Abstract
Ground source heat pumps (GSHPs) gained increasing interest owing to benefits such as low heating and cooling costs, reduction of greenhouse gas emissions, and no pollutant emissions on site. However, GSHPs may have various possible interactions with underground and groundwater, which, despite the extremely rare occurrence of relevant damages, has raised concerns on their sustainability. Possible criticalities for their installation are (hydro)geological features (artesian aquifers, swelling or soluble layers, landslide-prone areas), human activities (mines, quarries, landfills, contaminated sites), and groundwater quality. Thermal alterations due to the operation of GSHPs may have an impact on groundwater chemistry and on the efficiency of neighboring installations. So far, scientific studies excluded appraisable geochemical alterations within typical ranges of GSHPs (±6 K on the initial groundwater temperature); such alterations, however, may occur for aquifer thermal energy storage over 40 °C. Thermal interferences among neighboring installations may be severe in urban areas with a high plant density, thus highlighting the need for their proper management. These issues are presented here and framed from a groundwater quality protection perspective, providing the basis for a discussion on critical aspects to be tackled in the planning, authorization, installation, and operation phase. GSHPs turn out to be safe and sustainable if care is taken in such phases, and the best available techniques are adopted.
Highlights
Global warming trends are fostering the replacement of fossil fuels with low-carbon renewable energy sources (RES), and this applies to buildings’ heating and cooling systems, which account for about 40% of the world’s energy total demand [1]
Ground-source heat pumps are gaining increasing interest owing to their economic, environmental, and energetic benefits, but concerns have been raised on their compatibility with groundwater resources
Criticalgeological conditions for Ground-source heat pumps (GSHPs) installations have been identified among swelling anhydrites or soluble halite layers, landslide-prone areas, artesian aquifers, and shallow gas layers
Summary
Global warming trends are fostering the replacement of fossil fuels with low-carbon renewable energy sources (RES), and this applies to buildings’ heating and cooling systems, which account for about 40% of the world’s energy total demand [1]. Trenches, or heat exchange units such as geothermal baskets (Figure 1A); magnitude of exchangers such benefits depends on the characteristics of heat pump systems, the context heat (BHEs) are installed in vertical boreholes, generally with on a depth of 50 ÷. BHEs use water solutions containing anti-freeze compounds as a heat carrier fluid, and this has led to concerns on possible release of such compounds into groundwater in the unlikely event of pipe leaks, which are addressed in the works of [24,25,26] Another major concern is the possible (physio-)chemical alterations of groundwater due to temperature changes induced by the operation of GSHPs, in particular the temperature increases due to underground thermal energy storage [27].
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