are presented in the form of design guidelines

to enable the preliminary design decisions to be made regarding fenestration

location, type, configuration, and size. The energy calculations are presented

as functions of fenestration characteristics, so that the potential energy

advantages can be estimated for different fenestration designs.

Key words: building energy analysis, clerestories, daylighting, skylights,

windows

.

iii
$

TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES v LIST OF FIGURES vi

1. INTRODUCTION 1

2. BACKGROUND

2.1 THE BUILDING

2.2 RESULTS AND DISCUSSION

3. CONCLUSIONS 7

REFERENCES 8

<3

iv

ro

'S- m
LIST OF TABLES

Page

Table 1. Building Description 9

Table 2. Building Envelope Construction Details 10

Table 3. Parameters Used for Analysis 11

Table 4. Total Building Energy 12

v
LIST OF FIGURES

Page

Figure 1. Layout of the fenestration for the window, clerestory and

skylight cases 13

Figure 2. Energy performance of south-facing windows 14

*

* *1 ’ »

'

. , Figure 3. Energy performance of north-facing windows 15

Figure 4. Energy performance of south-facing clerestories 16

Figure 5. Energy performance of north-facing clerestories 17

Figure 6. Energy performance of skylights 18

Figure 7. Total energy use for each fenestration option, with and

without daylighting 19

vi
1. INTRODUCTION

Commercial buildings consume energy primarily in three ways: for heating,

cooling, and lighting. When designing a building, various trade-offs among

these three must be considered regarding the selection and sizing of fenestration, lighting, equipment, and HVAC systems [1]. Fenestration systems,

including windows, skylights, and clerestories, influence building energy

requirements also in three main ways. They transmit solar radiant energy, they

provide daylight illumination, and they transmit heat by conduction/convection.

However, fenestration in buildings has usually been associated with increasing

heating loads due to conduction and convection, and increasing cooling loads

due to solar gains, with little thought of the decreasing lighting loads and

cooling loads possible due to daylighting. The determination of the net effect

of a fenestration system requires that the impact of the system on the combined

heating, cooling and lighting loads and energy use be examined on an annual

basis. This requires the use of a building energy analysis computer program

with integrated daylight modeling capabilities. We have chosen to use the

NBSLD-2 computer program which has such an integrated daylighting model [2,3].

Other researchers have examined the daylighting and energy performance of

fenestration systems [4,5,6], however, the question of relative performance of

different sidelighting and toplighting fenestration designs has not been

addressed.

The NBSLD-2 computer program is used to perform a dynamic simulation of

hour-by-hour building thermal performance and energy requirements for a one- year period. The thermal and daylighting characteristics of several fenestration apertures are modeled to enable evaluation of the trade-offs associated

with the use of each fenestration type.

NBSLD-2 is an updated version of the NBSLD building energy analysis computer

program. The unique features of the program include a completely coupled hourby-hour daylight simulation capability to enable evaluation of the performance

of windows, skylights and clerestories for all types of sky conditions. The

daylighting algorithms have been validated against measured data for a variety

of fenestration designs and exterior daylight conditions [3].

The purpose of this paper is to examine the impact of different fenestration

options on building energies. Thirty-one options are compared, both with and

without daylighting, from six main groups:

I) No fenestration.

II) South facing windows (10,

III) North facing windows (10,

IV) South facing clerestories

area)

.

25, and 50 percent of south wall area).

25, and 50 percent of north wall area).

(10, 25, and 50 percent of south wall

1
V) North facing clerestories (10, 25 and 50 percent of north wall

area)

.

VI) Skylights (2, 5, and 10 percent of roof area).

The analysis was performed using Washington, DC, Test Reference Year (TRY) [7]

weather data, since Washington has both significant heating and cooling loads.

Throughout the report, the term "non-daylighting case" is frequently used. By

this term, it is meant that daylight is not used to offset electric lighting, even if the building has fenestration which admits daylight. A building without fenestration is a special case, since no potential exists for daylight

utilization.

2
2 . BACKGROUND

A simple building design was chosen for the analysis, consisting of a detached,

one-story, 2500 square foot (232 m2), commercial building. Different fenestration systems were added to the building and the annual energy requirements for

heating, cooling, and lighting were determined for each case. The energy

requirements were determined by modeling the performance of a simple HVAC and

lighting system responding to the calculated heating, cooling, and lighting

loads. The HVAC system modeled included a gas furnace and a packaged air

conditioner, serving a single zone.

