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Green Building News

Lab Hopes to Develop Paint-On Window Coating

Scientists are working to develop a simple-to-apply coating that would offer a cheaper alternative to window replacement or professionally applied films

A paint-on heat-reflective coating under development at the Lawrence Berkeley National Laboratory allows visible light to pass through the glass while bouncing the infrared portion of the spectrum back.
Image Credit: Garret Miyake, University of Colorado

Scientists at the Lawrence Berkeley National Laboratory are developing a paint-on low-solar-gain window coating that would offer the same energy benefits as a window replacement or commercially applied film at a small fraction of the cost.

The coating is designed to reflect infrared light but allow visible light to pass through, according to an article posted at the lab’s website.

New windows offer a variety of coatings designed to control both the amount of visible light and solar heat gain passing through window glass, but replacing old windows in order to get those energy-efficiency benefits is expensive. Retrofit window films also are available, but they require professional installation, the lab said.

“Instead of hiring expensive contractors, a homeowner could go to the local hardware store, buy the coating, and paint it on as a DIY retrofit — that’s the vision,” said Berkeley Lab scientist Raymond Weitekamp. “The coating will selectively reflect the infrared solar energy back to the sky while allowing visible light to pass through, which will drastically improve the energy efficiency of windows, particularly in warm climates and southern climates, where a significant fraction of energy usage goes to air conditioning.”

A low-cost option for improving window performance has the potential to save 35 billion kilowatt hours of electricity per year, according to the lab, reducing carbon emissions by 24 billion kilograms a year. That’s the same impact as taking 5 million cars off the road.

Program aids entrepreneurial researchers

The technology is based on a type of material called a bottlebrush polymer, which Weitekamp studied as a graduate student at Caltech. He went to the Berkeley Lab last year as part of a program for entrepreneurial researchers called Cyclotron Road with the goal of commercializing the polymers.

The Berkeley project is getting part of a $3.95 million award from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E).

The team’s goal is to develop a low-solar-gain coating that costs consumers $1.50 per square foot, which the lab says is 10% of the cost for commercially installed retrofit window coatings.

“ARPA-E invests in high-risk, high-reward projects,” said Arman Shehabi, a member of the research team. “The high reward in this project isn’t in the performance improvement. It’s transformative in how windows could be retrofitted — it’s something you can do yourself. The market need is very large, and there’s nothing low-cost out there that meets that need.”

The lab didn’t offer any estimates of when the coating might actually be ready for the commercial market. One remaining challenge is to make a coating that reflects infrared light but doesn’t make the visible light passing through the glass appear hazy.


  1. user-3549882 | | #1

    Paint-on Window Coating
    Leave it to LBNL. If a low cost infrared blocking film works, this could be a break-through product.

    In summer weather, such a film should be superior to solar screens or solar grates, assuming it's maintenance free and leaves the view unaffected. The energy saving should be comparable but the view would be unobstructed. Such a film also sounds like it could be the low cost option. Of course, like all conventional films, it would work all year long. That would mean it would be blocking infrared heating in winter as well as summer. In some climates that would be a problem but in the sunbelt, it could be a reasonable trade-off.

    At one point, LBNL was working on an electrified film that could be IR reflecting when 'on' and IR admitting when 'off' (... or vice versa). That would probably cost more and be more complicated but would produce marvelous energy savings.

    I hope and expect LBNL will succeed. They work on neat stuff.

  2. user-1089777 | | #2

    This sounds interesting... sorta. If you look at where most heat is lost out of windows, the majority of it is lost via the frame - even those with insulated frames. (Check out any IR camera image of any building.) With poor frames and spacers, I fail to see how any new magic glass coating is going to make much difference in a building's performance (or comfort) particularly given that replacement glass is not very expensive and leaves the weakest window component intact.

    The quote from researcher, Arman Shehabi, in this article is further perplexing: "The high reward in this project isn’t in the performance improvement. It’s transformative in how windows could be retrofitted — it’s something you can do yourself." Is LBNL simply funding cool projects for 'folks to do at home?'

    I do wish LBNL would spend less time on (endless amounts of geeky) glass research and more time where it is needed the most: on the frame and on exterior shades. Windows in the US are woefully behind the leading edge in terms of performance. Maybe it's because our top window research institution clearly keeps looking through the window, instead of at it?

  3. GBA Editor
    Martin Holladay | | #3

    Response to Bronwyn Barry
    I think you missed the point. You wrote, "If you look at where most heat is lost out of windows, the majority of it is lost via the frame." But the LBNL researchers are concerned with heat gain through glass, not heat loss through glass or frames.

    The aim of the coating under development is to lower the SHGC of the glass. So the issue of heat loss through window frames is irrelevant.

    When designing windows, one certainly cares about (wintertime) heat loss through window frames and glazing. But (summertime) heat gain is another issue entirely, and it is also worth addressing. If you are interested in reducing heat gain, the frame characteristics are unimportant -- because almost all of the heat gain occurs through the glazing.

  4. user-1089777 | | #4

    It just gets worse...
    Ok, Martin. You're right. I misread this as a fix for heat loss, but the laws of physics remain the same whether the heat source is on the inside or the outside: heat flows from hot to cold, always takes the path of least resistance and is transferred via conductance, convection and radiation.

    If we're to believe this LBNL article, their new magic molecular coating will keep the radiant heat of the sun outside for warm and southern climates. Great. However, the frame issue persists. How will the coating on the glass prevent conducted heat gushing through metal edge spacers and frames that the glass is held within? Even for single-pane wood windows, conductive and convective heat will still travel through these essentially pathetic windows. The buildings these windows are installed in will likely also receive large amounts of heat gain directly through the walls and roof.

    We already have great solutions to reduce cooling loads: they’re called ‘overhangs’ and ‘exterior shades.’ These solutions will actually keep the sun off walls and window frames too. They can be installed to allow heat in during the winter, when these same windows will benefit from the free solar gain. Shades and overhangs could also be promoted as DIY projects - since that aspect is clearly what these researchers are most excited about.

    I'm obviously frustrated with whoever (or whatever) is driving research-funding allocation at the DOE. I'm astounded that some our best research minds in the country are working on what sounds like another half-baked-gizmo-fix, hyped up with big words like 'technoeconomics,' that address the easiest part of our overall window problems – for either new or existing buildings. The DOE and LBNL appear fixated on finding the cheapest option available and trying to make that better, rather than finding the best option available and then working to make that cheaper. Our industry deserves better. Thanks for reading this far.

  5. Tim C | | #5

    Should have checked a home improvement store first...
    A DIY, low solar gain window coating for $1.50/square foot? The local home improvement store already carries it.

  6. user-287534 | | #6

    Re: Should have checked a home improvement store first
    In insulated glass units those window films, if applied to the interior #4 surface, can cause IGU seals to fail if the lite is in full sun. Even worse, differential heating due to partial shade on the lite can cause the glass itself to fracture. Presumably LBNL is interested in coatings that could be applied to the #1 surface and are tough enough to stand up to airborne abrasion and cleaning without losing optical clarity.

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