As popularity of translucence and see-through structures grow, architects use more and more glass in commercial buildings. Today’s federal buildings, newspaper offices, skyscrapers and bridges, all feature beautiful and striking glazing. Even extreme weather conditions or fear of terrorist attacks cannot keep architects from cladding buildings in glass.
In the following article, glazed structures in four kinds of extreme conditions are discussed: extreme heat, extreme cold, earthquake zones and hurricane-prone areas. Architects talk about the challenges and offer solutions to work around the obstacles.
Challenges of using structural glass in high heat
By Sahely Mukerji
Keeping up with the trend of “translucence is beautiful,” architects are using more and more glass in structures regardless of location and climate. However, extreme climates, such as high temperatures in Phoenix or in the tropical countries, challenge architects when using glass in a building project.
“While there are various issues concerning the extensive use of glass in hot climates, the predominant issue of increasing concern is that of thermal performance with respect to comfort and energy consumption,” says Mic Patterson, director, Pre Construction Services, ASI Holdings of Los Angeles, the advanced structures division of Enclos Corp., Eagan, Minn. “The increasing use of glass in architecture is driven by the designer’s, the owner’s and the user’s desire for the benefits produced thereby: natural daylight, transparency and view. And they are unwilling to sacrifice these benefits in the face of rising energy prices, even in areas of extreme climate. The challenge goes to the design-and-build teams, the material suppliers and fabricators, to devise new materials, products and techniques that improve the energy performance of large glazed spaces. And the industry is rising to this occasion in a most invigorating fashion.”
Thermally broken frames, isolation gaskets and double glazing are being used in glazing structures in extreme hot climates, says Dan Hajjar, vice president and regional manager Gulf, HOK. “One of the primary challenges that we have been trying to deal with is the avoidance of using reflective glass. It not only picks up the dust factor but also requires more maintenance due to its appearance. We have been utilizing high-performance glass, which is relatively clear but does not compromise the performance of the envelope.”
High-performance glass also controls solar heat gain, “by far, the biggest challenge of working in extreme heat,” says Greg Buchanan, principal, senior project architect and architectural discipline leader for the Phoenix office of SmithGroup. “Even in the desert, the specification of high-performance glass, with low-emissivity coating, and an appropriate solar heat gain and shading co-efficient can drastically reduce a building’s uptake of heat from the sun.” In addition the orientation of the project structure can have a significant impact on solar heat gain, he says. “By utilizing materials and techniques appropriate to extreme heat, the buildings of the desert can be energy efficient and appropriate to their environment.”
Energy efficiency and a renewed emphasis on sustainability are the primary reasons for more glass usage in structures even in extreme climates, says David Reese, director of HOK Houston Science + Technology Group. “The new approach is therefore to use indirect natural lighting strategies—windows deeply set into a building, shading devices and light shelves—to bounce light into the building interior without direct solar penetration and maximize the harvesting of natural light. High-tech glass and coatings are more technical means of maximizing natural light while minimizing undesired heat-gain.”
While mirrored surfaces and coatings aimed at modifying the transmittance of solar rays can significantly reduce penetration, using these technical approaches alone is often not enough, Reese says. “The design must ultimately employ strategies of its own, as part of an overall building plan, that determine the mechanical systems required to cool the space,” he says. “In such cases, limiting the amount and orientation of fenestration can become a driving force in design and building image in order to comply with mandated energy performance guidelines.”
Suvarnabhumi International Airport in Bangkok, completed in September 2006, uses a whole building design to tackle extreme hot conditions, Patterson says. He was the chairman of ASI Asiatic Co., Thailand, at the time of construction.
Designers typically become restrictive in their use of glass in a challenging climate such as Bangkok, Patterson says. “It is a hot place year round, and one of the hotter local climates in Southeast Asia,” he says. “Combine this with monsoon rains and high year-round humidity, and you have a climate rated as extreme.”
The climatic realities, however, could not stop the designers from being creative in their use of glass at the airport, Patterson says. The terminal building is essentially a glass box. At 563,000 square meters it’s the second largest single building enclosure in the world, only slightly smaller than Hong Kong’s Chep Lok airport. The concourse structures also make extensive use of glass in combination with fabric membranes.
“ASI’s work involved the design and engineering of the 120-foot tall cable truss system supporting the glass facades of the terminal building, but I took considerable interest in many aspects of this airport design, a bold statement by architect Helmut Jahn, engineer Warner Sobek, and climate consultant Mattias Schuler,” Patterson says. “Climate consulting firms, such as Schuler’s firm Transsolar, are playing an increasingly important role in projects such as this, with a primary focus on building facades and the use of glass.”
The thermal issues were not treated simply as a function of the facade system, but rather as a function of the whole building design, Patterson says. Instead of insulating glass units, the extensive facades use more than 200,000 square meters of laminated glass throughout the airport structures. “The glass was heat-strengthened rather than tempered to eliminate any potential for spontaneous breakage caused by nickel-sulfide inclusions,” he says. “There is a higher incidence of spontaneous breakage in Southeast Asia, although it is unclear whether this is a problem of the high ambient temperatures in the area or the result of lower quality glass supply.”
A polyvinyl butyral interlayer from DuPont, Wilmington, Del., was used to improve acoustics, resistance to fallout, and to provide safer breakage characteristics in blast conditions, Patterson says. The facade glass is clear and designed for high transparency. Deep roof overhangs all around the terminal building prevent direct solar penetration through the facades. The overhangs comprise a trellis system that serves to block solar radiation while encouraging maximum natural ventilation.
The terminal roof glass utilizes a bronze tinted PVB interlayer, with low-e coating and a ceramic frit in a black and white dot pattern barely discernible to the naked eye, to improve the shading coefficient of the glass and limit heat gain into the interior, Patterson says.
Glass sections alternate with fabric sections in the vaulted concourse structures. The glass in these areas uses a varying frit pattern, dense at the top of the structure where solar exposure is highest, and gradually decreasing in density to full transparency at the pedestrian levels at the base of the concourse structures.
A radiant cooling system is built into the floor, augmented by a low pressure cooling system at floor level. The cooling system is designed to provide a stratified temperature environment ranging from an optimum comfort level at the pedestrian floor level to ambient outdoor temperature at the top of the structures.
It is too early to know the success of the designer’s strategies in terms of energy consumption and year-round comfort. “I had my first opportunity to fly into the new airport a few months after it opened,” Patterson says. “I found it to be elegant, modern, brightly lit and comfortably cool; but it was a relatively mild December day in Thailand. The scorching heat of April will provide the true test.”