Several factors were considered before choosing this type of building design

for evaluating the thermal and lighting performance of fenestration systems.

First, it has been found that 58 percent of the total U. S. nonresidential

building stock, including 71 percent of the commercial buildings built since

1945, are single storied, and that a large portion of these are relatively

small buildings [8]. Furthermore, during the initial design phase, detailed

information concerning the building construction is usually not available;

consequently, the building should be as generic as possible. In fact, con- struction details are normally not selected until after the envelope is determined, which, in this case, involves the selection and sizing of the fenestration. Second, since the purpose of the analysis is to evaluate the relative

performance of several fenestration options, it is important to have a building

configuration which lends itself to side and overhead fenestration indiscriminantly. In addition, it is desirable at this stage of design to consider in

detail only those factors which influence the thermal and daylighting performance of the fenestration. This approach will minimize the influence of a particular HVAC system or component on the energy calculations, since the HVAC

system can be specified or changed following selection of the fenestration

design. Once the fenestration and building envelope design are determined, a more detailed analysis of the HVAC system can be performed to facilitate

calculation of energy consumption.

Although the simulated building model need not be excessively detailed, it must

include all factors which influence fenestration thermal and daylighting performance. Thus, the thermal resistance and thermal mass of the building envelope,

and the geometry of the building components must be carefully modeled. In

addition, decisions or assumptions must be made regarding the number of building

occupants, the use of office equipment, the building occupancy schedule, the

HVAC system control strategies, and, most importantly for our case, the lighting

system design.

There are two approaches to modeling the lighting system for the purpose of

evaluating fenestration performance. One would be to specify a particular

lighting system including luminaire type and its particular photometries,

and for the daylighting case, control strategy and control sensor location. A

separate calculation would then be made to determine the illuminance levels

due to the electric lighting at the points of interest within the building.

While this approach provides detailed information concerning the performance

of that particular lighting system, it has the disadvantage of tying the

analysis to a single lighting system. That would be appropriate at a later

design stage when the details of the lighting system would be known, but at

3
the preliminary design stage, one is seeking to determine the required

performance characteristics of the lighting system, and would benefit from a more general approach.

Thus, an alternate approach is used to model the lighting system. A lighting

power budget is specified in terms of watts/area, and a general (uniform)

lighting system is assumed which would exactly meet the budget at the required

illuminance level. In this manner, different lighting systems could be

specified based on the performance parameters.

When dimming of the lighting system is modeled in the analysis, it is assumed

that the illumination set point is just met when the lighting system is at

full power (with no daylight contribution). Thus, any contribution of daylight

illuminance results in a corresponding decrease in illuminance from the lighting

system. In practice, this would be achieved if the maximum output of the

lighting system was adjusted so the work-plane illuminance was at the set-point.

The change in lighting power consumption associated with the change in illuminance is not, in general, linear and is determined from a dimmer performance

curve (light output vs. power consumption) [9]. Most dimming systems have

similar performance curves. The computer model includes a typical dimmer performance curve. It should be noted that the glare conditions and other psychophysical parameters are not included in the analysis. Griffith [10] has noted

that the direct glare analysis methods presently in use are not valid for cases where daylighting is coupled with electric lighting, as used here, and Hopkinson

[11] has observed that even when they are valid they do not necessarily represent glare problems. Therefore, excluding such an analysis should not be

considered a severe weakness.

The details of the building and the operating parameters are contained in the

following section.

2.1 THE BUILDING

A single floor commercial building in Washington, D.C. is modeled for the

analysis. The building is shown in figure 1 and its operating conditions are described in Tables 1 through 3. Table 1 lists a basic description of the

building characteristics. Table 2 lists the sizes and construction details of

the building envelope components. Table 3 lists the building and HVAC operating

parameters, assumptions, and preliminary design choices, used for the analysis.

The assumptions used are representative of modern practice. The building

envelope thermal properties meet ASHRAE 90-80 standards for Type B buildings.

The wall, floor and roof construction details are typical. The HVAC system

controls utilize night-time setback, and the lighting system requires 2.5 watts

per ft2 (26.9 watts per m2) when fully energized. A gas heating furnace was

simulated.

4
2.2 RESULTS AND DISCUSSION

Lighting, heating, and cooling energy was calculated for each case for a one-year period. The results are plotted for each case as a function of

fenestration surface area, both for the daylighting case and for the nondaylighting case. These figures are plots of the annual electric energy,

heating energy and cooling energy as a function of fenestration area, for each

fenestration type.

