Refrigeration apparatus

A refrigeration apparatus comprising:

• a high-temperature side circulation circuit that forms a refrigerant circuit in which a high-temperature side compressor, a high-temperature side condenser, a high-temperature side expansion device and a high-temperature side evaporator are connected by a pipe, wherein the refrigerant circuit allows a high-temperature side refrigerant to circulate therethrough, the high-temperature side refrigerant has a carbon-carbon multiple bond in its molecular structure, and the high-temperature side compressor has a variable capacity and is configured to discharge the high-temperature side refrigerant;
• a low-temperature side circulation circuit that forms a refrigerant circuit in which a low-temperature side compressor, a low-temperature side condenser, a low-temperature side expansion device and a low-temperature side evaporator are connected by a pipe, wherein the refrigerant circuit allows a low-temperature side refrigerant to circulate therethrough, the low-temperature side refrigerant contains carbon dioxide, and the low-temperature side compressor is configured to discharge the low-temperature side refrigerant;
• a cascade capacitor formed of the high-temperature side evaporator and the low-temperature side condenser and configured to cause heat exchange between the high-temperature side refrigerant and the low-temperature side refrigerant;
• a pressure detector for detecting a pressure on a suction side of the high-temperature side compressor;
• and
• a controller for controlling an evaporating temperature of the high-temperature side refrigerant in the high-temperature side evaporator on a basis of the pressure according to detection by the pressure detector such that a pressure inside the high-temperature side circulation circuit does not have a negative pressure with respect to a pressure outside the circuit, wherein the controller is configured to
• activate the high-temperature side compressor at a minimum operation frequency, and
• reduce the pressure inside the high-temperature side circulation circuit until the pressure inside the high-temperature side circulation circuit is in a range where the evaporating temperature of the high-pressure side evaporator is at least at a target evaporating temperature so that a pressure inside the low-pressure side is prevented from decreasing.