Luka Tas, David Simpson, Thomas Hermans

The Member States of the European Union pledged to reduce greenhouse gas emissions by 80-95% by 2050. Shallow geothermal systems might substantially contribute by providing heating and cooling in a sustainable way through seasonally storing heat and cold in the shallow ground (<200m). When the minimum yield to install a cost-effective aquifer thermal energy storage (ATES) system cannot be met, borehole thermal energy storage (BTES), relying mostly on the thermal conductivity of the ground, is proposed. However, for large-scale applications, this requires the installation of hundreds of boreholes which entails a large cost and high disturbance of the underground. In such cases, ATES systems can nevertheless become interesting. In this contribution, we present a case study performed on a Ghent University campus, where the feasibility of ATES in an area with a low transmissivity was determined. The maximum yield of the aquifer was estimated at 5 m³/h through pumping tests. Although this low yield was attributed to the fine grain size of the aquifer, membrane filtering index tests and long-term injection tests revealed that the clogging risk was limited. A groundwater model was used to optimize the well placement while limiting the risk of interactions between the wells resulting in a thermal breakthrough or flooding at the surface. It was shown that a well arrangement in a checkerboard pattern was most effective to reach these objectives. Hence, for large-scale projects, a minimal CO2 output might be reached using a (more cost-effective) ATES system even in low permeable sediments.