Field Performance of Residential

Refrigerators and Combination

Refrigerator- Freezers

Yui-May L. Chang and Richard A. Grot

Building Thermal & Service Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

July 1979

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

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DEC 3 1379

NBSIR 79-1781

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FIELD PERFORMANCE OF RESIDENTIAL

REFRIGERATORS AND COMBINATION

REFRIGERATOR-FREEZERS

l o.

Yui-May L. Chang and Richard A. Grot

Building Thermal & Service Systems Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

July 1979

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, Director

FIELD PERFORMANCE OF RESIDENTIAL REFRIGERATORS

AND COMBINATION REFRIGERATOR-FREEZERS

Yui-May L. Chang and Richard A. Grot

ABSTRACT

Evaluation of the performance of household refrigerators and combination

refrigerator-freezers was undertaken in a field experiment to determine

the effect of room environment and occupant-usage habits on energy con- sumption of these appliances. This report presents the results of such

an experiment on ten townhouses at Twin Rivers, N.J. One-door manual

defrost and two-door frost-free models of various sizes were studied.

Energy consumption, kitchen temperature, refrigerator temperature and

door openings were measured for each model by data acquisition systems

located in the townhouse basements. Both daily and hourly averages

and variations about the average for each variable were calculated in

order to determine the occupant-usage patterns.

Statistical techniques were utilized to obtain the effect of parameters

on energy consumption of these appliances by linear regression of both one- and two-parameter models.

It was found that for a given model the temperature difference between

the kitchen and the refrigerator (either main or freezer section) had

the most effect on energy consumption, with a lesser, though still

important, contribution from the door openings.

In addition, the normalized energy consumption of each model, in different combinations of variables, was calculated from its regression coefficients and the overall average values of parameters from measurements.

The results of these normalized values turned out to be within 5%.

Therefore, their mean values could be considered as the typical energy

consumption for each refrigerator or combination, under usage conditions.

The linear relationship among the combination refrigerator-freezers

according to their physical sizes indicated an increase of about

0.55 kWh per day for each additional cubic foot increase in volume.

Energy conservation by using a manual-defrost refrigerator was predicted

at approximately 40% of that of a frost-free model.

Key Words: Combination refrigerator-freezer field data; daily load

profiles; energy consumption; field measurements; hourly

load profiles; refrigerator field data; usage profiles.

ill
.
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF TABLES vi

LIST OF FIGURES vii

1. INTRODUCTION 1

2. GRAPHICAL AND ANALYTICAL REPRESENTATION OF MEASUREMENTS ... 3

2.1 Analysis of Hourly Data 3

2.2 Analysis of Daily Performance 4

2.3 Analysis of the Parameter that Affect Refrigerator

Energy Consumption 5

3. DISCUSSION OF RESULTS 8

4. CONCLUSION 10

5. TABLES AND FIGURES 11

REFERENCES 39

v
LIST OF TABLES

(See Section 5)

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Refrigerator physical characteristics.

Occupant and townhouse characteristics.

Summary of average hourly energy and door openings

of the refrigerator in each townhouse.

Daily refrigerator performance.

Coefficients of linear regression performance

equation E = a

Q + a^X.

Coefficients of multiple regression performance

equation E = .

Overall values of the refrigerators.

Normalized energy consumption of the refrigerators.

Parameters for least-squares fit of refrigerator

energy consumption versus their sizes (see Figure 29)

vi
LIST OF FIGURES

(See Section 5)

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Figure 11.

Figure 12.

Figure 13.

Figure 14.

Figure 15.

Figure 16.

Figure 17.

Figure 18.

Figure 19.

Schematic of refrigerator instrumentation.

Refrigerator hourly energy consumption, townhouse #8.

Hourly main-section average temperature, townhouse #8.

Hourly freezer average temperature, townhouse #8.

Hourly main-section door-opening time, townhouse #8.

Hourly number of main-section door openings, townhouse #8.

Hourly number of freezer door openings, townhouse #8.

Hourly freezer door-opening time, townhouse #8.

Hourly average kitchen air temperature, townhouse #8.

Average profile of hourly energy consumption of

refrigerator for townhouse #8.

Average hourly profile for number of door openings of

main section for refrigerator in townhouse #8.

Average hourly profile for number of door openings

of freezer section of refrigerator in townhouse #8.

Frequency plots of energy consumption of refrigerator

in townhouse #8 —hours 1 to 6.

Frequency plots of energy consumption of refrigerator

in townhouse #8—hours 7 to 12.

Frequency plots of energy consumption of refrigerator

in townhouse #8—hours 13 to 18.

Frequency plots of energy consumption of refrigerator

in townhouse #8 —hours 19 to 24.

Plot of daily energy usage for refrigerator of townhouse #8.

Frequency plot of daily energy usage for refrigerator of

townhouse #8.

Plot of daily energy consumption and differential temperature versus days for refrigerator of townhouse #8.

Vll
LIST OF FIGURES (Continued)

Figure 20. Plot of daily energy consumption and differential temperature versus days for refrigerator of townhouse #7.

Figure 21. Plots of daily energy consumption versus main-section

differential temperature for refrigerator in townhouse #8.

Figure 22. Plots showing lack of correlation between refrigerator

energy consumption and main-section differential temperature for townhouses #4 and #9.

F igure 23. Plots showing differential in correlation in energy

consumption and differential temeprature of freezer

section for townhouses #4 and #9.

Figure 24. Plots of energy consumption versus differential temperature of main section for refrigerator in townhouses #1

and #2.

F igure 25. Plots of energy consumption versus differential temperature of freezer section for refrigerator in townhouses #1

and #2.

F igure 26. Plots of daily average differential temperature of main

section versus days for refrigerator in townhouse #8.

F igure 27. Plots of daily average differential temperature of freezer

section versus days for refrigerator in townhouse #8.

Figure 28. Plots of actual and predicted daily refrigerator energy

consumption for townhouse #8.

F igure 29. Energy consumption of household refrigerator versus refrigerator size.

viii
FIELD PERFORMANCE OF RESIDENTIAL REFRIGERATORS

AND COMBINATION REFRIGERATOR-FREEZERS

Yui-May L. Chang and Richard A. Grot

1. INTRODUCTION

A field experiment* was undertaken in ten townhouses at Twin Rivers,

N.J. to determine the occupant-controlled parameters which can affect

the energy consumption of a household refrigerator** and to assist in

a realistic appliance labeling program for evaluation of household

refrigerators

The site of Twin Rivers, N.J. was selected due to the previous extensive investigations on energy usage at that site by researchers at

Princeton University [1,2]. The ten townhouses in this study were selected on the basis of their previous energy usage data. The object

was to obtain, in a small sample, a distribution which reflected the

energy usage of the population of Twin Rivers. The refrigerators

studied were those already in the townhouses, either supplied by the

developer or purchased separately by the occupants. The refrigerators

in these townhouses were a one-door manual defrost and nine two-door

frost-free models of various sizes, including one side-by-side model.

The physical characteristics of the refrigerators in each town-house

are given in Table 1. The occupants were mostly typical families

containing two adults and one to three children, ages from 1 to 15

years old. A summary of occupants in each townhouse is given in

Table 2.

Instrumentation was installed in each townhouse so that the energy

usage of the refrigerator, the kitchen temperature, the refrigerator

main-section temperature, the refrigerator freezer-section temperature,

the number and duration of openings of the main section door, and the

number and duration of openings of the freezer section door were

recorded. Figure 1 is a schematic of the instrumentation. After the

completion of instrumentation, data collection was begun in April 1976.

