초록 ▼

In a heat-pump water heater, an ECU sets a target temperature difference 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 so that the target temperature difference is obtained. When

In a heat-pump water heater, an ECU sets a target temperature difference 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 so that the target temperature difference is obtained. When a refrigerant temperature discharged from a compressor 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.

대표청구항 ▼

1. A heat pump fluid heater for heating a fluid using a heat pump cycle as a heating source, comprising:a compressor which compresses sucked refrigerant to have a pressure equal to or higher than a critical pressure of refrigerant, and discharges compressed refrigerant; a heat exchanger which is dis

1. A heat pump fluid heater for heating a fluid using a heat pump cycle as a heating source, comprising:a compressor which compresses sucked refrigerant to have a pressure equal to or higher than a critical pressure of refrigerant, and discharges compressed refrigerant; a heat exchanger which is disposed to perform a heat exchange between refrigerant from the compressor and the fluid, in such a manner that a flow direction of refrigerant is opposite to a flow direction of the fluid in the heat exchanger; and a control unit for controlling operation of the heat pump cycle, wherein: the control unit controls a high-pressure side refrigerant pressure from the compressor and before being decompressed in the heat pump cycle, so that a temperature difference between the fluid flowing into the heat exchanger and refrigerant discharged from the heat exchanger becomes a target temperature difference; the control unit has a detection member for detecting one of a refrigerant temperature and a physical amount relative to the refrigerant temperature discharged from the compressor; and the control unit changes the target temperature difference to be increased when a detection value of the detection member is more than a predetermined value.