This article was originally published in the January/February 1993 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online January/February 1993
WHAT'S WRONG WITH REFRIGERATOR ENERGY RATINGS?
As refrigerators become more and more efficient, consumers and utility demand-side managers are faced with a number of questions. Does the U.S. Department of Energy's (DOE) test procedure adequately predict refrigerator energy consumption? How much energy can be saved by replacing an old refrigerator? Do conveniences like automatic ice makers increase energy use? How does refrigerator energy consumption change with the seasons? A 1991 study sponsored by Pacific Gas and Electric Co. (PG&E) shed new light on these questions.
In 1990 PG&E offered rebates for high-efficiency refrigerators purchased for use in its service territory:
Selecting The Homes
Automatic defrost refrigerators with top freezers in the 18-22 ft3 range represent the largest group of refrigerators rebated in 1990. All 20 of the refrigerators we studied had these characteristics and were located in Fresno, Calif. for logistical reasons.
The study established three groups of refrigerators based on the rebate scheme:
Group A. Models saving less than 10% of the federal standard (seven units).
Group B. Models saving 10-15% of the federal standard (seven units).
Group C. Models saving more than 15% of the federal standard (six units).
The study randomly selected refrigerator rebate participants--Groups B and C--from lists prepared by the Electric and Gas Industries Association (EGIA), which manages the rebate program for PG&E. The Fresno Montgomery Ward & Co. store provided a list of customers who bought refrigerators in 1990. Individuals with non-rebated refrigerators--Group A--were selected from that list. Proctor Engineering solicited participants by letter and phone. Those selected received $100 on completion of the study.
Obtaining The Data
PG&E technicians visited every site, installed a submeter, completed a short interview with the occupant, and recorded one-time measurements of temperatures and other factors that might influence refrigerator energy consumption. Table 1 shows the average characteristics of each monitored group.
The submeter, a 120V version of PG&E's residential time-of-use meter, recorded refrigerator consumption in 15-minute intervals. We obtained data for 20 refrigerators, submetered for three time periods:
Changing Seasons--and Consumption
We know intuitively that the energy consumption of a refrigerator will increase as the kitchen temperature rises. This study addressed the question: is daily average outdoor temperature a good predictor of refrigerator energy use? To investigate this relationship, we ran linear regressions, comparing the average daily consumption of each group against 71 days and three seasons of outdoor temperatures (see Figure 1). The results showed over 90% of the variations in group average use were predicted by variations in the ambient temperature.
DOE Testing--Adequate Predictor?
Whether the DOE lab test adequately predicts refrigerator consumption depends on the local climate. The laboratory test for complying with federal standards is conducted at a single temperature--90deg.F. It produces an estimate of annual energy without accounting for changes in temperature, food loading, door openings, and other variables that exist in the field. Nevertheless for some climates the lab test estimate may be quite close. (For more on ambient temperatures and refrigerator energy use, see box, Keep That Kitchen Cool.)
This study used linear regression models to estimate the annual refrigerator consumption in Fresno. The average annual temperature for Fresno is 65deg.F. Substituting this value into the models, we found that the laboratory test closely matched the estimate for Groups A and C, but not for Group B (see Table 2).
Group B, however, consumed substantially more energy than predicted. On average, these refrigerators used even more than their less efficient counterparts. When we analyzed the data, it became immediately apparent that two lemons (high-use refrigerators) caused a large portion of this excess consumption. Compared with the remaining units in group B, the lemons consumed 43% more energy over the first two test periods.
We visited those refrigerators to determine the cause of the high use. At the house of the first lemon, the occupants complained that they had to get up every morning and empty all the ice out of the freezer, otherwise they couldn't get to their frozen food. A bent ice maker shut-off arm created the overabundance of ice. Since the ice maker did not shut off, it produced ice around the clock, resulting in an impressive increase in electrical use. The total energy use from automatic ice makers is the total of four components:
Since the ice maker was not turned off, it cycled just as if it were making ice. Without water, it never made ice and the sensing arm did not halt the process. Every half hour the ice maker repeated the process. When the ice maker on this unit was turned off, it showed a usage reduction equivalent to 357 kWh annually. (For more on energy use and conveniences, see box Through-The-Door Energy Use.)
