Abstract
An air-to-water CO2 heat pump is used in combination with a domestic hot water storage tank, and the performance of this water heating system is affected significantly not only by instantaneous ambient air and city water temperatures but also by hourly changes in domestic hot water demand and temperature distribution in the storage tank. In this paper, the influence of operation conditions such as outlet water temperature during operation and inlet water temperature for shutdown of a CO2 heat pump on the performance of a water heating system is investigated by numerical simulation. The trade-off relationship between the system efficiency and the volume of unused domestic hot water as criteria for the system performance is clarified in relation to the operation conditions. The influence of seasonal changes in ambient air and city water temperatures on the trade-off relationship is also clarified.
