Cascade refrigeration system

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.