Heat-pump water heater

摘要

In a heat-pump water heater (1), an ECU (15) sets a target temperature difference ( DELTA T) between water flowing into a water heat exchanger and refrigerant flowing out from the water heat exchanger, and controls a valve opening degree of an expansion valve (8) so that the target temperature difference is obtained. When a refrigerant temperature discharged from a compressor (6) is higher than a predetermined value, the target temperature difference is increased until the refrigerant temperature discharged from the compressor becomes lower than the predetermined value. Further, when water-heating capacity is decreased due to the increase of the target temperature difference, a rotation speed of the compressor is increased. <IMAGE>