Dynamic seasonal energy management of borehole thermal energy storage and smart heat pump synergies in fossil-free, ultra-efficient buildings

Thermal energy demand in buildings represents one of the largest contributors to global energy use and CO₂ emissions. Advanced thermal energy systems, including borehole thermal energy storage (BTES) integrated with highly intelligent air handling units, offer promising solutions to reduce emissions while ensuring affordable and reliable comfort. This study examines a state-of-the-art commercial building in Uppsala, Sweden, that already employs a fossil-free and highly efficient BTES–district heating configuration. Although this system is well-designed and operates intelligently, it still has important limitations, including underutilization of borehole potential, limited thermodynamic efficiency from direct-use exchange, and a lack of flexibility under varying energy tariffs. Therefore, this work aims to make an already smart and efficient system even smarter by integrating a ground source heat pump with adaptive seasonal energy management. A comparative benchmarking analysis is carried out using validated TRNSYS simulations and real operational data to evaluate performance, economic viability, and environmental outcomes. The results show that integrating a clever heat pump system enhances the annual heat extraction from the ground by approximately 27 %, resulting in a 29 % decrease in overall heating costs, and improves long-term savings by around 20 %, despite an 11 % rise in upfront investment. Environmentally, the enhanced system substantially reduces CO₂ emissions, cutting the annual impact by more than 90 % compared to the current configuration, aligning with the Swedish zero-emission targets. However, the operational cost savings strongly depend on peak heat (power) costs, which are expected to rise under policymakers' frameworks. This indicates that the long-term viability of adding heat pumps in Sweden is shaped not only by technical performance and CO2 savings but also by evolving local energy price structures. Yet, the considerable CO₂ savings helped by Sweden's green electricity mix and the opportunity to enjoy hourly spot-price variability through advanced controllers make heat pump integration a compelling option for future-proofing ultra-efficient buildings.