Abstract
Heat pumps using CO_2 as a natural refrigerant have been developed, and are expected to contribute to energy saving in hot water supply. In its residential application, a CO_2 heat pump is used in combination with a hot water storage tank, and the performance of this system is affected significantly not only by instantaneous ambient air and feed water temperatures but also by hourly changes of hot water demand and temperature distribution in the storage tank. It takes a long time to conduct the performance analysis by experiment, and it is expected that numerical simulation enables one to do it very efficiently. The author has created simulation models of CO_2 heat pump water heating systems and has conducted the performance analysis by numerical simulation. In this invited lecture, the background and some examples of the numerical simulation are presented.
