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
REFRIGERATOR REPLACEMENT IN FLORIDA: A CASE STUDY
Florida's hot and humid climate challenges even the best refrigerators. Not surprisingly, refrigerators guzzle a lot of electricity in Florida. With roughly seven million refrigerators in the state, the average demand of these units exceeds 1,000 megawatts (MW). Over 25% of these refrigerators are old and inefficient--built before the advent of recent appliance efficiency standards. About 5% of them are replaced each year. To learn more about the energy-efficiency benefits of refrigerator replacement, the Florida Solar Energy Center conducted a study in which an 18-year-old unit was swapped for a more energy-efficient model.1
Collecting The Data
Energy consumption of the old refrigerator was measured for a year in the author's home. We measured kitchen, refrigerator, and freezer temperatures. In addition, the refrigerators were instrumented with contact switches which recorded door and freezer openings. The old unit was a 19.2 ft3 frost-free Sears Coldspot 106-762911 refrigerator-freezer with an automatic ice maker. It was replaced with the most energy-efficient model of its size with identical conveniences (automatic ice-maker, automatic defrost), an 18.6 ft3 1991 Frigidaire FPES19TIP. The two refrigerators look nearly identical, but the newer model has an estimated annual energy use of 760 kWh which is within 10% of being in compliance with the more stringent 1993 appliance efficiency standards. We monitored the replacement refrigerator for a full year.
Sizing Up Refrigerator Energy Demand and Use
Residential refrigerator-freezers are commonly assumed to possess a relatively flat load shape. Yet monitoring the old refrigerator showed that summertime utility peak hour demand (5-6 p.m.) averaged 283 W, while demand when no door openings or food-loading occurred (4-5 a.m.) was only 198 W. Maximum daily demand tended to occur at 7-8 p.m. and was 295 W. This represents an hourly load variation over the course of the day of 49% even though the house was air conditioned during the hottest part of summer!
Annual consumption totalled 1,963 kWh. Based on monthly utility bills, the old refrigerator represented over 25% of the total annual electrical use in the home. During the study, the refrigerator and freezer compartment was opened an average of 42 times per day. Analysis revealed that door openings were responsible for approximately 7% of overall refrigerator consumption. As expected, door openings mirrored meal preparation schedules and were heaviest after the evening meal, when refrigerator electrical consumption is also at its peak (see Figure 1).
Cool Savings With The New Refrigerator
A full year of data indicate that the new unit compares favorably with the value predicted by its Department of Energy (DOE) label, 760 kWh. The measured use was 740 kWh. The annual energy savings of the replacement refrigerator relative to the original unit totalled 1,223 kWh--a reduction in energy use of about 60%. The new unit accounts for 11% of total household consumption. The data show that the newer unit uses much less electricity on average, and that its demand is less sensitive to ambient temperature. Its daily electrical use exhibits less variation in general than the original unit. In fact, the reduction in the utility coincident peak demand at 5-6 p.m. from the refrigerator replacement was 166 W, a 59% decrease.
Assuming a new refrigerator price of $500, and an energy cost of 8cents/kWh, the new model will pay for itself in about five years. If a refrigerator needs to be replaced, the incremental cost of buying the most efficient unit (rather than buying one to save energy) is lower and the investment therefore pays for itself more quickly.
Electrical consumption for the old refrigerator also exhibited a stronger seasonal variation, whereas the new unit's energy use was more constant (see Figures 2 and 3). As expected, the refrigerator energy use responds strongly to variation in the daily kitchen temperature.
Assuming that similar reductions can be achieved for the 25% of Florida's refrigerator stock that is inefficient and awaiting replacement, the potential total state-wide peak demand reduction amounts to nearly 300 MW. This goal may be attainable because utility demand-side management programs will soon enjoy the further savings brought about by the more stringent 1993 appliance standards.
