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Model city district refurbishment: Weingarten West, Freiburg

EnEff:Stadt - Forschung für die energieeffiziente Stadt
Flagship project LowEx demonstration building Bugginger Strasse 50

Flagship project LowEx demonstration building Bugginger Strasse 50

© Markus Löffelhardt

Settlement summary

Urban district
Project status Projektstatus: Phase 4Evaluation
Location of local community 79098 Freiburg, Baden-Württemberg
Settlement in figures 153.05 km² area, 220,000 residents
Developer, organizer Freiburger Stadtbau GmbH, badenova WärmePlus Verwaltungs-GmbH, Fraunhofer Institut für Solares Energiesysteme ISE
Settlement Medium-density and high-density linear apartment blocks and high-rise apartment complexes
Utilisation type General living
Housing estate area 0,3 km²
Residents 5.800
Gross floor area before 270.242 m²
Gross floor area after 271.892 m²
Living area before 155.270 m²
Living area after 160.846 m²
Accommodation units before 3.292 m²
Accommodation units after 14.037 m²
Age structure Stock of buildings mainly from the period 1958-1968 (35 buildings)
State of construction and refurbishment Around 1400 accommodation units require considerable refurbishment, as non-refurbished buildings built between 1958 and 1977 predominate
Heating system Heating coverage largely (97%) provided by means of a district heating network
Ownership structure Freiburger Stadtbau GmbH: owner of around 94,000 m² of living area; also individual owners and public institutions (schools, University of Applied Sciences)
Project themes

Project description

Energy-optimised construction, such as the improvement of our supply structures' energy efficiency, is one of the key spheres of action in the German Federal Government's 5th Energy Research Programme. One aspect of these activities comprises the "implementation of the results from research and development in demonstration projects with the objective of testing the efficiency, practical applicability and future marketability of various elements, as well as the transfer of results from research and development to the training and further education of professional planners, architects and tradespeople". The joint project "Weingarten 2020" goes beyond this approach and combines the demonstration project (passive house refurbishment of a 16-storey residential building) with the planning and implementation of an energy-oriented city district refurbishment, incorporating the supply infrastructure.

Community and climate protection

The city of Freiburg has called for continuation of its 1996 climate protection concept and of the climate protection targets which were set at that time (25% CO2 reduction by 2010). In order to expedite local climate protection, the CO2 emissions in Freiburg are to be reduced by at least 40% by the year 2030. As of 2008, 1.2 million euros (10% of the badenova AG concession levy for grid usage in the city area) flow into additional city climate protection projects each year. At least another two million euros per annum are spent on energy-oriented refurbishment of city buildings. Other projects from the climate protection programme include compliance with the passive house standard as regards new buildings and extension work in the city, the operation of combined heat and power (CHP) plants in public buildings / schools and the promotion of non-motorised transport. A 12-point plan lays out the specifics of the projects up to the year 2010.

The neighbourhood: stock of buildings and heating coverage

The Freiburg city district of Weingarten was built between 1960 and 1965, and its western part comprises an area of around 30 ha, in which around 5,800 people live. Most of the flats are owned by Freiburger Stadtbau GmbH, the municipal building society of the city of Freiburg. Heating coverage is realised by means of a district heating network operated by Freiburger Fernwärme GmbH; 60% of this network's demand is covered by a gas CHP plant.

The stock of buildings in the Weingarten West neighbourhood covers a total area of 171,000 m², plus an extra 7,200 m² to be obtained through a planned redensification with new buildings, which is currently in implementation. In the refurbishment area, four types of building are present: 16-storey high-rise buildings, 8-storey and 4-storey blocks of flats, and non-residential buildings (Protestant University of Applied Sciences for Social Studies, retail, grocery market, church and community centre). In the last five years, redensification has been realised with terraced houses. As the social structure of the area is complex, it is planned that the refurbishment shall be accompanied by measures within the joint federal and state government programme "Socially Integrative City". Freiburger Stadtbau GmbH's stock of flats in the refurbishment area comprises 94,000 m² of living area.

Heating coverage is realised by means of a district heating network; only the stock of small blocks of flats and single-family houses referred to as a special settlement is heated with individual heating systems. With four lines, the district heating network also covers the neighbouring city district of Rieselfeld and the Weingarten Ost neighbourhood, in addition to the neighbourhood of Weingarten West addressed here. The heating network is supplied with heat from two CHP plants, each with a heating capacity of 7.27 MW, and from three heating boilers, each with a heating capacity of 10.11 MW. Over the course of a year, the CHP plants' CHP coefficient is 0.86 and their share of fraction is 57%. As the heating network has an 82% annual degree of utilisation, the resulting primary energy factor for the district heating is 0.79. The PE factor of the individual heating systems is rated as 1.2. The generated heat amounts to 60 GWh p.a., of which 16.5 GWh p.a. is delivered to the network in the neighbourhood Weingarten West. The buildings' heat demand is 13.9 GWh.

Project objectives and procedure

The objective of the project is the planning, implementation and measurement-based analysis of the energy-oriented refurbishment of the buildings and energy supply of this city district. The primary energy consumption of all energy services is to be reduced by 30% in comparison to present consumption and the project is thus to represent an exemplary, future-proof model for energy-oriented city refurbishment. The way to achieve a sustainable, climate-neutral energy supply is to be demonstrated. Starting with the neighbourhood's present primary energy consumption of 21.6 GWh p.a., a reduction to 14.5 GWh p.a. is to be aimed for, i.e. a reduction of 32%.

