Publications

NBSIR 79-1732

Computer Analysis of Energy

Requirements in Single-Family

Residences: A Limited Case

Study of the Effects of

Envelope Design

NATL INST. OF STAND & TECH R.I.C.

A 11 10 4 SSbfll?

William L. Carroll

James P. Barnett

Building Thermal and Service

Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

July 1979

Sponsored by

Department of Housing and Urban Development

Office of Policy Development and Research

Washington, D.C. 20410

(X ' 100 I

,056

79-1732
f * *'V.

/
II

NBSIR 79-1732

u « COMPUTER ANALYSIS OF ENERGY

REQUIREMENTS IN SINGLE-FAMILY

RESIDENCES: A LIMITED CASE

STUDY OF THE EFFECTS OF

ENVELOPE DESIGN

tanMt ww'' *** NOV 13 19 79

A

j

71 -wi

William L. Carroll

James P. Barnett

Building Thermal and Service

Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

July 1979

Sponsored by

Department of Housing and Urban Development

Office of Policy Development and Research

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

COMPUTER ANALYSIS OF ENERGY REQUIREMENTS IN A SINGLE-FAMILY RESIDENCE:

A Limited Study of the Effects of Envelope Design

by

William L. Carroll and James P. Barnett

ABSTRACT

A number of design variations of a typical one-story single-family

residence were analyzed to determine annual heating and cooling energy

requirements. The National Bureau of Standards Load Determination com- puter program, NBSLD, was used to accomplish the analysis. Design

details for each of the residence variations are described in detail.

Annual heating and cooling energy requirement calculations are presented

and discussed. The results show only a small dependence on the thermal mass of the building envelope for the two climates studied (Washington,

D.C. and Orlando, Florida). The thermal properties of the windows had

greater effect. Concluding the report are technical generalizations

based on the present study, and recommendations for further work in

order to produce a definitive study of the effect of selected building

design parameters on energy consumption.

Key Words: Building energy consumption analysis; computerized building

energy analysis; cooling load calculation; energy conservation; heating load calculation ; NBSLD analysis of residences; residential energy conservation; thermal mass

effect in buildings.

iii
FOREWORD

The work detailed in this report was initiated as an ad hoc task for the

Department of Housing and Urban Development several years ago, and was presented to the sponsor in preliminary form for their immediate use. It is reported here as useful background for current work at the National

Bureau of Standards and the Department of Housing and Urban Development,

and the data cited are still correct, but it does not represent the

present state of the art with regard to the effect of thermal mass on building energy performance.

iv
Table of Contents

Page

ABSTRACT iii

FOREWORD iv

1. INTRODUCTION 1

2. RESIDENCE MODELS 2

2.1 BASIC DESIGN 2 2.2 FIXED PARAMETERS 5 2.3 VARIABLE PARAMETERS 7

3. ANALYSIS METHODOLOGY 13

3.1 LOAD CALCULATIONS 13

4. ANALYSIS RESULTS 16

4.1 SUMMARY OF TEST CASES 16

4.2 RESULTS USING WASHINGTON, D.C. WEATHER 16

4.3 RESULTS USING ORLANDO WEATHER 19

5. CONCLUSIONS 22

5.1 TEST RESULTS 22

5.2 PARAMETRIC TEST PLAN 24

6. REFERENCES 25

v

COMPUTER ANALYSIS OF ENERGY REQUIREMENTS IN SINGLE-FAMILY RESIDENCES:

A LIMITED CASE STUDY OF THE EFFECTS OF ENVELOPE DESIGN

by

William L. Carroll and James P. Barnett

1. INTRODUCTION

As part of the overall national energy policy, the identification and

development of practices and techniques which conserve energy in residences will play a significant role. Methods for widespread implementation of such techniques would be used to accomplish national energy

conservation goals. For example, energy conservation practices and

techniques would be incorporated in federally developed model building

codes for energy performance.

At the specific request of the Office of Policy Development and Research

of the Department of Housing and Urban Development (HUD), the National

Bureau of Standards was asked to examine the effect of variations of

certain building design parameters, particularly envelope construction,

on the energy performance of typical single-family residences. The purpose of the task was to provide HUD with sufficiently accurate information on the energy performance of such a residence that they could

determine the reasonableness of insulation requirements which were proposed as revisions of the FHA Minimum Property Standards for singlefamily housing. The NBS response constituted an ad hoc task, aimed at

accomplishing limited goals which would satisfy HUD needs for information in a responsive time interval.

