抄録
Air-to-water heat pumps using CO_2 as a refrigerant have been developed. In addition, water heating systems each of which combines a CO_2 heat pump with a hot water storage tank have been commercialized, and are expected to contribute to energy saving in residential hot water supply. In this paper, the system performance of a water heating system is analyzed under a daily change in a standardized hot water demand. Especially, parametric studies are conducted by changing ambient and operation temperatures as well as magnitude of change in hot water demand. Some features of the temperature distribution in the storage tank and the system performance criteria such as heat pump coefficient of performance, storage and system efficiencies, and volumes of stored and unused hot water are clarified.
