A ground loop is an undesirable feedback condition caused by two or more circuits sharing a common electrical line, usually a grounded conductor.

 

In a geothermal heat pump system, a ground loop is a series of fluid-filled plastic pipes buried in the shallow ground, or placed in a body of water, near a building. The fluid within the pipes is used to transfer heat between the building and the shallow ground (or water) in order to heat and cool the building.