The heat pump moves heat from a low temperature source to a high temperature source. The process of elevating low temperature heat to over 100 degrees Fahrenheit and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat transfer medium, which circulates within the heat pump. The cycle starts as the cold liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low temperature source (liquid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed. The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to over 160 F. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the home at about 100 F. The refrigerant changes back to a liquid when it uses its heat. The liquid is cooled as it passes through an expansion valve and begins the process again. To air condition, the flow is reversed.

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