Double skin glass façade provides protective enclosure and additional thermal insulation

Operational since March 2012, Sowwah Square in Abu Dhabi’s new Central Business District (CBD) on Al Maryah Island recently announced enjoying success in its first year of activity with 185% increase in community size and being home to over 1,500 people and 46 multi-national companies.

In the lead up to Cityscape Abu Dhabi 2013, Ali Eid Al Mheiri, Executive Director, Mubadala Real Estate & Infrastructure (MREI), reflecting on the importance of Sowwah Square, said, “Sowwah Square marks the completion of Phase 1 of Al Maryah Island’s development and an important milestone in the Government’s strategic urban development plan.”

Climate Control Middle East, in its endeavour to find out more about the project’s energy-efficiency profile spoke to Goettsch Partners, the firm of architects that designed the structure. With regard to double-glazing systems and the built-in air pocket features, Matthew Berglund, Associate at Goettsch Partners, said: “Only double glazing or Insulated Glass Units (IGUs) have been used for the glass enclosures on Sowwah Square. The air pocket in an IGU restricts the direct exchange of radiation between the warm glass surface (outside) and the cold glass surface (inside). Glass in the IGU also has a thermal protection coating (low emissivity or “Low-E” coating) further reducing energy exchange. In addition, the glazing units have a solar control coating which allows selective light transmittance. That is to say, the coating is transparent to the spectrum of light that is visible, yet it reflects or absorbs the spectrum of light which causes heat gain within a building – long wave infrared radiation.

Throwing light on the active and passive sun shading elements installed in the buildings, Berglund revealed that there were two primary wall types typical to each tower of Sowwah Square. “Wall Type “A” is a unitised curtain wall façade with external horizontal sunshades,” he said. “The shades are laminated glass with an opaque dot frit with 50% coverage. The external shades on the south exposure are 750mm deep and fixed (passive) every one metre providing shade for the high sun angle at south exposures. The external shades on the east and west exposure are 750mm deep and spaced every one metre and rotate (active) to a near vertical position to provide shade from the low sun angles at east and west exposures. Rotation is controlled by BMS interface and can be set to track the sun’s path. Wall Type “B” is a double skin façade with 750mm cavity containing perforated aluminum venetian blinds and a continuous maintenance access platform.”

The primary effect of the double skin façade, Berglund explained, was to provide a protective enclosure for the venetian blinds, which are deployed automatically and are controlled by BMS to rotate and track the sun’s path. Since any shading device absorbs and re-radiates heat when blocking solar radiation, it is more effectively located outside of the building enclosure to prevent heat gain, Berglund pointed out, and added that in this case, shades within a glazed cavity were outside of the conditioned building interior, yet within a weather-tight protective enclosure.

“A second effect of this double skin façade was to provide additional thermal insulation, Berglund said. “Prior to being exhausted from the building, the extract air from the ventilation and air conditioning system is injected into the façade cavity and circulated to a final point of exhaust. The effect is to utilise the cavity as an insulating buffer between outside and inside temperatures,” he explained.

Abdulla Al Shamsi, Vice President Mubadala Real Estate & Infrastructure (MREI), added: “The ventilated, double skin façades provide a buffer – an external-coat that protects you from the external climate. In doing so, it reduces operational costs, reliance on air conditioning and is more efficient with the HVACR systems as well as enhances the end-user’s comfort.”

When asked if the buildings were also equipped with daylight sensors and dimming systems, Berglund replied: “Yes, each floor of every building is equipped with a lighting control system. The system is used to “harvest daylight,” that is to say, inputs from the daylight sensors in the ceiling allow the control system to dim individual fixtures in the locations where daylight is providing the required illumination levels. The BMS control and monitors the complete HVAC and electrical systems, the active shading devices and interfaces with the lighting control system.”