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District Heating and Cooling

Annex XII Project 01

The Research / IEA DHC Annexes / 2017-2020 / Annex XII / Annex XII Project 01

Effects of Loads on Asset Management of the 4th Generation District Heating Networks

View of the test specimen before the test, and shear strength test set-up


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Project summary

Future mechanical and thermal loads on District Heating (DH) networks are connected to the current development and implementation of the 4th generation DH in the cities.

In order to reduce heat losses, temperature levels of the supply and return have to be decreased. Flexible concepts for heat production and utilisation of waste heat or low exergy heat, and also loading and unloading of storages are required the near future.

The integration of renewable energy sources can be related to higher cyclic mechanical and thermal loads on the DH networks. This integration can significantly affect the operational lifetime of the DH networks, especially the DH piping systems. Hence, when considering investments, expansions and transformations of DH networks and also asset management of DH networks changed ageing behaviour has to be taken into account. 

DH piping systems in operation today and in future are mostly based on the pre-insulated (single and twin) pipe concept. Therefore, this project focused on the influence of future mechanical and thermal load spectra on operational lifetimes of these pre-insulated pipes.

This is especially relevant, for the efficient operation of DH networks, as well as the durability of the thermal insulation and the mechanical strength of the piping system. During operation, pre-insulated DH pipes are exposed to (large) temperature variations. Cyclic forces and stresses occur between the pipe and the soil, as well as within the pre-insulated DH piping system itself.  

Trends for future temperature levels and cyclic loading will be investigated for the partner countries. This analysis of the future load spectrum will be the foundation for further steps.

Deliverables / Outcomes

  • Temperature load data from existing DH networks in the partner countries with 3rd generation load conditions. 
  • New or improved models and test methods for lifetime prediction based on mechanical and thermal ageing tests. 
  • Estimation of how lifetime of DH networks will change, when operated at lower temperature levels and more cyclic loading compared to 3rd generation networks.
  • Recommendations to CEN TC 107 and suggestions for an improved asset management strategy 

Project lead

HCU HafenCity University
Überseeallee 16
20457 Hamburg

Prof. Dr. Ingo Weidlich,

Project partners

  • KDHC Korean District Heating Corporation, Korea
  • SP Technical Research Institute of Sweden, Sweden
  • FFI Fernwärme Forschungsinstitut in Hannover e.V., Germany
  • Hafslund, Norway