For south-facing windows (figure 2), the 50 percent area with daylighting

provided the minimum total energy use mainly due to a reduction in electric

energy of 44 percent compared to the non-daylighting cases. The lowest cooling

energy was also seen to occur at this configuration, indicating that the reduction in cooling energy due to decreased lighting energy more than compensated

for the increase in cooling energy due to solar heat gain through the large

windows. Daylighting is seen to be favorable for all window areas analyzed,

and for the non-daylighting cases the no fenestration option produces the

lowest total energy use. Heating energy decreases with increasing window

area for both the daylighting and non-daylighting cases, while cooling energy

decreases for the daylighting cases and increases for the non-daylighting

cases.

Looking now at the peak loads (figure 2a), the peak demand heating load is not

significantly influenced by the window area or daylighting strategy, since it occurs in winter during the early morning warm-up of the building. The peak

demand cooling load exhibits more variation, with a minimum occurring for the

25 percent area daylighting case. All of the daylighting cases show lower

peak demand cooling loads than any non-daylighting case.

For north-facing windows (figure 3), the minimum total energy use also occurs with the 50 percent area daylighting case. A 32 percent reduction in electric

energy is seen compared to the non-daylighting case. For the daylighting

cases, cooling energy decreases and heating energy increases with increasing

window area. For the non-daylighting cases, both cooling and heating energy

increase with increasing window area. The lowest peak demand cooling load is seen to occur with the 50 percent area daylighting case, with all of the

daylighting cases producing lower peak demand cooling loads than any

non-daylight ing case.

For the south-facing clerestories (figure 4), the minimum total energy use occurs for the 50 percent area daylighting case, where a reduction in electric

energy of 65 percent is seen. Cooling energy increases and heating energy

decreases with increasing window area for both the daylighting and non- daylighting cases, however, cooling energy is much lower for the daylighting

cases. Peak demand heating and cooling loads are significantly greater at the

larger clerestory area for both the daylighting and non-daylighting cases. For

each clerestory area, peak demand loads are less for the daylighting case than

for the non-daylighting case.

For the north-facing clerestories (figure 5), the minimum total energy use also occurs for the 50 percent area daylighting case, with a reduction in electric

5
energy of 65 percent compared to the non-daylighting case. Cooling energy

decreases and heating energy increases with increasing clerestory area for the

daylighting cases. This is because larger north-facing clerestories transmit

little additional solar heat gain while increasing thermal losses. However,

since the total energy use decreases with increasing clerestory area for the

daylighting cases, the decreases in cooling and lighting energy more than offset

the increases in heating energy. For the non-daylighting cases both heating and

cooling energy increase with increasing clerestory areas. The lowest peak

demand cooling load occurs for the 25 percent area daylighting case, while the

lowest peak demand heating load occurs for the smallest clerestory areas.

Although for the skylight cases (figure 6), the minimum total energy use occurs

for the 2 percent area daylighting cases, the curve is essentially flat beyond

this value with a reduction in electric energy of 77 percent compared to the

non-daylighting case. The minimum electric energy was produced by the 10 percent

area daylighting case. However, since for the daylighting cases the cooling

energy increases and heating energy decreases with increasing skylight area, the

increase in cooling energy for the 10 percent area as compared to the 2 percent

area more than offsets the decrease in heating and lighting energy. The skylights are so effective in reducing lighting energy that the total energy for

the daylighting cases never exceeded the electric energy alone for the non- daylighting cases. The peak demand heating loads did not vary significantly,

except for the 10 percent area daylighting case being larger than the others.

The lowest peak demand cooling load occurred for the 2 percent area daylighting

case, with the daylighting cases always lower than the non-daylighting cases.

Comparing the total energy of each of the thirty-one fenestration/daylighting

options, several results are apparent. The skylights with daylighting produced

the lowest total energy use, with the 2 percent area slightly better than the

5 percent area, followed by the south-facing 50 percent area window and the 25

percent area clerestories, all with daylight. Table 4 lists all 31 options

studied, in order of increasing total energy use. In figure 7, the total annual

building energy use is plotted for all fenestration types as a function of

fenestration area, with and without daylighting. This figure clearly shows the

energy-savings potential of daylight utilization, and a relative comparison of

daylighting performance of different fenestration types and orientations.

