Modifications to basic defrost schemes add yet another layer of complexity
off cycle defrost
It is inevitable that refrigeration systems operating with saturated suction temperatures below freezing will eventually experience an accumulation of frost on the evaporator tubes and fins. The frost serves as an insulator between the heat to be transferred from the space and the refrigerant, resulting in a reduction in evaporator efficiency. Therefore, equipment manufacturers must employ certain techniques to periodically remove this frost from the coil surface.
Methods for defrost can include, but are not limited to off cycle or air defrost, electric and gas (which will be addressed in Part II in HPAC‘s March issue). Also, modifications to these basic defrost schemes add yet another layer of complexity for field service personnel. When properly setup, all methods will achieve the same desired result of melting the frost accumulation. If the defrost cycle is not set up correctly, the resulting incomplete defrosts (and reduction in evaporator efficiency) can cause higher than desired temperature in the refrigerated space, refrigerant floodback or oil logging issues. Read more
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June 20, 2021