Cascade refrigeration system

Abstract

There is provided a cascade refrigeration system that promptly performs a start-up operation and suppresses a decrease in reliability of a compressor and suppresses an increase in power consumption. The cascade refrigeration system includes: a high-side refrigerant circuit ( 2 ) having a high-side first circulation path ( 17 ) containing a high-side compressor ( 10 ), a high-side heat exchanger ( 11 ), a high-side expansion valve ( 12 ), and a cascade heat exchanger ( 13 ) where a high-side refrigerant and a low-side refrigerant exchange heat, sequentially connected; and a low-side refrigerant circuit ( 3 ) containing a low-side compressor ( 20 ), the cascade heat exchanger ( 13 ), a low-side expansion valve ( 21 ), and a heat source-side heat exchanger ( 22 ) sequentially connected, in which the high-side refrigerant circuit ( 2 ) includes: a high-side second circulation path ( 18 ) in which a discharge side and a suction side of the high-side compressor ( 10 ) are connected by a high-side bypass path ( 15 ) and through which the high-side refrigerant discharged from the high-side compressor ( 10 ) circulates to the suction side of the high-side compressor ( 10 ) through the high-side bypass path ( 15 ); and a high-side opening and closing valve ( 16 ) performing switching between the high-side first circulation path ( 17 ) and the high-side second circulation path ( 18 ).

1 . A cascade refrigeration system comprising:
 a high-side refrigerant circuit containing a high-side compressor, a high-side heat exchanger configured to exchange heat with a heating medium, a high-side expansion mechanism, and a cascade heat exchanger sequentially connected by a refrigerant pipe and having a high-side first circulation path through which a high-side refrigerant circulates;   a low-side refrigerant circuit containing a low-side compressor, the cascade heat exchanger, a low-side expansion mechanism, and a heat-side heat exchanger sequentially connected by a refrigerant pipe, the low-side refrigerant circuit through which a low-side refrigerant circulates; and   a controller configured to control the high-side refrigerant circuit and the low-side refrigerant circuit, wherein   the high-side refrigerant and the low-side refrigerant exchange heat in the cascade heat exchanger, and   the high-side refrigerant circuit includes: a high-side second circulation path in which a discharge side and a suction side of the high-side compressor are connected by a high-side bypass path and the high-side refrigerant discharged from the high-side compressor circulates to the suction side of the high-side compressor through the high-side bypass path; and a high-side switching device configured to switch a circulation path such that the high-side refrigerant discharged from the high-side compressor circulates through the high-side first circulation path or the high-side second circulation path.   
     
     
         2 . The cascade refrigeration system according to  claim 1 , wherein
 the controller is configured to, in activating the cascade refrigeration system, activate the high-side compressor and control the high-side switching device such that the high-side refrigerant circulates through the high-side second circulation path,   when a discharge medium temperature of the high-side refrigerant exceeds a predetermined value, to switch the high-side switching device to the high-side first circulation path to circulate the high-side refrigerant through the high-side first circulation path, and   when the discharge medium temperature of the high-side refrigerant exceeds a temperature of the heating medium, to activate the low-side compressor.   
     
     
         3 . A cascade refrigeration system comprising:
 a high-side refrigerant circuit containing a high-side compressor, a high-side heat exchanger configured to exchange heat with a heating medium, a high-side expansion mechanism, and a cascade heat exchanger sequentially connected by a refrigerant pipe, the high-side refrigerant circuit through which a high-side refrigerant circulates;   a low-side refrigerant circuit containing a low-side compressor, the cascade heat exchanger, a low-side expansion mechanism, and a heat source-side heat exchanger sequentially connected by a refrigerant pipe and having a low-side first circulation path through which a low-side refrigerant circulates; and   a controller configured to control the high-side refrigerant circuit and the low-side refrigerant circuit, wherein   the high-side refrigerant and the low-side refrigerant exchange heat in the cascade heat exchanger, and   the low-side refrigerant circuit includes: a low-side second circulation path in which a discharge side and a suction side of the low-side compressor are connected by a low-side bypass path and the low-side refrigerant discharged from the low-side compressor circulates to the suction side of the low-side compressor through the low-side bypass path; and a low-side switching device configured to switch a circulation path such that the low-side refrigerant discharged from the low-side compressor circulates through the low-side first circulation path or the low-side second circulation path.   
     
     
         4 . The cascade refrigeration system according to  claim 3 , wherein the controller is configured to, in activating the cascade refrigeration system, activate the high-side compressor and the low-side compressor and control the low-side switching device such that the low-side refrigerant circulates through the low-side second circulation path. 
     
     
         5 . The cascade refrigeration system according to  claim 4 , wherein the controller is configured to, when a discharge medium temperature of the high-side refrigerant exceeds a temperature of the heating medium, switch the low-side switching device to the low-side first circulation path to circulate the low-side refrigerant through the low-side first circulation path. 
     
     
         6 . A cascade refrigeration system comprising:
 a high-side refrigerant circuit containing a high-side compressor, a high-side heat exchanger configured to exchange heat with a heating medium, a high-side expansion mechanism, and a cascade heat exchanger sequentially connected by a refrigerant pipe and having a high-side first circulation path through which a high-side refrigerant circulates;   a low-side refrigerant circuit containing a low-side compressor, the cascade heat exchanger, a low-side expansion mechanism, and a heat source-side heat exchanger sequentially connected by a refrigerant pipe and having a low-side first circulation path through which a low-side refrigerant circulates; and   a controller configured to control the high-side refrigerant circuit and the low-side refrigerant circuit, wherein   the high-side refrigerant and the low-side refrigerant exchange heat in the cascade heat exchanger,   the high-side refrigerant circuit includes: a high-side second circulation path in which a discharge side and a suction side of the high-side compressor are connected by a high-side bypass path and the high-side refrigerant discharged from the high-side compressor circulates to the suction side of the high-side compressor through the high-side bypass path; and a high-side switching device configured to switch a circulation path such that the high-side refrigerant discharged from the high-side compressor circulates through the high-side first circulation path or the high-side second circulation path, and   the low-side refrigerant circuit includes: a low-side second circulation path in which a discharge side and a suction side of the low-side compressor are connected by a low-side bypass path and the low-side refrigerant discharged from the low-side compressor circulates to the suction side of the low-side compressor through the low-side bypass path; and a low-side switching device configured to switch a circulation path such that the low-side refrigerant discharged from the low-side compressor circulates through the low-side first circulation path or the low-side second circulation path.   
     
     
         7 . The cascade refrigeration system according to  claim 6 , wherein
 the controller is configured to, in activating the cascade refrigeration system, activate the high-side compressor and the low-side compressor,   to control the high-side switching device such that the high-side refrigerant circulates through the high-side second circulation path, and   to control the low-side switching device such that the low-side refrigerant circulates through the low-side second circulation path.   
     
     
         8 . The cascade refrigeration system according to  claim 7 , wherein
 the controller is configured to, when a discharge medium temperature of the high-side refrigerant exceeds a predetermined value, switch the high-side switching device to the high-side first circulation path to circulate the high-side refrigerant through the high-side first circulation path, and   when the discharge medium temperature of the high-side refrigerant exceeds a temperature of the heating medium, to switch the low-side switching device to the low-side first circulation path to circulate the low-side refrigerant through the low-side first circulation path.