Critically Charged Systems

Since the advent of the mandated Process Safety Management program (PSM) the industrial refrigeration sector has been faced with attempts to maintain lower refrigerant charges (re: inventories of refrigerant used in the system).  To date, most of the efforts expended focus on keeping the ammonia refrigerant charge under 10,000 pounds.  To a degree, this has largely centered around minimizing the quantity or use of gravity-flooded air-cooling evaporators or flooded shell and tube heat chillers.  While these methods will drastically reduce the total refrigerant charge, other methods can be applicable.  These typically involve re-thinking the basic premise for the use of a refrigerant and the application of specific sub-systems that are used in ammonia refrigeration systems.

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I often see people interested in heat recovery asking questions about desuperheating.  This mode of heat recovery is based on circulating a fluid such as water through a heat exchanger to aid in transferring heat from one location to another.  One of the major issues with utilizing the superheat of the discharge gas from a refrigeration systems is; there is not a lot of available heat!  The available superheat in the discharge gas from a compressor is only a small percentage of the the total available heat energy.

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