Two-stage compression refrigeration cycle device

A two-stage compression refrigeration cycle device, comprising:

• a low-pressure side compression mechanism which compresses a low-pressure refrigerant into an intermediate-pressure refrigerant and discharges the compressed refrigerant;
• a high-pressure side compression mechanism which compresses the intermediate-pressure refrigerant discharged from the low-pressure side compression mechanism into a high-pressure refrigerant and discharges the compressed refrigerant;
• a radiator in which the high-pressure refrigerant discharged from the high-pressure side compression mechanism exchanges heat with outside air to radiate heat from the high-pressure refrigerant;
• an intermediate-pressure expansion valve which decompresses and expands the high-pressure refrigerant flowing from the radiator into the intermediate-pressure refrigerant to cause the intermediate-pressure refrigerant to flow to a suction side of the high-pressure side compression mechanism;
• a low-pressure expansion valve which decompresses and expands the high-pressure refrigerant flowing from the radiator into the low-pressure refrigerant;
• an evaporator in which the low-pressure refrigerant decompressed and expanded by the low-pressure expansion valve is evaporated by exchanging heat with air blown into a cooling space, to cause the evaporated refrigerant to flow to a suction side of the low-pressure side compression mechanism;
• and
• a controller including a CPU and a memory, the controller being in communication with both the low-pressure side compression mechanism and the high-pressure side compression mechanism, wherein
• the controller is programmed to intermittently control the low-pressure side compression mechanism and the high-pressure side compression mechanism such that a temperature of the fluid exchanging heat with the low-pressure refrigerant at the evaporator is adjusted to approach a target temperature, and,
• the controller is programmed, such that when the low-pressure side compression mechanism and the high-pressure side compression mechanism are to be restarted after both of the compression mechanisms are stopped:
• to calculate a low-pressure side pressure difference by subtracting a low-pressure suction side refrigerant pressure from a low-pressure discharge side refrigerant pressure of the low-pressure side compression mechanism,
• to calculate a high-pressure side pressure difference by subtracting the low-pressure discharge side refrigerant pressure from a high-pressure discharge side refrigerant pressure of the high-pressure side compression mechanism,
• to compare the low-pressure side pressure difference to the high-pressure side pressure difference,
• to first start up one of the low-pressure side compression mechanism and the high-pressure side compression mechanism based on the comparison of the low-pressure side pressure difference to the high-pressure side pressure difference, the one compression mechanism being the low-pressure side compression mechanism when the low-pressure side pressure difference is greater than the high-pressure side pressure difference, the one compression mechanism being the high-pressure side compression mechanism when the high-pressure side pressure difference is greater than the low-pressure side pressure difference, and
• to then start up the other of the low-pressure side compression mechanism and the high-pressure side compression mechanism by reducing the greater one of the low-pressure side compression difference and the high-pressure side compression difference.