6
3. CONCLUSIONS

Several conclusions can be drawn from the foregoing results. These conclusions

are limited to buildings similar to the study building, namely single-floor,

detached commercial buildings without movable shading or other window management

devices subject to weather conditions equivalent to Washington, D.C. While the

study building had no internal partitions, similar results would be expected

for the skylight and clerestory cases for buildings with a few properly placed

internal partitions. For a building with windows on one facade, internal partitions would have to be positioned to provide daylight for all interior zones, to

enable the results of the window analyses to be applicable.

The major conclusions are as follows:

• For any fenestration area, the use of daylighting reduces total

building energy as compared to the non-daylighting cases;

• Skylights are the most effective fenestration options in terms of

minimizing total building energy for heating, cooling, and lighting,

with between 2 percent and 10 percent of roof area performing almost

equally well;

• Skylights are the most effective daylighting source of the three

types studied, reducing electric energy by as much as 77 percent as compared to the non-daylighting cases;

• Clerestories are more effective than windows of the same size, both as daylighting sources and in terms of total building energy;

• South-facing clerestories and windows are more effective than

north-facing ones, with the 50 percent clerestory and window areas being the most effective;

• Peak demand cooling loads are less when daylighting is used than

for the non-daylighting case, for any fenestration option;

• Peak damand heating loads are not significantly influenced by the use of daylighting, but increase with increasing fenestration area;

• All of the fenestration options with daylighting are more effective

than the no fenestration option, in terms of total building energy.

7
REFERENCES

1. Kusuda, T. , Collins, B., Simplified Analysis of Thermal and Lighting

Characteristics of Windows - Two Case Studies , National Bureau of

Standards, Building Science Series 109, February 1978.

2. Kusuda, T., NBSLD, the Computer Program for Heating and Cooling Loads in

Buildings, National Bureau of Standards Building Science Series 69, July

1976.

3. Gillette, G. , A Daylighting Model for Building Energy Simulation , National

Bureau of Standards, Building Science Series 152, March 1983.

4. Johnson, R. , Selkowitz, S., Winkelman, F., Zentner, M. , Glazing

Optimization Study for Energy Efficiency in Commercial Office Buildings , Third International Symposium on Energy Conservation in the Built Environment, Dublin, Ireland, March 1982.

5. Jurovics, S. , Daylight, Glazing and Building Energy Minimization , IBM

Scientific Center publication, Los Angeles, CA. , 1981

6. Place, W. , Fontoynant, M. , Bauman, F. , Andersson, B., Howard, T.

Commercial Building Building Daylighting , LBLO-14348, Lawrence Berkeley

Laboratory, Berkeley CA, 94720, 1982.

7. National Climatic Center, Tape Reference Manual, " Test Reference Year ,"

Asheville, N.C. , 1976.

8. "Nonresidential Building Energy Consumption Survey: Building

Characteristics," U.S. Department of Energy, DOE/EIA-0246 , p. 2-5, March

1981.

9. Treado, S. and Kusuda, T., Daylighting, Window Management Systems and

Lighting Controls , NBSIR 802147, December 1980.

10. Griffith, J. W. , "BCD Judgements of Large Area Sources," Illuminating

Engineering, Vol. 63, No. 3, pp. 106-110, March 1968.

11. Hopkinson, R. , "A Note on the Use of Indices of Glare Discomfort for a Code of Lighting," Transaction of the Illuminating Engineering Society

(London)Vol. 25, No. 3, pp. 135-138, 1960.

8
Table 1. Building Description

Building Location Washington, DC

Lat. 38° Long. 77°

Building Dimensions 50 ft (15.2 m) long

50 ft (15.2 m) wide

10 ft (3.0 m) high

Building Type Single floor

Free-standing

Medium weight construction

No attic space

Building Use Commercial

Building Thermal Properties Meets ASHRAE 90-80

standards for Type B

buildings (except 10 percent

skylight case, which meets

BOCA and Southern Building

Code)

9
Component

Floor

Wall

Roof

Windows

Skylights

Clerestories

* Assuming no

Table 2. Building Envelope Construction Details

Area

Overall

Thermal

Conductance Layer

ft^ (m2) Btu

h»f t^.F

W

^m2«K

)

Thickness

in. (cm)

2500

(232)

*2000

(186)

*2500

(232)

0.133

(0.755)

0.155

(0.880)

