• 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 The use of shallow geothermal energy increasingly receives attention as a suitable alternative to fossil fuel-based space heating and cooling, warm water provision, as well as for seasonal heat storage throughout Europe. With the advent of shallow geothermal energy use on large scales, a vivid discussion of potential ecological and economic impacts has arisen but actual field data are scarce. An intensive groundwater temperature-monitoring program over a period of 3 years with consecutive measurements was, therefore, initiated at a residential neighborhood in the city of Cologne, Germany, under intense shallow geothermal use. The aim of the monitoring program was to overcome the existing data scarcity by pinpointing the effects of the intensive thermal use of the subsurface on groundwater temperatures and to foster understanding of urban groundwater temperature evolution. Results show that even though energy demands of the individual houses and energy extraction rates of the shallow geothermal systems were comparably small in this case, the accumulation of shallow geothermal users had a measurable impact on overall groundwater temperatures.