The electric energy use of the refrigerator was measured by installing

an electric meter modified so that a pulse was generated for each 1.8

watt-hours of electricity. The pulses from the electric meter were

summed by a specially designed electronic counter which produced an analogue signal proportional to the total number of pulses. The opening

*This research was initially sponsored by the Energy Appliance

Labeling Program of the Center for Consumer Products Technology of

the National Bureau of Standards through an interagency agreement

with the Federal Energy Administration.

**Refrigerator , as used in this report, refers to refrigerators as well

as combination refrigerator-freezer.

1
of the main section and freezer section doors were determined by

placing small magnets and miniature magnetic reed switches on the door

and refrigerator so that each time the door was opened or closed the

magnetic reed switch would open or close. These signals were fed into

an encoder card which produced an analogue signal from which the status

of the door positions could be determined (i.e., whether the door was open or closed). The computer analysis determined the number and

duration of door openings.

The encoder also generated a parity signal which changed state whenever

the status of the encoded events changed. This means, for example,

that when the refrigerator door was opened from closed position, or closed from the open position. The scan control card would generate

a pulse which would in turn cause a scan of the data acquisition.

From these event scans, the number and duration of each door opening

could be determined. The temperatures in the kitchen and refrigerator,

both main and freezer sections were measured with T-type thermocouples.

The kitchen temperature thermocouple was located above the kitchen sink.

The refrigerator main section temperature thermocouple was attached to

a center shelf at the rear of the refrigerator. The thermocouple in

the freezer section was located at the rear of the freezer section.

Since the refrigerators were in use by the occupants, these locations were dictated by the circumstances. It would have been impossible to

locate these thermocouples according to the standard test procedures

by AHAM and ASHRAE [3,4].

The instrumentation was installed so that one data acquisition system

would monitor a pair of townhouses. Townhouses #1 and #2 shared the same data acquisition system; likewise, townhouses #3 and #4, . . . etc. For each pair of townhouses, the data acquisition system would

scan and record measurements of the HVAC system, appliances and room environment periodically once every five minutes on a seven-track

incremental magnetic tape recorder. In addition, it also recorded the

event actuated scans caused by the opening and closing of the refrigerator doors. It took about six seconds to scan all channels of data.

There are approximately 4500 scans on each tape, which is equivalent

to seven days of data. The tapes were changed once a week and shipped

to the National Bureau of Standards (NBS) by researchers at Princeton

University, who also monitored the operation of the equipment.

The five-minute data were reduced on either the CBT minicomputer or the

NBS central computer facility into daily and hourly data files, which

were printed and stored on mass storage files for further analysis.

The hourly data of all measurements were analyzed to obtain average

hourly profiles by averaging measured values during each hour over

a period of certain days. As for refrigerator door openings, only

daily usage profiles were reduced from data, since hourly measurements

were immaterial. The graphs presented in the report include actual

measurements for four-day periods. From the graphical presentation of

the four-day plots of internal temperature, the defrost cycle of each

refrigerator can be observed.

2
On the daily data summaries, statistical analyses were performed to

obtain the variations from the average values and to determine the

effect of usage parameters on energy consumption. According to these

field measurements under actual usage conditions, the average daily

energy consumption of various refrigerators was found to depend mainly

on the size of the refrigerator, as expected. For a given refrigerator,

the temperature difference between the kitchen and the refrigerator

influenced the daily energy consumption of the refrigerator more than

did the number or duration of the door openings. The average daily

number of door openings for all refrigerators was found to be 48 for

the main section and 10 for the freezer section. It was also interesting to learn that the average length of time per door opening for the

two sections of these refrigerators turned out to be nearly the same,

21 seconds for the main section and 20 seconds for the freezer section. For all refrigerators, the average values of temperature differences between kithcen and the refrigerator, were calculated to be

AT^ = 42°F for the main section and ATp = 73.5°F, for the freezer

section, with kitchens at an average temperature of 78.4°F. In order

to study relationships among energy consumption, differential temperature between kitchen and refrigerators, and door openings, the leastsquares estimation of linear regression with both single and multiple

variant were used.

Simple performance equations (equations 1 and 2 in section 2.3) of

the mathematical model for energy usage and its dependent variables

were employed. From these equations and their calculated coefficients,

the predicted value and the actual data value were plotted together

to show their differences for each refrigerator. The energy consumptions of refrigerators of different sizes were compared by using the

overall average values of temperature difference between kitchen and

refrigerators, AT^ and ATp, and door openings.

2. GRAPHICAL AND ANALYTICAL REPRESENTATION OF MEASUREMENTS

2.1 ANALYSIS OF HOURLY DATA

The energy consumption and the usage pattern of the refrigerator in

each household are presented as averages for each hour. Refrigerator

in townhouse #8 is one of the six refrigerators for which a complete

set of data is available and has been arbitrarily selected for presentation. The actual hourly energy consumption and temperatures of

this refrigerator for a period of four days are shown in Figures 2, 3 and 4. From Figures 3 and 4, both main-section temperature and freezersection temperature can be observed to have peaks at the same time.

The refrigerator is controlled in an on-off manner by a single thermostatic switch, and the temperature controls of both sections depend

on their control knobs as well as a damper to limit air flow between

them. Time intervals between peaks in these two figures indicate the

period of defrost cycles because, at the beginning of each defrost

cycle, electric heat is applied to its evaporator to melt the frost [5].

3
These two figures also show that this frost-free refrigerator has its

defrost cycle occurring approximately every six hours. By studying all

three graphs, Figures 2, 3, and 4, it could be seen that the hourly

energy usage increases after the refrigerator self-defrosts, as the

refrigerator temperature has to be reduced immediately.

Furthermore, the number and duration of door openings of the refrigerator, shown in Figure 5-8, change the refrigerator temperature

patterns and therefore affect the energy usage indirectly. The periods

of door openings relate directly to the number of door opening. It can also be noticed that the door openings are either zero or a very

small number from midnight to 6:00 am., and the refrigerator's internal

temperature remains pretty much the same, except when the defrost cycle

comes on. Therefore, the hourly energy consumption at night is usually

lower than at any time of the day. This is also due to the fact that

the kitchen temperature is always fairly low at night, as shown in

Figure 9.

Figure 10 is an average profile of energy consumption for each hour of

the day, from days 96 to 180, of the refrigerator in townhouse #8. For

Figures 10, 11 and 12 the solid area is the average energy used, and

the dotted profile gives two standard deviations from the average.

In comparing Figures 2 and 10, the measurements of hourly energy con- sumption of the refrigerator for days 176-179 and the average hourly

energy consumption profile for days 96-180 do not show much similarity.

In fact, Figure 2 shows a slightly higher energy usage on those four

days than the average hourly energy usage given in Figure 10 and Table 3.

This might be due to the surprisingly high temperature in the kitchen on those four days as shown in Figure 9. Figure 9 indicates the kitchen

temperatures from measurements are much higher than the daily average

value of 77.6°F, given in Table 4.

Figure 10 shows that slightly more energy is used during lunch time and

dinner time, when refrigerator doors are opened more frequently, as indicated in Figures 11 and 12. The actual variation of refrigerator

energy used in townhouse #8 for each hour of the day is shown in the

set of 24-hour frequency plots (Figures 13-16). Table 3 is a summary

of these variations for each hour of the day in average energy consumption and door openings of all ten townhouses.

