NAT L INST, OF STAND & TECH R.I.C.

AlllDM DEaDSD

NBS

PUBLICATIONS

NBSIR 78-1496

Preliminary Data on the Field

Performance of Storage-Type

Residential Water Heaters

Richard A. Grot

Lawrence S Galowin

Building Thermal and Service Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

April 1979

WQQ. 1 Hi lEPARTMENT OF COMMERCE

100 JAL bureau of standards

.U56

78-1496

C.2

SEP 2 0 197S

NBSIR 78-1496

PRELIMINARY DATA ON THE FIELD

PERFORMANCE OF STORAGE-TYPE

RESIDENTIAL WATER HEATERS

Richard A. Grot

Lawrence S. Galowin

Building Thermal and Services Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

April 1979

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

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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PRELIMINARY DATA ON

THE FIELD PERFORMANCE OF STORAGE-TYPE

RESIDENTIAL WATER HEATERS

by

Richard A. Grot and Lawrence S. Galowin

ABSTRACT

The early results of a field experiment for determining the performance

of gas and electric residential storage water heaters are presented.

Energy requirements for hot water supply and hot water consumption and

usage pattern data are presented and analyzed using statistical techniques

in order to display average load curves and the variation about the

average. It is shown that the daily energy usage of these water heaters

is approximately a linear function of the energy content of the drawn

daily water consumption. This fact allows a simple procedure to be used

for evaluating the effects of retrofit actions on the performance of the

water heater.

Keywords: Energy usage; load profiles; water heaters.

ill
UNITS OF MEASURE AND S.I. CONVERSION FACTORS

In NBS Document LC 1056, revised August 1975, guidelines were established to reaffirm and strengthen the commitment of NBS to the

greatest practicable use of the International System of Units (S.I.)

in all of its publications and also in all of its dealings with the

science and engineering communities and with the public. In this

report the measurements are those of the U.S. customary units as they appear in the referenced standards, in order that the readers

may give full attention to the organization and compilation of the

criteria.

The following conversion factors are appropriate for the units of

measure that appear in this report:

Energy

1 British thermal unit (Btu) = 1055.056 joule (J)

1 kilowatt-hour (kWh) = 3600000.0 joule (J)

Temperature

1 degree Fahrenheit (°F) = (1.8)~^ kelvin (K) or (®K)

Temperature Fahrenheit (®F) = (459.67 + temp. ®F)/1.8 ( ®K)

Time

1 hour (h) = 60 minutes (min) = 3600 seconds (s)

Volume

1 U.S. liquid gallon (gal) = 0.003785412 meter^ (m^)

= 3.785412 liters (L)

Iv
Table of Contents

Abstract ill

1. Introduction 1

2. Test Program 1

3. Measurement Method 1

4. Discussion of Results 5

5. Summary 20

Table 1. Occupant and Townhouse Characteristics 2

Table 2, Water Heater Characteristics 3

Table 3, Water Heater Consumption, Townhouse 10 6

V
FIGURES

Figure 1. Water Heater Data Acquisition Schematic 4

Figure 2. Simplified Data Processing - Output 4

Figure 3. Hourly Hot Water Usage - Townhouse #10 7 Figure 4. Hourly Energy Content of Drawn Hot Water - Townhouse #10 7 Figure 5. Hourly Energy Used for Water Heating - Townhouse #10 8

