Searching for the Next Low-E

The U.S. Department of Energy’s Building Technologies Office is seeking the next game-changing, energy-saving window technology, says Karma Sawyer, technology manager and physical scientist for the BTO’s Emerging Technologies Program fenestration and building envelope technology portfolios. Essentially, this means the BTO is looking for the next low-E.

The BTO has established an “immense” goal to reduce building energy use by 50 percent by 2030, and windows will play a critical role in achieving that goal, Sawyer said Oct. 28 during the American Architectural Manufacturers Association’s National Fall Conference in Baltimore. To meet the challenging 2030 goal, the BTO is looking to work with the industry to develop energy-saving window technologies during the next decade. “The goal is to reduce building energy use, and according to our analysis, 18 percent of those savings can come from windows,” Sawyer said.

To show the potential of such government/glass industry partnerships, Sawyer discussed the development of low-emissivity glass that started out with a $2 million investment from the DOE. “I don’t have to tell people about the impact of low-E windows,” she said. Development of low-E began in 1976 with a Lawrence Berkeley National Lab/Southwall partnership, funded by the DOE. That partnership developed the first low-E in 1981. By 1988, low-E windows captured 20 percent of the residential market.

Sawyer said she recognizes that the incredible level of success of low-E glass in improving performance will be difficult to match. But, she said BTO is eyeing several top priority emerging window technologies that could greatly improve energy performance at as little cost to the end user as possible.

The highest priority R&D window technology for BTO is R-10 windows for commercial and residential applications. With 2025 cost targets of $6 or less per square foot (for the installed cost premium), R-10 windows have incredible potential to improve energy performance at a price point that will allow for market acceptance. However, Sawyer noted that, after R-7 is achieved, a reduction in price is more effective than an increase in R-value. “If you can reduce the cost, this will get your payback down. This is the major driver. At a certain point, we see diminishing returns from reducing the R-value,” she said.

Tier 2 R&D areas for the BTO’s window division include dynamic windows (for commercial and residential), and visible light redirection (for commercial only).

Sawyer also gave some exciting examples of R&D projects currently underway between the BTO and industry, starting with a smart residential dynamic highly insulating window being developed by LBNL (essentially a high-performing IGU with automated blinds controlled by sophisticated environmental sensors).

BTO is also working with the National Renewable Energy Laboratory on a transparent insulation for windows (a clear film retrofitted into windows, either as retrofit, or in the factory). And there’s the ITN Energy Systems Inc. retrofit, highly insulating EC window (a low-E film with high IR, with the potential of integrating an electrochromic film).

BTO is also looking at framing. In fact, the office has worked with Kawneer Co.’s Traco division to develop an R-5 commercial window with a U-factor of less than .22, while achieving architectural structural ratings. The funding helped the company achieve “cost-efficient product design, integrated with manufacturer upgrades,” Sawyer said. “This has been commercialized twice—once in early 2012 and once in June.”

BTO is actively seeking additional industry partners for development of even more energy-efficient window technologies. Sawyer recommended that industry companies look at developments within their own companies, seek out partnerships with others in the industry, and apply for Funding Opportunity Announcements within the BTO.

Devlin is senior editor for Glass Magazine. Write her at kdevlin@glass.org.