City-scale residential heating and cooling with Aquifer Thermal Energy Storage (ATES)

Achieving sustainable and climate-friendly space heating and cooling is essential to the energy transition. Aquifer Thermal Energy Storage (ATES) is a promising technology to significantly reduce greenhouse gas emissions compared to conventional heating and cooling technologies. Therefore, in this study the technical potential of shallow low-temperature ATES systems is quantified for the city of Freiburg im Breisgau, Germany in terms of reclaimable energy. Using 3D heat transport models, heating and cooling power densities are determined accounting for several different ATES configurations in various hydrogeological subsurface conditions. High groundwater flow velocities of up to 13 m d^-1 lead to a significant loss of stored energy limiting power densities to a maximum of 3.2 W m^-2. Nevertheless, comparing these power densities to the existing demands of heating and cooling energy reveals that substantial heating and cooling supply rates are possible with ATES. While heating energy supply rates of larger than 60 % are determined for about 50 % of all residential buildings, the cooling energy demand could be supplied entirely by ATES systems for 92 % of the buildings. For ATES heating alone, this results in greenhouse gas emission savings of up to 70,000 tCO₂eq a^-1. This equals about 40 % of the current greenhouse gas emissions caused by space and water heating in the study area’s residential building stock. In the future, the application of the modeling approach proposed in this study for other regions with similar hydrogeological conditions could obtain estimations of local ATES supply rates supporting city-scale energy planning.