Energy Use of Ice Making in Domestic Refrigerators

A. Meier

Most large domestic refrigerators sold in the United States are equipped with an automatic ice maker or designed so one can be easily added. Field monitoring studies have determined that refrigerators with automatic ice makers consume 7-26% more electricity than similar models without them. The U.S. Department of Energy (DOE) has an energy test procedure for refrigerators, but it does not include energy use of ice makers. This investigation sought to develop a modified test procedure that would include the electricity consumed by automatic ice makers and other new features.

Designs for automatic ice-making units in different domestic refrigerators are all very similar. The major components are a water reservoir, a motor/cam assembly, an ice mold, ejector blades and a heater, a harvest basket, and a shut-off arm. All residential units make cubes, which are then released through the application of heat. A typical cycle converts 140 cm3 of water into eight crescent-shaped ice "cubes." The elapsed time of one ice-making cycle depends upon the temperature setting of the refrigerator, but most ice makers can produce at least 2000 g of ice per day.

The automatic ice maker contains several heaters. Not only do they add to the cooling requirements, but they also require more energy than manual ice-production methods. The largest energy consumer is the mold heater, which typically draws 185 watts. Under maximum ice-harvesting conditions, the total energy devoted to ice making (including chilling and freezing the water) will be about 250 kWh/year, or about 25% of typical electricity use for these models of refrigerators. Under typical conditions, the additional load will be less.

At the same time, automatic ice making saves energy because the user does not open the freezer door as frequently. Producing 500 g/day saves roughly two openings per day or about 10 kWh/year.

The Figure shows the results of successive measurements of energy use for four refrigerators (expressed as averages). The first value is the labeled energy consumption as provided by the manufacturers. The second value is the actual DOE test values for each unit, as measured in the laboratory. (This is expected to differ somewhat from the labeled value due to sampling variation.) The third value is the energy use with the modified test that includes the automatic ice maker. After laboratory tests, the units were placed in real kitchens and monitored for two years. The results are summarized in the fourth value. The units were then returned to the laboratory and re-tested using both the DOE and modified procedures. These are the fifth and sixth values in the Figure.

Figure. Energy consumption of four refrigerators in laboratory and field measurements.

The measured increase in energy use due to ice making was roughly 60% greater than predicted. The range in energy use is probably due to different lengths of mold heater operation. The refrigerators used about 10% more electricity in actual kitchens than predicted by the conventional DOE test (which is used for the energy label). When the laboratory tests were repeated after two years, the refrigerators experienced 14% higher energy use.

This modification of the DOE test procedure was relatively easy to undertake. Other modifications to increase its realism, such as for food loading, may be more difficult. Each modification needs to balance the demands for realism with the need to maintain a simple procedure with acceptable accuracy and precision. Careful testing, both in the laboratory and in the field, would also be necessary to ensure that the test applies to all common units.

Reference

Meier A. Energy Use of Ice Making in Domestic Refrigerators. Lawrence Berkeley National Laboratory Report No. LBL-31976, 1995.

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