You don't need to seal yourself in to live green. That's the message from the engineers of the Westarkade, a colorful high-rise that officially opened in Frankfurt in July.
The 15-story glass tower glows with natural light and offers windows that open—a comfort that can wreak havoc with energy efficiency. But the Westarkade's first-of-a-kind "pressure ring" facade and sophisticated, sensor-rich control scheme promise to consume no more than 100 kilowatt-hours of energy per square meter per year. That would make it a world-class energy miser, using half as much energy as a conventional office building in Europe and as little as a third of the U.S. average.
"It's an aggressive goal, especially with this building that's all glass," says Mark Perepelitza, a facade expert with Zimmer Gunsul Frasca Architects, based in Portland, Ore.
The Westarkade's dynamic facade is a descendant of a 1990s German design that was developed to manage excess sunlight in glass towers. Horizontal venetian blinds installed outside of the tower's glass envelope reject unwanted summer heat, while a pane of glass installed over the blinds and ventilated at the top and bottom protects the blinds from high winds. The "double skin" design comes up short, however, when architects add windows that open, which is typically mandated under European labor codes. Winds create a pressure differential around the tower, sending drafts ripping across floors when workers exercise their right to natural ventilation. "Sheets are blowing from the tables and the doors are smashing and the heat is going out," says Tom Geister, a senior architect with Berlin-based Sauerbruch Hutton, the firm that designed the Westarkade.
Sauerbruch Hutton worked with Stuttgart-based firm Transsolar KlimaEngineering to solve the problem. The firms installed 180 vertical ventilation flaps in the outer skin to manage air flows, creating what they call a pressure-ring facade. The building's control system takes constant feedback from a rooftop weather station and from 40 sensors deployed throughout the building that measure temperature, pressure, and sunlight. The system continually opens and closes individual flaps to maintain a ring of consistent positive pressure around the structure, preventing strong winds from entering.