Geowarmth Heat Pumps

A heat pump is an electrically powered device that uses the earth’s natural storage of solar heat and moves this to provide heating, hot water (or cooling) for buildings.  A heat pump can extract heat from air (see Air source heat pump), water or the ground (ground source heat pump).  The technology and components in a heat pump are similar to a refrigerator.

In a ground source heat pump system there are three independent circuits: the ground loop, the refrigerant and the building’s heat distribution system.  They are connected via two heat exchangers within the ground source heat pump which transfers the low grade heat from the ground into useable heat to heat the building.  For more information see How a heat pump works

A ground source heat pump can extract heat from the ground in a number of different ways:

Horizontal ground loops

Horizontal ground collectors consist of polyethylene pipe installed just over a metre below the surface, for example under a garden.  There a number of different types of horizontal ground collector for a ground source heat pump.

Closed loop vertical bore holes

Bore holes around 150mm wide are drilled at depths of up to 150 metres and loops of pipe inserted in each borehole which is then filled and sealed with a thermally enhanced grout.  This is a more expensive method than horizontal ground collectors but boreholes can be installed where ground space is more limited and they can be put under a building.  The number of boreholes required varies according to the geology of the area, the heating demands of the property and the size of the ground source heat pump.

Open loop systems

In an open loop (or water to water) ground source heat pump scheme, ground water is abstracted, usually from an aquifer or possibly from a river and passed through the heat pump before being returned to the ground.  A constant supply of water is needed.  This type of ground source heat pump system is highly efficient because of the relatively high temperature of ground water, but the installation can be more complex and require regulatory approval.  Open loop ground source heat pump systems are usually confined to larger commercial buildings rather than domestic properties.