Reverse flow defrost apparatus and method

Abstract

The present invention provides a closed loop vapor cycle refrigeration system that includes a compressor, a condenser, an evaporator system having at least two parallel evaporator coils, means for discharging the compressed gas refrigerant into the outlet ends of each of the parallel evaporator coils and a flow control means coupled to the inlet end of each of the parallel evaporator coils. In an embodiment, a flow control valve is used as the flow control means. The flow control valves are independently controlled by a control circuit. During the defrost cycle, the control circuit closes each flow control valve when the temperature at the inlet end of its associated evaporator coil reaches or exceeds a preset value to ensure that no gas refrigerant passes from its associated evaporator coil to other elements of the refrigeration system during the defrost cycle. In another embodiment of the flow control means, a check valve, serially coupled with a velocity pressure drop device, is placed at the inlet end of each of the parallel evaporator coils to ensure that the inlet end of each of the parallel evaporator coils remains open so long as the compressed gas is discharged into their associated evaporator coils.