To meet HUD needs, it was decided to use the NBS load determination com- puter program, NBSLD, to calculate monthly and annual space heating

and cooling loads for several variations of a typical single-family

residence. While the basic geometry and orientation of the one-story

structure were kept constant, limited variations were made of certain

parameters, namely the relative area and U-values* of the windows, the

U-values and mass of the walls (roughly corresponding to wood-frame and

masonry construction), and the weather data used. The report is thus

not intended to be either a definitive or a systematic study of all

building design parameters which could affect the energy performance of

a residence. Subsequent sections of the report describe in detail tie

analysis methodology, define the house models analyzed, and present the

results which were obtained and their significance. Concluding the

* The U factor of a wall component is the overall conductance from

interior air to exterior air. It includes the conductance of the

solid part of the component and also accounts for the effect of

air film heat transfer on the inside surface.

1
report are technical generalizations based on the present study, and

recommendations for further work which would be necessary to produce

a definitive, systematic study of selected parameters which affect

energy consumption.

2. RESIDENCE MODELS

2.1 BASIC DESIGN

All analyses were accomplished using variations on a one-story, rectangular house model (see Figure 1). The model typifies the "rambler" or ranch-house design common in the residential construction industry.

The basic design included a peaked roof with a naturally ventilated

attic and unheated basement. Windows were located in all four walls.

Since the house interior was modeled as a single thermal zone, details

of the interior structural design of the house were not needed and were,

therefore, not developed. Interior heat sources such as the heat

released from lights, appliances , .^nd occupants were considered. Overall

floor area was approximately 110 vn (more precise values are given subsequently).

A complete, detailed description of all parameters used in the various

models can be conveniently divided into two broad categories: those

parameters which remained fixed throughout all analyses, and those which

were changed. Table 1 lists the parameters that fall into each of these

categories. The subsquent sections of this report and supporting tables

contain details of the values for each of these parameters.

It is important to point out that due to input limitations of the

thermal loads analysis computer program NBSLD (or any other program, for

that matter), it is sometimes necessary to make appropriate assumptions

to convert a particular physical design to that set of inputs which will

correctly represent the thermal model for that design. When done properly, the conceptual model will "behave" during the computer analysis

just as the actual structure would in real life, subject to the same environmental conditions. In this particular effort, such assumptions

had to be made to model the roof, the attic, and the unheated basement.

Although the subsequent descriptions of those components of the design

might appear to be physically different, they are modeled so that they

would behave thermally as would the actual physical design.

In all cases, the values of parameters were chosen to be typical of

those encountered for actual materials and designs for this type of

house. Many of the final choices were based on constraints placed

by the sponsor. Where possible, recognized sources such as ASHRAE

published data were used. No attempt was made, however, to define or quantify the nature of the typicality concept, or the normal range of

variation of parameters encountered in actual construction of this type.

It should be noted that not all aspects of the design of the residences

used in this study are optimal, with regard to energy consumption. The

2
Figure 1. Basic house design used for energy analysis.

3
Table 1. Parameter Summary List

Fixed Parameters

1. Orientation

2. Interior Air Design Conditions

3. Interior Loads

a. Lighting

b. Appliances

c. Occupants

4. Attic/Roof Design

5. Thermophysical Properties

a. Roof

b. Ceiling

c. Floor

d. Door

6. Basement

7. Window Shading Devices

Variable Parameters

1. Weather

2. Aspect Ratio

3. Window Area

4. Window Type/Thermophysical Properties

5. Air Infiltration

6. Wall Thermophysical Properties

3. • b.

c.

Wood Frame

Masonry

Massless
house orientation, assumptions regarding internal loads, thermostat

settings, and infiltration rates, and some other aspects of the design

could probably have used better assumptions or design choices. In all

instances where this might be the case, the values used in this study were those requested by the sponsor, in order to guarantee comparability

of these results with other studies.

2.2 FIXED PARAMETERS

Detailed descriptions of the fixed parameters are presented in the order

shown in Table 1.

1. Envelope Orientation: Long axis parallel to north-south

direction.