One Peach (a rotten one)
One refrigerator in Group A used far less energy than the rest of the refrigerators in that group. The owner of this refrigerator complained of melting ice cream and food spoilage. An on-site investigation revealed that the temperatures in both the fresh food compartment and the freezer were high. The thermostat on this unit was replaced, controlling temperatures at a more reasonable level.
Can Replacement Save Energy and Reduce Load?
The cost-effectiveness of refrigerator replacement clearly depends on how wasteful the existing refrigerator is. PG&E has monitored typical refrigerators for many years as part of the Appliance Metering Project (AMP). Their 1985-86 Residential Appliance Load Study reported the measured usage from 21 refrigerators.2 The annualized use for those refrigerators was 1,990 kWh.
All the new refrigerators submetered in the current study averaged 960 kWh--only 48% of the energy expended by the older refrigerators represented in the AMP sample. Refrigerators that meet or exceed the 1993 standard will use substantially less energy than these units.
Replacing old inefficient refrigerators will not only save the customer money, it will also assist the local utility by reducing demand during peak load periods. This sample indicates, an average reduction of over 100W per replacement refrigerator. Of course, neither the customer's energy bill nor the utility peak will decrease if the old refrigerator relocates from the kitchen to the garage where it cools liquid refreshment.
The DOE lab test provides a quick method of rating refrigerator efficiency, but it does not capture some of the more important variables that effect use in the field. These case studies indicate that ambient temperature and automatic ice makers are significant variables in refrigerator energy consumption. Yet the DOE test procedure is conducted at a single temperature and without an ice maker. At best, demand-side planners do not take these variables into account when estimating conservation savings. At worst, refrigerator energy use can increase 40-60% when the ice maker is malfunctioning or is not attached to a water source. For this reason, consumers should receive additional instructions about ice makers, how to turn them off if there is no water supply, and when to call a service person (when the freezer is filling with ice). -- John Proctor
1. PG&E Refrigerator Field Metering Project, Final Report 1991. Available from Proctor Engineering Group, 700 Larkspur Landing Cr., Ste. 259, Larkspur, CA 94939. Tel:(415)925-2322; Fax:(415)461-2925.
2. Brodsky, J. and McNicoll, S., principal investigators, Residential Appliance Load Study 1985-1986, Appliance Metering Project, Pacific Gas and Electric Co., Regulatory Cost of Service Dept., September 1987.
John Proctor is president of Proctor Engineering Group in Larkspur, Calif.
Figure 1. Refrigerator Energy Consumption versus Outside Temperature
Note: For regression lines, estimated daily consumption = constant + outside temperatures 2 coefficient of determination (R = .9).
Table 1. Monitored Refrigerators
Percentage Refrigerator Anti- DOE test better adjusted sweat With annual than volume1 heater automatic use minimum (ft3) on2 ice maker3 (kWh)4 efficiency5 ____________________________________________________________________ Group A 22.2 43% 14% 951 4% Group B 22.9 29% 71% 895 11% Group C 22.2 67% 20% 838 15% ____________________________________________________________________ 1. Adjusted volume, calculated as 1.63 X freezer volume (ft3) + refrigerator volume (ft3). Combines variable freezer and fresh food volumes.
2. The anti-sweat heater (electric resistance) controls condensation near the door seal and can be turned off.
3. Presence of an icemaker (not a through-the-door ice maker), a proven large energy use.
4. Annual consumption predicted by the Uniform Test Method for Measuring the Energy Consumption of Electric Refrigerators and Electric Refrigerator Freezers, Appendix A-1 to subpart B of part 430, Department of Energy, 10 CFR Chap. 11. January 1, 1991. This test determines the energy required to maintain a refrigerator at steady state in a 90deg.F room. Annual consumption predicted by the Uniform Test Method for Measuring the Energy Consumption of Electric Refrigerators and Electric Refrigerator Freezers, Appendix A-1 to subpart B of part 430, Department of Energy, 10 CFR Chap. 11. January 1, 1991.
