36 ASHRAE Journal ashrae.org August 2011 E arly practitioners of industrial refrigeration systems found they could increase the capacity of evaporators by supplying excess liquid refrigerant to the unit (overfeeding). In evaporators conigured to operate with overfeed, the quantity of liquid refrigerant supplied is greater than the minimum amount required to meet the cooling loads as it undergoes the phase change from liquid to vapor. In this case, a mixture of low temperature liquid and vapor leaves the evaporator and returns to a vessel designed to separate the liquid from the vapor prior to the vapor being recompressed. Within limits, the cooling capacity of an overfed evaporator increases due to the tendency for more of the evapora- tor’s interior surfaces being wetted with saturated liquid refrigerant. 1,2 Figure 1 shows a simple liquid overfed system typical of those designed and used today for large built-up industrial refrigeration systems. In a mechanically pumped overfeed system, a centrifugal pump draws low temperature saturated liquid refrig- erant from a vessel referred to as a “pumped recirculator,” “pumped ac- cumulator,” “recirculator,” or “low- pressure receiver” and raises the pres- sure of the liquid for delivery to one or more evaporators having a common refrigerant temperature requirement. Once pressurized by the pump, the saturated liquid becomes subcooled as it leaves the pump discharge and enters the “recirculated liquid supply line.” As individual evaporators call for cooling, local controls simply open a liquid feed solenoid valve, which al- lows low temperature pressurized liq- uid from the liquid supply line to flow into the evaporator. Manually adjust- able hand-expansion (i.e., metering) valves are used at each evaporator as a means of balancing the supply of About the Authors Todd B. Jekel, Ph.D., P.E., is assistant director and Douglas T. Reindl, Ph.D., P.E., is director of the Industrial Refrigeration Consortium and professor at the University of Wisconsin, Madison, Wis. By Todd B. Jekel, Ph.D., P.E., Member ASHRAE, and Douglas T. Reindl, Ph.D., P.E., Fellow ASHRAE Liquid Refrigerant Pumping In Industrial Refrigeration Systems TECHNICAL FEATURE This article was published in ASHRAE Journal, August 2011. Copyright 2011 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.