Patent ID: 7461515
Filing Date: 2008-12-09
Classification: F25B,F25D,Y10T

Abstract:
1. A method for sequentially defrosting each evaporator in a group of evaporators in a refrigeration system having a common compressor suction header and a common high pressure liquid supply header, wherein the system is characterized as having a refrigerant compressor which compresses low pressure vapor to high pressure gas in a high pressure gas header, a condenser which condenses the high pressure gas to high pressure liquid refrigerant available from a common high pressure liquid header, a high pressure gas line connecting the compressor outlet and the condenser inlet, a metering device, a high pressure liquid supply line taking high pressure liquid refrigerant from the condenser outlet to a high pressure liquid header and thence to a high pressure liquid supply valve, thence to a metering device which meters the high pressure liquid refrigerant into a distributor, evaporator coils which receive a mixture of low pressure liquid refrigerant and low pressure vapor from the distributor, an evaporator suction line taking low pressure vapor from the evaporator coils to an evaporator suction line valve and thence to the compressor suction header, a sensor located in the evaporator suction line between the evaporator coils and the evaporator suction line valve, a high pressure gas supply line taking high pressure gas from the high pressure gas header a high pressure gas line to an evaporator high pressure gas valve and, thence to the distributor, wherein the metering device meters high pressure liquid refrigerant into the distributor based on a measurement performed by the sensor, the method comprising the steps of: Step 1. Within each evaporator in the group of evaporators, providing a cross-feed isolation check line between the evaporator suction line and the distributor, wherein each cross-feed line contains a cross-feed isolation check valve adjacent the evaporator suction line, an orifice adjacent the distributor, a liquid injection check valve between the cross-feed isolation check valve and the liquid injection check valve, and a common cross-feed header connecting each cross-feed line at a location between the cross-feed isolation check valve and the liquid injection check valve; Step 2. Within the group of evaporators in the refrigeration mode with the compressors running, selecting an evaporator to be defrosted; Step 3. Shutting off the high pressure liquid supply valve between the high pressure liquid header and the metering device; associated with the selected evaporator Step 4. Shutting off the valve in the evaporator suction line associated with the selected evaporator; Step 5. Supplying hot gas refrigerant to the distributor associated with the selected evaporator; Step 6. After the selected evaporator is defrosted, returning the defrosted evaporator to service in refrigeration mode as follows: Step 7. Repeating steps 1 through 5 for each additional evaporator in the group of evaporators until each evaporator has been defrosted.