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Challenge / Goal

The project ‘Hauffgasse 37-47’ is a large housing block with 485 flats, completed in 1980 and owned by BWSG a ‘Limited Profit Housing Association’ (LPHA). With more than 53,000 m², it is the main refurbishment project undertaken in Vienna within SMARTER TOGETHER. The objectives were mainly focusing on the reduction of energy demand and the integration of renewable energy sources.


Main Measures implemented for the reduction of energy demand

▪ Refurbishment of the building envelope from 126kWh/m²a to 45kWh/m²a of final energy demand for heating and warm water
▪ Installation of highly efficient building equipment: lighting system (indoor and outdoor), elevator, HVAC components as well as new monitoring equipment
▪ Redesign and refurbishment of common open spaces, in particular the community centre by increasing its attractiveness and opening it up for inhabitants of the neighbourhood
▪ Redensification by construction of additional flats on top of the buildings (75 flats, 5.000 m², not included in the BEST table)

The project Hauffgasse 37-47 is supplied by a micro-district-heating-grid currently served from a gas-based heat plant, operated by the KWG

▪ Redesign and refurbishment of the heat transfer station and the hot water generation for the three separate heat sub-stations
▪ Hydraulic balancing of the heating system using a systematic approach to reduce energy consumption and system temperatures
▪ Installation of about 350m² of solar thermal energy on the roof of the buildings
▪ Feed-in of the solar thermal energy into the heat sub-stations in combination with buffer tanks
▪ Metering of the solar heat gains as well as the space heating and hot water consumption by radio heat meters

Main measures implemented for the integration of renewable energy

The district heating network was built at the beginning of 1976 and by now, it provides hot water for space heating and warm water for different customers (ÖBB railway, 1.200 flats and 20 companies) between the streets “Grillgasse” in the East and “Geiselbergstrasse” in the West.
The heating plant is located on the site of the ÖBB railway workshop with a capacity of 30 MW powered by three natural gas-boilers at a maximum of 110°C.

Additional to the building renovation, all three existing district heating stations and the four warm water stations will be renewed to raise their efficiency. On the roof of block 1 and block 3, PV panels are installed to use the solar-electric-power to sustain the warm water station with separate electric boilers to reduce the usage of the natural gas. The final concept was the result of in total four different feasibility studies done by KWG. That shows that especially the integration of renewable energy systems in existing buildings is always a question of the technical and legal circumstances.

Feasibility Study No. 1:
At the time of the projects start, the plan was to build up a thermal solar system. But because of the structure of the existing buildings the weight of the system is much too high to be installed on the roof. There was also not enough space for the high-capacity buffer, with a volume around 30 m³ (to produce warm water for around 150 MWh).
Feasibility Study No. 2:
In the follow up, the project refocused in order to install photovoltaic panels on the roof and on the outside walls in view of producing up to 150 kWp solar-electric-power. But there was also the problem with the statics of the building, the system was to heavy. Panels on the outside walls simply did not fulfil the requirements of earthquake security (walls are not thick enough).
Feasibility Study No. 3:
Research was undertaken in order to find less heavy panels and PV-panels, which could be taped on the roof and the walls. However, the panels had no certificate for high buildings (especially fire protection).
Feasibility Study No. 4:
Installation of normal PV-panels on the roof only at block 1 (ca. 275 m²) and block 3 (ca. 80 m²) with around the half of capacity, in total about 75 kWp located to the east and west side to use the sun from the hole day (morning to evening). The separate electric boilers use the solar power to heat up the circulating water for the warm water supply.

Citizen participation

The preparation phase already started in 2013 with a tenants information and participation process. From that time, many activities were organised by wohnbund:consult, an enterprise specialised on communication and participation activities in housing estates, together with the building owner BWSG. Furthermore, an information box ‘on site’ and a website for all questions and needs concerning the planned refurbishment were implemented, so that all information and results were documented and accessible for everyone. On this basis – of a trustful communication on eye-level – the further participation of the tenants within Smarter Together was possible.


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Time period

Planning time: 2 to 5 years

Implementation time: 2 to 5 years


KWG; City of Vienna; Construction Companies; GSD; Wohnbund:consult

Service providers

BWSG; KWG; City of Vienna; GSD; Wohnbund:consult

End users

BWSG (Building Owner); Tenants (about 1.000 Inhabitants in 485 flats)

    Main benefits

  • Decreasing energy consumption in buildings

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