Refrigerating apparatus and control device for refrigerating machine

A refrigerating apparatus comprising:

• a centrifugal compressor;
• a suction capacity control mechanism and a discharge capacity control mechanism configured to control a capacity of the compressor by changing opening degrees of the suction capacity control mechanism and the discharge capacity control mechanism;
• and
• a controller configured to compare a compressor-specific surge curve with an isentropic head to perform
• rotational speed control of the compressor,
• rotational speed adjustment control of the compressor in order to avoid surge, and
• emergency shutdown control of the compressor upon detection of surge,
• the controller being configured to determine a surge abnormality and perform the emergency shutdown control to stop the compressor when a sum of time in which the isentropic head surpasses the compressor-specific surge curve exceeds a preset time in a most recent fixed time period,
• the compressor-specific surge curve being stored in the controller, and the compressor-specific surge curve being defined by an actual rotational speed of the compressor, the opening degree of the suction capacity control mechanism, and the opening degree of the discharge capacity control mechanism, and
• the isentropic head being calculated based on a suction pressure, a discharge pressure, and a suction superheat during operation,
• the suction superheat being based on a suction temperature during operation.