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






As part of the Sacramento Municipal Utility District's (SMUD) high efficiency refrigerator program, the district offers an incentive of $100 to customers who trade in an older refrigerator in conjunction with the purchase of a new model. Dealers pick up the old models at the same time they deliver the new ones and bring the old models to a special recycling facility at SMUD, where refrigerant is pumped out and recycled, capacitors are removed and disposed, and the remainder of the unit is sold for scrap metal. The district has collected over 30,000 refrigerators through the program.

SMUD wanted to know how much electricity the refrigerator program was saving. To estimate energy use, we randomly selected 79 units. We measured each unit's annual energy use and documented its physical and operational condition. Of these, 28 units were also tested to determine savings from cleaning condenser coils.

SMUD constructed a make-shift test facility from a shipping container. It was insulated and fitted with a datalogger, thermocouples, power transducers, exhaust fan, electric heater, window air conditioner, and relays to control indoor ambient temperature. The facility is designed to control and maintain a constant temperature of 90deg.F throughout the entire test period regardless of outside ambient conditions or internal gains from the operating refrigerators. This temperature setting simulates loads in lieu of introducing internal heat loads from food and refrigerator door openings and closings, as specified by ANSI/AHAM HRF-1-1988 test procedures (more commonly known as the DOE test).

The condition of each unit as received was carefully documented, including cabinet and door seal integrity, dirt accumulation on the condenser, refrigerant charge, condenser/evaporator fan operation, defrost operation, and compressor motor windings. We found three common conditions affecting annual energy use. Seventy percent of the units had a substantial dirt accumulation on the condenser coils, 34% had an over or under-charged refrigerant level, and 18% had some type of door seal or cabinet damage.

Of the 79 functioning units tested, 56 had condenser fans, 23 had convection condensers, 38 had humidity switches, and 17 were equipped with icemakers. Sizes were10 ft3-25 ft3, with an average size of 17.6 ft3 (see Table 1).

We conducted a second test of 28 units from the sample to determine energy savings due to condenser coil cleaning. These tests were also performed using the DOE testing method. We calculated energy savings from the difference between test results under pre-cleaned and post-cleaned conditions. The testing reveals an average of 150 kWh, or 6%, annual energy savings attributable to condenser coil cleaning.

These results are overstated due to limitations of the testing procedure--annual energy use obtained using AHAM test procedures for an entire year in a consistently dirty condition is compared to the annual energy use for an entire year in a consistently clean condition. The difference in energy use between these two conditions does not account for any gradual coil fouling that may occur. Assuming energy savings decrease linearly between pre- and post-cleaned conditions, and that the coil is cleaned once per year, actual energy savings may be one-half of the above savings--75 kWh per year, or 3%. --Willem Bos

Willem Bos is a demand-side specialist with the Sacramento Municipal Utility District.

Summary of Annual Energy Use By Size

Volume Number Average Standard error Minimum Maximum (ft3) of units (kWh/yr) (kWh/yr) (kWh/yr) (kWh/yr) _________________________________________________________________________ 10-15 17 2,120 786 871 3,737 16-19 43 2,528 644 1,514 4,153 20-25 19 3,139 807 1,961 4,706 _________________________________________________________________________ Note: At a 10% level, the differences in average annual energy use between volumes are significantly different.


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