Figure 6. Hourly tlaximum Outlet Water Temperature - Townhouse #10 8

Figure 7. Hourly Minimum Inlet Water Temperature - Townhouse #10 9

Figure 8, Hourly Basement Air Temperature - Townhouse #10 9

Figure 9. Frequency Plot of Daily Water Consumption - Townhouse #10 11

Figure 10. Frequency Plot of Daily Energy for Water Heating - Townhouse #10 11

Figure 11. Daily Energy Consumption vs. Dally Water Energy

Content - Townhouse #10 12

Figure 12. Dally Energy Consumption vs. Dally Hot Water Used - Townhouse #10 12

Figure 13. Dally Water Energy Content vs. Dally Water Usage - Townhouse #10 13

Figure 14. Hourly Frequency Plots for Hourly Hot Water Usage - Townhouse #10 13

Figure 15. Hourly Frequency Plots for Hourly Energy Used for

Water Heating - Townhouse #10 15

Figure 16. Average Hourly Profile of Hot Water Usage - Townhouse #10 15

Figure 17. Average Hourly Profile for Water Heating Energy - Townhouse #10 16

Figure 18. Average Hourly Profile for Energy Content of Drawn

Hot Water - Townhouse #10 16

Figure 19. Average Hourly Profile for Hot Water Usage - Townhouse #10 17

Figure 20. Average Hourly Profile for Water Heating Energy - Townhouse #9 17

Figure 21. Average Hourly Profile for Energy Content of Drawn

Hot Water - Townhouse #9 18

Figure 22. Frequency Plot of Daily Water Consimiption - Townhouse #9 18

Figure 23. Frequency Plot of Daily Energy for Water Heating - Townhouse #9 19

Figure 24. Frequency Plot of Daily Heat Content of Drawn Hot

Water - Townhouse #9 19

vi
Table 2. WATER HEATER CHARACTERISTICS

Electric Water Heaters

Unit

No

Manufacturer Model

Capacity

gal

Input

watts

1 Westinghouse TB802LKKXO 82 4500/4500/4500

2 Westinghouse TB802LKKXO 82 4500/4500/4500

5 Westinghouse TB802LKKXO 82 4500/4500/4500

6 Westinghouse TB802LKKXO 82 4500/4500/4500

9 Westinghouse TB802LKKX1 82 4500/4500/4500

10 Westinghouse TB802LKKX1 82 4500/4500/4500

Gas Water Heaters

Manufacturer Model

Capacity

gal

Input

Btu/h

3 Bradford 40DBF5N-1 40 45000 /

4 Bradford 40DBF5N-1 40 45000

7 Bradford 40T5 40 48000

8 Bradford 40T5 40 48000

11 Bradford 40T5 40 48000

12 Bradford 40T5 40 48000

3
Figure 1. Water Heater Data Acquisition Schematic

GRAPHICS & TABLES

Figure 2. Simplified Data Processing - Output Schematic

4
PRELIMINARY DATA ON

THE FIELD PERFORMANCE OF STORAGE TYPE

RESIDENTIAL WATER HEATERS

1.

Introduction

The early results of a field experiment for determining the performance

of gas and electric residential storage water heaters are presented.

Energy requirements for hot water supply and hot water consumption and

usage pattern data are presented and analyzed using statistical techniques in order to display average load curves and the variation

about the average. It is shown that the daily energy usage of these

water heaters is approximately a linear function of the energy content

of the drawn daily water consumption. This fact allows a simple

procedure to be used for evaluating the effects of retrofit actions

on the performance of the water heater.

2.

Test Program

The data discussed in this article were collected as part of an effort

to evaluate the performance of eight major household appliances under

the Energy Appliance Labeling Program. The test measurements were made in single-family townhouse residences in Twin Rivers, N.J. , near

Princeton University. The choice of this site was motivated by prior

studies under a program for Energy Husbandry in Housing; extensive

knowledge about the homes and occupants was available from instrumentation located in several of the dwellings. Table 1 identifies the

household composition of each townhouse of this study: the number

of adults, the number of children, the ages of the children and the

size of the townhouse. Each townhouse was equipped with a dishwasher,

clothes washer and 1 1/2 baths, the full bath containing a shower-tub

combination. Table 2 presents the water heater information of primary

Interest here.

3.

Measurement Method

The data discussed in this article were collected by means of instrumentation and automatic data recording systems; the data tapes were processed by computer programs developed especially for this data reduction.

The instrumentation scheme for the water heater is depicted in Figure

1. Ordinary gas, electric and water meters were modified to produce

a pulse rate proportional to the rate of usage of the quantity monitored.

The pulse train from the meter was fed into a specially designed

counter which produced an analogue signal proportional to the number

of pulses received in an interval of time. These analogue signals

were recorded by a data acquisition system along with the outputs

of thermocouples attached to the inlet and outlet water lines. The

thermocouples were wrapped with insulation in such a way that any

transfer from the ambient air was negligible. The data acquisition

system scanned the data at least once every five minutes; thus, in

principle, 5-minute energy, water and temperature data were available.