2.2 ANALYSIS OF THE DAILY PERFORMANCE

When a refrigerator is being operated normally, its daily energy usage

does not vary greatly; however, those variations which do occur should

indicate the effect of such parameters as kitchen temperature and door

openings on the energy consumption of the refrigerator. Figure 17

is a plot of the daily energy consumption of the refrigerator of

townhouse #8. The frequency plot in Figure 18 shows the energy usage

of this refrigerator ranged from 4 kWh to 8 kWh per day, with a mean

4
of 6.45 kWh per day. A summary of the daily performance of the refrigerators in these ten townhouses is given in Table 4. By referring to

Tables 1 and 4, the dependence of the refrigerator average daily energy

consumption on its physical size can be noted. The values vary from

2.30 kWh per day for the refrigerator in townhouse #3 (an 11.5 ft J one-door manual-defrost model) to 8.33 kWh per day for the refrigerator

in townhouse #10 (a 19.0 ft J two-door side-by-side self-defrosted

model). Note that even though the data days were different, the com- parisons are still valid, since the average kitchen temperature, T^,

remained pretty much the same for each particular period of time,

except for townhouse #3.

For those refrigerators with the same physical characteristics as shown

in Table 1 (e.g., in townhouses #7 and #8) the temperature difference

between kitchen and refrigerator dominates their energy usage, with

small effects due to the door openings. Table 4 indicates that the

differential temperature between kitchen and freezer in townhouse #8,

72.1°F, was much higher than in townhouse #7, 65.6°F, while their differential temperatures between kitchen and main section were kept

approximately the same, 44.2°F and 44.7°F, respectively. This factor

could explain why the refrigerator in townhouse #8 has a higher energy

consumption than that in townhouse #7, as given in Table 4.

By sketching the refrigerator daily energy usage with temperature difference between kitchen and freezer of the refrigerator in townhouse

#8, given in Figure 19, it can be noticed that the two curves follow

a similar pattern and thus are related. Figure 20 shows the same com- parisons for townhouse #7. Comparing Figure 19 with Figure 20, it is

obvious that the average daily energy consumption of the refrigerator

in townhouse #8 is higher than that of townhouse #7. The refrigerator

door openings also affect the energy usage of the refrigerator, as shown in Table 4.

2.3 ANALYSIS OF THE PARAMETERS THAT AFFECT REFRIGERATOR ENERGY

CONSUMPTION

An attempt was made to obtain the effect of various parameters on energy consumption of the refrigerators. For each townhouse, major

emphasis was placed on two parameters: (a) the temperature difference

between the kitchen and the refrigerator, and (b) the number and duration of its door openings.

Figure 21 shows the daily energy consumption, E, versus temperature

difference between kitchen and main section, ATM , of the refrigerator

in townhouse #8. The mean value of E is also given as 6.45 kWh with

standard deviation equaled to 0.55 kWh, as shown in Table 4. By using

the least-squares linear regression technique, the one-parameter model

of these variables is given by

E — Oq + oij ( AT^) j (1)

5
where E is the daily energy consumption in kWh, and AT^ is the temperature difference between kitchen and main section of the refrigerator in

degrees F. The straight line is presented on the same graph and the

coefficient of equation 1 was calculated to be <Xq = 1.56 and = 0.11

In equation 1, could be interpreted as the energy consumed per

degree F of temperature difference. Non-zero Oq of equation 1 indicated that the linear relationship is applicable over a limited

range and also that other independent variables should be considered

for analysis. The correlation coefficient, R , and the standard deviation of the linear regression, cj £

, were obtained as 0.69 and 0.28,

respectively. The percentage gained in precision for linear regression

by reducing the standard deviation from 0.55 to 0.28, is 50 percent.

2 However, R of 0.69 means a better model could be adopted by the method

of multiple regression to include more independent variables. Table 5 gives the coefficients Oq and of equation 1 together with the correlation coefficient R^ and standard deviation a

£ for the following variables taken as independently as listed below as determined by the

measurements on the refrigerator in each townhouse:

AT^, temperature difference between kitchen and main section

ATp, temperature difference between kitchen and freezer section

NDM

1 number of door openings of main section

NDp, number of door opening of freezer section

tDM» duration of door openings of main section

tDp

,

duration of door openings of freezer section

. . . . . . . ? From the statistical point of view, the correlation coefficient R

is a measure of linear dependence of a dependent variable to the independent variables from the linear equation. Whenever R^ is extremely

small, they are linearly uncorrelated. The results from the linear

regression analysis for each of the ten refrigerators are displayed

in Table 5. The refrigerators in townhouses #4 and #9 have low R^ for

energy consumed, E, vs differential temperatures, ATM

or ATp. As shown

in Figures 22 and 23, the data points of E vs AT^ or ATp for both townhouses show random scatter. Therefore, low R

z might be due to data

being recorded incorrectly or the physical malfunctioning of the

refrigerators. The fitted straight lines are almost horizontal and even show a negative slope of E vs ATM ; i.e., is negative. Another

reason for the observed behavior of the data for the refrigerator in

townhouse #4 is that only approximately thirty days of data are available, excluding partial days. There might be insufficient data to

determine the results accurately. Therefore, the refrigerators in

townhouses #4 and #9 could not be represented correctly by the mathematical model of equation 1.

6
2 As for refrigerators in townhouses #1 and #2, the low values or R from

E vs AT^ again were due to random scatter of data and also the small

variations of AT^, approximately 5°F, for refrigerator in townhouse #1,

as given in Figure 24. The larger values of from E vs ATp indicates

for these townhouses the energy consumption is better correlated with

the differential freezer temperatures, as illustrated in Figure 25.

In townhouse #2, there is a highly correlated relationship between

energy consumption, E, and the number of main-section door openings,

ND^, of refrigerator.

Furthermore, Figures 24 and 25 also indicated that these two refrigerators were operated at the same range of ATp, while AT^ of the refrigerator in townhouse #1 is much higher than that in townhouse #2.

Hence, the average daily energy consumed by the refrigerator in townhouse #1 is slightly higher than that in townhouse #2.

In general, the correlation coefficient R had much higher values in

temperature differences, AT^ and ATp, than those in door openings, with

the exceptions discussed previously. That implies that from the linear

model of equation 1, the differential temperature between kitchen and

refrigerator (either main section or freezer section) affects energy

usage more than door openings. The second independent variable chosen

for multiple regression analysis may be either the daily number of door

openings or the length of door-opening times, since they are somewhat

related, as indicated in their hourly profiles (see Figures 3, 5, 6,

7, and 8). For example, an attempt to fit the refrigerator energy

usage, E, in townhouse #8 as a function of temperature differences

between the kitchen and main section, AT^, and number of main-section

door openings, ND^ is as follows. The multiple regression relationship

is given by

e = b 0 + e

1 (atm

) + b 2 (ndm) ( 2 )

where E is the daily energy consumption in kWh, AT^ is the temperature

difference between kitchen and main section of refrigerator in degree F,

and ND^ is the daily number of main-section door openings. The coefficients of equation 2 were found to be Bq = 1.29, B^ = 0.11 and B

2 = 0.007, where B 2 is the coefficient denoting energy used in kWh per each

door opening. From coefficients of equations 1 and 2, note that B^ = a^,

which implies the effect of differential temperature is fairly steady.

