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District Heating and Cooling

Annex XIII Project 07

The Research / IEA DHC Annexes / 2020-2023 / Annex XIII / Annex XIII Project 07

CASCADE: A comprehensive toolbox for integrating low-temperature sub-networks in existing district heating networks

Integrating LTDHN in the return line of an existing DHN, thus forming a sub-LTDHN and thereby reducing the main return temperature. In addition, local heat sources and storages can be used for operating grid friendly (e.g. reducing peak loads).

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Journal articles

Project summary

Low-temperature district heating networks (LTDHN) operating at supply temperatures of 50-70°C can very effectively utilize renewable heat sources such as solar or geothermal energy, ambient heat or low-temperature waste heat, as described in Lund et al. .

However, the vast majority of urban district heating networks (DHN) operate on relatively high temperatures, typically 90-110°C supply and 50-70°C return. The high-temperature mode of operation has a certain robustness and high-temperature DHNs cannot be easily transformed into a LTDHN, for example due to the characteristics of the building stock, the requirement of transporting sufficient amounts of energy with the given capacities and high-temperature heat e.g., from waste incineration.

CASCADE investigates an alternative approach: the integration of LTDHNs into the return line of an existing large urban DHN, thus creating a sub-LTDHN. This will reduce the return temperature of the overall DHN (see figure 1) and thus improve its efficiency and sustainability, as well as enable increasing its capacity for connecting new customers. Consequently, sub-LTDHN can be a key enabler for the decarbonization of urban DHN by enabling an efficient utilization of local energy sources and have the potential to reduce substantially the overall network temperatures.

At the same time, a high-temperature backup from the main network to the sub-LTDHN is available. Therefore, LTDHNs as sub-networks in the return line may represent a win-win situation. Implementation of energy cascades by means of a sub-LTDHN is possible when (i) there is a well-established high-temperature DHN and there is a planned (greenfield) urban area or larger customers with the ability to utilize heat at low temperatures.

These conditions are typical for many cities planning new districts. The utilization of renewable and waste heat and storage depends on the local potentials and a coordination with the overall network management and supply portfolio development is pivotal, including the business models.

The project addresses the following questions: How does the sub-LTDHN change the economics and hydraulic behavior of the entire network? Especially when the subsystem uses local storage and low-temperature sources? Under what circumstances is a sub-LTDHN advantageous for the overall efficiency of the overall DHN or the existing plants and actually allows for a win-win-situation?

What is the best operation strategy of the sub-LTDHN (optimizing for main DHN friendly behavior or for local supply), in particular during peak demand? What is the economic value of the sub-LTDHN and does it compensate for the implicit additional costs? How to integrate sub-LTDHN without disrupting contractual obligations with other users? How many sub-LTDHN are possible in an urban DHN?

Target Groups

  • National District Heating associations
  • District Heating operators
  • Housing companies
  • District developers

Deliverables / Outcomes

  •  Guidebook – including

    • international best practices and lessons learned for the technical operation of sub-LTDHN

    • review of existing regulatory and economic boundary conditions

    • description of novel and innovative business models for integrating sub-LTDlarge scale urbane DHN

    • large scale replication and interaction of different sub-LTDHN, including an economic methodology for assessing the transformation pathways for the DHN using sub-LTDHN 

  • Dynamic and open source (Modelica) sub-LTDHN simulation model description

Project lead

Energy Institute at the Johannes Kepler University Linz
Altenberger Str. 69
4040 Linz

Dr. Simon Moser
Phone: +43-676-4404755
E-Mail: moser@energieinstitut-linz.at.

Project partners

  • SINTEF Energy Research, Norway
  • Department of Energy Technology (DET) at Tallinn University of Technology, Estonia
  • AIT Austrian Institute of Technology GmbH, Austria