5. Calculated as:
Maximum allowable consumption-Laboratory estimated consumption ______________________________________________________________ Maximum allowable consumption The maximum allowable estimated consumption from the laboratory test is set by the Federal standards. For these units (refrigerator-freezer, with automatic defrost, top-mounted freezer, without through-the-door ice service) the 1990 standard = 23.5 2 Adjusted volume + 471 kWh. Directory of Certified Refrigerators, Freezers and Refrigerator Freezers, Califonia Energy Commission. Available from California Energy Commission, P.O. Box 944295, Sacramento, CA 94244-2950.
Keep That Kitchen Cool
A recent study in Rochester, N.Y., revealed the most reliable way to reduce an existing refrigerator's energy use. In the study, the kitchen temperature was monitored every 30 minutes (along with the energy use) in 22 homes. The results were surprisingly consistent: changes in kitchen temperatures explained almost all of the changes in the refrigerators' energy use during the eight-month monitoring period (see Figure 2).
Individual refrigerators were very sensitive to kitchen temperatures. Many experienced a doubling in energy use when the temperature rose from 65deg.F to 80deg.F. Refrigerators rarely achieved their labeled consumptions until the kitchen temperature rose above 80deg.F (see Figure 3).
Thus, keeping a cool kitchen is an important element for minimizing refrigerator energy use. (This does not mean air conditioning!) Adequate ventilation is the key strategy during those seasons where the outside temperature is cooler than the kitchen. It is also crucial to permit air to easily circulate around refrigerators. Modern kitchen designs can frustrate this strategy because most refrigerators are tightly enclosed in a cabinet. (See Leftovers, p. 41.)
Figure 2. Kitchen Temperature versus Energy Usage
Figure 3. One Year of Energy Consumption and Kitchen Temperature
Through-The-Door Energy Use
Most refrigerator manufacturers offer several models with through the door features. These features include cold water dispensers, ice dispensers, and some even have a little door to give access to frequently-used items. Often the manufacturers suggest that these features save energy because they avoid door openings. Unfortunately, the opposite is true: through-the-door conveniences increase energy use. Danny Parker, at the Florida Solar Energy Center, demonstrated this by a clever analysis.
Parker discovered that manufacturers typically use the same box for a standard unit and one with through-the-door features. Thus, by comparing the labeled energy use for two models, one can determine the extra energy used by those features. Parker identified 24 twins in the Association of Home Appliance Manufacturers directory. The through-door-features uniformly added 10% to the labeled energy use of the refrigerators, corresponding to 120 kWh per year, or about $12 (see Figure 4).
Parker's comparison may understate the difference because the measurements were performed in the laboratory where no water or ice is used. The differences simply reflect the thermal short circuits in the through-the-door features (because insulation cannot fit in that area). There is some anecdotal evidence that the in-kitchen increase will be considerably more, partly because the ease of access increases use (and waste) of chilled water and ice. There are no field data to confirm this estimate, but literally hundreds of door openings would be needed to achieve the same increase in energy use.
The consumer must decide if the added convenience of the through-the-door features is worth the added energy cost. In any event, through-the-door features are certainly not energy savers.
-- Alan Meier
Figure 4. Matched Pair Analysis of Side-by-Side Refrigerators
Table 2. Annual Consumption: DOE Test versus Submetered Seasonal Estimate Predicted annual use Estimated annual use according to according to Ratio of Annual use: DOE test 71-day sample sample/DOE test ____________________________________________________________________________ Group A 951 kWh 972 kWh 1.0 Group B 887 kWh 1,041 kWh 1.2 Group C 839 kWh 849 kWh 1.0 ____________________________________________________________________________ * Due to small sample size, sample means cannot be used to determine differences between rebated and non-rebated refrigerators with any degree of confidence.
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