2. Interior Air Design Conditions:

Winter (Octobe r-March) : 70°F, 20% rh mininuin;

Summer (Ap ril-Septembe r) : 75°F, 60% rh maximum;

Except for two test cases, NBSLD computed the load each hour

that was required to maintain the interior air temperature at

exactly the value specified above. Thus, there could be

instances in the winter where an abnormally high outdoor air

temperature, combined with interior heat generation, could cause

a net cooling load. Analogously, heating loads could occur

during the summer season. The relative humidity was allowed to

float above the minimum limit in the winter, and below the maxi- mum limit in the summer. A lower energy requirement would have

resulted if the interior room temperature had been constrained

to a band within the range of 70°F to 75°F, with heating or cooling required only to satisfy those constraints. Also, to

attempt was made to provide ventilation air to reduce cooling

loads during those hours when the outside air temperature would

have made it possible.

3. Interior Loads: Three types of interior energy sources, all of

which were heat-producing, were considered in the analysis.

They are listed below, along with corresponding minimum and max- imum values. Additionally, the values for each of these interior loads changed between the stated limits hourly according to

the schedules shown in Table 2.

Lighting: 0 to .079 W/m^

Appliances: .0056 to .0557 W/m^

Occupants: 1.5 to 5 persons. Each person contributes

132 W to the sensible heat gain in the space,

and 132 W to the latent heat gain.

5
Table 2. Hourly Schedules for Interior Load Sources

Hour

Lighting Appliances Occupancy

W/m^ (w/ft^) W/nr w/ft^ (// persons)

1 0

2 0

3 0

4 0

5 0

6 0

7 .03161 (.34)

8 .0474 (.51)

9 .0316 (.34)

10 .0158 (.17)

11 0

12 0

13 0

14 0

15 0

16 .0158 (.17)

17 .0474 (.51)

18 .0632 (.68)

19 .0790 (.85)

20 .0790 (.85)

21 .0790 (.85)

22 .0632 (.68)

23 .0316 (.34)

24 .0316 (.34)

0056 (.06) 5 0056 (.06) 5 0056 (.06) 5

0056 (.06) 5 0056 (.06) 5 0056 (.06) 5 0167 (.18) 5 0223 (.24) 5

0223 (.24) 4

0223 (.24) 3 0223 (.24) 2.5

0223 (.24) 1.5

0223 (.24) 1.5

0446 (.48) 1.5

0446 (.48) 1.5

0446 (.48) 1.5

0446 (.48) 2.5

0557 (.6 ) 5 0557 (.6 ) 5 0557 (.6 ) 5 0557 (.6 ) 5

0111 (.12) 5 Oil (.12) 5 0056 (.06) 5

6
4. Attic/Roof Design

The house was designed with a peaked roof (peak parallel to

length) approximately 2 m high with 30 cm overhangs on the

east and west sides. The attic thus enclosed was naturally

vented. Two air changes per hour were assumed. Although the areas were correctly modeled, NBSLD does not account for the

changed sun angles on a peaked roof, but rather assumes roofs are flat.

5. Thermophysical Properties: The roof and floor were assigned a fixed set of thermophysical properties based on their layered

construction. For each layer, the thermal conductivity,

density, specific heat, and thickness were specified. These

values are shown in Table 3. The ceiling was assumed to be

simply a thermal transfer medium with no thermal mass and a conductance of .28 W/m""*K (.05 Btu/h r* f X?~ • °F ) . Similarly, the

single door located in the east wall was assumed to have an area

of 1.67 m“ (18 ft^), a U value of 3.12 W/m^®K (.55 Btu/h r® f t^« °F)

and no thermal mass.

6.

Basement: Although the actual basement design was assumed to

be an unheated space under the whole house, this cannot be input

directly into HBSLD. The substitute thermal model chosen was therefore a special form of a slab-on-grade structure directly

beneath the floor construction. The floor construction consisted of layers of carpet, felt, 1.6 cm (5/8-inch) plywood, 1.9 cm

(3/4-inch) subfloor, and R7 insulation. Below that was a layer

of insulation (R=00. 176Km^/W) and finally a 15 cm (6-inch) layer

of sand and gravel. Experience with NBSLD has shown this type

of model to given reasonable results for the heat transfer

through the floor.

7.

Window Shading Devices: Awning-like devices were assumed to

shade each of the window areas. NBSLD accepts geometrical input

based on the design shown in Figure 2. Actual dimensions for

the geometry are also shown in the figure. No allowance was made for the possibility of different shading in the summer and

winter.

