Refrigeration cycle apparatus with heat storage for use during defrost

1. A refrigeration cycle apparatus comprising a controller and a refrigerant circuit through which refrigerant circulates in a forward direction in a heating operation sequentially through a compressor, a four-way valve, an indoor heat exchanger, a first expansion valve, a heat storage body, a second expansion valve, and an outdoor heat exchanger, and the four-way valve, and back to the compressor, and refrigerant circulates in an opposite direction to the forward direction in a defrosting operation,

the refrigerant circuit comprising

a first refrigerant pipe extending from the indoor heat exchanger through the first expansion valve, the heat storage body and the second expansion valve to the outdoor heat exchanger,

a second refrigerant pipe connecting the four-way valve and the indoor heat exchanger,

a third refrigerant pipe connecting the four-way valve and the outdoor heat exchanger,

a fourth refrigerant pipe connecting a suction port of the compressor and the four-way valve,

a bypass path branching off from a first portion in the first refrigerant pipe and leading to the fourth refrigerant pipe, the first portion connecting the indoor heat exchanger and the first expansion valve,

a first on-off valve provided in the bypass path,

a second on-off valve provided in the second refrigerant pipe; and

a third on-off valve provided in the first portion of the first refrigerant pipe so as to be located between the indoor heat exchanger and a branch point to the bypass path, wherein

the controller controls each of the second on-off valve and the third on-off valve to open during the heating operation and close during the defrosting operation.

2. The refrigeration cycle apparatus according to claim 1 , wherein

the four-way valve is configured to

cause the refrigerant to circulate in the forward direction in the heating operation and

cause the refrigerant to circulate in the opposite direction in the defrosting operation,

wherein the controller is configured to

when the heating operation is shifted to the defrosting operation, perform a defrosting preparation operation in such a manner that, while the first on-off valve is controlled to keep closed, the controller increases a degree of opening of the first expansion valve to larger than that in the heating operation, and reduces a degree of opening of the second expansion valve to smaller than that in the heating operation, and

control the first on-off valve to open in the defrosting operation.

3. The refrigeration cycle apparatus according to claim 2 , wherein the controller is further configured to

obtain, from at least one sensor, at least one of a pressure of refrigerant suctioned into the compressor, a temperature of refrigerant suctioned into the compressor, and a temperature of refrigerant at an outlet of the outdoor heat exchanger, and

start the defrosting preparation operation

(i) when the at least one of the pressure of refrigerant suctioned into the compressor, the temperature of refrigerant suctioned into the compressor, and the temperature of refrigerant at the outlet of the outdoor heat exchanger becomes smaller than a first value during the heating operation, or

(ii) when a prescribed time period is determined to pass since start of the heating operation.

4. The refrigeration cycle apparatus according to claim 2 , wherein the controller is configured to

obtain, from a sensor, an indoor temperature, and

during the heating operation, start the defrosting preparation operation when the indoor temperature is determined to reach a set value set by a user.

5. The refrigeration cycle apparatus according to claim 2 , wherein the controller is further configured to

obtain a temperature difference between the heat storage body and an indoor heat exchanger, and

end the defrosting preparation operation

(i) when the temperature difference between the heat storage body and the indoor heat exchanger becomes smaller than a first value during the defrosting preparation operation, or

(ii) when a prescribed time period is determined to pass since start of the defrosting preparation operation.

6. The refrigeration cycle apparatus according to claim 2 , wherein the controller is further configured to continue the defrosting preparation operation until the defrosting operation is started.

7. The refrigeration cycle apparatus according to claim 2 , wherein

the four-way valve is configured to switch a communication state inside the four-way valve between a first state and a second state, to allow a circulation direction of the refrigerant to be changed,

in the first state,

a discharge port of the compressor is in communication with the second refrigerant pipe, and

a suction port of the compressor is in communication with the third refrigerant pipe, and

in the second state,

the discharge port of the compressor is in communication with the third refrigerant pipe, and

the suction port of the compressor is in communication with the second refrigerant pipe.

8. The refrigeration cycle apparatus according to claim 1 , further comprising:

a first stop valve provided in the second refrigerant pipe; and

a second stop valve provided in the first portion of the first refrigerant pipe, wherein the first stop valve is located between the indoor heat exchanger and the second on-off valve, and

the second stop valve is located between the indoor heat exchanger and the third on-off valve.

9. The refrigeration cycle apparatus according to claim 1 , further comprising an inverter module for driving the compressor or for driving an outdoor blower, the inverter module being disposed to be in contact with the heat storage body.