Dear Reader,

For the 59th issue of our heatbeat Research Newsletter, we take a look at the latest research in district heating and cooling.

The first paper we want to share is “6th Generation District Heating and Cooling Networks: Design, Experimental Results and Future Challenges” from Lima introducing first investigations of a new generation of district heating networks using CO2 as working fluid. As a second study we want to share the publication of Droste et al. with the title “A Methodological Framework for Identifying District Heating Networks in Germany by Utilizing the Census Data” . In this study the authors present a framework to identify district heating networks based on German census data.

The first study investigates the design and experimental validation of a sixth-generation district heating and cooling network (6GDHCN) using CO₂ as the working fluid. Unlike previous generations, which relied on single-phase fluids and sensible heat transfer, the 6GDHCN leverages phase-change phenomena (evaporation and condensation) to achieve higher energy density and reduce infrastructure size. This approach addresses limitations of fifth-generation networks, such as large pipe diameters and urban deployment challenges, while enabling simultaneous heating and cooling services. The research aims to demonstrate the operational feasibility of this concept and identify design challenges for future large-scale implementation.

The experimental facility developed under the ROADMAP project consists of a 100-meter dual-pipe network with a central plant and two users: one for heating and one for cooling, each rated at 13 kW. The system operates with CO₂ in liquid and vapor phases at approximately 50 bar and 14 °C, controlled through subcooling and superheating scenarios. Tests validated the correct functioning of subsystems and the overall network, including automatic mode switching between heating and cooling. Results confirmed the concept’s viability and showed performance trends consistent with larger-scale facilities, reinforcing the emulation capability of the lab setup.

Key challenges identified include dynamic flow control during transient conditions, such as load variations and mode shifts, which caused oscillatory behaviors and risks like pump dry-out. Future research should focus on advanced control strategies, predictive algorithms, and system modularity to enhance stability, scalability, and resilience. The findings highlight the potential of CO₂-based 6GDHCNs for sustainable urban energy systems, offering improved efficiency, reduced space requirements, and compatibility with renewable integration.

The second study introduces a systematic framework for identifying and characterizing district heating networks (DHNs) in Germany using the 2022 census dataset. The approach leverages high-resolution spatial data on heating systems in residential buildings and applies a density-based clustering algorithm (DBSCAN) to detect clusters of district heating connections. These clusters are then modeled as presumed DHNs, with their annual heat demand estimated using the Hotmaps dataset and calibrated against official state-level statistics. The resulting AixDHN dataset comprises 8,684 DHNs, covering an estimated 50.16 TWh of annual residential heat demand. Notably, 90% of this demand is concentrated in only 944 networks, highlighting the dominance of large urban systems.

The AixDHN dataset provides detailed spatial and demand-related attributes, enabling advanced analyses for energy planning and renewable integration. A use case demonstrates its application by assessing the technical potential of shallow geothermal collectors (SGCs) for DHN supply. Using land-use data (CORINE Land Cover) and soil characteristics, the study estimates a geothermal energy potential of 15.31 TWh/a, which could be increased to 24.87 TWh/a when integrated with ground-source heat pumps (COP ≈ 2.6). This corresponds to a coverage of approximately 50% of the identified DHN demand, illustrating the significant role of shallow geothermal energy in decarbonizing heat supply.

The methodology’s strengths lie in its scalability, robustness, and reliance on publicly available datasets, making it suitable for nationwide application without additional regional studies. However, limitations include uncertainties in census data, lack of hydraulic network details, and simplified assumptions in renewable potential estimation. Despite these constraints, the AixDHN dataset represents a major improvement over existing sources, offering a high-resolution basis for municipal heat planning and the strategic integration of renewable energy sources into Germany’s heating sector.

Further Information

As always, we recommend reading the articles in full. In addition to this research newsletter and various blog posts, we have added a monthly feature update to our blog, summarizing important developments and new features in our heatbeat Digital Twin. Besides that, we would like to inform you about our new webinar format, further information at https://heatbeat.de/en/blog/83/ .

The next issue of our newsletter will be published on October 1st, 2025.