The correlation coefficients R^ of equation 2 increased to 0.822 and

the standard deviation was reduced to o

e = 0.22. This means equation 2 is a better model than equation 1. The precision gained in standard

error with equation 2 is 60 percent, a 10 percent improvement from that

with equation 1. Figure 28 is a sketch of predicted energy usage from

equation 2 and the data points from measurements.

7
Table 6 gives the regression coefficients and standard deviation for

refrigerators in each townhouse. With some exceptions, the majority

values of k have been increased by using a two-parameter model, as can

be seen by comparing Table 6 and Table 5. Therefore, it can be con- cluded that equation 2 is a better mathematical model than equation 1 for predicting daily performance of the standard refrigerators.

3. DISCUSSION OF RESULTS

In order to evaluate the performance of different refrigerator models,

a comparison of energy consumption of each refrigerator under the same conditions from its regression coefficients is a proper approach. The

overall average values of variables for all ten refrigerators is given

in Table 7. The normalized energy consumption of each refrigerator was calculated from its regression coefficients 8q, an^ 3 2

> Table 6, and

overall average values, Table 7. Four combinations of variables were considered in each case, as shown in the following expressions:

^MN

= ^0 +

^ 1

^ A I'm ) +

^FN

= ^0 + ^i^Tp) + 3 2 (NDp)

^Mt &0 + ^ 1 ^ ) +

E

F t = 3 0

+ 3 ! (ATp ) + B 2 (tDp)

where E^, Epjj, E^

t and Ept are normalized energy consumptions calculated from various combinations of overall average values, given in

Table 7, with their regression coefficients.

These results are presented in groups according to their type of model,

in Table 8, together with the actual measurements of energy consumption

and differential temperature between kitchen and refrigerators. Except

for the refrigerator in townhouse #7, the four values of energy consumption (Ej^, Epjj, Ej^ t and Ep

t

) of each refrigerator are within the range

of +5 percent and these values could be considered as the energy usage

of each refrigerator under usage conditions.

The refrigerator in townhouse #7 was operated at a fairly high freezer

temperature of 14°F, as compared to the overall average freezer temperature of 4.8°F. The average differential temperature between its

kitchen and freezer was 65.6°F, as compared to the overall average value

of 73.6°F. However, its average main-section temperature was measured

to be at 35°F, which is close to the overall value of 36.4°F. By using

the normalized freezer temperature difference, ATp = 42°F, to calculate

the energy consumptions, Ep^ and Ep

t

, the freezer temperature would

need to be decreased or ATp would have to be increased by 18°F or about

8
12 percent. Hence, the values of E FN and Epj. will be much higher than

EyjN and , since AT^ was decreased only about 2.7°F or 6 percent.

For comparison purposes, Ep^ and Ep

t are more realistic values to use under the normalized condition for the refrigerator in townhouse #7.

It should also be pointed out that, according to the field measurements,

it is possible to reduce energy consumption by maintaining a higher

freezer temperature. Usually running freezer temperature of a refrigerator at an average value of 14°F would not be recommended by food

scientists [5] or for laboratory tests. When operating the refrigerator

in townhouse #7 at this freezer temperature, energy consumption was reduced by 18 percent as compared to the normal condition.

Table 8 and Figure 29 also show that the energy consumption of refrigerators increases with their physical size, as expected. However, the

energy consumption of the refrigerator in townhouse #4, as compared

to other 14.7 ft

J models, do not fit the attempted correlation.

For the purpose of simplification, an average value E for these four

cases was considered to be the normalized energy consumption per day

for the refrigerator in each townhouse. These values are also included

at the last column in Table 8. The relationship between the daily nor- malized energy consumption and physical size of refrigerators also can

be seen to be linear. Again, regression analysis was utilized to fit

a straight line for these data. Figure 29 shows the data points as well as the regression line for refrigerators in all townhouses except

the one in townhouse #3. This refrigerator was a manual-defrost model

and the rest were frost-free models.

Table 9 gives the parameters from the regression analysis. From

Figure 29, Jjhe predicted value of E was found to be 3.54 kWh for

V = 11.5 ft . Comparing it to E^ = 2.14 kWh, the energy savings between

a manual-defrost model and the frost-free model with this size is 1.4

kWh, or about 40 percent per day. As for other size models, there was

no valid information available to make estimations. However, the

results of the laboratory test of refrigerators by Mulroy et al. [6] were found to be quite interesting when compared with Figure 29.

Under 75°F kitchen temperature with door-opening conditions, the daily

energy consumption for a 14.7 ft"5 frost-free refrigerator was found

to be 5.12 kWh.* The predicted value in Figure 29 is 5.3 kWh, only

a 3.5 percent difference. As for the manual-defrost model, the daily

energy usage for the 14.7 ft J refrigerator was found to be 2.91 kWh*,

which is 38 percent below the expected value, 4.7 kWh, for the frostfree model in the same size. Consequently, the regression line in

Figure 29 indicates the differences in energy consumption per day for

various sizes of frost-free refrigerators under the normal usage pattern. The energy usage was found to be 0.55 kWh for each additional

cubic foot of volume for the frost-free model. The approximate

* Average value for the two relative humidity settings.

9
percentage of saving in energy consumption of refrigerators from a frost-free model to a manual-defrost model could also be estimated

from Figure 29 and the above calculations.

4. CONCLUSION

The hourly profiles of the refrigerator showed that occupants opened

the doors much more at lunch time and dinner time. The door openings

usually dropped to zero from midnight to 6:00 am. The hourly energy

consumption was consistent with this pattern (heaviest at lunch and

dinner times) except at the time immediately following the refrigerator

self-defrost cycle, when additional energy was used to reduce the temperature inside the refrigerator.

By analyzing the daily performance of residential refrigerators, it was concluded that the differential temperature between the kitchen and the

refrigerator dominated its energy usage, with lesser, though still

important, effects from door openings.

The daily energy consumption is linearly related to the physical sizes

of refrigerators. It was estimated that there would be about 0.55 kWh

increase per day for each cubic foot increase in volume for the frostfree refrigerators. The energy conserved by using a manual defrost

refrigerator was found to be approximately 40 percent of that for the

frost free model.

10
5 TABLES AND FIGURES

TABLE 1

REFRIGERATOR PHYSICAL CHARACTERISTICS

Townhouse Model* Ft 3 Frost No. of

Number Free Doors

1 TBF-15S 14.7 yes 2

2 TBF-15S 14.7 yes 2

3 TA-12S 11.5 no 1

4 TBF-13S 14.7 yes 2

5 TBF-13S 14.7 yes 2

6 18-CMB 18.0 yes 2

7 TBF-16S 15.6 yes 2

8 TBF-16S 15.6 yes 2

9 TFF-15J 14.7 yes 2

10 TBF-19D 19.0 yes 2-S

* All refrigerator models were from the same manufacturer, as supplied by the developer or purchased by the occupants.

