This paper describes the development of a new hot gas defrost system primarily intended for central-type, dual-compression-stage, low-NH^inventory refrigeration systems for refrigerated storage facilities and other applications. The defrost concept described may also be considered for transcritical CO2 refrigeration systems and unitary low-charge NH3 plants of the packaged type. In these systems, the defrost method of choice is often electric due to difficulties associated with accommodating the refrigerant condensate returning to the package [s] during defrost. Conventional hot gas defrost in ammonia refrigeration systems, designed for low refrigerant inventory, requires a refrigerant reservoir that can accommodate the condensate returning from the evaporators during defrost. The LOGAS defrost system eliminates this requirement by employing a phase-change defrost fluid that utilizes several heat sources, including the glycol loop commonly used for subfloor heating in refrigerated warehouses.
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