Foto: Frontansicht des sozialen Wohnbaus Utendorfgasse Wien

TFlex - Temperature-flexibilisation in low-load operation of local district heating systems

Within the research project TFlex it is planned to check if the losses adherent to small district heating networks during low-load periods can be reduced. One possible solution is by deactivating the network and supplying the customers from previously charged decentralized storages. The optimal clustering of the storages and the possibility of solar-charging the storage will be calculated with the aim of a guaranteed one-hundred percent heat supply.

Short Description




Starting point / motivation

It is the aim of this project to present a method to reduce the losses of small district heating networks during low-load periods. Ten years ago losses of about 30% of the delivered heat were quite common. Today, provided that there is a good quality control, losses account for approximately 15% of the delivered heat.

Losses are characterized by following parameters:

  • Temperatures of supply and return lines (thermal losses)

  • Diameter of tubes (thermal losses and pumping losses)

  • Insulation of the tubing (thermal losses)

  • Length of the network (thermal losses and pumping losses)

Those parameters have been optimized as far as possible. A further improvement of the losses without changing the network topology and working principle is economically difficult.

Contents and goals

With the help of decentralized storage units, which are to be installed at the heat-customers location the losses can be minimized without expensive changes in the network layout. In low-load periods the network can be shut down and the heat customers will be supplied by the previously charged storage units. This method proves particularly efficient in networks with a high portion of low-load operation. It can already be estimated today that with the use of decentralized storage the losses can be reduced by up to 50%.


Methodically the project is split into three parts. Part A deals with data-collection and the energetic modelling of the considered heating-grids. After modeling storage-sizes and appropriate control-algorithms are optimized. A further working package deals with the integration of solar-thermal energy for additional load-relieving in the grid. In Part B questions in regard to grid-technology will be answered. The grid-models and boundary-conditions developed will be implemented into the models used in Part A. Finally, the results are subsequently analyzed according their economic impacts. Also sensitivity and risk analysis are carried out.

Expected results

With the help of calculations and simulations based on a broad dataset the following questions are to be answered:

  • What is the size of the storage units for maximum savings in different scenarios?

  • Can storage losses and investment costs be reduced by clustering the storage units?

  • What is the optimal control strategy for differing network topologies?

  • What mechanical strain does TFlex put on the tubes?

Aside from the charging the storage units from the network solar charging shall be investigated. This leads to an additional load shedding of the network.

  • What is the optimal size of solar collectors to reduce heat losses with the highest possible cost-effectiveness?

The defined technical goals and their calculated results will be evaluated economically. With the help of sensitivity analysis the network parameters which have the largest influence on profits and payback-times will be identified.

Project Partners

Project management

Chair of Energy Network Technology, Montanuniversität Leoben

Project or cooperation partners

  • FH JOANNEUM Gesellschaft mbH

  • Lehrstuhl für Wirtschafts- u. Betriebswissenschaften, Montanuniversität Leoben

  • TB Harald Kaufmann GmbH

Contact Address

Univ. Prof. DI Dr. techn. Thomas Kienberger
Franz-Josef-Straße 18
A-8700 Leoben
Tel.: +43 (3842) 402-5400

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