Glass apart

Glass buildings have redefined the landscapes of growing cities such as Dubai

The construction industry has increased the use of glass in public buildings and office complexes over the past few decades, and the trend looks set to continue.

A relatively inexpensive material, glass offers superior properties in many applications. It is also environmentally friendly and fully recyclable - increasingly important considerations.

Arthur Millwood technical and training manager at Emirates Glass, one of the leading providers of architectural glass in the Middle East, says, "The climate in the Gulf is characterised by almost 340 days of bright sun and more or less about 200 days of high temperatures.

"Even during the cool season, the sun (now at lower angles) can penetrate into buildings, especially in the afternoon, and cause solar heat-gain, which can necessitate the use of air-conditioning.

"Therefore, the sun is often considered ‘the enemy' and if one uses a solar reflective glass for all-year protection, one will enjoy the additional benefit of protection, from conducted heat-gain (air-to-air) when ambient temperatures are high during the summer."

Energy savings
He adds, "Remember that the main source of heat-gain is through the windows, not the structure itself. In the UAE, most buildings are glazed with solar reflective glass, much of it being ‘high performance' glass which can cut solar energy transmission by a factor of x6 based on RHG (Relative Heat Gain-W/square metre) compared to clear glass.

"There are many less-effective glass products, which give increased light transmission, but also more heat-gain (more light emits more heat)."

Established in 1948, the National Glass Association (NGA) is the largest trade association representing the architectural and automotive glass industry. Consisting of about 4,000 member companies and locations, the NGA organizes the industry's leading events and publications.

According to the NGA, "The origin and use of glass goes back almost 5,000 years. Archaeologists discovered evidence of glass objects dating as early as 3,000 B.C. The ancient Greeks used glass in their buildings. Historical records from the period refer to baths and rooms lined with glass."

Modern buildings
Modern glass buildings have redefined the landscapes of growing cities such as Dubai. Millwood says, "Dubai municipality is the first emirate to put legislation in place to control the minimum acceptable performance of energy-saving glass for buildings.

"The municipality's ‘least-acceptable' glass would have a heat-gain reduction of about x 2.5 (based on RHG) compared to clear glass, but clearly they are hoping that developers and architects will go for better-performing options in order to minimise solar heat gain, to optimise cooling loads and costs and to control the rapidly increasing demand for cooling power on the UAE power generators."

Extreme discomfort
He adds, "Without the use of solar-control glass, building facades would cause unacceptable indoor environments with excessive glare and heat, only mitigated by extensive use of blinds, curtains and huge air-conditioning bills.

"In commercial buildings, where floor-rentals are very high, it is necessary to locate employees close to the windows. Potentially, bad selection of glass can cause extreme discomfort and poor working conditions."

Emirates Glass has been used on a number of commercial buildings including Dubai airport, Emirates Towers, Dusit Hotel, Dubai Exhibition Centre, Capital Towers, Emaar Office Complex and Burj Dubai Business Park.

The techniques used to make glass have been redeveloped over time. "Today, all energy-efficient glass consists of sealed double-glazing in which, typically, two sheets of 6mm glass are bonded with special highly durable sealants to a 12mm hollow aluminium space to create a 24mm thick unit.

"The 12mm inter-glass cavity provides a 50 per cent improvement in thermal insulation compared to clear single glass," says Millwood.

"However, the air-space by itself, will not protect air-conditioned buildings from strong solar heating, and so a reflective coating has to be applied on the inner face of the outside pane, which furthermore can be tinted to create a reflective coloured appearance," he adds.

Economic benefits
Millwood cites some of the eco-friendly benefits of having ‘treated glass' facades.

He says, "Apart from the obvious advantages of solar and light control, glass facades are usually highly durable, easy-to-maintain, and are very cost-effective from initial cost to life-cost.

"In addition, good solar control glass, especially sputter-coated glass types, may give excellent privacy in densely occupied areas like Bur Dubai or Dubai Marina, because you cannot see inside the building during the day."

He further explains, "Here, in Dubai, a large range of solar control metallic coatings, thin enough to see through, can be manufactured locally by means of a highly sophisticated process in which the metal coatings are applied by cathodic sputtering in a full vacuum.

"Sputtering technology offers a huge range of colours reflectances and transmissions to the designer - a true rainbow of options, typified by the EmiCool range of high performance produced by Emirates Glass.

"Alternatively, and also in widespread use, is the ‘pyrolitic' type of reflective glass, not locally produced, in which the metallic coating is applied during the actual floatation of the glass itself. Pyrolitic glass is characterised by a much narrower range of coating options, with more restricted choices of colour and performance."