Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus includes a first circuit, a second circuit, a cascade heat exchanger, and a control unit. The first circuit circulates a first refrigerant. The second circuit circulates a carbon dioxide refrigerant and refrigerating machine oil. The cascade heat exchanger heats carbon dioxide refrigerant with first refrigerant. The second circuit includes a second compressor and a container. The container is provided on suction side of the second compressor. The container stores the carbon dioxide refrigerant and the refrigerating machine oil. The control unit controls the operation of the first circuit so that the temperature or pressure of the carbon dioxide refrigerant and the refrigerating machine oil in the container is equal to or higher than a predetermined temperature or predetermined pressure corresponding to a boundary temperature at which the density of the carbon dioxide refrigerant and the density of the refrigerating machine oil in the container become equal.

1 . A refrigeration cycle apparatus comprising:
 a first circuit that circulates a first refrigerant;   a second circuit that circulates a carbon dioxide refrigerant and refrigerating machine oil a cascade heat exchanger that heats the carbon dioxide refrigerant with the first refrigerant; and   a control unit having processor circuitry,   wherein the second circuit includes
 a second compressor and 
 a container that is provided on a suction side of the second compressor and that stores the carbon dioxide refrigerant and the refrigerating machine oil, and 
   the processor circuitry of the control unit is configured to cause the control unit to control an operation of the first circuit so that a temperature or pressure of the carbon dioxide refrigerant and the refrigerating machine oil in the container is equal to or higher than a predetermined temperature or predetermined pressure corresponding to a boundary temperature at which a density of the carbon dioxide refrigerant and a density of the refrigerating machine oil in the container become equal.   
     
     
         2 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the first circuit includes a first compressor, and   the processor circuitry of the control unit causes the control unit to control a rotational speed of the first compressor in the first circuit so that the temperature or pressure of the carbon dioxide refrigerant and the refrigerating machine oil in the container is equal to or higher than the predetermined temperature or the predetermined pressure.   
     
     
         3 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the control unit is configured to switch operation of the cascade heat exchanger between
 a first mode of operation that heats the carbon dioxide refrigerant with the first refrigerant and 
 a second mode of operation that cools the carbon dioxide refrigerant with the first refrigerant. 
   
     
     
         4 . The refrigeration cycle apparatus according to  claim 2 , wherein
 the control unit is configured to switch operation of the cascade heat exchanger between
 a first mode of operation that heats the carbon dioxide refrigerant with the first refrigerant and 
 a second mode of operation that cools the carbon dioxide refrigerant with the first refrigerant. 
   
     
     
         5 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the second circuit further includes a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the refrigerating machine oil on the suction side of the second compressor.   
     
     
         6 . The refrigeration cycle apparatus according to  claim 2 , wherein
 the second circuit further includes a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the refrigerating machine oil on the suction side of the second compressor.   
     
     
         7 . The refrigeration cycle apparatus according to  claim 3 , wherein
 the second circuit further includes a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the refrigerating machine oil on the suction side of the second compressor.   
     
     
         8 . The refrigeration cycle apparatus according to  claim 4 , wherein
 the second circuit further includes a sensor that measures at least one of the temperature and pressure of the carbon dioxide refrigerant and the refrigerating machine oil on the suction side of the second compressor.   
     
     
         9 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the second circuit further includes
 a suction pipe that connects the suction side of the second compressor to the container, 
 an oil return passage that returns the refrigerating machine oil from a lower portion of the container to the suction pipe, and 
 a valve that is provided in the oil return passage, and 
   the control unit is configured to change an opening degree of the valve on a basis of a degree of superheating of the carbon dioxide refrigerant discharged from the second compressor.   
     
     
         10 . The refrigeration cycle apparatus according to  claim 2 , wherein
 the second circuit further includes
 a suction pipe that connects the suction side of the second compressor to the container, 
 an oil return passage that returns the refrigerating machine oil from a lower portion of the container to the suction pipe, and 
 a valve that is provided in the oil return passage, and 
   the control unit is configured to change an opening degree of the valve on a basis of a degree of superheating of the carbon dioxide refrigerant discharged from the second compressor.   
     
     
         11 . The refrigeration cycle apparatus according to  claim 3 , wherein
 the second circuit further includes
 a suction pipe that connects the suction side of the second compressor to the container, 
 an oil return passage that returns the refrigerating machine oil from a lower portion of the container to the suction pipe, and 
 a valve that is provided in the oil return passage, and 
   the control unit is configured to change an opening degree of the valve on a basis of a degree of superheating of the carbon dioxide refrigerant discharged from the second compressor.   
     
     
         12 . The refrigeration cycle apparatus according to  claim 5 , wherein
 the second circuit further includes
 a suction pipe that connects the suction side of the second compressor to the container, 
 an oil return passage that returns the refrigerating machine oil from a lower portion of the container to the suction pipe, and 
 a valve that is provided in the oil return passage, and 
   the control unit is configured to change an opening degree of the valve on a basis of a degree of superheating of the carbon dioxide refrigerant discharged from the second compressor.   
     
     
         13 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         14 . The refrigeration cycle apparatus according to  claim 2 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         15 . The refrigeration cycle apparatus according to  claim 3 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         16 . The refrigeration cycle apparatus according to  claim 5 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         17 . The refrigeration cycle apparatus according to  claim 6 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         18 . The refrigeration cycle apparatus according to  claim 7 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         19 . The refrigeration cycle apparatus according to  claim 8 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.   
     
     
         20 . The refrigeration cycle apparatus according to  claim 9 , wherein
 the first refrigerant contains R32, R454C, propane, R1234yf, R1234ze, or ammonia.