1
Table 1. OCCUPANT AND TOWNHOUSE CHARACTERISTICS

Unit No . of No . of Children's

No. Adults Children Ages Bedrooms

1 2 2 6,8 3

2 2 1 6 3

3 2 1 3 2

4 2 3 6,7,9 3

5 2 2 10,13 3

6 2 2 10,13 4

7 2 2 2,4 3

8 2 2 1,3 3

9 3 1 15 3

10 2 2 2,6 2 converted

to 3

11 2 2 11,13 3

12 2 2 5,11,4 3

2
To the present, however, the data analysis has been confined to time

intervals consisting of either one hour or one day. The hourly

and daily data were printed in summary form (see Table 3 or graphs.

Figures 3-8) and also outputed to mass storage files for later

data analysis (see Figure 2). In Table 3 representative data for

a limited number of days are illustrated for Townhouse 10.

4. Discussion of Results

The homes comprised several with gas-fired appliances and others with

electric, as indicated in Table 2. The data discussed in this

report are for the electric installations and treat only the water

heater. Representative data are presented which illustrate the

usage patterns, water consumption, energy content and energy required

for heating the water. The electric water heaters have an 82-gallon

capacity and are rated at 4500/4500/4500 watts with manufacturers'

data sheets providing other specifications.

Townhouse number 10 represents a household of two adults and two

children, ages 2 and 6. Figures 3, 4, 5 represent the hourly distribution of water and energy used during a four-day period in the

Christmas holiday of 1976. In Figure 3 the hot water usage is

shown to be less than 25 gallons in any hour. The energy content

of the water used and the energy required for heating are presented

in Figures 4 and 5. The periods of time from zero to ten hours

of days 360 and 361 are of speci^al interest in that very little

water consumption occurs so that heating of the incoming cold water

supply is at a minimum. The energy required for heating to make

up for stand-by losses can be observed by noting the isolated

usage of 0.8 kWh about every 5 or 6 hours in the night. At other

times it is necessary to establish the heat balance equation to

compare the heat addition required to make up for the heat removed

by the usage due to the replenished supply of incoming cold water

and then to raise the temperature of the mass of the water stored

in the tank.

The range of temperatures measured on the hot water supply line (see

Figure 1) are shown in Figure 6. The thermocouple mounted on the pipe

does not provide the stored water temperature. When there is no hot

water flow the reading represents only the pipe wall temperature due

to heat conduction from the tank; during periods of flow the wall

temperature measurement is very close to the water within the pipe.

The differential of the control sensor element within the hot water

heater appears to be approximately 5°F for delivery of hot water

except during periods of heavy demand. The temperature of the

incoming supply of water (measured as for hot water) is indicated

in Figure 7. The temperature is close to 55°F. In Figure 7 the

minimum value during each hour interval is shown in order to obtain

the representative situation when cold water is flowing (rather

than the idle pipe wall temperature or some intermediate value).

5
Day

283

284

285

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

314

315

316

317

318

319

3. WATER HEATER CONSUMPTION—TOWNHOUSE 10

Energy

(kWh)

13.97

17.09

22.27

15.62

12.16

32.70

18.60

34.30

23.19

26.32

14.26

19.45

16.44

31.17

21.91

14.73

31.45

20.57

16.88

34.54

22.07

40.75

15.88

30.80

15.90

28.08

34.89

19.07

21.42

22.31

12.61

28.25

25.33

41.84

17.32

29.85

Water Heat Content of

(gal) Drawn Water

(kWh)

37.50

50.40

68.90

46.20

28.20

108.20

57.20

114.80

73.40

86.10

38.40

60.70

49.10

99.40

74.20

38.70

104.10

62.90

48.70

119.50

69.90

140.20

40.00

107.20

41.00

91.50

115.60

57.20

61.00

67.40

30.00

88.60

82.10

140.20

47.10

94.30

8.77

11.97

16.31

10.44

6.64

25.53

13.77

27.34

17.53

20.31

9.07

14.35

11.48

23.49

17.93

9.24

25.09

15.28

11.64

28.25

16.86

33.47

9.55

24.38

9.87

22.26

28.51

13.80

14.95

16.73

7.24

22.03

19.90

34.28

11.59

23.32

6
WATER

ENERGY

CONTENT

IN

50 00

Figure 3. Hourly Hot Water Usage - Townhouse #10

DAY358 DAY359 DAY360 0AY361 Figure 4, Hourly Energy Content of Drawn Hot Water - Townhouse //lO

