The LOGAS hot gas defrost system.

The paper describes the development of a new hot gas defrost system for central type, dual compression stage, low NH3 inventory refrigeration systems for refrigerated storage facilities and other applications. Conventional hot gas defrost in ammonia refrigeration systems designed with focus on low refrigerant inventory require a refrigerant reservoir that can accommodate the condensate returning from the evaporators during defrost. The LOGAS defrost system eliminates this by employing a phase change defrost fluid that is capable of utilizing a range of heat sources including the glycol loop commonly used for subfloor heating. The paper describes the laboratory test rig and the defrost test results compiled during a series of hot gas defrost tests. Using an existing system as the basis for the calculation example, the paper further details the refrigerant inventory reductions that are possible by implementing the LOGAS defrost system in combination with a new intercooler design that replaces the conventional closed coil flash intercooler. The paper further describes specific refrigerant inventories in kg/kW for more than ten existing, central type, dual compression stage, low refrigerant inventory refrigeration systems constructed in Australia between 2012/13 and 2018. The potential for further NH3 inventory reductions through implementation of LOGAS defrost in these systems is discussed as are the recorded energy performances over a number of years.