The Direct exchange geothermal heat pump
A geothermal heat pump or ground source heat pump (GSHP) is a central heating and/or cooling system that pumps heat to or from the ground. It uses the earth as a heat source (in the winter) or a heat sink (in the summer). This design takes advantage of the moderate temperatures in the ground to boost efficiency and reduce the operational costs of heating and cooling systems, and may be combined with solar heating to form a geosolar system with even greater efficiency.
Geothermal heat pumps are also known by a variety of other names, including geoexchange, earth-coupled, earth energy or water-source heat pumps. The engineering and scientific communities prefer the terms "geoexchange" or "ground source heat pumps" because geothermal power traditionally refers to heat originating from deep in the Earth's mantle. Ground source heat pumps harvest a combination of geothermal power and heat from the sun when heating, but work against these heat sources when used for air conditioning.
The Direct exchange geothermal heat pump is the oldest type of geothermal heat pump technology. It is also the simplest and easiest to understand. The ground-coupling is achieved through a single loop circulating refrigerant in direct thermal contact with the ground (as opposed to a refrigerant loop and a water loop). The refrigerant leaves the heat pump appliance cabinet, circulates through a loop of copper tube buried underground, and exchanges heat with the ground before returning to the pump. The name "direct exchange" refers to heat transfer between the refrigerant and the ground without the use of an intermediate fluid. There is no direct interaction between the fluid and the earth; only heat transfer through the pipe wall. Direct exchange heat pumps are not to be confused with "water-source heat pumps" or "water loop heat pumps" since there is no water in the ground loop. ASHRAE defines the term ground-coupled heat pump to encompass closed loop and direct exchange systems, while excluding open loops.