7
TKMrEKATUKK

IN

DEC

6 12 18 24 6 12 18 24 6 12 18 24 6 12 18 24 DAY368 0AY359 OAY360 0AY361 Figure 5. Hourly Energy Usage for Water Heating - Townhouse # 10

Figure 6. Hourly Maximum Outlet Water Temperature - Townhouse // 10

8
TEMPERATURE

IN

OEG F

DAY359 OAY359 DAY360 OAY361 Figure 7. Hourly Minimum Inlet Water Temperature - Townhouse //lO

Hourly Basement Air Temperature

9

Figure 8.
Figure 8 shows the temperature in the basement areas where the hot

water storage tank is located. In this home the hot air furnace and

distribution ducts are in the basement so that for periods during which

heating occurs, the basement temperature rises; those events are mostly

noted in the late afternoons and evenings.

Further examination of the data from Townhouse 10 is presented in

Figures 9-13. The frequency plots are presented of water consumption

and energy for water heating for more than 60 days. Table 3 represents

a partial history for 36 days of the corresponding daily utilization of

energy required for hot water in kWh, hot water consumed in gallons per^

day and the heat content of the hot water consumed in kWh units.

The frequency graph in Figure 9 shows that the greatest hot water con- sumption ranges over 60-70 gallons per day and 40-50 gallons per day,

each occurring about 16% of the time. The extreme minimum lies between

20-30 gallons with a frequency of about 2% of the time and the maximum

140-150 gallons usage occurs with a probability of 4% of the time.

From examination of the data from other homes, it is known that there are significantly ranging diversity factors between occupants demand/

usage pattern and consumption. Figure 10 shows a corresponding frequency plot for the daily water heater energy usage. The most frequent

range of energy consumption is between 15 and 20 kWh, with an occurrence

of 29%. The minimum daily energy usage of between 10 and 15 kWh has an occurrence of 14%; the maximum usage range of 40 to 45 kWh occurred

about 4% of the time.

The graphs of Figures 11, 12, and 13 illustrate the essentially linear

relationship between the daily energy consumed or daily energy content

of the drawn hot water and the water consumed. The data collected seem

to indicate that for intervals of a day, storage and transient effects

are negligible and the water heater performs in a linear manner. From

linear extrapolation of the data in Figures 11 and 12, the standby

losses of the hot water storage tank are about 4.5 kWh per day. Since

the data demonstrate the linear -dependency between the parameters, the

standby losses due to conduction, convection, and radiation losses together are nearly a constant increment of energy consumed. In Figure 13

the linear extrapolation through the origin of the data relationship

for energy content of the water vs. water consumption provides a level

of confidence for the results. Since the operating range of temperatures of the water and the elements of the tank is narrow, non-linear

temperature factors affecting the temperature-dependent properties

tend to be a constant small part of the losses or are perhaps negligibly

small in the loss terms for time intervals of a day or longer. This

frequency also indicates that, even at maximum daily usage, the water

heater is capable of maintaining the required hot water temperature.

10
FREQUENCY

1.00

90

80

70

60

.50

40

.30

.20

20 00 40.00 60.00 80.00 100 00 120 00 140 00 160 00 180 00 200 00 I

WATER CONSUMPTION IN GALLONS Figure 9. Frequency Plot of Daily Hot Water Consumption - Townhouse #10

1.00 —

90

80 —

70

60

G 50

40

30

.20

ENERGY CONSUMPTION IN KWH Figure 10. Frequency Plot of Daily Energy for Water Heating

11
ENERGY

COMSUMEO

PER

DAY

IN

KWH

ENERGY CONTENT OF HOT WATER USED IN EOUIVALENT KWH Figure 11. Daily Energy Consumption vs. Dail;> Di‘ avm Water Energy