2.3 VARIABLE PARAMETERS

1. Weather: Actual hourly weather data for a one-year period and

for two specific locations were used in this analysis. The

respective locations and calendar years used were Washington,

D.C., 1954, and Orlando, Florida, 1957.* Hourly data required

*Neither of these years are ASHRAE selected test reference years. It is

also not known how typical or representative those weather years are,

since no analysis of weather data characteristics was made.

7
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this report.

9
by NBSLD for an analysis include dry-bulb temperature, wet-bulb

temperature, dewpoint temperature, wind speed, barometric pressure, cloud-cover index, and type of cloud cover.

2.

Aspect Ratio/Wall Geometry: All walls were 2.44 m (8 ft) in

height. Two different geometries were used in the various

analyses performed. One assumed a house width of 8.54 m (28 ft)

and length of 13.41 m (44 ft), giving an enclosed floor area of

114.6 m (1232 ft^) and an aspect ratio (width/length) of .64.

The other assumed a width of 10.58 m (34.7 ft) and a length of

11.98 m (39.3 ft), giving an area of 126.8 m^ (1364 ft^) and

an aspect ratio of .88.

3.

Window Area: The total window area was, in all cases, approximately 19.7 m^ (212 ft^). The actual distribution on each wall

varied slightly in some cases, and is described in detail in

Table 4.

4.

Window Type: Two types of windows were considered. Singleglazed windows were assumed to have a maximum U value of about

6.2 Wm^*K (1.10 Btu/hr* f t

* °F). Storm windows were assumed to

have a maximum U value of 3.7 W/m *K (0.65 Btu/hr* ft^* °F) «. The

maximum in each assumed an exterior surface air film heat transfer coefficient based on a 6.7 m/s (15 mph) wind speed. For a particular hour, the U value varied based on the actual wind

speed at that time. The value was computed by NBSLD using

actual weather data for wind speed.

5.

Air Infiltration: The air infiltration rate is calculated by

NBSLD on an hourly basis. The value is dependent on the wind

speed at the particular time, and is scaled from a maximum value

specified as input to the program. In this effort, the maximum

value was assumed to be dependent only on the type of window

used in a particular model configuration. Maximum values

assumed in this study were 1.5 air changes/hour associated with

single glazing and 1.3 air changes/hour associated with storm

windows

.

Additionally, there was assumed to be no mechanical ventilation

for any of the cases studied.

6.

Thermophysical Properties - Walls: Three general types of wall

construction were considered in this study. The first two were layered constructions which were intended to be typical of woodframe and masonry designs found in current residential construction. The details of the thermophysical properties of these

constructions are presented in Table 5. Note that the variation

in overall U value for these constructions was due only to a variation in the thickness of the insulating layer for each

10
Table

4.

Varying

Aspect

Ratio

and

Window

Distribution

Comparison * * i

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percentage

ratios

of

window

area

to

total

wall

area.
Table

5.

Thermophysical

Properties

of

Wall

Components

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Gypsum

board

1.27

(1/2)

.73

(.42)

801

(50)

837

(.2)
construction type. All other parameters and properties were

held constant. Table 6 summarizes the calculated U value as a function of insulation thickness for wood-frame and masonry wall

types.

The third type of wall was a hypothetical heat-transfer medium

represented by only a thermal conductance or U factor and having

no thermal mass effect.

Summarizing this section, Table 7 shows how all the variable parameters

described above were combined to form the actual test configurations

analyzed in this study. A total of 22 different variations were analyzed. Results of the analyses performed on each of the combinations

are discussed in detail in Section 4 of this report.

3. ANALYSIS METHODOLOGY

In order to evaluate the relative performance of the various test cases,

a single indicator of energy performance was chosen. That indicator was

the net hourly interior space thermal load for heating and cooling. The

hourly loads were summed for each month and for the year to obtain cumu- lative heating and cooling requirements for those periods. Heating and

cooling systems were not modeled, and subsequently actual energy consumption required to satisfy the computed cumulative load by real equipment

was not obtained. For the purpose of this effort, i.e., determining the

relative performance of various residential envelope designs, the cumulative heating and cooling loads are a sufficient performance indicator.