11
TABLE 2

OCCUPANT AND TOWNHOUSE CHARACTERISTICS

Townhouse

Number

Number of

Adults

Number of

Children

Children'

s

Ages

Number of

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

12
TABLE 3 SUMMARY OF AVERAGE HOURLY ENERGY AND DOOR OPENINGS

OF THE REFRIGERATOR IN EACH TOWNHOUSE

1

8

D U ENERGY CONSUMED (KWH) BY HOURS

1

t

1 2 3 4 5 6 7 8 9 10 n 12 13 14 15 16 17 18 19 20 21 22 23 24

1 0. 19 0.19 0 . 18 0. 17 0.18 u.:o

P- 21 9,1? 0,20 0.20 0.18 0.21 0.21 0.20 0.23 0.23 0.23 0.24 0.2? 0.25 0.25 0.23 0.21 0.19

2 0.18 0.16 0.16 0-14 0.16 0.14 JU5 0.17 0.20 0.20 0.18 0.21 0.22 0.20 0.20 0.20 0.23 0.24 0.24 0.23 0.22 0.22 0.20 0.18

3 0.07 0.07 0.07 0.07 0.07 0.06 0.08 0.06 0.06 0.08 0.08 0.09 0.08 _0 , 0f JUii 0.09 Q.OS 0.10 n ns 0.09 0.09 0 (Id 0.06 0.08

* o.:e 0.28 0.28 0.28 0.27 0.27 0.27 0.28 0.26 0.26 0.26 0.25 0 . 3C 0 . 2 ! 0 . 2 ! 0 . 2 ! 0.25 0.36 0.3d 0.30 0 . 3 C 0 . 3 C 0.29 0.29

5 0.21 0.15 0 . 1 ! 0.19 0.18 0.15 0.17 0.20 0 . 2 ( 0.21 0.21 0 . 2 C 0.21 0 . 2 ( 0.22 0.21 0.22 0.24 0.23 0.21 0.21 0.23 0.22 0.20

6 0.25 0.25 0 . 2 ! 0.25 0 . 2 ! 0.24 0.25 0.29 0.21 0.25 0.31 0 . 2 ! 0 . 3 ! 0 . 3 ( 0.29 0.28 0.33 0.35 0.36 0.34 0.33 0 . 3 C 0.30 0.30

7 Ml 0 ,?] P- 2 ( o.js 0.15 o. 2<; 0.19 0 , 2 C 0.24 0.24 0.24 0.26 0.26 0.26 0.26 0.25 0.27 0.29 0.28 0.26 0.24 0 . 2 ! 0.22 0.22

8 0.25 0.25 0.24 0. 24 0.29 9,2] 0,2' 0,21 (1,2(1 0,28 0.28 0,2? 0.26 0.27 0.27 0.28 0.29 0.29 0.30 0.30 0.30 0.27 0.27 0.26

9 0 . 1 ! 0. 18 0 . 1 ! 0.17 0.18 0.17 0.17 0.23 0.19 0.21 0.21 0-21 0.22 0.22 0.23 0.25 0.23 0.23 0.22 0 . 2 C 0.20 0.19

10 0.35 0.35 0 . 3 ! 0.33 0.32 JUiOUi JU2 0.32 0.35 0.34 0.35 0 . 3 ! 0.34 0.35 0.35 0.35 0.36 0.37 0 . 36 0.36 0.36 0.35 0.34

T

0S H0

u1

NUMBER OF MAIN SECTION DOOR OPENINGS BY HOURS

1 2 3 ^

4 5 6 7 8 9 10 11 12 U . }4 1 ? 17 18 ?? .22 2.3 24

1 0. 0 0.04 0 0.06 2.64 4 . 1 } l- 6>7 2.)4 1.23 1,91 2-51 1.42 1.59 2.62 9,70 9,12 3,17 1,00 1,19 P,?l 0.19

l 0 . 1 s C.fl2 fl.16 0

0 0 . 1 7 1.17 2.95 4.67 J .14 2j12 4.62 4.06 2 . 1 C 2.07 2.37 4.90 5.88 3,90 2.94 2.49 1 .67 0.88 0.33

3 0.17 0 0 0.07 0 0 . 4 C 1.57 2 . 4 ! 2.97 2 .41 2.32 2.45 2.07 2.00 1.82 2.43 3.87 7.50 3.91 2.74 3.56 1.95 1.26 0.74

4 0.05 0 0 0 0 . 0

^ 0.86 0 . 4 ( 2 . 9 ; 2.45 2.10 3.77 3.84 1.77 1.25 3.18 2.20 3.71 5.22 3.38 2.28 1.40 1.19 0.67 0.21

5 0.16 0.11 0.11 0.03 1 0.01 0.74 1.79 2.12 1 .B 9 1.37 1.79 1.15 0.97 1.47 1.04 2.41 3.15 1.63 1.07 1.78 2 .02 0.61 0.36

i 0,92 0.09 0.2? 0.12 0,17 0.06 1,21 2.19 2.44 3.17 3.13 r- 00 2.98 1.64 1.53 1.95 3.42 6.25 3.59 2 . 30 2.33 1.86 2.05 0 . 9 ^

7 0,11 0.02 0 0 0.05 1.08 0.14 1.54 7.40 4.93 3.99 5.73 4.96 2.28 3.49 3.75 5.43 8.23 4.86 1.70 1.57 0.65 0.25 0.21

e 0,1? O 0 1

' 0 0 0 0.25 1 . 9C 5.8C 5.27 4.05 4.78 4.20 4.10 2.19 2.85 3.39 4.42 6.00 5.72 4.81 3.06 1.02 0.75 0.56

9 0.05 0.20 0.01 0.05 0.03 0.76 1.16 5.62 4.29 3.25 2.76 4.19 2.94 2.48 2.86 2.83 5.05 5.55 2.68 1.42 2.34 2.08 0.72 0.50

10 0.16 0.03 0 0 0.03 0.61 0.04 0.25 2.84 5.23 2. 30 2.90 3.16 1 . 73 1.61 1.03 1.21 5.09 4 . 16 3.20 2.17 1 . 34 1.05 0.30

S H n 0

U

Bt

9

NUMBER OF FREEZER DOOR OPENINGS BY HOURS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 5

~ 16 17 18 19 20 2 ) 22 23 —

24

1 0 03 0 o.oi 0 0 0.05 P -12 9,97 0,11 0,09 0.49 JL21 0.44 _L21 1.15 1.34 1.25 0.91 1.76 0.90 0.77 0.11 0.11

2 * * * * • • * * * * * * * * * * * * * * * * * *

3

0 0 0 0 a 0 0 0.48 0.15 0.41 P,J4 0.36 0.30 0.41 0.48 0,93 0.67 1.85 0.71 0.12 0.19 0.21 0.19 0

? 0.04 0.01 0.02 0.02 0 0 0.01 0.21 0.26 0.31 0.15 0.47 0.44 0.39 0.35 0 . 4 ] 1.02 1.15 0.45 0.42 0.75 0.50 0.22 0.13

ft 0.05 0.03 0.06 0.03 0.03 0 0.11 0.21 0.24 0.48 0.52 1.05 0.47 0.18 0.42 0.23 0.80 1.58 0.77 0. 34 0.53 0.55 0.38 0.14

7 0 0 0 0 0 0 0 0.02 0.27 0.24 0.59 0.48 0.83 0.25 0.57 0.61 0.94 1.99 0.82 0 . 201 0.40 0.20 0.04 0

8 0 0 0 0 0 o.oZ 0.25 0.39 0.57 0.40 0.40 0.77 0.54 0.31 0.51 0.80 2.04 1.71 1.55 1.21 0.81 0.19 0.08 0.06

9 0.01 0.01 0 0 0 0.22 0.30 0.58 0.42 0.65 0.45 0.58 0.53 0.53 0.68 0.92 1.24 1.51 0.76 0.55 0.75 0.55 0.20 0.09

10 0.05 0 0 0 0.01 0.18 0 0.01 0.28 0.49 0.16 0.31 0.56

’ O O 0.28 0.16 0.59 1.30 0.33 0.83 0.88 0.64 0.38 0.08

* Missing Data

** No Measurements

13
TABLE 4

DAILY

REFRIGERATOR

PERFORMANCE

l4_ E O QJ O' O' o o O

O

O o <T 'd’

u

<3* <T 00

X 00 00 oo 00 r-^

X 3

CNl Csl| CN1 CM1 CN CN r-H rH r-H rH

>, C/3 03 03

XX sC sO sO sD sO sC CN CN

Q 01

X sO r-H r-H O' O' O' O'

T. rH rH CN CN r-H rH c

Q) /•n /-V s uh fa 0- • m ac sD CNI 00 C cn /-H /H o <y o CJ • • NT 00 <r oo r-i

X -o

N 0) »H

GO sC rO NT • •

fa. 0) <U fa C/J

m rH * O NT in sD sC cn

x <T <T nm

O E o c

rH •—* * r-H r-H cn cn NT sC sc cn

m

H

m c r-H

U *H fal o

V-/ ^

V--' VH rH CN rH rH rH Cn

H fa.