-- Danny Parker and Ted Stedman
1. The complete report on which this article is based, is available in Proceedings from the 1992 American Council for An Energy-Efficient Economy Summer Study on Energy Efficiency in Buildings, Vol. 3. Contact: ACEEE, 1001 Connecticut Ave. NW, Suite 801, Washington, D.C. 20036. Tel: (202)429-8873; Fax: (202)429-2248.
Danny Parker is a senior research scientist, and Ted Stedman is a research assistant with the Florida Solar Energy Center in Cape Canaveral, Fla.
Figure 1. Door openings
Analysis of 1991 Refrigerator Energy Use Characteristics
Our study represents an ideal case, because the old refrigerator was replaced with a unit of identical size and type. However, in a real-world setting the savings available from replacing older, less efficient refrigerators with newer models may be limited by the energy use characteristics of the new stock and how consumers select from the various options and features. Utility refrigerator demand-side management programs face several potential hazards in this regard:
To determine the potential impact of such a tendency, we examined all available refrigerators in the 1991 Consumer Selection Guide for Refrigerators and Freezers, published by the Association of Home Appliance Manufacturers. The 1,541 refrigerator-freezers were classified into eight distinct types based on their major features. Two configurations, top-freezer and side-by-side units with automatic defrost capability make up 87% of the models. Yet the data show that the side-by-side models use 41% more electricity on an absolute basis and 11% more energy even when corrected for the differences in interior volume, than do models with top-freezers. A statistical analysis showed that, all other things equal, each additional cubic foot of refrigerator volume will increase energy consumption by an average of 27 kWh/year.
This underscores the need for more efficient refrigerators which incorporate consumer conveniences. Projects such as the Super Efficient Refrigerator Program (see Chasing The Golden Carrot, p. 36) should insure that side-by-side models and improvements to convenience feature efficiency are not overlooked in the quest for improved efficiency. To ignore consumer demand for such conveniences will miss mainstream efficiency improvement opportunities. (For more on ratings and modern conveniences, see What's Wrong with Refrigerator Energy Ratings? p. 30.)
--Danny Parker and Ted Stedman
Comparison of 1991 Refrigerator Models
Average Normalized Annual Annual Number of Volume energy use energy use Configuration refrigerators (ft3) (kWh) (kWh/ft3) ____________________________________________________________________________________ single door, manual defrost 133 5 377 112 single door, automatic defrost 14 13 602 64 side-by-side doors, automatic defrost 434 23 1,251 56 top freezer, partial automatic defrost 36 12 708 62 top freezer, automatic defrost 905 18 885 50 bottom freezer, partial automatic defrost 2 4 544 140 bottom freezer, automatic defrost 14 21 1,145 54 top freezer, manual defrost, superinsulated 3 15 261 18 ____________________________________________________________________________________ Total/Average 1,541 18 938 57
Tale of Two Refrigerators Standard OLD REFRIGERATOR Average Deviation Minimum Maximum Fresh-food temperature (deg.F) 37.8 3.0 32.2 59.5 Freezer temperature (deg.F) 9.3 4.3 - 4.2 44.4 Kitchen temperature (deg.F) 82.6 5.71 65.4 97.2 Daily door openings 42.2 29.0 0.0 142 Daily use (kWh) 5.38 1.17 3.24 8.28 Summer demand (W) June-September 267.7 60.7 22.5 446.5 2-8 p.m. (Utility peak period) 280.5 62.2 22.5 446.5 NEW REFRIGERATOR Fresh-food temperature (deg.F) 39.5 1.96 28.0 55.8 Freezer temperature (deg.F) 10.6 2.49 - 4.1 25.4 Kitchen temperature (deg.F) 79.3 5.42 64.8 93.9 Daily door openings 42.2 26.9 0.0 173.0 Daily use (kWh) 2.03 0.52 0.0 3.71 Summer demand (W) June-September 116.4 44.1 12.6 251.1 2-8 p.m. (Utility peak period) 125.6 44.1 55.8 247.5
Figure 2. Old
Figure 3. New
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