0.092

(.552)

Carpet & Pad 1 ( 2.5)

Concrete Slab 4 (10.2)

Polystyrene Insulation 1 ( 2.5)

Earth 6 (15.2)

Face Brick 4 (10.2)

Cement Mortar 0.5 ( 1.3)

Insulated Hollow Cinder

Block 8 (20.3)

Air Space 0.75 ( 1.9)

Gypsum Drywall 0.5 ( 1.3)

Built-up Roofing 0.375 ( 1.0)

Rigid Insulation 2 ( 5.1)

Concrete Slab 2 ( 5.1)

Air Space 0.75 ( 1.9)

Metal Lath & Plaster 0.75 ( 1.9)

50, 125, or 250

(5, 12, or 23) .50

(2.84)

Double glazed clear

north or south facing

50, 125, or 250

(5, 12, or 23) .43

(2.44)

Double dome clear over

white, insulated curb

Double glazed clear

north or south facing

50, 125, or 250

(5, 12, or 23) .50

(2.84)

fenestration

10
Table 3. Parameters Used for Analysis

1) Thermostat Set-Points min. 60°F (15.6°C) Unoccupied

min. 68 °F (20.0°C) Occupied

max. 78° (25.6°C) Occupied

max. 85° (29.4°C) Unoccupied

2) Occupancy Schedule hours 1-6 Unoccupied

hour 7 50% occupied

hours 8-17 100% occupied

hour 18 50% occupied

hours 19-24 Unoccupied

weekends Unoccupied

holidays Unoccupied

3) Number of Occupants 20

4) Office Equipment 0.25 watts per ft2

2.69 watts per m2

625 watts total

5) Lighting 0.25 watts per ft2

2.69 watts per m2

Fixed

2.5 watts per ft2

26.9 watts per m2

Primary fluorescent

luminaires con- trolled in five

banks

100% lighting power

dissipated as heat

to interior space

6) HVAC system Heating furnace 80%

efficiency

Cooling COP = 3.0

11
Rank

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

Table 4

Total Building Energy

Fenestration Area Day lighting?

Total

Building

Energy

Skylights 2% Y 13718 kwh

Skylights 5% Y 13929

Skylights 10% Y 14853

Clerestories, south 50% Y 19065

Clerestories, north 50% Y 19893

Window, south 50% Y 21035

Clerestories, south 25% Y 22008

Clerestories, north 25% Y 22748

Window, north 50% Y 24426

Window, south 25% Y 24631

Clerestories, south 10% Y 26091

Clerestories, north 10% Y 26483

Window, north 25% Y 27827

Window, south 10% Y 28732

Window, north 10% Y 30421

None 0% N 32125

Window, south 10% N 32312

Window, north 10% N 32408

Window, south 25% N 32701

Skylights 2% N 32734

Window, north 25% N 32780

Clerestories, south 10% N 32856

Clerestories, north 10% N 32947

Window, north 50% N 33407

Skylight 5% N 33685

Window, south 50% N 33687

Clerestories, north 25% N 34195

Clerestories, south 25% N 34864

Skylight 10% N 35486

Clerestories, north 50% N 36371

Clerestories, south 50% N 39607

12
NORTH

AS METERS (FEET)

PLAN VIEW •F BUILDING

SECTION VIEW OF

CLERESTORY SCENARIO

SECTION VIEW OF SKYLIGHT SCENARIO

SECTION VIEW OF WINDOW SCENARIO

Figure 1. Layout of the fenestration for the window, clerestory and skylight

cases

15.24 (50) V

I 1

I I

I I

I I

I 1

I I

I I

I I

I—

1

I I

!

i

j

I 1

i

i

i i

i i

lr\

i j

«—

i

i i

i i L__

I I

r—

i

iLJ

V'—SKYLIGHTS—'

7

152 3.05 3.05 3.05 305 1.52 V 110 )

i 1 no) r~

(10 ) “i i s! i

15

)’

4

| '4

1

1 » 2 4

» ! 1

ALL STAT

15.24

150)

I I I I

15-24 (50)-

13
SOUTH UIHDCU

IMX. COOLING . MU). KXT INC ftg)

THOUSANDS SOUTH UIHDOW NMML COOLING . HEATING . ELECTRIC (CUNI

Figure 2. Energy performance of south-facing windows

14
p

0

u

c•

K

II

MOUTH WINDOW MX. COOLING . MX. HEATING <KW>

it .