C

w

W >w'

C/3 fa oc u- o> c

n-v

H s O N >1 •H m x c sC C rH 00 NT sD m x X vT m CT'

fa. 0) 0 c • • • • Q • <D O OJ cn x * tn x O' NT O' nT 00 NT CN vC in 2 O fa Q a rH w K * 'w' 'w' rH W rH ^ 2 fa- o • C o OJ

«4-

O CL /•N. Hs

N /—

C

W c in CN

m *-h

X sC cn o O sO

O NT NT

C O' O' NT O'-

X fa S Qj C fa o NT r-. f'' nt cn rH 00 oc cn o NT O' rH 'sD rH X X fa O' C E -h 0 OJ nt -fa •H C cn »-fa O' X 00 CN m \c H <3" x C NT 00

•U *|H CO

C on <r cn rH CO vC cn SO sC

O so o m rH

X CN O' r-H

h s; c rH r-H

N-*/ 'w rH rH CN -fa 'W' ' ^H H'

u cr. <u oc

u-i

x c

''“

v /—*s /^N /-^s

H /H

c? ° c fa •Hc X

x CNI

X

m O' CN CN sO cn cn

O NT O'

X O'

X CN 0C 2 ••r4 0 OJ CM LTi m O' <r m 1^ r-H i-n x cn NT SO X o C NT 0 CO 0 c. nt cn m i— NT fa <r cn CN rH <T r-H sO CN sC CN in rH NT CN 2 z: Q o W w W 'w' Vfafa

<u • faH J-N rs /—

faN Cfa /H rH Cn

m O'

O TN

X

H 0) E • rH 00 rH cn o

01 01 oc • • • • * • • NT CN in o CN CN

fa E- 0) cn

m cn r-l * cn * rH ^ 'w'

fa. c 'w o

0) . /H

H

H C/3 C- fa- ZC 0 •

00 CN

H

O CNJ

X NT CN

C CN

m o O 00 NT O'

X LTl o' c x -fa ch rg O' rH oo m in rH 00 -fa in c cn o NT O CN rH

H *H

H OC cn

W nt n^ cn

w cn

w cnw cn

w cn ^ cn ^ cn ^ cn

w

CO <U s c c /H /H /*“s s H

HH /H

OJ • faX tn cn o 00 CNI cn o CN O' r"- cn

x

m cn O' CN CN

x o. HOE- cO VO rH

m cn Tn cn 00 -—1 OO rH os cn cn

X -fa O' CN

•fa o u rwX 'fa

ww

w

•H £h Q> ^ Q• >. a. co « E C /H /'-N

H

H / S fa 3 ^ cn cn "d *H O r-~ hH Cn rH NT sO CN m m rH r^* CN X fa! (U It £ O m vo m cn cni oo m Os O sO m os nt in O' X CN NT

tC I-S

faJ o m c nt o CN o so o NTO

n

O in o x o NT o 00

C

u 'W' '•w' 'w'

w 'w'

01cn3 fa O 0)

=Sfc J= -D p E r-H CN cn NT

m sD oo O' c 3 3 rH O 2 H

14

Numbers

in

Parentheses

Indicate

Standard

Deviation *

Missing

Data

**

No

Measurements
TABLE

5

COEFFICIENTS

OF

LINEAR

REGRESSION

PERFORMANCE

EQUATION

x

r-4 a+

s

ii uj

in X CM o o in 0 0 > o CO X m O'

00 n* o -H co a c > NT r^. o

CM c

^3 CO <—

1

i—i c c » o K •K CM o c o o o o

a: O o o O d o o c c i o O o c o o o o

u> D o

CM

in

O'

nt

<r

nt

CM m

o

CO

ONom

CMX

m

00X

00

<r

>3

cr

V

1/ O'o

in -K *

CM

NT

CO m

X

m

>3

irX

CMo

ON

*H^3

in

NTm

m

NT

NT o o o o o d o o c c o d o c o o o O

2 Q

u

0

XoOo

CMo

o

-3- O

o

o

NTO

oo

m

o

O

o

COo

o

o

CMo

o

COo

oo

c

c

OC

ccc

U-> Q

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II

nto

o

o * *

«HO

o X

oo

o

CNc

cc mo

o

ino

O

o

CMo

o

rHo

oo

X o o o o o o o o c c X o o o c o o o o

o

0

nt n*m 00

076 rOf

652 x

nCM

<*X

O’

CNa .905 * *

NT

ON .671 o

CNo

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.258

<r >3 O

CM m

X

<r vr *3 X r" a

NT * X <r X m X >3 X

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cc

ON

CM X 232 CO

rHo

CMX

CM o

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CM

00

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c

c’

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r— m

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NTo

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ntX

co

O' o co ON o r—

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r> CN X

o X o CN CO X

C". ONX

NT

NT Q

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<r CM NTCM

i"H in X

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ac 00nt if <d m * * m

CO NT X X >3 m NT c ° o O o c C o c C o K o

o c O o o O

T. Z

a 5

CMo

X

o

o

CMo

o

CMO

c

o

c m

r—c X

o

o

o

CNo

CNc

c

iu QZ

co

rHo * *

CMO

NTX

o

r>>3cCOX

o

^3

CNa

o

CMo

.017.

X o o o o c d o o c II o K o o c o a o O

©

Cs

r>

.528 CMo m00 rH

r»

