System and method for control of a transcritical refrigeration system

A method for a CO2 refrigeration system operable in a subcritical mode and a transcritical mode, the method comprising:

• monitoring, with a valve controller, an outdoor ambient temperature;
• monitoring, with the valve controller, a pressure and a temperature of refrigerant exiting a heat exchanger of the CO2 refrigeration system, the heat exchanger receiving refrigerant discharged from at least one compressor and being operable as a gas cooler when the CO2 refrigeration system is operating in the transcritical mode and as a condenser when the CO2 refrigeration system is operating in the subcritical mode, the first valve being connected between the heat exchanger and a liquid receiver and controlling a flow of the refrigerant from the heat exchanger to the liquid receiver;
• determining, with the valve controller, whether the CO2 refrigeration system is operating in the subcritical mode or in the transcritical mode;
• determining, with the valve controller, a pressure setpoint based on the monitored outdoor ambient temperature when the valve controller determines that the CO2 refrigeration system is operating in the transcritical mode;
• controlling, with the valve controller, a first valve based on a comparison of the determined pressure setpoint and the monitored pressure of the refrigerant exiting the heat exchanger when the valve controller determines that the CO2 refrigeration system is operating in the transcritical mode;
• determining, with the valve controller, a subcooling temperature of the refrigerant based on the monitored pressure and temperature of the refrigerant exiting the heat exchanger when the valve controller determines that the CO2 refrigeration system is operating in the subcritical mode;
• and
• controlling, with the valve controller, the first valve based on a comparison of the calculated subcooling temperature with a predetermined subcooling when the valve controller determines that the CO2 refrigeration system is operating in the subcritical mode.