New town hall in Freiburg (D): Concept, performance and energy balance after the first year of monitoring of a large net plus-energy building

The town-hall building (Rathaus im Stühlinger: RIS) of the city of Freiburg (D) has been designed and built with the objective of a plus-energy balance and has been handed over to the city in November 2017. With a net floor area (NFA) of 22.650 m 2, it is to date one of the largest designed and built plus-energy building in Europe. The boundaries considered in the annual energy balance are limited to the loads of the heating, ventilation and cooling systems (HVAC), of the domestic hot water (DHW) and of the lighting; user-dependent energy demands are not considered. To achieve a positive primary energy balance, the building envelope is highly insulated, the energy supply is based on a low-exergy concept and onsite energy is generated by a large Building Integrated Photovoltaic (BIPV) plant combined with photovoltaic-thermal combined collectors (PVT). The central component of the heat generation is a ground-water coupled heat pump system supplying thermal activated concrete slabs, heating ceilings and air handling units (AHUs). Cooling is ensured over the geothermal well. To the date of this publication, the building has been intensively monitored for one-and-a-half year. Here, we present the energy concept as well as the results of the first monitoring period and provide an assessment of the energy balance in comparison to the plus-energy objective as well as an initial analysis of the load curves and of the heating and cooling systems.