Use of thermal heat - case study

The "Active Townhouse" (Aktiv-Stadthaus) just south of Frankfurt's main train station is the first multi-story residential building in Germany to comply with the Efficiency Plus Standard, which the Federal Ministry of Building introduced in 2012. On an annual basis, the new build is expected to achieve a net positive energy balance (including household electricity) both in terms of primary energy and final energy. Due to its elongated footprint, the architects had to think about how to minimise the overall external wall thickness for a better insulated external envelope. Therefore, they decided to use prefabricated elements in timber frame construction. In contrast, the primary structure of the building consists of load bearing dividing walls and reinforced concrete floor slabs.

The Stadthaus was conceived as an electricity-only building, including the heat and hot water supply as well as any other energy demands being powered by electricity. The entire heating requirement is provided by a 120 kW heat pump. The only backup power source is a 140 kW gas condensing boiler. The public sewer, 200 meters away, serves as a heat source into which a 55-metre-long stainless steel heat exchanger was installed. From here, a heat pipe leads into the ground floor of the building and back again.

The heat from the heat pump is fed into three 5000 l buffer storage tanks and from there into two separate heat cycles: a low temperature cycle (flow temperature 30-35 degrees C) for hot water supply as well as for additional radiators in the bathrooms. All apartments are fitted with decentralised MVHR units. These have been designed such that fresh air intake and exhaust air are separated from each other. Generally fresh air is drawn in from the courtyard to the north and exhaust air expelled on the street side to the south.

What an innovative way to sustain a building!