The Council on Tall Buildings and Urban Habitat recently gave its Award for Innovation to a remarkable new system of sun shading that was developed for two towers in Abu Dhabi.
Engineer Peter Chipchase of Arup and Peter Oborn of Aedas Architects describe their design of a dynamic shading screen that wraps around the Al Bahar Towers in a video interview recorded by CTBUH. The interview is one of several recorded at the CBTUH awards symposium held at the Illinois Institute of Technology last October.
The shading system consists of "umbrella" like units in a geometric star-shaped pattern that open and close as the sun moves around the 25-storey buildings over the course of a day. Each unit is about two storey's high and they are connected in a lattice, standing about 2 metres off the glazed wall. There are around 1,000 shading units on each tower. The system is operated by solar power and keeps out solar glare and heat, thus providing energy savings, while allowing diffuse light inside.
Chipchase and Oborn suggest that the building challenges the typology of tall buildings, "especially in this part of the world." Oborn explains that the Al Bahar screen concept is based on Islamic geometric designs and is similar to the traditional mashrabiya. He suggests that designers should be considering vernacular architectural traditions more often.
Although the system is only 15% transparent, there is still plenty of indirect light entering inside. Occupants see through the screen to the outside as if through a "lightly gauzed net." The designers didn't have to use heavily tinted glass, so the views out are relatively clear.
When asked if the dynamic screen is a solution that might be used elsewhere, Oborn replies: "This is unique, designed for a particular building in a particular moment in time." He says that at the time they were commissioned for the project, which is the headquarters for the Abu Dhabi Investment Council, there was a lot happening in Abu Dhabi in terms of new initiatives to encourage more environmental ways of building, such as the introduction of new standards and guidelines.
Chipchase says that while the El Bahar screen system is unique, it is just one of many different options that could be used on buildings for shading. He questions: "Why start with glass?" He points out that solid facades, for example, are "fantastic"; they are thermal and structural and give great value for money "if treated in the right way."
People question whether the mechanical opening and closing devices will be durable in the harsh environment of Abu Dhabi, said Chipchase. Given the extreme dust and amount of ultra-violet light that punishes buildings in this climate, the selection of materials is very important, he said. But these units are somewhat self-cleaning and they have been tested through hundreds of thousands of cycles. The shading system is designed to last 150 years.
The video shows drawings and photographs of the system.
The CBTUH website has several other videograph interviews with winners of the 2012 awards, including one with the developer and architect (Ma Yansong of MAD Architects) of the Absolute Towers in Mississauga, Ontario that won the 2012 Best Tall Building Americas.
Images of the screening system of the Al Bahar Towers in Abu Dhabi, Aedas Architects.