it . 1 1

t . •-

c . A—*t1AX. COOLING WITH DAYLIGHT O • °MX. COOLING NO DAYLIGHT

•- -•MX. HEATING with DAYLIGHT •--“MX. HEATING HO DAYLIGHT

4 .

i . —1

1 1 1 1 1 1

1 1 • S 10 15 20 2S 30 X 40 45 55

PERCENTAGE AREA OP ONE WALL

E

N

ER

G

VKW

H

THOUSANDS NORTH WINDOW

ANNUAL COOLING , HEATING . ELECTRIC (KWH)

THOUSANDS NORTH WINDOW

Figure 3. Energy performance of north-facing windows

15
SOUTH CLERESTORIES MX. COOL I NC . MX. *AT INC <(U>

thousands south clerestories

ANNUAL COOLING , HEATING . ELECTRIC (KIWI

THOUSANDS SOUTH CLERESTORIES

TOTAL (KUH). WITH AND WITHOUT daylight

Figure 4. Energy performance of south-facing clerestories

16
NORTH CICRCSTMICS MX. COOLING . HAX. HEATING

EN

ER

G

V

KU

M

THOUSANDS NORTH CLERESTORIES

ANNUAL COOLING . HEATING , ELECTRIC (KUH)

THOUSANDS NORTH CLERESTORIES

TOTAL (KUH), WITH AND WITHOUT DAYLIGHT

Figure 5. Energy performance of north-facing clerestories

17
cH

CR

CV

KUH

THOUSANDS

ANNUAL COOLING SrVLIGMTS

. meatinc . EUCTRIC (CUM I

cN

ER

CV

KU

H

THOUSANDS SKYLIGHT*

TOTAL <KUH>, with AND WITHOUT DAYLIGHT

M

PERCENTAGE OF ROOF AREA

Figure 6. Energy performance of skylights

18
THOUSANDS TOTAL (KUH), WITHOUT DAYLIGHT

THOUSANDS TOTAL (KUH), UITH DAYLIGHT

T

0

TA

L

EN

ER

G

V

KU

H

• 85 M 75 190 12S 150 17S 8M E2S BSD FENESTRATION AREA (SO FT)

Figure 7. Total energy use for each fenestration option, with and without

daylighting

19
iV. 2*60

)

:j.3. dept, of comm. BIBLIOGRAPHIC DATA1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 83-2726 June 1983

4. TITLE AND SUBTITLE

EVALUATION OF THE DAYLIGHTING AND ENERGY PERFORMANCE OF

WINDOWS, SKYLIGHTS, AND CLERESTORIES

5. AUTHOR(S)

Stephen Treado, Gary Gillette and Tamaml Kusuda

S. PERFORMING ORGANIZATION (If joint or other than NBS, see Instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

I. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Naval Facilities Engrg .Command Directorate of Civil Engrg . Office of Chief Engrs.

U.S. Navy U.S. Air Force U.S. Army

Washington, DC 20390 Washington, DC 20330 Washington, DC 20314

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) This paper examines the impact of several fenestration options on building space

heating, cooling, and lighting loads. The use of skylights, windows, and clerestories

is evaluated for a single floor commercial building, using the NBSLD-2 building energy

analysis computer program, which possesses a fully integrated daylight model (DALITE)

.

The evaluation focuses on: a) the impact of daylighting on heating and cooling energy

and equipment sizing, b) the potential reduction in electric lighting energy requirements through daylight utilization, c) the relative daylighting/thermal performance of

skylights, clerestories, and windows, and d) the effect of building orientation on fenestration optimization and selection.

The NBSLD-2 computer procedure performs a dynamic simulation of hour -by-hour building

thermal performance and energy requirements for a one-year period. The thermal and

daylighting characteristics of each fenestration aperature are modeled to enable

evaluation of the trade-offs associated with the use of each fenestration type. The

results are correlated in the form of design guidelines to enable the preliminary

design decisions to be made regarding fenestration location, type, configuration, and

size. The energy calculations are presented as functions of fenestration characteristics, so that the potential energy advantages can be estimated for different

fenestration designs.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Building energy analysis; clerestories; daylighting;

skylights; windows.

13.

AVAILABILITY

| xl Unlimited

| | For Official Distribution. Do Not Release to NTIS

| | Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[X] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

26

15. Price

$8.50

USCOMM-DC 6043-P80