Managing open-loop GWHP operation in urban aquifers to reduce thermal interference and background warming: the THERMAL approach

Open-loop groundwater heat pump (GWHP) systems provide low-carbon heating and cooling by exchanging heat with pumped groundwater. In dense urban settings, however, this advantage can become a liability: overlapping thermal plumes and persistent warming may progressively elevate background groundwater temperatures, constrain resource availability, and reduce long-term system reliability. To address this, we introduce THERMAL (Shallow geoTHERmal energy MAnagement through hoListic optimization), a decision-support approach that integrates conventional performance metrics with aquifer-centred sustainability indicators to guide GWHP operation. THERMAL screens operating strategies designed to preserve the ambient thermal baseline while reducing thermal cross-interference between neighbouring installations.
We apply THERMAL to three GWHP systems in Zaragoza’s urban alluvial aquifer, testing 27 alternative operating configurations against the current baseline. The scenario ensemble reveals substantial trade-offs: several configurations perform worse than present operation, whereas multiple options improve both environmental and economic outcomes. The best-ranked strategy achieves an emissions reduction of 14.94 t CO₂-eq yr⁻¹ and €7.53k yr⁻¹ in cost savings. However, the scenarios that maximize cost and CO₂ benefits do not systematically coincide with those that most effectively reduce the spatial footprint of strongly warmed groundwater (areas with ΔT > 4 °C). These results show why single-objective, “performance-only” optimization is insufficient in cities: robust planning requires multi-criteria decisions that explicitly protect the aquifer’s thermal integrity. THERMAL offers a practical route to align GWHP operation with the long-term conservation of urban groundwater thermal conditions.