r> c

* CO

co oCM

"3

C" .865 *

CMX X X 1-i r—rx m ON o CM a Cc o X * * CO X o X O

NT co CM X >3 is < X CO X

nt X X m X >3 X

CM o m CO ^3 CM ^3 CO CO OCMo nCM

Om o CO ONo

rHm

c

<3 Xr> O'X

O

o

Xm in

CO

NT ON

rH XCM * *

rHX XX

Oo

co C d o o o C C o o o o o d o o d o o

X

X

CM

f*-* m

ono CN IT rHX

m

r*^

i—i On X X X ON X rH, nt NT

rHCM CO

>3 ir ^3 CM m CM CO CO -3

CM

co

CO « « ON

COo

X fN. in

CO

CN o d o o o c d o o o d o o o o o o

T

H o CM o> o lu

<3 rH <T©

CMo r-. CN CM X

IN. *H On H

< X rH CO

CM o

X

^3 ONo

CMoin 0( o o o

X

rH X

CN o

CM o

rH O COrH II o CM o o « * *H •H o rH

1 o o o o

0

1 o X o O o o o d o o

rH

LO, co CO O' o *— >3 X CM CM X <r X X co X

x

*3

in

ONX

o

a

>—

H

r< o

r^» 00

CMCOCMm

X ON m

m mfN. CM O' m « « m to n* CO O Ln O r*^ CM

1 co CO1 rH m •"1 CM

1 O'i O CM Nf

1 rH

) NT CM

f

XOOC/DQJ HC2C CM CO >3 m X r^. CO o\ LO

rH o CO < m X r- 30 ON a

rH

CO

4J

•K * -K

15

Missing

Data
00 uC*

16

*Missing

Data
TABLE 7

OVERALL VALUES OF THE REFRIGERATORS

°F Number Seconds

Average Kitchen Temperature Tp 78.4

Average Main Section Temperature T^ 36.4

Average Freezer-Section Temperature Tp 4.8

Average Temperature Difference

Across Main Section, AT^ 42.0

Average Temperature Difference

Across Freezer Section, ATp 73.5

Average Number Main-Section Dooropenings per Day, ND^ 48

Average Time of Main Section

Door-openings per day, tDM

1019

Average Number of Freezer Section

Door-openings per day, NDp 10

Average Time of Freezer Section

Door-openings per day, tDp 199

17
TABLE 8

NORMALIZED

ENERGY

CONSUMPTION

OF

RECRIGERATORS * 1

ai z P tu

u

—1|

W

G

ct) * 1 w > > z cc

", vP CN

G CO u~i 00 CN LO 00

lr , . S -o c tH ON <r

G 00

G

G rH LO

OC 4-1

X > t- T, 3

CM <r cP LO cD < O 1 W * tco e co P X G >> O • O' CO CN cP m cC U r. a ^ • r- 1 * o CN o H vD

m

IX >, || iX

X

W 00 I Q -2

4c U~> 4C 4C

m

G 4C P IH 4-J U2 W <3 j— rr -

CO fc CJi >-, p o >-H co O <N C Q

w

CP <3" •—1 —

m tH

O o oo <r LO o •

II II

g CM On) CO

G LO o o CO co

tu' 0C| h1

X CM

m <r X>

m LO cD ip O" P <3 4-J w

CO fx P o >, C CN O cfl CP ^ t—1 G r—1

rH 00 co ip • II II ^ co o G LO LO 2 ^ ixfcj: 4C • • . . a- M H Q 3 W C -3 Z 32

4C 4: 4c cC 4C

w

CO px. <T Co • > C CN 00 CO v <r o- G <r

m LO

G c co CN 00 • ii ii ^ o uo 00 O CO G LO

g Sn Z 2G § C3CIH CP 3 CM x> LO vP

w

C <3 2 3 w

Temp. F^ F

in o co \D rH

m U-i • H • • • ' • X ' • • E

1 U—i 1 cxO 4C CM CO »H m CN 00

<3 M- P2 QJ 4C 4C cD

r- Di (T

D

aEO ^ lx X! o CM <r CN o CN cn‘ ' on H s • • • • ^L, * H • X) co 00 CO G <r o vP

t—1 C4-I 1 00

<j >4-4 02 QJ <r co co CO <r - H Q Q

Pn C- Pn 00 E CO CO CO rH x)

m CN PPG CO o vP 00 ON G m o CN

W JJ B)\ • • • • • . C P G a o 3

CN

m X) <fr

m vD 00

cp : p2.

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H ; \*

v , r.

cu • E w LT) o- vD iP o O > fx P [X • • • • . W rH • iH

<r

m LO 00

G OP O P > CP rH H rH rH rH rH rH rH iH rH

0)

cop

X o cu G -O § p

co T—\ CN LO 00 \D 10 o z H

18 *

Missing

Data

**

No

Measurements
LUX

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Xo

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® 0 6 12 18 0 6 12 18 0 6 12 18 0 G 12 18 0 DRY 176 DRY 177 DRY 178 DRY 179 TIME-HOURS

Figure 2 Refrigerator Hourly Energy Consumption (Townhouse 8)

20
1 1

I

I

-i

21
o®

DAY 176 DAY 177 DAY 178 DAY 179 TIME-HOURS

Figure 5 Hourly Main Section Door Opening Time (Townhouse 8)

o

DAY 176 DAY 177 DAY 178 DAY 179 TIME-HOURS

Figure 6 Hourly Number of Main Section Door Openings (Townhouse 8)

22
o®

CO

e>

<S o

o

o ®

a ®-

03

DAY 176 DAY 177 DAY 178 DAY 179 TIME-HOURS

Figure 7 Hourly Number of Freezer Door Openings (Townhouse 8)

'-’s

DAY 176 DAY 177 DAY 178 DAY 179 TIME-HOURS

Figure 8 Hourly Freezer Door Opening Time (Townhouse 8)

23
Figure 9 Hourly Average Kitchen Air Temperature (Townhouse 8)

PVG. ENERGY CONSUMPTION

BVG. ENERGY CONSUMPTION PLUS 2 STD. DEVIATIONS

UJ I®3

l

HOUR OF DAY

Figure 10 Refrigerator Hourly Profile (Townhouse 8, days 96-180)

24
NO. OF MAIN DOOR

NO. OF MAIN DOOR

OPENINGS

OPENINGS PLUS 2 STD. DEVIATIONS

0 4 8 12 16 20 24 HOUR OF DRY

Figure 11 Refrigerator Hourly Profile, Main Section Door Openings

(Townhouse 8, days 96-180)

NO. OF FREEZER DOOR OPENINGS

kin nc nnne dpfninas Pi US ? STD. DEVIATIONS

HOUR OF DRY

Figure 12 Refrigerator Hourly Profile, Freezer Door Openings

(Townhouse 8, days 96-180)

25
I

S.D. =0.03 N = 64

• M «.N *,11 KWH

HOUR = 3 HERN *e.2M

• 19 4 24 «.M «.«M ».M KWH

«

tA

o.

1.

«

HOUR = 2 meh;: = 0.25

s.d. = 0.04

N = 84

Figure 13 Frequency Distributions,

Townhouse 8 Hourly Energy

Consumption (hours 1-6)

HOUR =8 MEAN =0.27

S.D. =0.04

N = 64

«.U* 0 54

HOUR =10 MEAN = C. 26

S.D. =0.04

N = 63

Figure 14 Frequency Distributions,

Townhouse 8 Hourly Energy

Consumption (hours 7-12)

HOUR =11 MERN = 8.38

• H 0.M «.U0 tU

KWH KWH

26
J

*

Figure 16 Frequency Distributions,

Townhouse 8 Hourly Energy

Consumption (hours 19-24)

r

27

Figure 15 Frequency Distributions,

Townhouse 8 Hourly Energy

Consumption (hours 13-18)

HOUR = 19 MEAN =0.30

8.D. =0.05

KWH HOUR = 21 HEAN =0.3O

S.D. =0.05

N = 84

HOUR =20 MEAh' =0.30

S.D. =0.85

«.M «.M «.U3 I.M KWH

KWH KWH
MEAN =6.45

S.D. =0.55

Figure 17 Daily Refrigerator

Performance (Townhouse 8)

“1 1 190 210

<

(6

<3> " Figure 18 Refrigerator Daily

Frequency Plot g

(Townhouse 8) ®'

«

<s 0.0

MEAN =6.45

S.D. =0.55

ENERGY CONSUMED

16.0 KWH

20.0 PER DRY

24.0 (E)

28
Figure 19 Energy Consumption and Differential Temperature versus Days

for Refrigerator (Townhouse 8)

DAY

Figure 20 Energy Consumption and Differential Temperature versus Days

for Refrigerator (Townhouse 7)

85

80

75

70

65

60

55

50

I

85

80

75

70

65

60

55

50

29

DIFFERENTIAL

TEMPERATURE

—

DEG.

