Abstract: In a control unit of a hot-water supply system, a boiling time period is estimated based on a hot-water amount stored in a tank at a time of 23:00, a boiling start time is adjusted so that boiling operation is finished at a time immediately before 7:00. For example, when the hot water amount stored in the tank is smaller at the time of 23:00, the boiling time period is made longer and the boiling start time is made earlier. On the other hand, when the hot water amount stored in the tank is larger at the time of 23:00, the boiling time period is made shorter and the boiling start time is made later.

Abstract: A heat exchanger includes a first tube in which water flows and a second tube in which refrigerant flows, and performs heat exchange between water and refrigerant. The first tube and the second tube are bonded to each other by brazing at joint surfaces thereof such that water flow crosses refrigerant flow perpendicularly. The joint surface of the first tube is divided into several surface regions by grooves. Accordingly, the joint surface of the first tube can be brazed to the joint surface of the second tube uniformly.

Abstract: In a hot water supply system with a heat pump cycle, an oil separator for separating refrigerant and oil flowing from a compressor from each other is provided, and oil separated from refrigerant in the oil separator returns to the compressor through an oil returning passage after passing through an oil passage of a water heat exchanger. The water heat exchanger includes a first heat exchanging portion in which refrigerant from the oil separator and water from a tank are heat-exchanged, and a second heat exchanging portion in which oil from the oil separator and water from the tank are heat-exchanged. In the heat exchanger, a flow direction of water is set opposite to that of refrigerant and oil.

Abstract: A hot water supply system wherein a flow of a refrigerant on a high-pressure side of a supercritical heat pump cycle and a flow of hot water are oppositely directed, and wherein water heated by the refrigerant on the high-pressure side is stored in heat insulating tanks of a vacuous and double structure. Water is heated with heat absorbed from the atmosphere and by the supercritical heat pump cycle having a high heat exchange efficiency &eegr;, to reduce the power required to heat the water. Therefore, hot water can be generated even in the daytime during peak power rates. Accordingly, because it is unnecessary to store hot water for daytime use in insulated tanks, system space requirements are reduced.

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 control unit of a hot-water supply system, a boiling time period is estimated based on a hot-water amount stored in a tank at a time of 23:00, a boiling start time is adjusted so that boiling operation is finished at a time immediately before 7:00. For example, when the hot water amount stored in the tank is smaller at the time of 23:00, the boiling time period is made longer and the boiling start time is made earlier. On the other hand, when the hot water amount stored in the tank is larger at the time of 23:00, the boiling time period is made shorter and the boiling start time is made later.

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: A hot water supply system wherein a flow of a refrigerant on a high-pressure side of a supercritical heat pump cycle and a flow of hot water are oppositely directed, and wherein water heated by the refrigerant on the high-pressure side is stored in heat insulating tanks of a vacuous and double structure. Water is heated with heat absorbed from the atmosphere and by the supercritical heat pump cycle having a high heat exchange efficiency &eegr;, to reduce the power required to heat the water. Therefore, hot water can be generated even in the daytime during peak power rates. Accordingly, because it is unnecessary to store hot water for daytime use in insulated tanks, system space requirements are reduced.

Abstract: A hot water supply system wherein a flow of a refrigerant on a high-pressure side of a supercritical heat pump cycle and a flow of hot water are oppositely directed, and wherein water heated by the refrigerant on the high-pressure side is stored in heat insulating tanks of a vacuous and double structure. Water is heated with heat absorbed from the atmosphere and by the supercritical heat pump cycle having a high heat exchange efficiency &eegr;, to reduce the power required to heat the water. Therefore, hot water can be generated even in the daytime during peak power rates. Accordingly, because it is unnecessary to store hot water for daytime use in insulated tanks, system space requirements are reduced.

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.

Abstract: In a hot water supply system with a heat pump cycle, an oil separator for separating refrigerant and oil flowing from a compressor from each other is provided, and oil separated from refrigerant in the oil separator returns to the compressor through an oil returning passage after passing through an oil passage of a water heat exchanger. The water heat exchanger includes a first heat exchanging portion in which refrigerant from the oil separator and water from a tank are heat-exchanged, and a second heat exchanging portion in which oil from the oil separator and water from the tank are heat-exchanged. In the heat exchanger, a flow direction of water is set opposite to that of refrigerant and oil.