IEA ECES Annex 39: Large Thermal Energy Storages for District Heating

Project manager overall project: AEE INTEC

Project leader University of Innsbruck: Fabian Ochs (UIBK - Energy Efficient Building)

Project team: Abdulrahman Dahash, Alice Tosatto

 Project partner:

  • AIT Austrian Institute of Technology GmbH (Austria)
  • SOLID Solar Energy Systems GmbH (Austria)
  • Ramboll (Germany)
  • Steinbeis-Innovationszentrum (Germany)
  • Solmax (Germany)
  • PlanEnergi (Denmark)
  • Technical University of Denmark (Denmark)
  • Ramboll (Denmark)
  • CREAR (Italy)
  • Ecovat (Netherlands)
  • newHeat (France)
  • Chalmers University (Sweden)

Funding body: (FFG, Energieforschung, flagship)

Duration: 01/11/2020 – 31/12/2023

Project website:


In future, large thermal energy storages play a central role in increasing the necessary flexibility of district heating networks and in enabling the further increase of renewable sources and the integration of waste heat in these systems. The present knowledge about large thermal energy storages is restricted to a small number of countries and projects. The necessary broad roll-out of this technology is only possible if, based on the existing knowledge and experience, cooperative adaptations and further developments are made and broadened to a large number of countries and experts in order to overcome the technological as well as non-technological challenges in the design, realisation and operation of this technology. This is why the IEA Technology Collaboration Program "Energy Conservation through Energy Storage" (ECES), after a one-year definition phase, has decided to launch the new Annex "Large Thermal Energy Storages for District Heating" (Annex 39).

The main objectives and expected results of the Annex are the definition of representative application scenarios, the associated boundary conditions and key performance indicators; the definition of dedicated storage concepts for selected application scenarios and the techno-economic evaluation of these concepts; the development, improvement and implementation of new material testing methods and the compilation of a database of materials suitable for the use in large thermal energy storages; the inventory and comparison of the performance of numerical simulation models as well as recommendations for the simulation of large thermal energy storages; and the creation of dedicated information material for relevant stakeholder groups (decision makers of energy utilities and heating network operators, interest groups, cities and municipalities, etc.) and the active, targeted dissemination of this information.

Due to existing synergies regarding the application scenarios, the integration into district heating systems and the numerical simulation, in the Annex not only large water thermal energy storages, such as tank and pit thermal energy storages (TTES and PTES), but to some extend also large thermal energy storages with other storage mediums, such as aquifer and borehole thermal energy storages (ATES and BTES), are considered.

In this collaboration of at least 10 countries, Austria plays an important role. Besides leading the Annex 39 as Operating Agent, the participating Austrian institutes also contribute valuable knowledge and experience from finished and currently ongoing projects. Especially the current Austrian flagship project "giga_TES" (18 partners including 12 industrial partners) provides important contributions to the Austrian participation and the central knowledge about the needs of Austrian industries in this field.
In addition to the expansion of the Austrian research expertise, the declared aim of the project is to intensify the cooperation with the participating partners in the international consortium. At the same time, the project results of Annex 39 and the emerging networks are to be transferred to the Austrian industries, active in this field, in order to further improve their international market positions. Moreover, dedicated results of the Annex are communicated to relevant national stakeholder groups to optimally initiate the implementation of this technology in Austria.

Expected results from Annex 39:

  • Definition of a number of representative application scenarios, the connected boundary conditions and Key Performance Indicators
  • Improve LTES materials and materials performance measurement methods
  • Prepare guidelines for obtaining proper water quality
  • Compare the performance and accuracy of simulation models for LTES
  • Derive validation tests for LTES simulation models
  • Generate information packages for decision makers and actively disseminate the information

Research focus of the University of Innsbruck:

Given the experience gained by UIBK, it plays a role of consultant partner in the development of reliable numerical models on both levels (system and component). Besides, it runs several simulations for calibration and optimization of specific case studies. 

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