The energy concept for the VW library in Berlin, which was built in 2004, centers on a ground foundation absorber (GFA) that uses concrete core temperature control to freely cool the building in the summer and cover the building's base heating load in the winter via a heat pump. Due to unexpectedly high subsurface temperatures beneath the building, as well as difficulties in controlling the concrete core temperature control system, the GFA has been largely decommissioned in recent years. The goal of this research is to work with building engineers and engineering geologists to determine the cause of the elevated temperatures and to transition the GFA to optimized seasonal operation. To this end, detailed thermal models were created for the building and the subsurface, validated with measured data, and coupling approaches between the models were investigated. This should ensure a better evaluation of the interaction between the subsurface and the building during operation. Model-based parameter studies will then be used to determine an optimally adjusted operation of the GFA. In addition, the temperature development of the subsurface of the study area will be investigated to ensure sustainable operation. Optimized reactivation of the GFA shows significant ecological and economic potential with annual savings of 15% of the building's CO2 emissions and €23,000 in energy costs compared to the current building operation. The developed adjustments to the operating and control parameters will be tested and monitored in the building during the coming heating periods.