KfW is a government-owned German Bank that helped bankroll the German solar renaissance in recent years - and it just moved into what it hopes will be the most energy-efficient office tower in Europe. The new addition to the company's Frankfurt headquarters by Sauerbruch Hutton is an aggressively engineered and colorful tower which is aiming for an astonishingly low energy consumption of 7 kW hr per square foot each year. That's more than two times more efficient than code, but the occupants actually benefit as the building is naturally cooled by fresh prevailing breezes thanks to a unique double skin composed of thousands of computer-controlled windows which that let just the right amount of air in.
Sauerbruch Hutton designed the building to harmonize with its surrounding environs. The shape of the building is angled to let the prevailing breezes slip by, reducing uneven air pressures across its surface. The sawtooth façade of the 400,000 square foot tower controls, with great precision, the amount of air that enters the building. Environmental monitors on the exterior and interior calculate when and how much the exterior windows should open, accounting for wind direction, temperature and speed.
The incoming air pressurizes the envelope sending fresh air evenly through floor vents around the exterior floor plate. Occupant can also open the interior windows to access the breeze. All of this engineering effort is to reduce cooling equipment demand to just for a couple of months of the year and supply healthy air without creating a disruptive breeze, especially near the windows. The double windows also cut incoming heat gain significantly while still providing ample natural light. The building also uses waste heat from the server rooms to preheat floor slabs and it distributes heat efficiently via a raised floor distribution system.
The building is a perfect example of how energy-efficient design can create a healthier work environment. The building’s colorful façade is layered with a different hue for each level, and it has been awarded the Best Tall Building in Europe. The tower is undergoing energy efficiency tests this summer to determine if it has earned the crown for the most efficient building in Europe.