Co-Simulation of a District Heating and Cooling System in Combination with Mine Thermal Energy Storage
A Case Study in Germany
T.S.V.G. Spengler (TU Delft - Electrical Engineering, Mathematics and Computer Science)
D.F. Bruhn – Mentor (TU Delft - Civil Engineering & Geosciences)
Alexandros Daniilidis – Mentor (TU Delft - Civil Engineering & Geosciences)
Willem Hagemann – Mentor (Fraunhofer IEG)
Stefan Klein – Mentor (Fraunhofer IEG)
R. Santbergen – Graduation committee member (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
The increasing global demand for heating and cooling is predominantly met by fossil-based energy sources, contributing to greenhouse gas emissions and placing growing pressure on energy infrastructure. Although greater use of renewable energy is crucial for decarbonisation, its generation frequently does not coincide with demand, creating a seasonal mismatch. Seasonal thermal energy storage offers a promising solution to balance this mismatch between energy supply and demand. This thesis investigates the technical, environmental, and economic feasibility of Mine Thermal Energy Storage (MTES) by coupling a virtual MTES model with the heating and cooling system of Ruhr-University Bochum (RUB).
To achieve this, separate Python and Modelica models of the MTES and campus heating and cooling systems were developed and linked through an orchestrator algorithm. The co-simulation was conducted to evaluate system performance. Sensitivity analyses were performed to assess the influence of system design parameters, operational parameters, and input data. In addition, the long-term effects were monitored and the optimal setup was determined.
Results demonstrate that MTES can reliably store excess heat in summer and supply it during winter while maintaining stable operational temperatures. The integrated system achieved a total COP which is lower than a stand-alone heat pump, but appropriate for a combined heating-cooling configuration with seasonal storage losses. The system reduced reliance on the gas boilers and cooling tower, and it also delivered the highest CO₂ reduction among comparable storage technologies. Economic assessment shows that the levelised cost of heat is competitive with similar storage systems, even under conservative operational assumptions.
Sensitivity analyses showed that the optimal heat pump size and operational variables such as the heat pump ΔT value and MTES temperature critically influenced performance, while the MTES size had a weaker but still noticeable effect. The optimal practical and theoretical setups further demonstrated the system’s potential, showing significant increases in recovered waste heat and CO₂ reduction.
Overall, this thesis demonstrates that MTES offers a technically, economically and environmentally viable solution for seasonal thermal energy storage in the heating and cooling system of the Ruhr- University Bochum. Ultimately, MTES can represent an important step toward achieving the EU’s long-term climate targets by enabling more efficient and resilient sustainable energy systems.