Refrigeration cycle device and method of controlling the same

A refrigeration cycle device comprising:

• a compressor that compresses a combustible refrigerant;
• a condenser that condenses the combustible refrigerant compressed by the compressor;
• a heat exchanger that subcools the combustible refrigerant discharged from the condenser;
• an expansion valve that expands the combustible refrigerant subcooled by the heat exchanger;
• an evaporator that evaporates the combustible refrigerant expanded by the expansion valve;
• a bypass pipe that connects an upstream pipe of the compressor to an downstream pipe of the heat exchanger;
• a bypass expansion valve provided on the bypass pipe to expand a secondary stream that diverges from a primary stream of the combustible refrigerant flowing through the downstream pipe;
• a controller that controls an amount of heat exchange of the heat exchanger in accordance with a temperature or pressure of the combustible refrigerant between the condenser and the expansion valve;
• an evaporator upstream pressure sensor that detects a pressure of a refrigerant in a pipe between an upstream side of the evaporator and a downstream side of the expansion valve;
• an evaporator downstream pressure sensor that detects a pressure of a refrigerant in a pipe between a downstream side of the evaporator and an upstream side of the compressor;
• and
• a superheat degree detection section that detects a superheat degree of the combustible refrigerant at a downstream side of the heat exchanger in the bypass pipe,
• wherein the controller includes a superheat degree control section and is configured to:
• acquire a detected pressure value from the evaporator upstream pressure sensor and a detected pressure value from the evaporator downstream pressure sensor;
• calculate an evaporator pressure difference wherein the evaporator pressure difference is the difference between the detected pressure value from the evaporator upstream pressure sensor and the detected pressure value from the evaporator downstream pressure sensor;
• set a superheat control target value based on the calculated evaporator pressure difference;
• and
• control the opening of the bypass expansion valve such that the superheat degree detected by the superheat degree detection section becomes the superheat control target value.