Forschungsgruppe-NET - Hochschule Offenburg

Solar Heat

Apartment Complex Freiburg, Wilmersdorfer Straβe 3 and 5

The apartment complex on Wilmersdorfer Straβe in Freiburg is under the administration of Familienheim Freiburg Baugenossenschaft e.G.. The complex consists of 14 individual buildings with a total of 257 apartments and about 600 inhabitants. The buildings were erected in 1970. The majority was renovated between 1992 and 1996 (heat insulation measures, facade renovation). The two 8-storey buildings on Wilmersdorfer Straβe 3 and 5 were refurbished between 1999 and 2001. Apart from outer insulation and all-glass balconies, the renovation included the addition of another storey creating attico apartments with the additional benefit of a flat roof.

In addition, the entire central heating facilities situated in Wilmersdorfer Straβe 3 were renovated. From there, the other buildings of the residential complex are supplied with potable water and warm water via a four-pipe-network. Two conventional oil-fired boilers generate the heat. one low temperature boiler with 895 kW and one condensing boiler with 800 kW.

To use the solar energy, two new buffer storage tanks were installed, each with a capacity of 4.500 liters. The two existing potable water tanks (dating from 1970) with a capacity of 4.500 Liters each were replaced by two new potable water tanks with a capacity of 2.000 liters each.

The new flat roofs of both buildings were covered with welded copper sheets. To begin with, special steel brackets had to be mounted on the concrete ceiling to secure the collector elevation. The exact azimuth of the collectors is 0; for reasons of space they had to be mounted on both roofs (28 meters high). Via an underground pipeline, the partial field on house nr 5 is connected to the central facility management building, which houses all the remaining solar technology (storage tanks, heat exchanger, pumps and system’s control).

The apartment complex on Wilmersdorferstraße was chosen for Solarthermie2000 for several reasons. First, the complete refurbishment of the conventional facilities (especially the central heating) and the buildings themselves, which accounted for an improved insulation. Second, the attractive and well-maintained impression of the entire complex and eventually the fact that the heat production costs would more than likely remain below 0.25 DM/kWh. 

We based our expectation of meeting the cost limit on the favorable climate location of Freiburg, for one, but also on the good quality of the buildings themselves (azimuth of the collector field, roof space, compact housing of the facilities and easy installation of the entire systems thanks to renovation). Together this ensured a very cost- effective installation of the entire solar thermal system. 

The large display panel is a special feature of the solar thermal system of the apartment complex on Wilmersdorfer Straße. Each ST-2000 Solar thermal systems has been equipped with a display panel (1.40 x 0.90 m) for demonstration and publicity purposes. It displays a simplified diagram of the solar thermal system and shows some real-time data, such as temperature, irradiation and solar yield. Yet, discussions with passers-by revealed that the technical diagrams showing heat exchangers and separate system circuits were not as easy to comprehend and that the values were thus not really informative to outsiders. 

This is why we tried to reduce the details of the display to a bare minimum and provide values that could be understood by anyone. The measured values are transmitted to the display panel in real-time from the actual location of the solar thermal system 300 meters away. People can thus see them instantaneously and compare them to the total sums, which are provided by a special interface integrated into the display panel. Thus, the amount of energy produced and consumed as well as the immediate impact on saving fossil fuel and the reduction of CO2 emissions become clear immediately.

Project Partners


Familienheim Freiburg
Baugenossenschaft e.G.
Gauß Straße 5
79114 Freiburg
Werner Eickhoff (Managing director)
phone +49 (0) 761/88887-0


Wilmersdorfer Straße 3 and 5
79114 Freiburg


Andreas Geiser Planungsbüro für Haustechnik
Untergarten 28
77966 Kappel-Grafenhausen
phone +49 (0) 7822 76122
fax +49 (0) 7822 866602


Firma Wagner & Co Solartechnik
Zimmermannstr. 12
35091 Cölbe
phone +49 (0) 6421/8007-0
fax +49 (0) 6421/8007-22

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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
Dr. Peter Donat
phone + 49 (0) 30 20199-427

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