Solar Assisted Heating Networks

An investigation of the economic and ecological usefulness of coupling two CO2 neutral energy sources; solar installations for multi-family houses, producing standardised systems concepts and planning guidelines.

Content Description




In Austria an increasing number of district heating systems and central heating systems in multi-family houses are being assisted by solar plants. The fuel for small and medium district heating networks is mainly biomass. At the end of 1998, 444 biomass-fired district heating networks were in operation in Austria, 12 of them were assisted, mainly in summer, by a solar plant. About 300 to 350 solar thermal plants have been installed in multi-family houses in recent years. Both applications open a new market segment for solar plants.

The two applications have different development needs, though, due to the different conditions surrounding them. Therefore they are dealt with separately in this project.

District heating networks

  • The plants are big enough to mean that the solar plant is normally planned by a specialist.
  • In solar assisted biomass-fired district heating networks two renewable energy sources are competing. CO2-emissions are not criteria for the decision to use an assisting solar plant
  • District heating networks have to be operated economically
  • Therefore the main question for this project is to analyse the economical and ecological (excluding CO2) advantages and disadvantages of a coupling of biomass-fired district heating networks with solar plants.

The main goal of this part of the project is to build up criteria to determine in which cases (plant size, plant lay-out, amount and kind of subsidies) the coupling of solar and biomass in district heating networks makes economical and ecological sense. The results will be available to public sponsors and planners in particular.

Multi-family houses

  • Solar plants in multi-family houses are normally planned by the installer of the whole heating system, who is not a specialist in solar plants.
  • The conventional heating systems operates with all kinds of fuels
  • Solar plants for multi-family houses are normally not built for economy but for marketing reasons (pushed of course by high economic incentives).
  • The research demand for solar plants in multi-family houses is therefore to enhance functionality and reliability and to develop easy to use but fail-safe planning handbooks for non-specialist installers.

This part of the project focuses on new buildings and on retrofit. Besides the solar plant and its integration into the heating system, efficient heat distribution to users will be worked on. The results are summarised in a handbook that will be available to all the companies involved, and to other interested planners and installers.

Project Partners

Project manager: Ao. Univ.-Prof. Dipl.-Ing. Dr. techn. Wolfgang Streicher
Institut für Wärmetechnik, Technische Universität Graz

Dipl.-Ing. Richard Heimrath
Dipl.-Ing. (Fh) Andreas Heinz
Institute of Thermal Engineering , Graz University of Technology

Ing. Christian Fink
Dipl.-Ing. Gottfried Purkarthofer
Richard Riva
AEE INTEC, Arbeitsgemeinschaft ERNEUERBARE ENERGIE, Institut für Nachhaltige Technologien

Ing. Harald Kaufmann
Technisches Büro für Biomasse, Solaranlagen und Nahwärmenetze

Dr. Christian Holter


Prof. Dipl.-Ing. Dr. Wolfgang Streicher
Institute of Thermal Engineering, Graz University of Technology
Inffeldgasse 25
A 8010 Graz
Tel.: +43 316 873-7306
Fax: +43 316 873-7305