Munich, Germany, August 5, 2025. District heating is good for the climate – in theory at least. In practice, only around 30 percent of it is currently generated from renewable energy in Germany1. Heat pumps could make a difference. They draw on environmental heat as a source instead of gas and coal, using electricity to efficiently raise it to a higher useful temperature level. However, integrating them into existing heating networks has so far been complex and expensive. As part of the joint heating network project TrafoWärmeNetz, an interdisciplinary research team is now developing solutions and strategies for a systematic and standardized integration of heat pumps into existing local and district heating networks. Their aim is to develop a digital planning tool that helps especially smaller and medium-sized energy suppliers and network operators to convert their fossil-fueled heating networks into heat pump-based networks, quickly and easily. Project participants are Drees & Sommer – the consulting firm specializes in the fields of construction and real estate –, HM Hochschule München University of Applied Sciences, Fraunhofer Institute for Solar Energy Systems ISE, Überlingen-based municipal utility company Stadtwerke am See GmbH, the utility firm Stadtwerke Pfaffenhofen a. d. Ilm, and the heat supply and contracting organization Danpower GmbH. Funded by the Federal Ministry for Economic Affairs and Energy, the research project started in January 2024 and is scheduled for completion at the end of 2026.
From blocks of buildings to entire urban districts, local and district heating networks supply around six million households in Germany with heat2. Most of this (around 86 percent) is generated by combined heat and power plants, or CHP for short. The principle behind CHP is that the waste heat generated when producing energy is used for heating purposes. The crucial point is that the main fuels used are fossil energy sources such as natural gas, heating oil or coal. Sustainable alternatives such as biogas or vegetable oil are also used, but are not available in sufficient quantities.
“According to estimates, around 200 thousand metric tons of carbon dioxide can be saved per year through the sustainable transformation of existing small and medium-sized district heating networks. With the planned expansion of heating networks and the complete decarbonization of the heating supply, this figure could potentially rise to as much as 10 million metric tons of CO2 per year. Heat pumps or hybrid systems are an excellent way of leveraging this potential,“ explains Dr. Madjid Madjidi, Professor of Integral, Computer-Aided Planning in Building Services Engineering at Munich University of Applied Sciences. Fraunhofer ISE and the university contribute a scientific perspective to the TrafoWärmeNetz research project. Project partner Drees & Sommer brings in a wealth of project delivery expertise in the areas of planning and construction engineering. As experienced suppliers and energy network operators, Stadtwerke am See GmbH Überlingen and Stadtwerke Pfaffenhofen a. d. Ilm, as well as Danpower GmbH, share their knowledge of the current challenges that the sector faces. The project is being supervised by the project sponsor Jülich (PtJ) on behalf of the Federal Ministry for Economic Affairs and Energy.
Numerous Hurdles Slow Down Conversion of Heating Networks
Drees & Sommer’s project manager Mathias Lanezki is convinced that: “The transformation of existing heating networks has been quite complex so far. In particular, small and medium-sized heat suppliers and network operators quite often do not have the technical and planning knowledge that is required for a timely and cost-effective conversion of their heating networks. Moreover, there are several bureaucratic hurdles. The sustainable transformation of these heating networks can only succeed with standardized and systemic conversion processes.” According to the expert team’s definition, typical existing small and medium-sized district heating networks have a power range of between 300 kilowatts (kWth) and 10 megawatts (MWth). They supply neighborhoods and urban districts with about one hundred to several thousand residents.
The research team is developing a digital planning tool to standardize the planning and implementation processes for existing heat pump-based networks. The aim is to use simulations to show how a wide range of consumers in a network are supplied with heating, and how different heat generators and their combinations interact. At present, many operators do not know what potential their existing heating networks actually have, or how they can convert them in a way that is both technically feasible and energy-efficient. They often simply lack data and comparisons for accomplishing this. With our research results and the digital planning tool we intend to close this gap in future,“ adds Mathias Lanezki.
Software Demonstrator Delivers First Findings
In order to create the necessary basis for doing this, the team of experts first assessed the baseline situation and defined the requirements for integrating heat pumps into existing heating networks. What are the transformation strategies and possible solutions for existing heat pump-based networks? When can hybrid systems be considered and when does a single-energy system make sense? To what extent are they technically feasible and how much carbon dioxide can be saved as a result? The study focuses on these and other questions.
The project team has already developed the first version of a software demonstrator that is able to precisely simulate the heating requirements of a building – and looking ahead, possibly more than one building. Validation of the demonstrator has shown that the simulation results are comparable to those provided by established tools such as IDA ICE, while taking significantly less time. Lorenz Lange, responsible for planning at Drees & Sommer and developer of the software artefact comments: “These results form a solid foundation for configuring heat pumps efficiently and planning their integration into existing heating networks on a sound basis, from both technical and economic viewpoints. This is our first success. It clearly demonstrates that we are on the right track.”
Once the project has been completed, the digital planning tool will provide practical guidance to heating network operators and energy suppliers, and it will drive forward the heating and energy transition. The research project runs until the end of 2026.
Additional Information: Gradual Process Chain Based on Open-Source Tools
Another module in the software demonstrator illustrates the relevant heating requirements of any area in Germany. This is achieved through a chain of open-source tools, using a bowser-based integrated development in OpenStreetMap, a freely accessible digital map of the world. These requirements can be used to plan economically optimized topologies for the expansion or new construction of heating networks. The computed pipeline networks can then be analyzed to highlight the least favorable points, using a thermohydraulic calculation. The chain of tools makes use of the fact that Excel is used in every intermediate step. As a result, users can also apply other tools, e.g. for a cross-comparison, or design each process step individually. The following diagram shows the process that has been developed.