US Patent 7143594 Control method for operating a refrigeration system

A method of controlling a heating cycle of a refrigeration system is provided that includes a refrigerant circuit. The refrigerant circuit includes a compressor having a suction port and an outlet having a discharge port with a hot gas compressor discharge line, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant and an expansion valve. The method includes using refrigerant from the hot gas compressor discharge line to heat the evaporator during a heating cycle, detecting periodically a discharge superheat of the refrigerant leaving the outlet of the compressor, producing a control signal representing a difference between the detected discharge superheat and a minimum discharge superheat setpoint, adjusting the flow rate of the refrigerant to the suction port of the compressor according to the control signal so as to maintain the discharge superheat of the refrigerant at the outlet of the compressor substantially at the minimum discharge superheat setpoint.