Dear Reader,

Happy new year to everyone, may 2025 bring new opportunities, good health and endless joy. For the 51st issue of our heatbeat Research Newsletter, we take a look into two recently published research papers.

The first research paper is "Achieving climate neutrality in district heating: The impact of system temperature levels on the supply mix of EU-27 in 2050" from Kök et al. investigating the impact on lowering the district heating network temperatures on an EU wide level. The second research paper "Design, construction, and commissioning of a 500 kW high-temperature heat pump plant for the district heating network of Bochum, Germany" from Passamonti et al. explains the overall design, planning and construction process on a mid to large size high temperature heat pump for a district heating network.

The first research paper examines the impact of system temperature levels on district heating (DH) systems in the EU-27, focusing on their decarbonization potential by 2050. By leveraging the Hotmaps DH Gen model, the study compares two scenarios: high-temperature (3rd generation DH) and low-temperature (4th generation DH) systems. These scenarios evaluate their respective supply mixes, levelized cost of heat generation (LCOHG), and renewable energy integration.

Key findings indicate that low-temperature systems significantly reduce LCOHG—by up to 20 %—due to increased efficiency and the integration of renewable and excess heat sources. Technologies like large-scale heat pumps and geothermal energy emerge as critical contributors to low-temperature systems, while high-temperature systems rely more on wastewater heat pumps and biomass. The study highlights geothermal energy’s potential in low-temperature scenarios, though its adoption faces barriers due to high initial investment costs.

Sensitivity analyses reveal that biomass and hydrogen play roles influenced by price fluctuations, with biomass becoming competitive at lower prices. Carbon pricing on waste-to-energy plants also shifts the supply mix, discouraging waste incineration.

The study emphasizes the economic and environmental benefits of transitioning to low-temperature DH systems, advocating targeted investments in geothermal and heat pump technologies. It underscores the importance of aligning DH system upgrades with EU climate neutrality goals while addressing challenges like infrastructure costs, policy support, and the optimization of diverse renewable resources. Future research should incorporate more detailed spatial data and consider emerging technologies like Power-to-X and carbon capture.

The second paper presents the design, construction, and commissioning of a 500 kW high-temperature heat pump (HTHP) pilot plant integrated into the district heating network of Bochum, Germany. The system uses a high-temperature mine thermal energy storage (HT-MTES) and solar thermal energy as heat sources, representing an innovative approach to reducing CO2 emissions in densely populated urban areas with existing district heating grids.

The HTHP system is a two-stage configuration using ammonia and butane as refrigerants, capable of achieving a supply temperature of up to 120 °C. This system is coupled with a mine-based thermal energy storage facility, where solar thermal energy heats water stored in abandoned, flooded coal mines during summer. This energy is extracted and raised in temperature to meet winter heating demands. The project successfully demonstrated the feasibility of integrating HTHPs with seasonal storage systems, saving up to 4800 tons of CO2 emissions annually by replacing fossil fuel-based heat generation.

The study highlights the plant's ability to operate efficiently under dynamic conditions, with modular components designed for future expansion. While technical challenges like limited mine water volumes and thermal constraints were addressed with innovative solutions, such as buffer tanks and adaptable system configurations, the plant demonstrates significant potential for replication in other urban areas, especially in regions with abandoned mining facilities.

Future research focuses on scaling the system, integrating additional heat sources like geothermal or waste heat, and refining the operational efficiency for industrial applications and further decarbonization of district heating networks.

Further Information

As always, we recommend reading the articles in full. We would also like to share a little note on our own behalf: In addition to this research newsletter and various blog posts, we have added a monthly feature update to our blog in December, summarising important developments and new features in our heatbeat Digital Twin. You can find the first entry at "https://heatbeat.de/de/blog/60/ "

The next issue of our newsletter will be published on February 5, 2025. For us, 2024 was a year of growth and milestones, thank you all for your support. Together, we’ve achieved remarkable things, and we look forward to even more in 2025.