• Energy Research

Abstract This paper presents a case study using calibrated numerical models to evaluate the thermal impacts and long-term sustainability of intensive geothermal use on a neighborhood scale. The subsurface heat transport model is configured with site-specific parameters and validated against monitoring data from a typical urban living quarter in Germany. Based on the simulated ground temperature profile, the heat pump performance is approximated. In addition, the effects of groundwater flow on the thermal interaction and economical operation of the shallow geothermal systems are examined. The results indicate limited thermal impacts as the groundwater temperature will maintain above 3.2 °C and that the area undergone severe temperature drop is less than 1% size of the neighborhood. Since the estimated seasonal coefficients of performance (SCOPs) are at least 3.8, the sustainability of the shallow geothermal applications is confirmed economically. Nevertheless, financial disadvantages up to 92 € year - 1 are anticipated due to gradual efficiency losses of the heat pump, which are meant for the owners of downstream installations. In addition, uncertainties in groundwater flow rate are also analyzed. For the negligible advection case, simulation results suggest that some systems can only operate sustainably for eight years. Conclusions are drawn regarding the general feasibility of neighborhood-scale shallow geothermal utilization and the importance of hydrogeological site investigations during the planning phase of such projects.

Abstract Ground source heat pump (GSHP) systems have been considered to be a low-carbon technology to provide heating and cooling for buildings in urban environments. This study focuses on the short-and long-term evolution of groundwater temperature induced by high-density GSHP installations in an urban residential area in Cologne, Germany. Specifically, a 2D heat transport model considering both thermal convection and conduction has been constructed using the finite element simulator OpenGeoSys. The simulated temperature changes within the initial few years were compared to the monitored dataset, while the GSHP heating load and thermal conductivity were calibrated. Subsequently, the validated model was run for 25 years to evaluate the long-term trend of the subsurface temperature. Also, effects of model uncertainties were explored with different simulated scenarios. Results indicate that sufficiently large groundwater flow and a high cooling ratio can effectively mitigate ground cooling. Based on these findings, best and worst-case scenarios were formulated for the studied case and the sustainability of GSHP operation were evaluated accordingly. As an outcome, specific design and operation criteria were proposed for the sustainable utilization of shallow geothermal energy for the heating and cooling of buildings in urban areas.