In the Middle East, glass office towers have sprung up without sufficient thought paid to the harsh desert climate. In order to prevent unbearable glare and solar thermal gain inside, the glazing chosen for these buildings allows only 10 or 15 percent daylight transmission on average. So instead of enjoying the region’s most abundant natural resource at their desks, building occupants illuminate their workplaces electrically.
Photo © Aedas
Long before glass curtain walls existed, regional architects had mastered the sun. The traditional wood shade-screen known as mashrabiya controls daylight penetration in the intricate geometric patterns signature to Islamic culture. For the Al Bahar Towers, a pair of 25-story offices headquartering the Abu Dhabi Investment Council, the global architecture firm Aedas put a futuristic spin on the medieval technique.
Although Aedas could have simply adapted the historic latticework to the scale of a glass-and-steel high-rise, the Al Bahar design team decided against a traditional static response. Instead, it installed 1,000 ‘umbrellas’ on the towers’ sun-facing elevations, and they individually open and close over the course of the day. The motorized shades—each one actually a six-part triangle whose subdivisions can fold in or outward—are programmed to respond to daily sun trajectories for the year.
Each unit of the modern mashrabiya includes 30 components, with PTFE-coated fiberglass mesh attached to a frame made of aluminum and stainless steel. Mounted two meters (6.5 feet) from the building via brackets, the umbrellas provide 80 percent shading, allowing Aedas to specify glazing with 40 percent light transmission while still reducing Al Bahar’s cooling load by 20 percent. The motors are powered by photovoltaic arrays installed on the twin towers’ south facing roofs.
In June, the Chicago-based Council on Tall Buildings and Urban Habitat awarded the project its first-ever Innovation Award, thanks precisely to the computer-controlled shading system. The book Al Bahar Towers: The Abu Dhabi Investment Council Headquarters (John Wiley & Sons, 2012) provides further details about this amalgam of past, present, and future.