Content - Townhouse //lO

Figure 12. Dally Energy Consumption vs. Daily Hot

Water Used - Townhouse #10

12
ENERGY

CONTENT

OF

WATER

IN

KWH

WATER CONSUMED IN GALLONS Figure 13. Daily Water Content vs. Dally Hot Water Usage - Townhouse //lO

voo — 1.00

.80

g

.60

UJsoUJ£ 40

20

100

80

g

.60 U

3ahU£ 40

.20

HOUR 9 MEAN= 1 00 VAR.^ 1.8S

12 50 25 00 37 50 50 00

WATER IN GALLONS

HOUR 11 MEAN= 10.21 VAR = 6.08

HOUR 10 MEAN= 3 47 VAR = 3 85

"t80 —

80

40

20

1250 25 00 3750 50 00 WATER IN GALLONS

HOUR 12 MEAN- 11.32 VAR - 9 24

0 12 50 25 00 37.50 50 00

WATER IN GALLONS

12 50 25 00 37 50 50 00 WATER IN GALLONS Figure 14. Frequency Plots for Hourly Hot Water Usage - Townhouse //lO

13
The data in Figures 11, 12, and 13 can be approximated by the equations:

E = 4.50 (±0.25) + 0.107 (±0.013) H ( 1 )

E - 4.42 (±0.31) + 0.259 (±0.004) W ( 2 )

H = - 0.08 (±0.18) + 0.241 (±0.002) W (3)

where E is the daily energy consumption of the water heater in kWh, H

is the heat content of the daily drawn hot water in kWh, and W is the

daily water consumption in gallons. The numbers in parentheses in

equations (1), (2) and (3) are the standard errors of the estimated

coefficients. The average service efficiency of the water heater over

this period was 75.0%.

Detailed analysis of the hourly usage is presented in Figures 14 and 15

by the frequency plots. Only a small sample of the available reduced

data is presented here. These hourly data plots represent values for

all the days of data collected, averaged for each hour of the day. In

Figure 14 there is about a 5% frequency of hot water usage above 20

gallons within one hour in the intervals of hours 9, 10, 11, and 12.

In other data for this home (not shown on these graphs) it was observed

that up to 40 to 50 gallons of hot water usage occurred in the 20th

hour with a 5% ocurrence. Figure 15 illustrates for those same hours,

9, 10, 11, 12, the frequency for energy used for water heating. Note

that for small water usage in hour 9 there is about 50% operation

between zero and 1 kWh. When the water usage is greater (in Figure 14)

the range of energy expended is less than 5 kWh with about 20% frequency.

The energy content depends on the flow delivered (gallons) and the temperature rise of the water. Since this temperature rise is fairly con- stant except for periods of excessive usage, there is a close correspondence with Figure 14.

The hourly distribution for a 24-hour period is shown in Figures 16,

17, and 18. These energy and water-usage distributions again represent

the average values for each hour of all the days of data collected,

i.e., from day 283 to 324, or 41 days. The average hourly usage

(i.e. , gallons or energy consumed in each hour) is designated

by the shaded area. Also shown by the solid line on the graphs 16,

17 and 18 are the plots of 2o (two standard deviations) about the

average. The meaningful utilization of such data will be for designsupply requirements of tanks and pipes. Such new design criteria

are required when the energy requirements are no longer economic

or are constrained by mandatory or voluntary limiting factors.

Selective samples of data are presented in Figures 19 to 24 from Townhouse 9, to illustrate and compare the effects of different household

compositions and different household practices.

14
HOURLY

WATER

CONSUMED

IN

GAL

100 HOUR 9 MEAN= .52 VAR.= 52 ^ 100 HOUR 10 MEAN^ 1 00 VAR ^ 90

0 2.50 5.00 7.50 10.00 ELECTRICITY IN KWH

0 2.50 5 00 7 50 10 00

ELECTRICITY IN KWH

0

Figure 15.

250 5 00 750 10 00

ELECTRICITY IN KWH

0 2 50 5 00 7 50 10 00

ELECTRICITY IN KWH Frequency Plots for Hourly Energy Used for Water Heating

- Townhouse #10

Figure 16. Average Hourly Profile of Hot Water Usage - Townhouse #10

15
HOURLY

WATER

ENERGY

CONTENT

IN

KWH

I

10 00 —

9 00 -

8 00 -

7 00 -

HOUR Figure 17. Average Hourly Profile for Water Heating Energy - Townhouse #10

10.00 -

9 00 -

8.00 -

7 00 -

6 00 -

5 00 -

4 00 -

3 00 -

Figure 18.

