Heat - pump water heater

A heat-pump water heater for heating water, comprising:

• a tank for storing water;
• a heat pump cycle for heating water, used as a heating source;
• and
• a control unit for controlling operation of the heat pump cycle, wherein:
• the heat pump cycle includes
• a compressor which compresses sucked refrigerant and discharges compressed refrigerant,
• a water heat exchanger which is disposed to perform a heat exchange between refrigerant from the compressor and water supplied from the tank, in such a manner that a flow direction of refrigerant is opposite to a flow direction of water in the water heat exchanger,
• an expansion valve decompressing refrigerant flowing from the water heat exchanger,
• an air heat exchanger disposed to perform a heat exchange between refrigerant decompressed in the expansion valve and outside air,
• an accumulator disposed between the air heat exchanger and the compressor, for separating refrigerant from the air heat exchanger into gas refrigerant and liquid refrigerant so that only gas refrigerant is introduced into the compressor,
• a first adjustment valve, disposed between the expansion valve and the air heat exchanger in a refrigerant flow direction, for adjusting a flow amount of refrigerant from the expansion valve to the air heat exchanger,
• a bypass passage through which refrigerant from the expansion valve bypasses the first adjustment valve and the air heat exchanger, and
• a second adjustment valve for adjusting a flow amount of refrigerant flowing through the bypass passage;
• the control unit controls the operation of the first and second adjustment valves to set one of a general cycle operation where the first adjustment valve is opened and the second adjustment valve is closed, and a bypass operation where both the first and second adjustment valves are opened and an opening degree of the first adjustment valve is made smaller than that of the second adjustment valve;
• the control unit has a water temperature sensor for detecting a water temperature flowing into the water heat exchanger, and a heat-radiation determining member which determines whether or not a heat radiation from refrigerant to outside air causes in the air heat exchanger based on the water temperature;
• and
• the control unit performs the bypass operation when the heat radiation is determined by the heat-radiation determining member.

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 and discharges compressed refrigerant;
• a fluid heat exchanger which is disposed to perform a heat exchange between refrigerant from the compressor and the fluid;
• an expansion valve decompressing refrigerant flowing from the fluid heat exchanger;
• an air heat exchanger disposed to perform a heat exchange between refrigerant decompressed in the expansion valve and outside air;
• a bypass pipe defining a bypass passage through which refrigerant from the fluid heat exchanger bypasses at least the air heat exchanger;
• and
• an adjustment valve for adjusting a flow amount of refrigerant flowing through the bypass passage, wherein:
• the control unit is disposed to set one of a general cycle operation where all refrigerant flowing from the fluid heat exchanger is supplied to the air heat exchanger after being decompressed in the expansion valve, and a bypass operation where refrigerant from the fluid heat exchanger mainly flows through the bypass passage while bypassing at least the air heat exchanger;
• the control unit has a fluid temperature sensor for detecting a fluid temperature flowing into the fluid heat exchanger, and a heat-radiation determining member which determines whether or not a heat radiation from refrigerant to outside air causes in the air heat exchanger based on the fluid temperature;
• and
• the control unit performs the bypass operation when the heat radiation is determined by the heat-radiation determining member.