Figure 1: Illustration of the concept of different generations of district heating systems.
ceptions are possible. In the end any new DHS must minimize overall resource consumption and greenhouse gas emissions for the available budget. In many cases, aiming for 4DHNs is a sensible first step to consider but openness must remain towards choosing a district heating network generation that leads to the lowest environmental impact overall. Authors of the article "4th Generation District Heating (4GDH) Integrating Smart Thermal Grids into future sustainable energy systems" from March 2014: Henrik Lund (Aalborg University, DK), Sven Werner (Halmstad University, Sweden), Robin Wiltshire (BRE, UK), Svend Svendsen (Technical University of Denmark, DK),
need to be introduced to disinfect domestic hot water. These measures usually cause additional resource consumption and greenhouse gas emissions that can outweigh the reductions achieved by further decreasing temperatures. Therefore, from the perspective of IEA DHC it makes little sense to talk about further generations when DHNs are established with supply temperatures lower than 70°C. Consequently, the IEA DHC ExCo recommendation is not to use the term "5th generation district heating", as it can be mis- understood as an upgrade in general to 4GDH. Instead, the IEA DHC ExCo suggests to label pipe networks that are main- ly used as a source for decentralized technologies as "thermal source networks" (TSN). These TSNs should be considered a subclass of 4GDH networks.
Jan Eric Thorsen (Danfoss District Energy, DK), Frede Hvelplund (Aalborg University, DK) and Brian Vad Mathiesen (Aalborg University, DK).
In summary IEA DHC agrees with using the generations termi- nology in district heating as a general guideline to which ex-
Participating countries in IEA DHC as of 2024: Austria Belgium Canada China Denmark Estonia Finland France Germany
Ireland Italy Korea
Norway Sweden The Netherlands
UK IDEA (USA)
21 www.dbdh.dk
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