Dual-Source Heat Pump Application for Boiler Replacement—Investigation by Simulation and Field Monitoring

In many decarbonization scenarios, heat pumps are seen as a key technology for future heating needs. However, market shares for large-capacity heat pumps are still low despite the potential for significant CO₂ reduction. In particular, boiler replacements face the obstacle of insufficient heat sources due to restrictions imposed by the built environment. In this study, overcoming the restriction of individual heat sources through dual-source integration has been investigated, both by simulation and field monitoring. The results confirm that by downsizing the individual heat sources, limitations relating to noise emissions or drilling space can be overcome. For instance, by combining the ground as a heat source for 50% of the peak load coverage with outdoor air as the base load heat source, the length of the borehole heat exchanger can be reduced by up to 80% compared to when using only the ground as a heat source. Through regeneration of the ground, boreholes can be drilled closer together, and their length can be reduced by more than 50%. Cost-optimal regeneration rates were found to be between 40 and 80%. The related cost savings can make the dual-source system more cost-effective than a single-source system, even without limitations on any individual heat source. Simulation results are verified in a pilot and demonstration (P&D) plant for a boiler replacement in two larger multi-family homes. The first winter measurements confirm the basic simulation results. CO₂ saving potentials are estimated to be around 90%. Ongoing monitoring will further verify results and derive standard configurations and best practices.