Refrigeration cycle apparatus and method for controlling refrigeration cycle apparatus
A refrigeration cycle apparatus includes: a low-stage refrigeration cycle including a low-stage compressor, a low-stage condenser, a low-stage pressure reducing device, and a low-stage evaporator, and circulating low-stage refrigerant; a high-stage refrigeration cycle including a high-stage compressor, a high-stage condenser, a high-stage pressure reducing device, and a high-stage evaporator, and circulating high-stage refrigerant; a cascade condenser exchanging heat between the low-stage refrigerant in the low-stage condenser and the high-stage refrigerant in the high-stage evaporator, and a controller. The low-stage refrigerant is a refrigerant that undergoes disproportionation. The low-stage refrigerant is maintained at a pressure lower than a disproportionation pressure at which the low-stage refrigerant undergoes disproportionation.
1. A refrigeration cycle apparatus comprising:
a low-stage refrigeration cycle including a low-stage compressor, a low-stage condenser, a low-stage pressure reducing device, and a low-stage evaporator, and circulating low-stage refrigerant;
a high-stage refrigeration cycle including a high-stage compressor, a high-stage condenser, a high-stage pressure reducing device, and a high-stage evaporator, and circulating high-stage refrigerant;
a cascade condenser configured to exchange heat between the low-stage refrigerant in the low-stage condenser and the high-stage refrigerant in the high-stage evaporator; and
a controller,
the low-stage refrigerant being a refrigerant that undergoes disproportionation,
wherein the controller is configured to maintain the low-stage refrigerant at a pressure lower than a disproportionation pressure at which the low-stage refrigerant undergoes disproportionation.
2. The refrigeration cycle apparatus of claim 1 , wherein the controller is configured to change a low-pressure side pressure of the high-stage refrigeration cycle to maintain the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
3. The refrigeration cycle apparatus of claim 2 ,
wherein the controller is configured to reduce the low-pressure side pressure of the high-stage refrigeration cycle when a cooling load on the low-stage refrigeration cycle increases, and
the controller is configured to increase the low-pressure side pressure of the high-stage refrigeration cycle when the cooling load on the low-stage refrigeration cycle decreases.
4. The refrigeration cycle apparatus of claim 2 , wherein the controller is configured to control the high-stage compressor to change the low-pressure side pressure of the high-stage refrigeration cycle.
5. The refrigeration cycle apparatus of claim 1 , wherein the controller is configured to operate the high-stage compressor while the low-stage compressor is not operating, thereby maintaining the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
6. The refrigeration cycle apparatus of claim 1 , wherein the low-stage refrigeration cycle includes a low-stage liquid receiver provided in a passage communicating between the low-stage condenser and the low-stage pressure reducing device.
7. The refrigeration cycle apparatus of claim 6 , wherein the low-stage refrigerant in the low-stage liquid receiver is cooled while the low-stage compressor is not operating.
8. The refrigeration cycle apparatus of claim 6 ,
wherein the low-stage refrigeration cycle includes
a check valve provided in a passage communicating between the low-stage compressor and the low-stage condenser, and
a valve provided in a passage communicating between the low-stage liquid receiver and the low-stage pressure reducing device, and
wherein the controller is configured to, when the high-stage compressor is stopped, maintain a state of operating of the low-stage compressor while closing the valve and then stop the low-stage compressor to maintain the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
9. The refrigeration cycle apparatus of claim 1 , wherein the low-stage refrigeration cycle includes a pressure relief device.
10. The refrigeration cycle apparatus of claim 1 , wherein the controller is configured to stop, when at least one of a pressure and a temperature of the low-stage refrigerant exceeds a reference value, the low-stage compressor to maintain the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
11. The refrigeration cycle apparatus of claim 1 , wherein the high-stage refrigerant is a refrigerant that allows operating efficiency of a refrigeration cycle to be higher than that of the refrigeration cycle using the low-stage refrigerant.
12. The refrigeration cycle apparatus of claim 1 , wherein the low-stage refrigerant contains HFO-1123 refrigerant.
13. The refrigeration cycle apparatus of claim 12 , wherein the low-stage refrigerant is a refrigerant mixture of HFO-1123 refrigerant and a HFC-based refrigerant.
