A geothermal heat pump (GHP) or ground source heat pump (GSHP) 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 (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. They are also known by other names, including geoexchange, earth-coupled, earth energy systems. Binary cycle power plants are usually appropriate for low and medium enthalpy geothermal fields, where the heat content of the geothermal fluid can be exploited to heat a working fluid via heat exchangers in a closed loop. The working (or else “binary”) fluid is typically an organic compound (often isopentane) with a low boiling point (Mannvit hf 2013). Heat from the geothermal fluid (most existing binary plants recover heat of geothermal fluid in the range of 100–200°C (causes the working fluid to vapour and accordingly turns the turbines and in extension the generators. Binary power plants are closed-loop systems, mitigating drastically the emissions to the atmosphere.
 Mannvit hf. 2013. Environmental Study on Geothermal Power GEOELEC Project – WP4 D4.2.
See also: CROWDTHERMAL DELIVERABLE D1.2: SYNTHESIS OF ENVIRONMENTAL FACTORS (page 9)