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Thermal Performance of Residential Electric Water Heaters Subjected to Various Off-Peak Schedules.


pdf icon Thermal Performance of Residential Electric Water Heaters Subjected to Various Off-Peak Schedules. (859 K)
Fanney, A. H.; Dougherty, B. P.

American Society of Mechanical Engineers (ASME); Japan Solar Energy Society (JSES); and Korean Solar Energy Society (KSES). International Solar Energy Conference, 1992. Volume 2. April 5-9, 1992, Maui, HI, American Society of Mechanical Engineers, New York, NY, Stine, W.; Kreider, J.; Watanabe, K., Editor(s)(s), 1221-1230 pp, 1992.

Journal of Solar Energy Engineering, Vol. 118, 73-80, May 1996.

Sponsor:

Department of Energy, Washington, DC

Keywords:

electric heaters; water heaters; tests; computer models; thermal efficiency

Abstract:

A number of electric utilities use residential water heaters for reducing electrical demand. A water heater used in this manner is typically called an off-peak water heater because resistive heating is unrestricted during utility off-peak periods. During on-peak periods, by comparison, the utility seeks to limit and delay resistive water heating. Laboratory tests, where the off-peak period and hot water draw schedule were varied, were conducted on two residential storage water heaters. A computer model of an electric water heater was developed and validated. The laboratory tests and the model were used to quantify the effect that various off-peak and hot water draw schedules have on water heater thermal efficiency. Thermal efficiency was found to vary up to 7% for water heaters which meet the 1991 minimum efficiency standards as specified within the National Appliance Energy Conservation Act. The energy factor, as measured using the Department of Energy Test Procedure for Water Heaters, was found to be independent of the off-peak schedule because of a "normalizing" that occurs as part of the calculation procedure.