Hot-water supply system with heat pump cycle

A hot-water supply system comprising:

• a heat pump cycle including a refrigerant compressor for compressing refrigerant, a refrigerant passage in a fluid heat exchanger for performing a heat exchange with a fluid in a fluid passage, an expansion valve for decompressing refrigerant and an air heat exchanger for performing a heat exchange between refrigerant and air, which are connected to form a closed refrigerant circuit;
• a fluid circuit having therein a tank for storing the fluid for a supply, and a pump for flowing the fluid in the fluid circuit, the tank being connected to the fluid passage of the fluid heat exchanger;
• and
• a control unit for controlling a temperature of the fluid to be supplied to a target fluid temperature;
• wherein:
• the control unit controls the operation of the expansion valve in a first direction increasing an opening degree of the expansion valve, when a temperature difference, between a refrigerant temperature at an outlet side of the refrigerant passage in the fluid heat exchanger and a fluid temperature at an inlet side of the fluid passage in the fluid heat exchanger, is smaller than a target temperature difference;
• the control unit controls operation of the expansion valve in a second direction decreasing the opening degree of the expansion valve, when the temperature difference is larger than the target temperature difference;
• and
• when the control unit determines a heat radiation from the refrigerant to air in the air heat exchanger, the control unit maintains a high-pressure side refrigerant pressure before being decompressed in the heat pump cycle to be higher than a predetermined refrigerant pressure at least until the heat radiation stops.

A hot-water supply system comprising:

• a heat pump cycle including a refrigerant compressor for compressing refrigerant, a refrigerant passage in a fluid heat exchanger for performing a heat exchange with a fluid in a fluid passage, an expansion valve, for decompressing refrigerant and an air heat exchanger for performing a heat exchange between refrigerant and air, which are connected to form a closed refrigerant circuit;
• a fluid circuit having therein a tank for storing the fluid for a supply, and a pump for flowing the fluid in the fluid circuit, the tank being connected to the fluid passage of the fluid heat exchanger;
• and
• a control unit for controlling a temperature of the fluid to be supplied to a target fluid temperature, wherein:
• the control unit controls operation of the expansion valve in a first direction increasing an opening degree of the expansion valve, when a temperature difference, between a refrigerant temperature at an outlet side of the refrigerant passage in the fluid heat exchanger and a fluid temperature at an inlet side of the fluid passage in the fluid heat exchanger, is smaller than a target temperature difference;
• the control unit controls operation of the expansion valve in a second direction decreasing the opening degree of the expansion valve, when the temperature difference is larger than the target temperature difference;
• and
• when the fluid temperature at an inlet side of the fluid passage in the fluid heat exchanger exceeds a predetermined temperature, the control unit sets a target pressure to an upper limit pressure that is lower than a compression resistance pressure of materials constituting the heat pump cycle, so that the high-pressure side refrigerant pressure of the heat pump cycle corresponds to the target pressure.

A hot-water supply system comprising:

• a heat pump cycle including a refrigerant compressor for compressing refrigerant, a refrigerant passage in a fluid heat exchanger for performing a heat exchange with a fluid in a fluid passage, an expansion valve for decompressing refrigerant and an air heat exchanger for performing a heat exchange between refrigerant and air, which are connected to form a closed refrigerant circuit;
• a fluid circuit having therein a tank for storing the fluid for a supply, and a pump for flowing the fluid in the fluid circuit, the tank being connected to the fluid passage of the fluid heat exchanger;
• and
• a control unit for controlling a temperature of the fluid to be supplied to a target fluid temperature, wherein:
• the control unit has heat-storing amount calculating means for calculating a heat storage amount based on an amount of fluid in the tank and temperature of the fluid in the tank;
• in a midnight time zone in which the power rate is set at the lowest, the control unit starts a boiling-up operation when the heat storage amount of hot water within the tank is smaller than a first predetermined amount, and stops the boiling-up operation when at least one of a first condition, where the temperature of the fluid on the inlet side of the fluid flow passage is higher than a first preset temperature, and a second condition, where the heat storage amount of hot water within the tank becomes larger than the first predetermined amount, is satisfied;
• in a morning and evening time zone in which the power rate is set comparatively low, the control unit starts the boiling-up operation when the heat storage amount of the fluid within the tank is smaller than a second predetermined amount, and stops the boiling-up operation when at least one of a third condition, where the temperature of fluid on the inlet side of the fluid flow passage exceeds a second preset temperature, a fourth condition where the heat storage amount of the fluid within the tank is larger than the second predetermined amount, is satisfied;
• and
• in a daytime time zone in which the power rate is set high, the control unit starts the boiling-up operation when the heat storage amount of fluid within the tank is smaller than a third predetermined amount, and stops the boiling-up operation when at least one of a fifth condition, where the temperature of the fluid on the inlet side of the fluid flow passage exceeds a third preset temperature, and a second condition, where a heat storage amount of the fluid within the tank reaches the third predetermined amount, is satisfied.

