page_title: Geothermal heat pump
section_title: Vertical
hierarchical_section_title: Geothermal heat pump / Ground heat exchanger / Closed loop / Vertical
caption_attribution_description: English: Drilling of a borehole for residential geothermal heating in Northern Finland
context_page_description: A geothermal heat pump or ground source heat pump is a central heating and/or cooling system that transfers heat to or from the ground.
  It uses the earth all the time, without any intermittency, as a heat source or a heat sink. 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. They are also known by other names, including geoexchange, earth-coupled, earth energy systems. The engineering and scientific communities prefer the terms "geoexchange" or "ground source heat pumps" to avoid confusion with traditional geothermal power, which uses a high temperature heat source to generate electricity. Ground source heat pumps harvest heat absorbed at the Earth's surface from solar energy. The temperature in the ground below 6 metres is roughly equal to the local mean annual air temperature.
context_section_description: A vertical closed loop field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically 50 to 400 feet (15–122 m) deep, or a foundation pile of a building in which a circulating heat-carrying fluid absorbs (or discharges) heat from (or to) the ground. Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole or comprises two small-diameter high-density polyethylene (HDPE) tubes thermally fused to form a U-shaped bend at the bottom. The space between the wall of the borehole and the U-shaped tubes is usually grouted completely with grouting material or, in some cases, partially filled with groundwater. The borehole is commonly filled with a bentonite grout surrounding the pipe to provide a thermal connection to the surrounding soil or rock to improve the heat transfer. Thermally enhanced grouts are available to improve this heat transfer. Grout also protects the ground water from contamination, and prevents artesian wells from flooding the property. Vertical loop fields are typically used when there is a limited area of land available. Bore holes are spaced at least 5–6 m apart and the depth depends on ground and building characteristics. For illustration, a detached house needing 10 kW (3 ton) of heating capacity might need three boreholes 80 to 110 m (260 to 360 ft) deep. During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil. Reliable heat transfer models have been developed through sample bore holes as well as other tests. In a foundation pile GHE (or energy pile), the heat transfer tubes are inside the steel frame of a foundation pile. There are various possible shapes. Foundation piles are usually much shallower than boreholes and have a greater radius. Since energy piles generally require less land area, this technology is evoking increasing interest in the ground-source heat pumps community.
caption: Drilling of a borehole for residential heating
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