HEAT PUMP WATER HEATER

PROBLEM TO BE SOLVED: To suppress variation of the temperature of boiled-up hot water heated by a heat pump. SOLUTION: This heat pump water heater is structured such that a gas coolant discharged from a compressor 1 is delivered to a water-coolant heat exchanger 2, low-temperature water supplied from a hot-water storage tank 11 to the water-coolant heat exchanger is heated to a boiling-up preset temperature Two* to be returned to and stored in the hot-water storage tank, and the hot water in the hot-water storage tank is supplied. In the heat pump water heater, a target value Tg* of the temperature of the gas coolant discharged from the compressor is determined according to a preset function (expression (1)) based on a temperature Ta of outside air, a temperature Twi of an influent water entered into the water-coolant heat exchanger, and the boiling-up preset temperature Two* (31); the temperature of a casing of the compressor is detected by a thermal sensor 26; and the opening of an expansion valve 4 of a heat pump cycle is controlled to adjust the detection temperature Tg of the temperature of the casing to the target value (33, 34). COPYRIGHT: (C)2008,JPO&INPIT