3.1 LOAD CALCULATIONS

Net hourly heating or cooling loads were computed using ASHRAErecommended response-factor load calculation methodology [1]* by means

of the National Bureau of Standards Load Determination Program, NBSLD

[2]. NBSLD computes the dynamic thermal behavior of a building due to

external weather and solar insolation data, and also based on hourly

summations of internal heat gains due to lighting, appliances, occupants,

etc. Hourly loads are calculated based on all of these factors and a specification of the interior temperature and humidity conditions of the

room. These specifications may be either fixed single values or a range

of allowable values. For this effort, all except two test cases were analyzed using a single fixed value of temperature and an allowable range

of humidity. The values were different for winter and summer periods,

as described in the previous section. The two exceptions assumed an acceptable interior temperature band from 21°C to 23.9°C (70°F to 75°F).

The program also includes a routine which can calculate the actual

interior temperature as it floats from hour to hour in the case that no heating and/or cooling (or a limited amount) is supplied to satisfy the

net load. This option was not used in the present study.

* Numbers in brackets refer to references in Section 6 of this report.

13
Table 6. Calculated U for Different Wall Types

Wall Type Insulation Thickness U Value

cm (in) W/’m2 *K (Btu/hr° f t

Masonry 2.54 (1) 1.05 (.185)

•• 3.70 (1.458) .082 (.150)

•• 6.35 (2.5) .596 (.105)

Wood Frame 5.59 (2.2) .573 (.101)

• 1 00 6.30 (2.48) .522 (.092)

.. 8.89 (3.5) .369 (.065)

"Hypothetical" - - .568

t

(.100)

14
Table

7.

Parametric

Configurations

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4. ANALYSIS RESULTS

4.1 SUMMARY OF TEST CASES

A total of twenty-two test cases were analyzed, based on the parameters

described in Section 2 of this report. These test cases are itemized in

Table 7. Seventeen tests were performed using Washington, D.C. weather,

and five Orlando, Florida weather, respectively. The test cases for

Washington were about equally divided between envelope design of

masonry, wood-frame and zero thermal mass. For Orlando, tests involved

masonry and wood-frame cases only. U values for the walls ranged from

3.7 to 10.5 W/m *K (.65 to 1.85 Btu/hr*ft ,0 F). The number of tests

involving single glazing and storm windows was about equal. Except for

two of the zero-mass wall cases, the house geometry and distribution of

window areas did not change throughout the effort. The same assumptions

regarding schedules for all sources of internal loads were used in all

ana lyses.

A complete summary of analysis results for all test cases is given in

Table 8. For each case, data are presented for the cumulative annual

heating and cooling requirements (AHR, ACR, respectively). Total values,

and values normalized per unit floor area of the model, are both presented. The following two sections separate discussion of the results

according to the weather data used for the analyses.

4.2 RESULTS USING WASHINGTON, D.C. WEATHER

The first seventeen test case results shown in Table 8 represent total

and area-normalized AHR's and ACR's for Washington, D.C. weather. For

all test cases, the maximum normalized ACR is about 1.8 times as large

as the minimum, while the maximum normalized AHR is about 1.6 times as large as the corresponding minimum. The maximum for each occurred for

the same test case (#1) which had the highest solid wall U-value and

single glazing. The minimum AHR and ACR did not occur with the same

model. The minimum AHR occurred for test case #13, which represents a combination of the lowest U-value studied and storm windows. The mini- mum ACR occurred for test case #7, a masonry constructed model and the

only test case (with complete annual results) that allowed a variable

temperature band instead of maintaining a constant interior temperature.

The particular test case will be discussed in greater detail in the following section of this report. Neglecting consideration of the variable

temperature analysis of test case # 7 , then test case #8 (the same model

using a fixed-temperature analysis) and test case #13 (having the lowest

AHR) had the two lowest ACR's and were almost exactly the same value

(0.2% difference).

The effect of envelope heat transfer performance on annual energy requirements is shown in Figure 3, which shows plots of normalized AHR’s and

ACR's as a function of the U-value of the solid portion of the wall.

The points divide into two groups, both of which approximate straight

16
Table 8. Annual Heating and Cooling Requirements, Total and Normalized

Test

#

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Total

GJ (MBtu)

Heating

Normalized

MJ/m2 (kBtu/ft 2

)

Cooling

Total Normalized

GJ (MBtu) MJ/m2 (kBtu/ft 2

)

49.31 ( 46 . 74 ) 389.2 ( 34 . 27 ) 36.56 ( 34 . 65 ) 288.6 ( 25 . 41 ) 33.64 ( 31 . 88 ) 265.5 ( 23 . 38 ) 42.75 ( 40 . 52 ) 337.4 ( 29 . 71 ) 29.90 ( 28 . 34 ) 236.0 ( 20 . 78 )

