Changing coats

Technology, products evolve as green structures become the norm
Sahely Mukerji
March 25, 2009
FABRICATION : COATINGS AND FILMS, GREEN, SOLAR

Coating, an integral part of glass manufacturing, can be divided into roughly two types: low-emissivity coatings, which improve the energy efficiency of glass used in architectural and automotive applications; and specialty coatings, which enhance the electro-optical, catalytic, or conducting properties of glass. Specialty coatings have currently become a major value-added market for the flat glass industry.

Flat glass is coated either offline by magnetron sputtering in a vacuum or online by chemical vapor deposition. The first low-E coatings were deposited by sputtering, a well established method for manufacturing a wide range of thin films.

Coating technology has come a long way since those first days of low-E. “In the past decade, we have seen a quantum leap in the technology of glass coatings and glass substrates,” says Donn McCann, manager, architectural design group, Viracon. For example, 10 years ago, a double silver low-E coating on clear glass offered a solar heat gain coefficient of .38. Today, newer coating technologies on clear glass have a SHGC of .26.”

Likewise, glass substrates have improved dramatically. McCann says. “New spectrally selective flat glass products such as Guardian’s CrystalGray and PPG’s OptiBlue offer greater energy efficiency than previous substrate offerings.”

More improvements are in the pipeline. With President Obama's focus on energy efficiency and consequent new building codes, more high-performance products will populate the market and coating technologies will become more sophisticated and offer more choices.

A significant industry trend for the next five years will be the enhancement of existing products to increase energy performance, McCann says. “Application methods such as sputter coating and vacuum deposition are improving and can meet today’s demands for reducing the carbon footprint along with thermal comfort and glare reduction for building owners and occupants.”

 
The California Academy of Sciences in San Francisco features one of the largest solar canopies in the world.

Mike Rupert, director, Technical Services, Performance Glazings, PPG Industries, Pittsburgh, agrees.

“Advances in new materials and nanotechnology are leading to products with quality and performance that could only be imagined a dozen years ago,” he says. “But many product advances will still come from basic refinements to float glass chemistry--soda and lime--and the current coating technology platforms: chemical vapor deposition and magnetron sputtering vacuum deposition.”

Spectrally selective products will see further improvements, Rupert says. “Gains will continue to be made on solar heat gain coefficients, balancing maximum visible light transmittance against minimum solar infrared transmittance.

“Switchable products made with transparent conductive oxide coatings likely will see further development, particularly for electrochromatic glazing to have broad commercial success,” Rupert adds.

CVD & MSVD also are vital to the future of solar energy applications, Rupert says. “Again, it starts with the basic composition to produce glass of high visible light transmittance, which is then deposited with anti-reflective coatings using CVD and MSVD technologies.”

MSVD also can be used to make mirrors that will improve the production cost of solar energy, Rupert says. PPG is working with the U.S. Department of Energy to develop and commercialize large-area, high-performance mirrors to support the development of efficient Concentrating Solar Power.

“We’re also using existing technologies in new ways,” McCann says. “Silk-screening, once primarily used for decorative purposes, has been repositioned to become a highly effective way to improve energy performance of glass.”

What will drive new technology, product development?

“Increased concern for occupancy comfort, reducing carbon footprints and meeting LEED requirements,” will lead to changes in coating technologies and product development, says Christine Shaffer, marketing manager, Viracon.

New building codes from ASHRAE and International Energy Conservation Code also will accelerate the development of new products, Rupert says. “Stricter building codes will push building owners and architects to specify better glass. Glass suppliers who don’t currently have products to meet these codes will be forced to develop such products. A manufacturer currently making these products will have a competitive advantage and will continue to improve their products’ performance to maintain that advantage.”

As Building Information Modeling continues to evolve, more real-world data will quantify the dramatic impact of high performance products, Rupert says. “That data will be factored into new product development.”

The growth of new glass products will depend on manufacturers’ abilities to more efficiently produce products, Rupert says. The development of glass coatings that offer greater durability for fabrication and handling also will be rewarded.

In regards to new technologies, “we continue to learn more about solar BIPV [building integrated photovoltaics] and switchable glass,” McCann says. “These technologies have some limitations that will need to be addressed for widespread growth in the future.”

Looking ahead, “clearly, the stage is set for new solar technologies to become more widely accepted in the U.S. over the coming years,” McCann says. One of the challenges with solar BIPV is that most glazing is vertical, rather than set at an angle or sloped, which is not an optimal for harvesting the sun’s rays, he says. "Any shading, from the building itself, nearby buildings or even light shelves can reduce the technology’s effectiveness. Solar cells cannot be covered by coatings, which generally limit the use of BIPV to the spandrel areas of buildings.”

BIPV systems can be complicated to install, and can require engineering expertise. "Due to the limited areas of use and the expense of the product and installation, payback is fairly long for the investment," McCann says. "This technology will move forward, but we expect the most progress to be made in European countries where BIPV technology is heavily subsidized by the government."

In summary, "the future of the architectural glass industry will be driven by products that perform better and deliver greater value to both the glass channel participants, as well as end users,” Rupert says.
 

E-mail Sahely Mukerji, senior editor, at smukerji@glass.org.