More than 100,000 ground-source heat pumps are currently operating in Switzerland, providing geothermal heat for homes and buildings. Borehole heat exchangers (BHEs) combined with heat pumps for this application offer a high coefficient of performance but installations must not be so closely spaced as to lead to an over-exploitation of the heat capacity of the ground, caused by the thermal interference between neighboring boreholes. This thermal interference and the available area for the installation of BHEs limit the technical potential of heat pumps, defined as the maximum annual heat energy that may be extracted by these systems.

A method for quantifying the potential of ground-source heat pumps and assessing potential over-exploitation of the heat capacity of the ground was applied to data for two regions of western Switzerland. The available area for geothermal exploitation was estimated using existing topographical data excluding built environments and natural habitats. Ground-source heat pumps installed in the study area were then simulated based on ground temperature, thermal conductivity and thermal diffusivity to define the optimal borehole spacing that would both comply with installation standards and maximize the extractable heat.

The annual technical potential of the region studied is 4.6 TWh, which corresponds to about a third of its total heating demand, with a maximum energy density of 15.5 kWh/m². The results published in Renewable Energy indicate that the cumulative installed borehole depth should not exceed 2 km per hectare in order to avoid over-exploitation of the heat capacity of the ground. Urban planners can use this information in technical and economic feasibility studies of ground-source heat pump system deployment.

Researchers from Ecole Polytechnique Federale de Lausanne (Switzerland), University College London and Royal Holloway University of London contributed to this study.

Workflow for modeling the technical potential of ground-source heat pumps. Source: Alina Walcha et al.