Open-loop ground source heat pumps (GSHP)

Open-loop ground source heat pump. (Image: courtesy of US Department of Energy.)

Groundwater temperatures are relatively stable at depths of 10–15 m below ground surface (approximating the annual air temperature at that location) and with further depths increase according to the geothermal gradient (UK average 3ÂșC per 100 m depth).

As a result, there is a temperature difference between above-ground (air) temperatures and below-ground (including groundwater) temperatures for most of the year, with the ground/groundwater being colder than air during summer and warmer than air during winter.

Ground source heat pump (GSHP) systems exploit this natural temperature difference for heating or cooling demands.

In open-loop systems, groundwater is abstracted at ambient temperature from the ground, passed through a heat pump before being re-injected back into the ground or discharged at the surface.

For buildings with heating/cooling demands of 100 kW or more (e.g. a large office building), such open-loop GSHPs can be more economic than closed-loop systems.

However, they rely on certain hydrogeological and economic conditions including:

  1. the presence of an aquifer of sufficient productivity and water quality
  2. reasonable installation and pumping costs
  3. regulatory requirements conducive to efficient abstraction (and discharge)

Screening tool for England and Wales

Download the screening tool for England and Wales

The British Geological Survey (BGS) in collaboration with the Environment Agency (EA) has developed a web-based tool that provides an indication of whether these conditions exist in a given area.

The tool is developed within a GIS and maps the potential for open-loop GSHP installations (heating/cooling output >100kW) in England and Wales at the 1:250 000 scale.

The Open-loop GSHP screening tool (England and Wales) considers hydrogeological and economic factors, including the presence and productivity of an aquifer and depth of abstraction, as well as potential restrictions (e.g., location within protection zones).

The tool also provides information on the currently licensed water abstraction volumes as well as water quality information for locations for which such data are available.

The principal viability for GSHP installations (>100kW) is displayed in form of a screening map which shows all areas where the basic requirements for successful GSHP installations (>100kW) are fulfilled.

More detailed information on the underlying hydrogeological and economic factors is available from summary data tables and through the exploration of the underlying thematic maps.

The Open-loop GSHP screening map (England and Wales) is also available to view as a web map service (WMS).

Screening tool for the West Midlands

Download the Open-loop GSHP tool (West Midlands)

The BGS has also conducted a more detailed pilot study of the (open-loop) GSHP potential in the West Midlands.

Here, the suitability for GSHP installations is mapped at 1:50 000 scale using a similar methodology to the one described above.

However, the Open-loop GSHP tool (West Midlands) is applicable to schemes of all sizes. It displays all relevant data in the form of tables and graphical displays that are easy to read and understand.

Contact

For further information please contact Dr Corinna Abesser