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Alloys

Living within metal skin

By Gretchen Salois

Taking an entirely new look at infrastructure, one architect uses metals to let buildings breathe

May 2013 - An ectotherm is an organism that relies on its environment to control body temperature. That’s why many reptiles will lie in the sun during the day to conserve heat for colder hours. Although examples are prevalent in the animal kingdom, metal alloys aren’t usually thought of as a skin, like the hide or pelt of an animal, having qualities that allow it to adjust its temperature throughout the day. 

Over the years, Doris Sung, assistant professor at the University of Southern California and principal at DOSU Studio Architecture, Rolling Hills, Calif., thought of ways to make building skins more responsive and reactive to their surrounding climate. “In the past, building envelopes were static and separated the interior from the exterior,” Sung explains, “but now they can be considered mediators between changing climate conditions on the exterior and changing human needs on the interior.” 

Sung is in the process of developing smart thermobimetals and other shape-memory alloys, which represent a third skin beyond human flesh and clothing and will be used in architecture. “Thermobimetal is a lamination of two alloys of metal,” explains Sung. “When heated, one side will expand more than the other, resulting in a curl. When cooled down, expansion reduces and the sheet material goes back to its starting position—the metal remembers to return to its original state.

“The metals I’ve been using are different combinations of nickel, manganese and iron,” she continues. “It can be used as a screen that you add to the outside of a building or inside a double-skin facade to control the amount of sunlight coming through. The bimetal system can automatically open and shut as the sun’s rays move across the surface.” 

In other situations, Sung says different screens can sit between two layers of glass and the bimetal will open and close within the window system so it’s not necessary to use drapes or curtains to control temperature or light. Bimetal is also used in thermostats, gutters, downspouts and trim, as well as industrial parts. “It’s a relatively common and available material—it’s just never been used for architectural surfaces before,” she says.

From the outside, it’s easy to see the metal opening and closing. “The metal will blossom open and close as the sun moves. What we’re currently working on now is the balance between keeping the view as much as possible while still constricting the sun from entering the building,” Sung says. The right balance can help decrease the amount of air conditioning needed to cool down the interior of a building and ultimately reduce energy usage. 

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Changing the industry

Nickel, manganese and iron commonly are used in coil for thermostats in industrial buildings or cars and aren’t exactly ideal for exterior needs, but these materials served as a good jumping off point for experimentation. Sung says she’s currently working with manufacturers to develop metals such as titanium, stainless steel and aluminum to be used for exteriors. Unlike nickel, manganese and iron, stainless steel and aluminum are not brittle and can withstand the constant onslaught of the weather. 

Once durability is achieved, maintenance is minimal. If the metal skin is inside a glass apparatus, or in a vacuum state, there’s virtually no maintenance needed. If not, then cleaning off the exterior from time to time is necessary to remove dust and dirt from the exterior. The skin itself can be riveted, bolted or soldered together, similar to typical cladding processes. “No fancy tools are needed,” Sung adds. 

This combination of metals isn’t the only option for Sung as she continues to look for smart materials to be  used in architectural applications. Sung says she will continue to work with manufacturers and metallurgists to find the most efficient metal combinations to improve metal facades. “Buildings use about 40 percent of all energy in the world. We need to find ways to reduce the energy used in building skins,” she says. “In addition to the new assembly systems that are being developed, more effort is needed in the development of new and smart materials for building construction. We have a long way to catch up to other industries.” MM

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