F.(

ATF)

DIFFERENTIAL

TEMPERATURE

—

DEG.

F.

(ATF)

(KITCHEN

&

FREEZER)

(KITCHEN

&

FREEZER)
ENERGY

CONSUMED

-

KWH

PER

DRY

Figure 21 Daily Energy Consumption versus Main Section Differential

Temperature for Refrigerator (Townhouse 8, days 96-180)

30
ENERGY

CONSUMED

-

KWH

PER

DRY

0)

CO

O)

00

O)

O)

CD

0)

ID

cn

* TOWNHOUSE # 4

X MEAN =38.88

X S.D. =4.86

Y MEAN =6.93

Y S.D. =0.39

o TOWNHOUSE # 9

X MEAN =39.01

X S.D. =2.10

Y MEAN =4.91

Y S.D. =0.57

o

o

o

OJ

“ I I 1 I I I 25.0 30.0 35.0 40.0 45.0 50.0 55.0

DIFF TEMP - MR IN SECTION - DEG. F (*Tm)

Figure 22 Lack of Correlation Between Refrigerator Energy Consumption and

Main Section Differential Temperature (Townhouses 4 and 9,

days 92-174)

31
0) 0)

LU

0)

00

TOWNHOUSE # 4

MEAN =72.99

S.D. =3.27

MEAN =6.93

S.D. =0.39

TOWNHOUSE # 9

MEAN =71 .29

S.D. =3.68

MEAN =4.91

40.0

100.0

(aTf ) Figure 23 Differential in Correlation in Energy Consumption and Differential

Temperature of Freezer Section (Townhouses 4 and 9)

50 ~

0 __ 60-0 70.0 80.0 90 0 DIFF TEMP - FREEZER DEG. F

32
ENERGY

CONSUMED

-

KWH

PER

DRY

LU

O)

00

« TOWNHOUSE # 1 X MEfiN =43.99

X S.D. =1.26

Y MEfiN =5.01

Y S.D. =0.48

o TOWNHOUSE # 2

X MEfiN =33.21

X S.D. =2.23

Y MEfiN =4.62

Y S.D. =0.49

Q

CO

« LO

<n

oi “i 1 1 1 1 1 1 25.0 30.0 35.0 40.0 45.0 50.0 55.0

DIFF TEMP - MAIN SECTION - DEG . F (*Tm)

Figure 24 Energy Consumption versus Differential Temperature of Main

Section for Refrigerator (Townhouses 1 and 2, days 167-249)

33
ENERGY

CONSUMED

-

KWH

PER

DRY

(E)

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

Figure 25 Energy Consumption versus Differential Temperature of Freezer

Section for Refrigerator (Townhouses 1 and 2, days 167-249)

34
DIFF

TEMP

-

MR

I

N

SECTION

DEG.

- F

(

20.0

40.0

80.0

80.0

100.0

120.0

140.

Figure 26 Daily Average Differential Temperature of Main Section versus

Days for Refrigerator (.Townhouse 8)

35
DIFF

TEMP

-

FREEZER

DEG.

- F

UTf)

20.0

40.0

60.0

80.0

100.0

126.0

140.

MEAN =72.11

S.D. =3.88

o

\yuJV]J

-

-lr'kr/

'

Q H I I I I 1 I 00 110 130 150 170 100 210

DRY

Figure 27 Daily Average Differential Temperatures of Freezer Section versus

Days (Townhouse 8)

36
ENERGY

CONSUMED

—

KWH

PER

DAY

(E)

Figure 28 Actual and Predicted Refrigerator Energy Consumption (Townhouse 8)

PHYSICAL SIZE OF REFRIGERATOR - CU.FT.

MODEL—LINEAR—E-A0+A1XU

FROST-FREE MODELS ONLY

Figure 29 Energy Consumption of Refrigerator vs. Refrigerator Size
'

.

1
REFERENCES

1. Grot, R.A. and Socolow, R.H. , "Energy Utilization in a Residential

Community" in Energy Demand, Conservation and Institutional Problems , ed. Michael Macrakis (Cambridge, Mass., MIT Press 1974).

2. Socolow, R.H. , "The Twin Rivers Program on Energy Conservation in

Housing: Highlights and Conclusions" Energy and Buildings , Vol. 1,

No. 3, April 1978.

3. Association of Home Appliance Manufacturers (AHAM) Standard

No. HRF-2-ECFT, Test Procedure to Determine the Freezer Temperature and Energy Consumption of Household Refrigerators, Combination

Refrigerator-Freezers and Freezers.

4. American National Standard B 38.1-1970, Methods of Testing for

Household Refrigerators, Combination Refrigerator-Freezers, and

Household Freezers.

5. Newton, G.C., Jr. "Energy and the Refrigerator" Technology Review,

January, 1976.

6. Mulroy, W.J., Grimes, J.W. and Shomaker, B.L. "Effect of Usage

Conditions on Household Refrigerator - Freezers and Freezer Energy

Consumption" ASHRAE Transactions Vol. 83. Part 1. 1977.

39
NBS-1 !4A (REV. 0-78)

U.'. DEPT. OF COMM,

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1781

3. Recipient' s Accession No,

4. TITLE AND SUBTITLE

FIELD PERFORMANCE OF RESIDENTIAL REFRIGERATORS

AND COMBINATION REFRIGERATOR-FREEZERS

5. Publication Date July 1979

7. AUTHOR(S)

Yui-May Chang and Richard A. Grot

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

hhSI

11. Contract/Grant No.

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

15. Supplementary notes

13. Type of Report & Period Covered

1|. Sponsoring Agescy Code

16. ABSTRACT

Evaluation of the performance of household refrigerators and combination refrigeratorfreezers was undertaken in a field experiment to determine the effect of room environment and occupant-usage habits on energy consumption Q f these appliances. This report

presents the results of such an experiment in ten townhouses at Twin Rivers, N.J. Onedoor manual defrost and two-door frost-free models of various sizes were studied. Energy

consumption, kitchen temperature, refrigerator temperature and door openings were measured for each model by data acquisition systems located in the townhouse basements. Both

daily and hourly averages and variations about the average for each variable were calculated to determine occupant-usage patterns.

Statistical techniques were utilized to obtain the effect of parameters on energy consump-’

tion of these appliances by linear regression of both one- and two-parameter models.

It was found that for a given model the temperature difference between the kitchen and

the refrigerator (either main or freezer section) had the most effect on energy consumption, with a lesser, though still important, contribution from the door openings.

In addition, the normalized energy consumption of each model, in different combinations

of variables, was calculated from its regression coefficients and the overall average

values of parameters from the measurements. The results of these normalized values

turned out to be within 5%. Therefore, their mean values could be considered as the typical energy consumption for each refrigerator or combination, under usage conditions.

The linear relationship among the combination refrigerator-freezers according to their

physical sizes indicated an increase of about 0.55 kWh per day for each additional cubic

foot increase in volume. Energy conservation by using a manual-defrost refrigerator was predicted at approximately 40% from the available measurements and other related

laboratory test results.

17. Key Words: Combination refrigerator-freezer field data; daily load profiles; energy

consumption; field measurements; hourly load profiles; refrigerator field

data; usage profiles.

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