A geothermal system is a type of heating and cooling system that uses the constant temperature of the Earth to heat and cool a building. These systems consist of a network of underground pipes, called a ground loop, which is used to transfer heat to or from the building, depending on the season.

In the winter, a geothermal system uses the ground loop to extract heat from the Earth and bring it into the building. The heat is then distributed throughout the building using a forced-air or hydronic system. In the summer, the system works in reverse, using the ground loop to transfer heat from the building to the Earth, effectively cooling the building.

In simple terms, the geothermal loop "tempers" the condensor or the evaporator of a heat pump. For example, if the ambient temperature is 95 degrees F in May, an airside system would require the condenser to operate at around 100 degrees (assuming a 5 degree approach).

However, a condenser attached to a ground loop will operate near the temperature of the ground loop, which might be 60 degrees F. Naturally, this will make cooling more efficient, as it is easier to generate cool air from a cool source.