How does a geothermal heat pump work?

Heat pumps don’t create heat. They take existing heat and move it. Anyone with a refrigerator has witnessed the operation of a heat pump. Refrigerators collect heat from the unit’s interior and moves it to the exterior for cooling purposes. Unlike a refrigerator, a heat pump can reverse itself. An air-source heat pump, for example, can extract heat from outdoor air and pump it indoors for heating purposes.

A geothermal heat pump works the same way, except that its heat source is the warmth of the earth. The process of elevating low-temperature heat to over 100° F 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 that passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source. Fluid from the gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to more than 180° F. The hot gas then circulates through a refrigerant to air heat exchanger where heat is removed and pumped into the building at about 100° F. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system’s flow is reversed.