The modernisation will be carried out from 2007 until around 2018. The refurbishment shall take place in 3 stages. The first stage sees the start of refurbishment of the four high-rise buildings, one of which is to be realised in 2010. The planning for the other building types began in 2009. One key objective is the networking of the parties involved: building society, energy supplier and tenants.

Concept and measures

For implementation of the project objectives, it is necessary to draw up an energy concept for the neighbourhood. This should encompass the refurbishment of the stock of buildings and optimisation of the energy supply.


A. To this end, the stock of buildings is to undergo the following measures in the period leading up to 2017:

1. Refurbishment of Freiburger Stadtbau GmbH's entire stock as KfW Energy Efficiency Buildings with 60 kWh/m² p.a. for heating and hot water.
2. Refurbishment of selected buildings belonging to Freiburger Stadtbau GmbH as KfW Energy Efficiency Buildings with 40 kWh/m² p.a. for heating and hot water.
3. Redensification of the city district by means of new buildings.
4. Refurbishment of the Adolf Reichwein School with 60 kWh/m² p.a. for heating and hot water.
5. Refurbishment of the protestant church's stock.
6. Further refurbishment of buildings in the Weingarten West neighbourhood realised by other owners and a reduction of electricity consumption are to be initiated by means of information meetings, but shall not be included in the balance.


B. The primary energy factor of the heat supply is to be reduced from today's 0.79 to 0.5 in the period leading up to 2017, by means of the following measures:

1. Reduction of the gas boiler's share of the heat supply from 43% to 25%, based on a lower heating requirement.
2. Optimisation of the network topology by means of downsizing network sections and decommissioning oversized subsections constructed in 1965.
3. Reduction of supply temperatures from the present 108 °C to 98 °C.
4. Integration of the heating of selected buildings ("research buildings" at Buggingerstr. 47 to 67) into the return line and corresponding reduction of return temperatures.
5. Reduction of output via the use of decentralised storage management.


C. LowEx demonstration buildings:

In three types of "research buildings", the following measures and innovative technologies are to be implemented as pilot projects:

Bugginger Strasse 50, 16-storey high-rise building

1. Use of new aerogel-based thermal insulation materials with thermal conductivity of 0.013 W/mK.
2. Downsizing of floor plans and an increase in net floor area. Improvement of the A/V ratio and reduction of the heating requirement to 35.7 kWh/m² p.a. as per DIN 4108-6.
3. Heating: Reduction to system temperatures 50/38.
4. Ventilation: Use of a central ventilation device with heat recovery; use of high-efficiency fans (Nova system), which are unusual in residential buildings; two-stage control of the ventilation system with thermal actuator.
5. Hot water: Reduction of circulation losses by means of pipe-in-pipe system.
6. Reduction of connected load via the use of decentralised storage management.

With a different concept to that applied for the Bugginger Strasse high-rise building, alternative decentralised heat exchangers are to be used for the hot water supply of 8-storey and 4-storey blocks of flats on Bugginger Strasse (numbers 47 to 67), in order to realise a system temperature of less than 60 °C here as well. As regards the heating, integration of the heating supply line into the district heating return line is planned.

Financing and support

Freiburger Stadtbau's planned investment volume for the building refurbishment amounts to around 114 million euros on its own. On top of this come the investments of other owners and all the measures related to the energy supply. These refurbishment measures are supported by the joint federal and state government programme "Socially Integrative City".

Energy characteristics

before potential after unit
Final energy requirements (electricity) 172.599,00   178.175,00
Final energy requirements (heat) 30,00   30,00 kWh/m²
Primary energy requirement (electricity) 84,00   45,00 kWh/m²
Primary energy requirement (heat) 81,00   81,00 kWh/m²
Primary energy ratio (electricity) 50,00   18,00 kWh/m²
Primary energy ratio (heat)     2,70
  • BINE projektinfo publication "On route to a low-energy urban district"

Additional information:

Related topics

News & events
Planning, project management
Freiburger Stadtbau GmbH
Planning, energy/heat supply
badenova WärmePlus Verwaltungs-GmbH
Research, evaluation
Fraunhofer Institut für Solare Energiesysteme ISE, Abteilung Thermische Anlagen- und Gebäudetechnik
Planning, architecture
Architekturbüro Rombach
Planning, technical building services equipment
Lenz Ingenieurbüro VDI
  • Aerial photo of the Weingarten West city district
  • Site plan of the refurbishment area: Freiburger Stadtbau's stock of buildings is coloured orange; the planned demonstration buildings are coloured red
  • Look at LowEx demonstration building Bugginger Strasse 50: Already refurbished 16-storey high-rise building
  • Bugginger Strasse 50 high-rise building in reconstruction
  • Objective: refurbishment to passive house standard
  • High-rise building refurbishment in detail: complex logistical requirements
  • Comparison of the neighbourhood's present final energy requirements and primary energy requirement with the target values (including household electricity)
  • Comparison of the present final energy requirements and primary energy requirement of the high-rise building Buggingerstr. 50 with those after refurbishment
  • Effects of the energy supply measures on the primary energy sources used for CHP and boilers, heat generated, electrical work and heat provided to the customers by the district heating network
  • Unloading of a 12-cylinder motor aggregate for the CHP system