Refrigeration cycle system

A refrigeration cycle system comprising:

• a first cycle;
• and
• a second cycle,
• wherein
• the first cycle is connected with a first compressor, a cascade heat exchanger, a first expansion unit, and a first heat exchanger, has a carbon dioxide refrigerant circulating through the first cycle, and includes a first flow path that connects the first compressor to the cascade heat exchanger, a second flow path that connects the cascade heat exchanger to the first expansion unit, a third flow path that connects the first heat exchanger to the first compressor, and a bypass flow path that connects at least one of the first flow path and the second flow path to the third flow path,
• the second cycle includes the cascade heat exchanger, and has a heat medium different from the carbon dioxide refrigerant circulating through the second cycle, and
• in a case of using the cascade heat exchanger as a radiator of the first cycle and a heat sink of the second cycle, the first compressor of the first cycle is started after a flow of the heat medium generates in the cascade heat exchanger in the second cycle,
• wherein the bypass flow path includes an on-off valve that can be opened and closed, and
• in the case of using the cascade heat exchanger as the radiator of the first cycle and the heat sink of the second cycle, the on-off valve is in an open state from after the heat medium starts to flow in the cascade heat exchanger in the second cycle until the first compressor is started, and the on-off valve is switched to a close state when or after the first compressor is started.