Geothermal heat pumps (ground-source heat pumps) (GHP or GSHP) are used in two basic modes: ground coupled (vertical and horizontal)--closed loop, or groundwater types - open loop. These have been described extensively in a previous Geo-Heat Center Bulletin (Vol 18, No. 2 - April 1997) and in more detail in “An Information Survival Kit for the Prospective Geothermal Heat Pump Owner” by Kevin Rafferty