Cascade refrigeration system

Abstract

Provided is a cascade refrigeration system capable of suppressing a decrease in heating performance due to a rapid startup operation. The cascade refrigeration system includes: a high-order side refrigerant circuit (2) through which a high-order side refrigerant circulates; a low-order side refrigerant circuit (3) through which a low-order side refrigerant circulates, the low-order refrigerant circuit (3) including a first circulation path (23) that performs heat-exchange with the high-order side refrigerant in a cascade heat exchanger (13), and a second circulation path (26) that performs heat-exchange with a heat medium in a low-order side heat exchanger (24); and a heat medium circuit (4) through which a heat medium circulates, the heat medium exchanging heat with the high-order side refrigerant in the high-order side heat exchanger (11) and exchanging heat with the low-order side refrigerant in the low-order side heat exchanger (24). The heat medium circuit (4) includes: a first heat medium circulation path (35) in which the heat medium circulates through the high-order side heat exchanger (11) and the low-order side heat exchanger (24); and a second heat medium circulation path (36) in which the heat medium circulates through the high-order side heat exchanger (11).

1 . A cascade refrigeration system comprising:
 a high-order side refrigerant circuit configured such that a high-order side compressor, a high-order side heat exchanger, a high-order side pressure reduction mechanism, and a cascade heat exchanger are sequentially connected via refrigerant pipes to circulate a high-order side refrigerant through the high-order side refrigerant circuit;   a low-order side refrigerant circuit including a first circulation path and a second circulation path,
 the first circulation path being configured such that a low-order side compressor, the cascade heat exchanger, a low-order side first pressure reduction mechanism, and a heat-source side heat exchanger are sequentially connected via refrigerant pipes to circulate a low-order side refrigerant through the first circulation path, 
 the second circulation path being configured such that a portion of the first circulation path between the low-order side compressor and the cascade heat exchanger is connected to a portion of the first circulation path between the low-order side first pressure reduction mechanism and the heat-source side heat exchanger via refrigerant pipes including a low-order side heat exchanger and a low-order side second pressure reduction mechanism such that the low-order side compressor, the low-order side heat exchanger, the low-order side second pressure reduction mechanism, and the heat-source side heat exchanger are sequentially connected via the refrigerant pipes to circulate the low-order side refrigerant through the second circulation path; 
   a heat medium circuit including a first heat medium circulation path and a second heat medium circulation path,
 the first heat medium circulation path being configured such that a first circulating pump, a use side heat exchanger, the low-order side heat exchanger, and the high-order side heat exchanger are sequentially connected via pipes to circulate a heat medium through the first heat medium circulation path such that the high-order side refrigerant exchanges heat with the heat medium in the high-order side heat exchanger, and the low-order side refrigerant exchanges heat with the heat medium in the low-order side heat exchanger, 
 the second heat medium circulation path including a first bypass path connecting a portion of the first heat medium circulation path between the use side heat exchanger and the low-order side heat exchanger to a portion of the first heat medium circulation path between the low-order side heat exchanger and the high-order side heat exchanger such that the first circulating pump, the use side heat exchanger, the first bypass path, and the high-order side heat exchanger are sequentially connected via pipes to circulate the heat medium through the second heat medium circulation path, 
   the high-order side refrigerant and the low-order side refrigerant exchanging heat with each other in the cascade heat exchanger;   a first switching unit configured to switch the heat medium circuit between a state where the heat medium flows through the first heat medium circulation path and a state where the heat medium flows through the second heat medium circulation path; and   a control unit configured to control the high-order side refrigerant circuit, the low-order side refrigerant circuit, and the heat medium circuit.   
     
     
         2 . The cascade refrigeration system according to  claim 1 , wherein
 at startup of the cascade refrigeration system, the control unit starts the high-order side compressor, the low-order side compressor, and the first circulating pump and switches the first switching unit to cause the heat medium to flow through the first heat medium circulation path.   
     
     
         3 . The cascade refrigeration system according to  claim 2 , wherein
 the control unit switches the first switching unit to cause the heat medium to flow through the second heat medium circulation path in a case where the heat medium passing through the use side heat exchanger has a temperature exceeding a first predetermined temperature or in a case where a difference between the temperature of the heat medium passing through the use side heat exchanger and a refrigerant condensing temperature in the low-order side heat exchanger of the low-order side refrigerant circuit is less than a second predetermined temperature.   
     
     
         4 . The cascade refrigeration system according to  claim 1 , comprising:
 a four-way valve connected to a discharge side of the low-order side compressor in the low-order side refrigerant circuit, the four-way valve being configured to switch between a state where the low-order side refrigerant discharged from the low-order side compressor flows toward the cascade heat exchanger side and the low-order side heat exchanger side and a state where the low-order side refrigerant discharged from the low-order side compressor flows toward the heat-source side heat exchanger side.   
     
     
         5 . The cascade refrigeration system according to  claim 4 , wherein
 the low-order side heat exchanger includes a first heat accumulation unit including a heat accumulation material.   
     
     
         6 . The cascade refrigeration system according to  claim 5 , wherein
 when the heat accumulation material has a temperature equal to or more than a predetermined temperature, the control unit switches the four-way valve to the heat-source side heat exchanger side and performs a defrosting operation using heat accumulated in the heat accumulation material.   
     
     
         7 . The cascade refrigeration system according to  claim 1 , comprising:
 a third heat medium circulation path provided in the heat medium circuit and including a second bypass path connected in parallel to the first bypass path, the second bypass path including a check valve, a second circulating pump, and a second heat accumulation unit including a heat accumulation material, the third heat medium circulation path being configured such that the second circulating pump, the check valve, the low-order side heat exchanger, and the second heat accumulation unit are sequentially connected via refrigerant pipes to circulate the heat medium through the third heat medium circulation path;   a second switching unit configured to switch the heat medium circuit between a state where the heat medium flows through the first heat medium circulation path and a state where the heat medium flows through the third heat medium circulation path; and   a four-way valve connected to a discharge side of the low-order side compressor in the low-order side refrigerant circuit, the four-way valve being configured to switch between a state where the low-order side refrigerant discharged from the low-order side compressor flows toward the cascade heat exchanger side and the low-order side heat exchanger side and a state where the low-order side refrigerant discharged from the low-order side compressor flows toward the heat-source side heat exchanger side.   
     
     
         8 . The cascade refrigeration system according to  claim 7 , wherein
 at startup of the cascade refrigeration system, the control unit starts the high-order side compressor, the low-order side compressor, and the first circulating pump and switches the first switching unit and the second switching unit to cause the heat medium to flow through the first heat medium circulation path.   
     
     
         9 . The cascade refrigeration system according to  claim 8 , wherein
 the control unit switches the first switching unit to cause the heat medium to flow through the second heat medium circulation path and switches the second switching unit to cause the heat medium to flow through the third heat medium circulation path in a case where the heat medium passing through the use side heat exchanger has a temperature exceeding a first predetermined temperature or in a case where a difference between the temperature of the heat medium passing through the use side heat exchanger and a refrigerant condensing temperature in the low-order side heat exchanger of the low-order side refrigerant circuit is less than a second predetermined temperature.   
     
     
         10 . The cascade refrigeration system according to  claim 9 , wherein
 when the heat accumulation material has a temperature equal to or more than a predetermined temperature, the control unit switches the four-way valve to the heat-source side heat exchanger side and performs a defrosting operation using heat accumulated in the heat accumulation material.