Patent ID: 8578722

Claim:
A method for operating a closed circuit vapor compression refrigeration system containing a charge of refrigerant in an expansion process with at least two pressure level stages, the method comprising: providing the closed circuit vapor compression refrigeration system having a high pressure side, an intermediate pressure level, and a low pressure side, the system further including: a compressor; a heat rejector; a first heat absorber; a second heat absorber arranged in parallel with the first heat absorber; a first variable expansion member upstream of the first heat absorber and a second variable expansion member upstream of the second heat absorber; an intermediate pressure receiver; a level detector configured to measure a liquid level in the intermediate pressure receiver; a third expansion member; and a control unit for controlling the first variable expansion member and the second variable expansion member, wherein the control unit is coupled to a plurality of sensors disposed along the system; and controlling flow of the refrigerant through the first variable expansion member and the second variable expansion member in a coordinated fashion with the control unit to maintain a control parameter within a set range, and buffer any surplus charge, resulting from the controlling on the low pressure side of the system; wherein the control parameter is the liquid level measured by the liquid level detector, and wherein a pressure of the intermediate pressure receiver and the high pressure side is controlled by the third expansion member.