Patent ID: 8096141

Claim:
A method of controlling a chiller that includes a compressor, a condenser, an expansion valve and an evaporator, wherein the expansion valve is adjustable between a closed position and open position, and the chiller circulates a refrigerant at an actual mass flow rate that may vary with a suction pressure between the expansion valve and a suction inlet of the compressor, a discharge pressure between the expansion valve and a discharge outlet of the compressor, and a suction temperature between the evaporator and the suction inlet of the compressor, wherein the refrigerant in the evaporator becomes saturated at a saturation temperature and a saturation pressure, the method comprising: sensing the suction pressure; sensing the suction temperature; determining a target superheat, wherein the target superheat is a desired difference between the saturation temperature and the suction temperature; determining a target mass flow rate through the evaporator that could achieve the target superheat, wherein the target mass flow rate is at least partially determined based on the suction pressure; determining an estimate of the actual mass flow rate through the evaporator; and adjusting the expansion valve to help maintain the actual mass flow rate at the target mass flow rate.