KfW Westarkade, Frankfurt, Germany

First high-rise office building worldwide below 100 kWh/m²/a primary energy consumption. 15-storey extension to the KfW Banking Group’s headquarters in Frankfurt, completing an existing ensemble of buildings from the 70s, 80s and 90s. Situated in the city’s West End, it lies adjacent to the central Palmengarten park. It offers space for some 700 workplaces, as well as conference facilities. The 184 ft-tall (56 m) tower is integrated into the cluster of existing office towers, in its materiality and colour the new building extends and complements the existing ensemble. The double-layered wind-pressurized facade offers natural ventilation independent of external conditions, high thermal insulation values and efficient solar protection. Facade wind pressures were analysed according to their impact on natural ventilation of the offices. The design and active control of the facade guarantees ventilation from the facade via operable windows while limiting unwanted cross ventilation and draft between the offices. The developed pressure ring facade concept enables a hybrid ventilation approach for the building: Mechanical ventilation with heat recovery in winter periods, natural ventilation via the facade in intermediate seasons and precooled supply air via a ground coupled duct in hot summer periods.
Activated radiant slabs in all office areas enhance thermal comfort in summer and winter. Optimized solar protection, glare control and daylight redirection assure good daylight conditions for all office areas at minimized artificial lighting energy consumption. A connecting to the KfW’s efficient heating and cooling network with use of trigeneration, biomass heating, use of excess heat from data center and free cooling energy from evaporative cooling towers helps to further reduce the building’s primary energy consumption. Assessments by dynamic thermal building and system simulations show a primary energy consumption of well below 100 kWh/m²/a including the savings from the natural ventilation concept.
2011 „best tall building Europe“ (www.ctbhu.org)