Scheffelstraße 48

Freiburg, Germany

Multi family house | 20 sqm installation

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Project summary · Technical description · Financing · Development · Downloads

Project Summary

This is a listed builiding which was errected in 1899. The building got two more apartments in the attic floor and was retrofitted energetically. Following measures were done in 1999: insulation of the whole attic, cellar walls and facades; installing of dual-pane windows, glazing of the west faced balconies (loggias and conservatories), installing of historical box-type windows and a vestibule; installing of a central hot tap water and space heating system based on renewable energies (vacuum tube collector solar thermal system, rape oil CHP and a borehole heat pump)

The motivation for this project was to verify the possibility of retrofitting and modernisation of a listed building with systematic measures. The occasion was the 5th European conference "Solar Energy in Architecture and Urban Development" which took place in May 1998 in Bonn where the owner got the impulse to renovate a historical building. He had wanted to change a multi family building from 1899 into a Zero-Emission House. A combination of renewing the technical building equipment (including solar heat, geothermal and rape oil usage) with insulation measures using renewable materials.



Type of building

Multi family house

Number of users / dwellings, floors

6 dwellings
4 floors

Year of construction


Total effective area (heated)

604 m2

Hot tap water consumption (measured/estimated)

93.6 m3/a, measured

Whole energy consumption for heating purpose after CSTS implementation

51,000 kWh/a

System engineering

Year of construction of CSTS


Type of collectors

Vacuum tube collectors

Thermal power

14 kWtherm.

Aperture area of collectors*)

20 m2

Buffer storage

2.05 m3

Hot tap water storage

0.3 m3

Total capacity of boilers with energy source

64.98 kW, rape oil CHP + borehole heat pump

Type of hot tap water heating


Type of heating system



Total cost solar system

not available

Cost of the CSTS / gross area of collectors

not available 


not available


Output of solar heat**)

7,600 kWh/a

Reduction of final energy***)

10,100 kWh/a

CO2-emissions avoided

0.22 t CO2/a

Solar performance guarantee

*) Aperture area = light transmitting area of the front glass
**) measured, between storage and piping to taps (solar system output)
***) related to the measured output mentioned before



Technical description

About 20 m² of vacuum tube collectors are south oriented installed on the kerb roof. The collectors are not visible from the street.
Beside the collectors the heating system consists of a rape-oil CHP (combined heat and power unit) with 8 kW electrical and 16 kW thermal power and a geothermal heat pump. The old natural gas boiler was integrated into the whole concept to deliver peaks demands. Electricity is delivered by the rape-oil CHP; surpluses are sold to the local utility. Heat from the CHP is stored in the buffer storage. Hot tap water is heated via a 300 litre hot water buffer storage.
All components are linked and controlled via a BUS-system. This includes heat generators, storage-system and pumps.



Frau Weissflog
68161 Mannheim, Germany
Phone: +49 621 15901-0


Rothweiler Architekten
Zasiusstrasse 12
79102 Freiburg, Germany Phone: +49 761 704270

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