A hot-water supply system comprising:

• a heat pump cycle including a refrigerant compressor for compressing refrigerant, a refrigerant passage in a fluid heat exchanger for performing a heat exchange with a fluid in a fluid passage, an expansion valve for decompressing refrigerant and an air heat exchanger for performing a heat exchange between refrigerant and air, which are connected to form a closed refrigerant circuit;
• a fluid circuit having therein a tank for storing the fluid for a supply, and a pump for flowing the fluid in the fluid circuit, the tank being connected to the fluid passage of the fluid heat exchanger;
• and
• a control unit for controlling an opening degree of the expansion valve and a capacity of the pump, wherein:
• when temperature of the fluid at an inlet side of the fluid passage is lower than a control change temperature, the control unit controls the opening degree of the expansion valve so that a temperature difference between the refrigerant temperature at an outlet side of the refrigerant passage and the fluid temperature at the inlet side of the fluid passage is within a predetermined range;
• and
• when the temperature of the fluid at the inlet side of the fluid passage is equal to or higher than the control change temperature, while the control unit controls the capacity of the pump at a constant value, the control unit controls the opening degree of the expansion valve to be increased when the temperature of the fluid at an outlet side of the fluid passage is higher than a first set temperature, and controls the opening degree of the expansion valve to be decreased when the temperature of the fluid at the outlet side of the fluid passage is lower than a second set temperature lower than the first set temperature.

A hot-water supply system comprising:

• a heat pump cycle including a refrigerant compressor for compressing refrigerant, a refrigerant passage in a fluid heat exchanger for performing a heat exchange with a fluid in a fluid passage, an expansion valve for decompressing refrigerant and an air heat exchanger for performing a heat exchange between refrigerant and air, which are connected to form a closed refrigerant circuit;
• a fluid circuit having therein a tank for storing the fluid for a supply, and a pump for flowing the fluid in the fluid circuit, the tank being connected to the fluid passage of the fluid heat exchanger;
• and
• a control unit for controlling an opening degree of the expansion valve and a capacity of the pump, wherein:
• when temperature of the fluid at an inlet side of the fluid passage is lower than a control change temperature, the control unit controls the opening degree of the expansion valve so that a temperature difference between a refrigerant temperature at an outlet side of the refrigerant passage and the fluid temperature at the inlet side of the fluid passage is within a predetermined range;
• and
• when the temperature of the fluid at the inlet side of the fluid passage is equal to or higher than the control change temperature, the control unit controls the opening degree of the expansion valve to be decreased when a refrigerant temperature discharged from an outlet of the compressor is equal to or lower than a first refrigerant set temperature, and controls the opening degree of the expansion valve to be increased when the refrigerant temperature discharged from the outlet of the compressor is equal to or higher than a second refrigerant set temperature set higher than the first refrigerant set temperature;
• and
• the control unit controls the capacity of the pump to be increased when the temperature of the fluid at an outlet side of the fluid passage is equal to or higher than a first fluid set temperature, and controls the capacity of the pump to be decreased when the temperature of the fluid at the outlet side of the fluid passage is equal to or lower than a second fluid set temperature lower than the first fluid set temperature.