Investigation of the conservation potential of residential heat pumps with thermal energy storage. Final report

This study examined the operational and economic feasibility of heat pump systems with thermal storage to: reduce annual electric cost for residential customers by operating the system during hourly periods, both summer and winter, when the most favorable coefficient of performance can be obtained; and provide the potential for a reduction in peak electric utility demand, by delivering mid-day cooling from storage, with the compressor operating only during utility off-peak periods. To meet these objectives the performance characteristics of two storage system concepts, a liquid tank storage system and a rock-bed storage system were evaluated using computer simulation techniques. Integral energy requirements calculated during the simulation were converted into annual operating costs for each system. Incremental installation costs and incremental performance benefits, relative to the Base system, were analyzed to derive an approximate payback period for the two storage concepts. The results showed that a heat pump-thermal energy storage system would consume 8 to 9% less electrical power than a conventional heat pipe installation which, at 4.5 cents/kWh, translates to annual savings of from $30 to $39. Due to installation costs, the payback period would be from 65 to 94 years. It is concluded that heat pumps with thermal storagemore » will not be economically attractive for residential applications, and that further research on thermal storage for comfort systems should concentrate on applications for large commercial and industrial buildings. (LCL)« less