14. The refrigeration cycle apparatus of claim 13 , wherein the HFC-based refrigerant is HFC-32 refrigerant.
15. The refrigeration cycle apparatus of claim 12 , wherein the low-stage refrigerant is a refrigerant mixture of HFO-1123 refrigerant and HFO-1234yf refrigerant.
16. A refrigeration cycle apparatus comprising:
a low-stage refrigeration cycle including a low-stage compressor, a low-stage condenser, a low-stage pressure reducing device, and a low-stage evaporator, and circulating low-stage refrigerant;
a high-stage refrigeration cycle including a high-stage compressor, a high-stage condenser, a high-stage pressure reducing device, and a high-stage evaporator, and circulating high-stage refrigerant;
a cascade condenser configured to exchange heat between the low-stage refrigerant in the low-stage condenser and the high-stage refrigerant in the high-stage evaporator; and
a controller,
the low-stage refrigerant being a refrigerant that undergoes disproportionation,
the low-stage refrigerant being maintained at a pressure lower than a disproportionation pressure at which the low-stage refrigerant undergoes disproportionation,
wherein the low-stage refrigeration cycle includes
a low-stage high-pressure side pressure detecting unit configured to detect a high-pressure side pressure of the low-stage refrigeration cycle, and
a low-stage low-pressure side pressure detecting unit configured to detect a low-pressure side pressure of the low-stage refrigeration cycle, and
wherein the controller is configured to control the high-pressure side pressure, detected by the low-stage high-pressure side pressure detecting unit, to be close to a geometric mean of the disproportionation pressure of the low-stage refrigerant and the low-pressure side pressure detected by the low-stage low-pressure side pressure detecting unit, thereby maintaining the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
17. A refrigeration cycle apparatus comprising:
a low-stage refrigeration cycle including a low-stage compressor, a low-stage condenser, a low-stage pressure reducing device, and a low-stage evaporator, and circulating low-stage refrigerant;
a high-stage refrigeration cycle including a high-stage compressor, a high-stage condenser, a high-stage pressure reducing device, and a high-stage evaporator, and circulating high-stage refrigerant;
a cascade condenser configured to exchange heat between the low-stage refrigerant in the low-stage condenser and the high-stage refrigerant in the high-stage evaporator; and
a controller,
the low-stage refrigerant being a refrigerant that undergoes disproportionation,
the low-stage refrigerant being maintained at a pressure lower than a disproportionation pressure at which the low-stage refrigerant undergoes disproportionation,
wherein the low-stage refrigeration cycle includes
a check valve provided in a passage communicating between the low-stage compressor and the low-stage condenser, and
a valve provided in a passage communicating between the low-stage liquid receiver and the low-stage pressure reducing device, and
wherein the controller is configured to maintain a state of operating of the low-stage compressor while closing the valve and then stop the low-stage compressor to cool the low-stage refrigerant between the check valve and the valve, thereby maintaining the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
18. The refrigeration cycle apparatus of claim 17 , wherein the controller is configured to maintain, when the high-stage compressor is stopped, the state of operating of the low-stage compressor while closing the valve and then stop the low-stage compressor to maintain the low-stage refrigerant at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
19. The refrigeration cycle apparatus of claim 8 , wherein a total capacity of components providing communication between the check valve and the valve is greater than a maximum volume of the low-stage refrigerant in a liquid state at a pressure lower than the disproportionation pressure of the low-stage refrigerant.
20. A method for controlling a refrigeration cycle apparatus including: a low-stage refrigeration cycle including a low-stage compressor, a low-stage condenser, a low-stage pressure reducing device, and a low-stage evaporator, and circulating low-stage refrigerant; a high-stage refrigeration cycle including a high-stage compressor, a high-stage condenser, a high-stage pressure reducing device, and a high-stage evaporator, and circulating high-stage refrigerant; and a cascade condenser configured to exchange heat between the low-stage refrigerant in the low-stage condenser and the high-stage refrigerant in the high-stage evaporator, the low-stage refrigerant being a refrigerant that undergoes disproportionation, the method comprising
maintaining the low-stage refrigerant at a pressure lower than a disproportionation pressure at which the low-stage refrigerant undergoes disproportionation.