Low-temperature district heating systems: New guidebook proves technical feasibility and profitability

District heating systems are a key technology when it comes to mitigating the effects of climate change in the buildings sector. In order to incorporate renewables and waste heat into these systems to maximum effect, they need to be operated at lower temperatures. Fraunhofer IEE has worked closely with AGFW (the German Energy Efficiency Association for Heating, Cooling and CHP) and European research partners to produce a guidebook that shows how existing district heating systems can be converted and new low-temperature systems created. In this publication, experts outline both the technical and the economic side of the issue, with numerous case studies proving that low-temperature district heating is technically feasible under all kinds of conditions — as well as being economically viable.

The guidebook has been produced as part of Annex TS2 of the International Energy Agency (IEA) Technology Collaboration Programme on District Heating and Cooling. Research institutes from Austria, Denmark, Germany, Norway, Sweden and the United Kingdom have worked together on this project. The project has been coordinated by Halmstad Univesity, Sweden. The German institutes involved are the Fraunhofer Institute for Energy Economics and Energy System Technology IEE, the University of Kassel and the Technical University of Darmstadt, with the Hochschule für Technik Stuttgart (a University of Applied Sciences) also lending its expertise. The AGFW district heating association supported the project. Fraunhofer Verlag has published a printed English version of the guidebook.

“The buildings sector will only be able to achieve its climate protection targets with the help of low-temperature district heating. Our guidebook points the way: It shows suppliers, politicians and other interested parties how to implement these systems in a wide variety of circumstances,” says Dr. Dietrich Schmidt, Head of the Thermal Energy System Technology department at Fraunhofer IEE.

Dr. Heiko Huther, Head of Research & Development at AGFW, is pleased to see the guidebook completed too: “The issue of lowering temperatures is an important one as far as incorporating renewables into district heating systems is concerned. The case studies collated here provide empirical data and so will help with further development.” He went on to say that AGFW will continue to support the project going forward.

Many advantages over high-temperature district heating

Until now, district heating in Germany has been based overwhelmingly on fossil fuels, just as it has in most other European countries. As part of the drive toward decarbonization, renewables and waste heat now need to replace natural gas and coal as heat sources. However, the temperature level of these new sources is usually lower than that of the heat generated in fossil-based combined heat and power (CHP) plants. It is therefore difficult to feed the resulting heat into existing high-temperature district heating systems.

The solution is to convert existing district heating systems so they can run at lower temperatures — while constructing new low-temperature district heating systems at the same time. “Climate protection targets call for Germany to basically double the proportion of district heating systems we use to produce our heating energy by 2030. So we are going to need a lot of new systems,” explains Schmidt.

In the guidebook, the experts show that these types of district heating system, which are designed for average temperatures below 70°C (158°F), have a number of advantages over high-temperature systems. For example, suppliers will have access to much larger amounts of usable waste heat, as well as heat from geothermal sources. Heat pumps work more efficiently if they need to reach a lower temperature level; solar thermal systems become more efficient too. Suppliers are also able to use flexible plastic pipes instead of steel where appropriate. Last but not least, lowering temperatures will reduce the stress on existing pipes. The researchers have calculated that total potential savings of 14 billion euros per year could be achieved throughout Europe.

No compromise on comfort

In another chapter, the experts demonstrate how buildings can manage very well with lower supply temperatures. The case studies examined here show that, as a general rule, the temperatures in question are sufficient for a save and hygienic hot water preparation. Customers on low-temperature district heating systems do not have to compromise on comfort: The temperatures reached are high enough to heat rooms to the desired level. In any case, more and more properties will have to reckon with lower supply temperatures in the future after undergoing energy renovations — which is great news for low-temperature district heating systems.

The experts also state numerous ways of converting existing district heating systems in the guidebook. These include carefully analyzing a customer’s temperature requirements in advance or getting local politicians and the public at large involved at an early stage. The opportunities provided by digitalization should be exploited as well, for example in terms of open and closed-loop system control.

In addition, the researchers use a detailed case study into Campus Lichtwiese at the Technical University of Darmstadt to highlight the potential pitfalls of low-temperature district heating systems.

Case studies show the wide range of systems

Fraunhofer IEE’s major contribution to the guidebook was a detailed study of existing low-temperature systems. Researchers at Fraunhofer analyzed in close cooperation with the international partners in the project almost 140 examples from many countries in Europe, 40 of them in depth. They then included a total of 15 projects in the guidebook.

These case studies reflect the wide range of different designs used for such systems, depending on the particular local circumstances — which heat sources are available or what the consumer’s requirements are, for example. They also show that regulatory conditions sometimes stand in the way of low-temperature district heating. What’s more, the examples covered indicate that payback times are usually relatively long — but that does apply to district heating systems with higher temperatures too. In some of the case studies examined here, the costs of low-temperature systems were as much as 10% below those of conventional solutions.

A wealth of expertise and experience in district heating systems

Fraunhofer IEE has been dealing with district heating systems for many years. Researchers focusing on the area of “Energiesystem Stadt" ("Urban Energy System”), for example, are developing cross-sectoral integrative concepts for districts that open up climate-friendly energy sources — district heating systems are a key aspect of this work. Plus, with its District LAB experimental and test center, Fraunhofer IEE will offer an extensive infrastructure for suppliers, planners and manufacturers who want to test out components of innovative district heating systems.

Researchers working in the field of energy economics are looking at district heating systems in depth too, for instance in terms of their investment structures. District heating systems are also a significant aspect of the work done by researchers focusing on the area of “Thermal Energy Technology”. Fraunhofer IEE is involved in international research projects looking at this issue as well. For instance, Fraunhofer researcher Dietrich Schmidt led the IEA project “Annex TS1: Low Temperature District Heating in Future Energy Systems”, which paved the way for the collaborations that went into producing this guidebook.

Platform Grüne Fernwärme

AGFW has set up a digital information platform to help municipalities plan and implement new district heating systems: On the Platform Grüne Fernwärme (the Green District Heating Platform, found at www.gruene-fernwaerme.de), the association pulls together expertise and contacts for the different regions of Germany. Network mentors share their knowledge and experience with interested municipalities, thus playing an active part in pressing ahead with the thermal energy transition.


Free download of the English version of the guidebook from Fraunhofer Verlag: https://publica.fraunhofer.de/entities/publication/05516ac6-479a-43f0-8f9a-d24f27d49f84/details


Expert contact:

Dr. Dietrich Schmidt, Head of Thermal Energy System Technology, Fraunhofer IEE,
Email: dietrich.schmidt@iee.fraunhofer.de

Dr. Heiko Huther, Research & Development Division Director, AGFW | Der Energieeffizienzverband für Wärme, Kälte und KWK e. V.,
Email: H.Huther@agfw.de

Further information:


Project Partners

AGFW | Der Energieeffizienzverband für Wärme, Kälte und KWK e. V. is an effective, independent and neutral umbrella association promoting combined heat and power, (district) heating and cooling at a national and an international level. As a standards development organization and provider of services to the sector, AGFW has spent the last 50 years representing the interests of more than 550 companies involved in combined heat and power, the thermal energy industry and other facets of industry with its expertise on technical matters, energy policy, environmental policy, legal affairs and business issues.

The Fraunhofer Institute for Energy Economics and Energy System Technology IEE in Kassel pursues research into transforming energy systems. It develops solutions to technical and financial challenges in order to further reduce the costs of using renewables, to safeguard supply despite volatile production, to ensure a high level of grid stability and to guide the energy transition to economic success. 

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