Patent ID: 8011192

Claim:
A method for defrosting an evaporator in a refrigeration circuit for circulating a CO2 refrigerant in a predetermined flow direction, the refrigeration circuit comprising in flow direction a compressor unit to compress the CO2 refrigerant to a high-pressure hot CO2 gas, a heat-rejecting heat exchanger, an expansion device and an evaporator having a plurality of fins, wherein the evaporator comprises at least two refrigerant conduits for receiving the CO2 refrigerant at a low-pressure during a cooling mode, at least one of the refrigerant conduits being a high-strength refrigerant conduit capable of receiving the high-pressure hot CO2 gas from a hot gas CO2 line having a defroster valve during a defrost operation, and at least one of the refrigerant conduits being a lower-strength refrigerant conduit having a strength lower than the high-strength refrigerant conduit, the lower-strength refrigerant conduit not being capable of receiving the high-pressure hot CO2 gas during the defrost operation, and the refrigeration circuit further comprises: a liquid line having a liquid feed valve and leading to the evaporator; an expansion device positioned after the liquid feed valve and before the first refrigeration conduit in flow direction; an entrance bridge connecting the liquid line to the hot gas CO2 line before the refrigerant conduits, the entrance bridge comprising an entrance valve; and wherein the method comprises the following steps: (a) operating the refrigeration circuit in the cooling mode where the CO2 refrigerant exiting the heat-rejecting heat exchanger flows through the expansion device and through both refrigerant conduits of the evaporator and towards the compressor unit; (b) terminating the cooling mode by interrupting the flow of the refrigerant exiting the heat-rejecting heat exchanger into the evaporator and closing the liquid feed valve between the compressor unit and the evaporator; and (c) initiating the defrost operation by directing the high-pressure hot CO2 gas refrigerant through only the high-strength refrigerant conduit(s) of the evaporator for defrosting substantially all of the fins on the evaporator.