Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Solar Cooling of the Telekom buildings at Rottweil

In April 2011, a novel solar thermal system commenced operation in the buildings of Deutsche Telekom at Rottweil. It was meant to support the cooling and heating of the buildings. The solar thermal system is the third heat source feeding into the Telekom heating network. The existing absorption chillers used to be operated with gas boilers and the waste heat of the local independent thermal power station. The collector field covering 503m2 was installed on the roof of a factory building. The storage tank was installed on the outside next to the building. Together with the pumps and other monitoring equipment, the heat exchanger, situated between the collectors and the storage tank, was placed in the basement of the building. The solar thermal system saves a considerate amount of fuel used for air conditioning and space heating thus reducing greenhouse gas emissions as well as costs. 

The cold that is generated cools down offices, the call center as well as the server rooms of the Telekom company grounds. 

The solar heat reaches the consumer via a distributor. This distributor is also connected to chillers and other consumers of heat, like the central heating of the buildings. Thus, solar heat can be used either for heating or cooling purposes. To improve the efficiency of the collectors, the set system temperature must be lowered when cooling is not required. Thus, the solar yield is higher than what it would be if it were used exclusively for the absorption chillers.

The Telekom complex in Rottweil was chosen for Solarthermie2000plus for several reasons:

  • the  suitability of the existing roof for the installation of the collectors,
  • the years of experience with adsorption chillers,
  • the suitability of the adsorption chillers for solar thermal applications,
  • the good demonstration effect,
  • the high potential of reducing CO2 emissions.

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Project Partners


STRABAG Property and Facility Services GmbH
Projektleitung RLT
Berliner Allee 1
79114 Freiburg
Dipl.-Ing. (FH) Michael Imbery
phone +49 (0)761/40076513


Deutsche Telekom Network Projects & Services GmbH
Seig 27
78628 Rottweil


Johannes Friedlin Ingenieurbüro
Gröbenzeller Str. 5
82178 Puchheim
phone +49 (0) 89/80 12 92
fax +49 (0)89/80 16 72


Karl Böhme GmbH
Löbauer Straße 32a
02747 Herrnhut
phone +49 (0)35873 4830
fax 035873 48333

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Project Management Jülich on behalf of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety
Berlin Office
Breite Straße 3
10178 Berlin
Kerstin Krüger
Telephone 030/20199-530

Scientific and Technical assistance

University of Applied Sciences Offenburg
Badstraße 24
77652 Offenburg
Professor Elmar Bollin
Dipl.-Ing. (FH) Klaus Huber
phone +49 (0) 781/205-294

Program Monitoring

ZfS Rationelle Energietechnik GmbH
Verbindungsstraße 19
40723 Hilden
Dr. Felix Peuser
Dipl.-Ing. Reiner Croy
phone +49 (0) 2103/2444-0