The new, officially inaugurated building comprises six storeys with approx. 22,500 of gross floor area, where 840 employees of the local city administration are working. Two additional, similarly constructed, oval units are to follow to accommodate the new townhall, amongst other administrative offices. In its call for tenders for the 2013 design competition, the City of Freiburg not only defined the objective of concentrating all administrative bodies in one location, but also requested a highly functional, architecturally sophisticated and particularly energy-efficient administrative building.

The implemented concept of an energy-plus house was presented with thermal insulation and full-length triple glazing, permitting optimal use of daylight through the external blinds. To meet the electricity demand, particularly of the IT infrastructure, one has relied on PV modules integrated in the roof and on the facades – and PVT hybrid collectors were also partly installed. Heat pumps take over the heating and cooling functions and are supported in summer by a heat exchanger on the roof. Whilst a solar thermal plant heats the drinking water for the canteen, a biogas-fired boiler covers the peak loads. The ventilation system is equipped with a highly efficient heat recovery plant.

Since no energy-plus house of a comparable size has been built in Europe to date, a research project will follow this building project, funded by the Federal Ministry for Economic Affairs and Energy (BMWi) as part of the Energiewendebauen research initiative – an funding programme promoting innovative energy technologies. The City of Freiburg, DS-Plan planning office and the Fraunhofer ISE are investigating to what extent the targets set for energy saving and production of this building – tested for the first time while in operation – can be achieved. The performance of an intelligent control system, which controls the fluctuating production of energy from renewable sources, will also be analysed. A model-based analysis is to provide valuable information, particularly on the supply and control of energy in buildings of the future.