Researchers use nanotechnology for new techniques that could cut your cooling and heating bills
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Modern windows can do a decent job of saving energy by keeping indoor and outdoor climates apart, but they have some big shortcomings.
It is tough, for example, to reap the benefit of sunlight streaming through a window without also taking in the sun’s heat, which isn’t welcome on a steamy summer day. Conversely, that same heat—so desirable in winter—comes with light whether you want it or not. If only windows could control heat and light independently—and at a low enough cost that this feature could be used in all kinds of buildings.
Researchers at the University of Texas at Austin and the Lawrence Berkeley National Laboratory have been working on the problem. In 2013, they used nanotechnology to come up with a two-part coating that, when triggered by a small electrical impulse, let windows admit light while repelling heat.
In two new papers, they describe some significant advances. In the journal Nano Letters, they describe having accelerated the switching process from hours to minutes so windows can adjust far more rapidly to changing environments. Smart windows with this technology could block most heat while admitting varying amounts of light.
In the second paper, in the Journal of the American Chemical Society, the researchers describe the development of a different coating that permits a “warm” mode that lets windows admit heat while blocking light. This embryonic technology wouldn’t help much in, say, Miami, but it could be handy in Minneapolis, where people want heat yet may not like glare.
Lead scientist Delia Milliron, a professor of chemical engineering at UT-Austin, says the team’s research relies on coating materials that are basically invisible when applied to the inside of the outer pane of a dual-pane window. When triggered by a small electrical impulse, the coating tints the windows darker—but not so dark as to obviate the need for blinds or window treatments. The electrical impulse to make these smart windows work could be controlled by a thermostat with a manual override.
Dr. Milliron notes that existing “electrochromic” window technology, which doesn’t typically rely on nanotechnology, is used sparingly because the resulting windows are expensive. Her goal is to make them affordable enough to be commonplace, like such current technologies as dual window panes, argon gas between panes or “Low E” coatings (the last two improve a window’s insulating properties). These technologies would still be needed, Dr. Milliron says.
Many windows still lack even these enhancements. Dr. Milliron estimates that the package of features her team is building into windows could save 10% to 25% of the energy used for heating and cooling compared with standard building-code windows that don’t have argon and other improvements. And the thermal benefits would occur during the day, when energy usage is heaviest, suggesting that the technology might help power utilities better handle spikes in demand during extreme weather.
“Nanocomposite Architecture for Rapid, Spectrally-Selective Electrochromic Modulation of Solar Transmittance,” Jongwook Kim, Delia J. Milliron et al, Nano Letters (July 20)
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