33.54 ( 31 . 79 ) 264.7 ( 23 . 31 ) 29.59 ( 28.05 233.7 ( 20 . 58 ) 29.88 ( 28 . 32 ) 235.9 ( 20 . 77 ) 42.00 ( 39 . 81 ) 331.5 ( 29 . 19 ) 29.17 ( 27 . 65 ) 230.3 ( 20 . 28 ) 40.14 ( 38 . 05 ) 316.8 ( 27 . 90 ) 27.33 ( 25 . 90 ) 215.7 ( 18 . 99 ) 42.68 ( 40 . 45 ) 336.8 ( 29 . 66 ) 29.92 ( 28 . 36 ) 236.2 ( 20 . 80 ) 41.71 ( 39 . 53 ) 329.2 ( 28 . 99 ) 41.83 ( 39 . 65 ) 330.2 ( 29 . 08 ) 1.78 ( 1 . 69 ) 14.08 ( 1 . 24 ) 1.56 ( 1 . 48 ) 12.38 ( 1 . 09 ) 0.70 ( 0 . 66 ) 5.45 ( 0 . 48 ) 1.61 ( 1 . 53 ) 12.72 ( 1 . 12 ) 0.73 ( 0 . 69 ) 5.79 ( 0 . 51 )

31.67 ( 30 . 02 ) 250.0 ( 22 . 01 ) 30.83 ( 29 . 22 ) 243.4 ( 21 . 43 ) 30.51 ( 28 . 92 ) 240.9 ( 21 . 21 ) 30.88 ( 29 . 27 ) 243.7 ( 12 , 46 ) 30.14 ( 28 . 57 ) 237.9 ( 20 . 95 )

19.74 ( 18 . 71 ) 155.8 ( 13 . 72 ) 30.08 ( 28 . 51 ) 237.5 ( 20 . 91 ) 30.51 ( 28 . 92 ) 240.9 ( 21 . 21 ) 31.22 ( 29 . 59 ) 246.

4

( 21 . 70 ) 30.43 ( 28 . 84 ) 240.2 ( 21 . 15 ) 30.98 ( 29 . 36 ) 244.5 ( 21 . 53 ) 30. 16 ( 28 . 59 ) 238.0 ( 20 . 96 ) 31.44 ( 29 . 80 ) 248.1 ( 21 . 85 ) 30.64 ( 29 . 04 ) 241.8 ( 21 . 29 ) 30.75 ( 29 . 15 ) 242.8 ( 21 . 38 ) 31.13 ( 29 . 51 ) 245.8 ( 21 . 64 ) 90.76 ( 86 . 02 ) 716.4 ( 63 . 08 ) 89.32 ( 84 . 66 ) 705.0 ( 62 . 08 ) 84.04 ( 79 . 65 ) 663.3 ( 58 . 41 ) 89.29 ( 34 . 63 ) 704.8 ( 62 . 06 ) 83.94 ( 79 . 56 ) 662.5 ( 58 . 34 )

17
COOLING,

MJ/m

2

HEATING,

MJ/m

400 35

CNI

300 -

200

175

MASONRY O —

FRAME A A

ZERO-MASS

.4 .5

SINGLE GLAZING O-A-D

DOUBLE GLAZING •

S .7 .8 U W/m2 • K

lOHn

30

25

20

15

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J I _J ! I I l_ J1.0 1.1

.06 .08

~T~

U Bfu/hr • ft 2 • °F

.10 .12 .14 .16 .IS .20

-15

-20

c -25

-30

-35

Figure 3. Annual heating and cooling requirements calculated

using Washington, D.C. weather data.

18

kBtu/ft"

kBtu/ft
lines. The AHR points of the upper group all represent test cases with

single glazing, while those of the lower group all represent test cases with storm windows. Similarly, the ACR points divide into two groups

based on the type of glazing. While the frame and masonry envelopes

generally had different U-values, it is evident that they (and also the

zero-mass envelope) all fall approximately on the same straight line.

Near the value of .57 W/m^’K (.1 Btu/hr* f t^* °F) for U, where tests can

be directly compared for all three envelope types, there is a maximum

difference in AHR of about 1% and in ACR of about 1.8% for storm window

cases. From this figure, it is seen that the relative effect of window

type is greater than that of envelope type, for a given U-value

of the solid portion of the wall.

