Abstract: In a heat-pump water heater, a control unit has a heat-radiation determining means for determining a heat radiation from refrigerant to outside air in an air heat exchanger based on a water temperature flowing into a water heat exchanger, and the control unit selectively performs a general cycle operation and a bypass operation in accordance with a determination result of the heat-radiation determining means. That is, when the water temperature flowing into the water heat exchanger is lower than 60° C., the general cycle operation is performed. On the other hand, when the water temperature is equal to or higher than 60° C., the bypass operation is performed.

Abstract: In a hot-water supply system with a heat pump cycle, a control unit controls operation of an expansion valve based on a temperature difference between a refrigerant temperature at an outlet side of a refrigerant passage in a water heat exchanger and a water temperature at an inlet side of a water passage in the water heat exchanger. When the expansion valve is controlled in a direction increasing a valve opening degree, the control unit sets an upper limit opening degree of the expansion valve, for obtaining a refrigerant pressure corresponding to a target hot-water temperature, and controls the expansion valve in an opening degree range smaller than the upper limit opening degree.

Abstract: 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.

Abstract: A heat pump type hot-water supply system performs an ordinary operation for heating liquid stored in a reservoir by circulating the liquid in a heat exchanger for supplying hot water. When an outlet temperature of an exterior heat exchanger is lowered to about −5° C., the ordinary operation is switched to a defrosting operation, and an opening degree of an expansion valve is decreases as compared to that at the ordinary operation. Accordingly, hot gas discharged from a compressor radiates a decreased amount of thermal energy in the heat exchanger for supplying the hot gas. Hot gas discharged from the compressor can reach the exterior heat exchanger without lowering its temperature largely to perform defrosting of the exterior heat exchanger.

Abstract: In a hot-water supply system with a heat pump cycle, a control unit controls operation of an expansion valve based on a temperature difference between a refrigerant temperature at an outlet side of a refrigerant passage in a water heat exchanger and a water temperature at an inlet side of a water passage in the water heat exchanger. When the expansion valve is controlled in a direction increasing a valve opening degree, the control unit sets an upper limit opening degree of the expansion valve, for obtaining a refrigerant pressure corresponding to a target hot-water temperature, and controls the expansion valve in an opening degree range smaller than the upper limit opening degree.

Abstract: In a heat-pump water heater, a control unit has a heat-radiation determining means for determining a heat radiation from refrigerant to outside air in an air heat exchanger based on a water temperature flowing into a water heat exchanger, and the control unit selectively performs a general cycle operation and a bypass operation in accordance with a determination result of the heat-radiation determining means. That is, when the water temperature flowing into the water heat exchanger is lower than 60° C., the general cycle operation is performed. On the other hand, when the water temperature is equal to or higher than 60° C., the bypass operation is performed.

Abstract: 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.