Al Bahar Towers Responsive Facade by AHR

Abu Dhabi is a city known for its weather of intense sunshine, temperatures steadily above 38 Celsius degrees with 0% chance of rain. In such extreme weather conditions, architects need to consider environmental design as their top priority. Never mind that the sand can compromise the structural integrity of the building, the intense heat and glare can render a comfortable indoor environment relatively impossible if not properly addressed. 

AHR (former Aedas Architect ) have designed a responsive facade which takes cultural cues from the “mashrabiya”, a traditional Islamic lattice shading device.

Completed in June 2012, the 145 meter towers’ Mashrabiya shading system was developed by the computational design team at AHR. Using a parametric description for the geometry of the actuated facade panels, the team was able to simulate their operation in response to sun exposure and changing incidence angles during the different days of the year.

Each unit comprises a series of panels stretched PTFE (polytetrafluoroethylene) and is driven by a linear actuator to progressively open and close once per day, in response to a pre-programmed sequence that is calculated to avoid direct sunlight to From the moment it hits the facade and to limit direct solar gain to a maximum of 400 watts per meter. The whole system is protected by a variety of sensors that open the units in case conditions change, or raise to cloud winds. The effects of this system are global: reduce glare, improving the penetration of daylight, less reliance on artificial lighting, and over 50% reduction in solar gain, which results in a reduction of CO2 emissions of 1,750 tons per year. Geometric patterns that make up this giant screen include more than 1,000 mobile elements that contract and expand during the day, depending on the sun position.

The system is powered by renewable energy derived from photovoltaic panels. Wraps giant Lattice almost two towers completely except for the area north-facing facades.

Roofs facing south each tower incorporate photovoltaic cells, generating approximately five percent of the total energy required renewable energy sources, used for heating water. The towers have been one of the first buildings in the Gulf that received a LEED Silver rating.

The screen operated as a curtain wall, sitting two meters outside the buildings' exterior on an independent frame. Each triangle is coated with fiberglass and programmed to respond to the movement of the sun as a way to reduce solar gain and glare. In the evening, all the screens will close.

"At night they will all fold, so they will all close, so you'll see more of the facade. As the sun rises in the morning in the east, the mashrabiya along the east of the building will all begin to close and as the sun moves around the building, then that whole vertical strip of mashrabiya will move with the sun", said Peter Oborn, the deputy chairman of Aedas.

It is estimated that such a screen will reduce solar gain by more than 50%, and reduce the building's need for energy-draining air conditioning. Plus, the shade's ability to filter the light has allowed the architect to be more selective in glass finished. 

"It (the screen) allows us to use more naturally tinted glass, which lets more light in so you have better views and less need of artificial light. It's using an old technique in a modern way, which also responds to the aspiration of the emirate to take a leadership role in the area of sustainability", added Oborn.

The towers were awarded the 2012 Tall Building Innovation Award by the Council of Tall Buildings and Urban Habitat for the project's sustainable engineering and sensitive cultural and urban approach.

"The façade on Al Bahar, computer-controlloed to respond to optimal solar and light conditions, has never been achieved on this scale before. In addition, the expression of this outer akin seems to firmly root the building in its cultural context", explained Awards Juror Chris Wilkinson Eyre Architects.

Such an award acknowledges the importance of the necessary integration of architectural form, structure, systems, and sustainable design strategies.

Al Bahar Towers - Abu Dhabi

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