Tests cases #14, #16, and #17 examined the effect of minor variations in

geometry and window area distribution for the zero-mass envelope model,

as detailed in Section 2 of this report. The maximum variations in

normalized AHR and ACR for these cases were about 2.3% and about 2.2%,

respectively. It is difficult to make any generalized conclusions of

the effect of geometry and window variations based on these data, since

neither the parameter variations nor the resultant AHR and ACR values

were greatly changed. The largest normalized AHR and ACR occurred for

the test case (#14) which had the lowest aspect ratio (was most nearly

square), which also had the greatest area of wall exposed to the south.-

Although it is reasonable to expect that this was a contributing factor,

it is not possible to separate the relative importance of this effect

from those due to changes in window areas and distributions among the

test cases.

The results in Figure 3, which indicate the relative significance of

window type, led to an examination of the dependence of AHR and ACR on overall or effective U-values based on an average of the properties of

the different parts of the wall (solid portions, windows, doors).

Table 9 shows the computed equivalent U-values, U , and the data on which the computations were based, for each of the Washington, D.C.. test cases. Figure 4 shows a resultant plot of AHR and ACR values versus U 0

. Compared to the good fits to straight lines represented by the data in

Figure 3, the data shown in Figure 4 show a much wider variation of

individual points from the lines shown, which were fitted to the data

by a linear regression analysis. The conclusion that results from examination of this figure is that the concept of a simple, linear, generalized heat conduction approach (i.e. , AHR=U

2

* A* "A T") based on a generalized representation of average annual temperature difference (e.g.,

heating degree days) and equivalent average U-values, U

0 , does not have

a great degree of validity for the data developed in this study.

4.3 RESULTS USING ORLANDO WEATHER

Test cases #18 through #22 of Table 8 represent the five analyses accom- plished using Orlando weather. The largest area-normalized ACR is about

8% larger than the smallest. The ACR's are so small that comparison is

19
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MJ/m

2

HEATING,

MJ/m

2

2 20 -

(Vi

10 A •

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-330

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"1

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FRAME A — A

SINGLE GLAZING 0 —— A

DOUBLE GLAZING • —— A

-58

-59

-60

—61

-62

-63

-64

Figure 4. Annual heating and cooling requirements calculated using

Orlando, Florida weather data.

20

kBtu/fH

kBtu/ft
Table

9.

U

-

Equivalent

U-value

for

Total

Walls

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21
not meaningful. In a manner similar to Figure 3, Figure 5 shows the

AHR and ACR values plotted as a function of the U-value of the solid

portion of the wall. As was seen for the earlier data, the Orlando

results also closely approximate a straight line dependence on U, with

two lines depending on the window type. The agreement of AHR. and ACR

for masonry and frame envelope types for similar U-values is good.

Again, the greatest effect is due to type of window, not the type of

envelope. All the data represent constant-temperature analyses. No

attempt was made to examine the validity of the generalized, equivalent

U (U

e

) concept for these data.

For the conditions of the analysis, it is worth while to note that any

advantageous effects on ACR due to the thermal mass of masonry walls

do not appear to be evident. The ACR value for the frame envelope type

differs from the line extrapolated from the two ACR points calculated

for masonry walls by less than 0.5%, for the single-glazing test cases.

5. CONCLUSIONS AND RECOMMENDATIONS

Because of the ad hoc nature of this effort, and its attempt to supply

a limited amount of data based on specific test cases, the number of

conclusions that can be made are limited. To the degree that such con- clusions can be made, they are summarized below, and are based on

the preceding discussions of analysis results. Following those and

concluding the report are some recommendations for a more generalized

subsequent study effort. Such an effort would have as its objective the

generation of sufficient data to answer questions raised by the present

effort (particularly regarding the effect of thermal mass of the envelope on AHR and ACR), but which remain unanswerable based on the present

data.

5.1 TEST RESULTS

It is clearly shown in Figures 3 and 5, for the test cases analyzed, that

the greatest single effect on AHR and ACR is due to the type of window

(single or double pane). This effect is significantly larger than that

caused by variation in the U-value of the walls, particularly in the

AHR's computed for Orlando where cooling dominated.

The same figures show that, for the conditions of analysis that were

used, the effect of wall construction type (and consequently its related

thermal mass) on AHR or ACR was not readily discernible for a given Uvalue. The reasonableness of the constant interior temperature assumption comes into question here, since it is generally held that the full

potential of thermal mass cannot be realized unless the interior

temperature is allowed to float in a limited band of acceptable values.

