A Building That Responds to the Sun
On most days in Abu Dhabi, the air is dry and clear, and the sun is fierce. Controlling the effect of the sun on a building’s interior environment is a challenge. The Al Bahr Towers, the new headquarters of the Ahu Dhabi Investment Council, meet this challenge with a solution that is both ingenious and aesthetically fascinating. The 29 story-towers were designed by the international design firm, Aedas Architecture.
Two meters outside the building wall, there is a screen that wraps around the east-, south-, and west-facing sections of each tower. It is composed of hundreds of articulated triangular FRP-clad panels arranged in hexagonal “flowers.” The entire panel system is supported on a steel frame independent of the building. The orientation of each panel is fully adjustable, and they are controlled by computer. The programming responds to light conditions, and adjusts the position of each panel to provide shade from the correct angle, controlling heat solar gain and optimizing daylighting within the building.
The screen wall recalls a mashrabiya, an element of traditional Arabic architecture dating back centuries. The mashrabiya is a projecting window, usually on the second floor of a home, that is surrounded by a latticework screen. The lattice provides both shade and privacy, but still allows occupants a view of the exterior. In this case, the intricate Arabic lattice-work has been modernized into a continuously evolving geometric pattern.
The Al Bahr Towers mashrabiya fold back completely at night, presenting the maximum exposure of the actual building façade. As the sun rises in the east each morning, the panels facing East close in order to shield the building. Each panel adjusts to an optimal angle – which changes as the day progresses, and as the time of year progresses – to allow view and daylight while shielding from heat-gain and direct glare. As the sun moves across the sky, the closed stripe of panels follows it around the building, and panels no longer exposed to direct sun may partially or fully open.
This means that the responsive façade is not only constantly changing throughout the day, but will present a varying “texture” throughout the year as the sun’s altitude in the sky changes with the seasons.
The shielding action makes the building far more sustainable. It is estimated to reduce solar heat gain by 50%, allowing a major reduction in energy consumption for air conditioning. It also enabled the designers to select glazing with a fairly light tint, allowing more daylight to enter, reducing the need for artificial lighting, and giving occupants a more naturally-tinted view of the outside world. The towers have solar (photovoltaic) panels on the roof which supply power for, among other things, controlling the position of the mashrabiya panels.
The selection of FRP to take all this heat is interesting. Polymers are often thought of as heat-sensitive, but this application clearly shows that they can withstand some of the most demanding climate conditions our planet has to offer.
The project was awarded the 2012 Tall Building Innovation Award by the Council of Tall Buildings and Urban Habitat.
From Aedas Architecture:
“Aedas was appointed to design the new Abu Dhabi Investment Council Headquarters following an invited international competition. The 25-storey twin office towers in the United Arab Emirates will each accommodate between 1,000 and 1,100 employees. The design concept is both culturally and environmentally appropriate and complies with the aspirations of the recently published 2030 Abu Dhabi Development Plan.
“The south facing roofs of each tower incorporate photo-voltaic cells, generating approximately five percent of the total required energy from renewable energy sources.
“The cocoon-like buildings are based on a pre-rationalised geometric form, fine-tuned via parametric design tools to achieve optimal wall to floor area ratio. A solar-responsive dynamic shading screen further decreases solar gain. This ‘Mashrabiya’ acts as a secondary skin that mediates daylight and reduces glare. The system is driven by renewable energy derived from the photo voltaic panels.
The project was featured in the November Eco Solutions edition of CNN. http://www.youtube.com/watch?v=GSbJIlpv4Dc”
Images via Aedas Architecture, except as noted: