District heating and cooling (DHC) offers an efficient and flexible, organizational and technical solution for the energy transition in the heating and cooling sector. It provides a broad platform and a major lever for the integration of all kinds of renewable energy sources (RES). Furthermore, it increases the overall efficiency of the energy system by enabling the use of combined heat and power and other hybrid technologies for coupling the energy sectors as well as the use of surplus heat from a variety of energy conversion or industrial processes. Due to its structure, DHC enables fast transition processes, including the introduction of high shares of RES.

The research of IEA DHC Annex TS5 has investigated and evaluated the state-of-the-art and best practices at international level for introducing RES into existing large urban DHC systems and thus transforming and decarbonizing their heat supply. The overall objective of Annex TS5 was to contribute to a faster and more cost-effective transformation and decarbonization of existing DHC systems in IEA DHC member countries.

Annex TS5 activities focussed on gathering and providing knowledge regarding RES technologies for DHC, their integration into DHC systems and overall DHC system transformation processes. The topics addressed and the results obtained by Annex TS5 shall be partial solutions and answers from the DHC R&D community regarding the DHC transformation challenges. These solutions should contribute to the abovementioned overall objective within the framework of this broad-based international IEA collaboration.

The Annex TS5 was a four-year international collaboration from 2021 to 2024 including international R&D and industry partners. The participating countries were Austria, Canada, China, Denmark, France, Germany, Italy, Irland, South Korea, Sweden, Switzerland and United Kingdom.