Geological and groundwater aspects of ground-source heat pump systems for buildings: an overview

In recent years, the European Union has been moving towards low-carbon energy systems, which has led to a growing number of ground-source heat pump (GSHP) installations with vertical borehole heat exchangers (BHEs). These systems help to reduce greenhouse gas emissions, but their influence on the subsurface environment needs to be properly evaluated during both the design and the operational phase. This paper presents a literature review of the environmental aspects related to the installation and long-term use of closed-loop vertical BHEs. The review analyses thermal changes in the ground around the boreholes, including cases where thermal depletion may occur in arrays of multiple boreholes. Particular attention is given to the hydrogeological effects of borehole construction in difficult geological conditions, such as karst areas, where drilling through soluble carbonate rocks may encounter cavities and conduit networks, and may create unwanted hydraulic connections between aquifers.