For the one test case (#7) for which annual AHR and ACR were computed

using such an allowable band, comparison with the companion test case,

(#8) which used the constant-temperature assumption, shows a lower ACR,

but it also indicates a higher AHR. The present results are felt to

be too limited to be conclusive.

22
z W/m0>l

o

cvi

N

<£>

ro

cm

O

2 uu/pi^ 2 uj/piaj

Figure 5. Annual heating and cooling requirements calculated us Washington, D.C. weather data and plotted as a function of

equivalent U-value, U

e

, for the building envelope.

23

-260 t

1

-23
Small variations in geometry (i.e. aspect ratio) and window area distribution produced only small changes in AHR and ACR. A detailed explanation for the changes and their specific causes cannot be determined from

the present limited set of data.

Finally, the concept of a generalized linear transfer equation, based on an average U-value, U

e , computed from the properties and respective areas

of the different wall components, is not well supported by the data presented here. There is a relatively large amount of scatter of individual

AHR and ACR data points from the line fitted to the points by linear

regression. Thus, for approximately the same computed U

e , different test cases showed significantly different AHR and ACR values. The discernible

differences are mostly due to the type of window involved, in support of

the conclusions stated above. This indicates that the solar contribution

to AHR and ACR is the portion of the total that does not obey the

generalized linear-heat-transfer concept.

5.2 PARAMETRIC TEST PLAN

The most interesting and significant areas for future study are felt to

be on the real effect of thermal mass, and a more detailed study of the

effect of geometry and window distribution. In addition, peak heating

and cooling loads should be studied as well as AHR and ACR. A wider

range of climates should also be considered.

The thermal mass effect should include studies with a wider range of

U-values and thermal mass values than the ones presented here. Distribution of thermal mass (i.e. walls, floor, ceiling, interior) should be

considered. Most importantly, the analyses should be done using a variable interior temperature assumption, for several allowable temperature ranges. A number of climates representative of different weather

regions should be used to determine those regions and other conditions

for which the thermal mass effect is most significant.

Additional studies should be performed for different geometries, representing a wider range of aspect ratios. For each of these cases, a range

of cases using varying window areas and distributions among the walls

should be studied, in order to find the optimum combination of such parameters.

It is also recommended that actual energy consumption be computed by

developing a realistic set of assumptions and subsequent simulations

for actual heating and cooling equipment. This level of simulation

should be done in at least a few cases. If it is found that AHR and

ACR correlate well with actual energy use for each component, then the

system simulations could be discontinued.

24
6 REFERENCES

1. "Procedure for Determining Heating and Cooling Loads for Computerizing Energy Calculations" Algorithms for Building Heat Transfer

Subroutines, American Society of Heating, Refrigerating, and Air

Conditioning Engineers, Inc., 1975.

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

in Buildings," National Bureau of Standards Building Science Series

BSS 69, July 1976.

25
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS IR- 79-1732

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Computer Analysis of Energy Requirements in Single-Family

Residences: A Limited Study of the Effects of Envelope Design.

5. Publication Date July 1979

6 . Performing Organization Code

7. AUTHOR(S)

William L. Carroll, James P. Barnett

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. U6o 6370

11. Contract/Grant No.

RT 193-72

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Department of Housing and Urban Development, Off ice of

Policy Development and Research; Washington, D.C.

20U10

13. Type of Report & Period Covered

Final j 2/75-6/7$

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

A number of design variations of a typical one-story single-family residence

were analyzed to determine annual heating and cooling energy requirements. The

National Bureau of Standards Load Determination computer program, NBSLD, was used

to accomplish the analysis. Design details for each of the residence variations

are described in detail. Annual heating and cooling energy requirement calculations

are presented and discussed. The results show only a small dependence on the

thermal mass of the building envelope for the two climates studied (Washington, D.C.

and Orlando, Florida). The thermal properties of the windows had a greater effect.

Concluding the report are technical generalizations based on the present study,

and recommendations for further work in order to produce a definitive study of the

effect of selected building design parameters on energy consumption.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

Building energy consumption analysis; Computerized building energy analysis ;Cooling

load calculation; Energy conservation; Heating load calculation; KBS CD analysis of

7 - 3 *' 18. AVAILABILITY (xl Unlimited 19. SECURITY CLASS 21. NO. OF PAG. S (THIS REPORT)

1 For Official Distribution. Do Not Release to NTIS

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