Geothermal
Geothermal heat pumps (geoexchange systems)
Geothermal heat pumps (also called ground-source heat pumps or geoexchange system) use the earth as a heat source in winter and a heat sink in summer.
A geothermal heat pump comprises of an external loop buried under the ground to capture heat from the ground or reject heat to the ground, and a circulation system either in the form of open loop or closed loop to keep the heat transfer fluid moving.
In winter the soil is warmer than that of the ambient air. When the working fluid (either air or water) passes through the external loop, it picks up the heat from the surrounding soil and becomes warmer than the ambient air. In summer, it rejects heat to the surrounding soil and becomes cooler than the ambient air. Such systems utilize the relatively constant temperature of the ground for space heating or water heating in winter and for cooling in summer.
Depending on the types of the external loops, geothermal heat pumps can be categorized into open loop type and closed loop type.
In an open loop system, water is used as the working fluid. It enters the system from one end, exchanges heat with the heat pump, and is discharged into a collection reservoir, and will not be re-circulated back to the system. This option is suitable when water is abundant.
In a closed loop system, the heat transfer fluid circulates between the external loop and the heat pump unit in a closed loop manner. There is another type of closed loop system called the "pond closed loop system" in which the external loop is submerged in a water body instead of buried underground. It uses the water body as heat source and heat sink.
Depending on the layout of the external loops, geothermal heat pumps can also be categorized into vertical loop and horizontal loop systems.
Vertical loop systems are systems with their external loop inserted vertically into deep boreholes in the ground. They are applied in locations with limited open space for installing the external loop.
Horizontal loop systems are systems with the external loop laid horizontally in shallow trenches.
(Source for above: This link will open in a new windowThis web page has hyperlinks which may transfer you to third-party website.the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy)