I

HOUR Average Hourly Profile for Energy Contents of Drawn Hot

Water - Townhouse #10
HOURLY

WATER

CONSUMED

IN

GAL

sooo

45.00

40.00

35.00

30.00

25 00

20.00

15.00

10 00

5.00

HOUR Figure 19. Average Hourly Profile for Hot Water Usage - Townhouse #9

t

10.00

9.00

8.00 -

7.00

6 00

5.00 -

4.00

3.00 -

2.00 -

1 00

Figure 20. Average Hourly Profile for Water Heating Energy-Townhouse //9 17
HOURLY

WATER

ENERGY

CONTENT

IN

KWH

Figure 21. Average Hourly Profile of Energy Content Dravm Hot

Water - Townhouse #9

WATER CONSUMPTION IN GALLONS Figure 22. Frequency Plot of Daily Water Consumption - Townhouse #9

18
90 —

80 —

70 —

1.00

60 —

ENERGY CONSUMPTION IN KWH Figure 24. Frequency Plot for Daily Heat Content of Drawn Hot

Water - Townhouse #9

19

6.00 10 00 15 00 20 00 25 00 30 00 35 00 40 00 45 00 50 00

ENERGY CONTENT OF HOT WATER USED IN EQUIVALENT KWH Figure 23. Frequency Plot of Dally Energy for Water Heating - Townhouse //9

5.00 10.00 15.00 20 00 25.00 30 00 35.00 40 00 45.00 50 00
5 . Summary

The amount of hot water used by a household can vary greatly from day

to day and from hour to hour. Though average daily usages and average

hourly usage profiles can be derived, experimental data indicate that on the level of an individual dwelling there is a large variation in

usage about these averages, both on a daily and hourly basis, A

broader range of data is required to establish a generally valid

statistical data base. The energy losses from the water heaters

measured are nearly constant on a daily basis and though the quantity

of daily hot water drawn varies greatly, there exists an essentially

linear relationship between the daily amount of energy consumed by

the water heater and the dally amount of hot water used.

20
NBS-114A (REV. a-781

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 78-1A96

No. %. Nei6)ptent‘$ Access ion No,

4. TITLE AND SUBTITLE

PRELIMINARY DATA ON THE FIELD PERFORMANCE OF STORAGE-TYPE

RESIDENTIAL WATER HEATERS

5. Publication Date April 1979

"4. PeffCi^ng Organization Code

7. AUTHOR(S)

Richard A. Grot and Lawrence S. Galowin

8. Performing Organ. Report No. 742 1207

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. ProJect/Tat^/WQi4( Unit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (-Sfreor. City. State, ZIP) 13. Type of Report & Period Covered

14. Censoring Agency Code

15. SUPPLEMENTARY NOTES

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

16. ABSTRACT (A 200-‘word or leas (actual summary of moat aighiticant inlormation, l( document includes a significant bibliography or

literature survey, mention it here.) The early results of a field experiment for determining the performance

of gas and electric residential storage water heaters are presented.

Energy requirements for hot water supply and hot water consumption and

usage pattern data are presented and analyzed using statistical techniques

in order to display average load curves and the variation about the

average. It is shown that the daily energy usage of these water heaters

is approximately a linear function of the energy content of the drawn

daily water consumption. This fact allows a simple procedure to be used

for evaluating the effects of retrofit actions on the performance of the

water heater.

17, KEY WORDS fsix to twelve entries; alphabetical order; capitalize only the first tetter of the first key word unleaa a proper name;

separated by semicolons) _ r- i Energy usage; load profiles; water heaters.

18. AVAILABILITY ^Unlimited

For Official Distribution. Do Not Release to NTIS

[ ] Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

' 20402, SD Stock No. SN003-003-

I I Order From National Technical Information Service (NTIS), Springfield,

’ VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

22. Price

USCOMM-DC
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