by Erin Larsen
The US Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) researchers are in the process of developing a paint-on coating for windows to increase energy efficiency. It is estimated that 10 percent of aggregate energy consumption in buildings in the US is due to window performance. Warm and southern climates are particularly impacted because a significant fraction of energy usage goes to air conditioning. This inefficiency costs building owners about $50 billion annually. While window replacement or other commercially available retrofits would resolve this problem, the high cost of these options is prohibiting. Berkeley Lab’s polymer heat-reflective coating that can be painted on would be $1.50 per square foot, one-tenth the current market for commercially installed energy efficient retrofit window coatings.
A team of scientists at the Berkeley Lab is the recipient of a $3.95 million award from the DOE’s Advanced Research Projects Agency-Energy (ARPA-E) to develop this product. The lead researcher for the multi-institutional team is Garret Miyake at the University of Colorado Boulder.
The coating works by selectively reflecting infrared solar energy heat, while still allowing visible light to pass through. It relies on a type of material called a bottlebrush polymer; this polymer has one main rigid chain of molecules with bristles coming off the sides. Its molecular structure prevents it from entangling easily. A researcher on the project explains this through a metaphor: “Imagine spaghetti versus gummy worms. Spaghetti can be tied up in knots. If you want to rearrange cooked spaghetti back to its uncooked alignment, you would have to put significant energy into unwinding it. But with gummy worms you can line them all up easily because they’re pretty rigid.”
The concept of window coatings to increase building energy efficiency is not new. There are already retrofit window films commercially available, but a professional contractor is required to apply them. A low-cost alternative that allows homeowners and building owners to paint on the coating themselves would significantly expand the adoption of this technology. If adoption occurs at the levels researchers have predicted, the annual potential energy saving could reach 35 billion kilowatt-hours. Carbon emissions would also be reduced by 24 billion kilogram per year -– the equivalent of taking 5 million cars off the road.
One of the challenges remaining before this technology hits the market is ensuring the view though the windows is not scattered or hazy. The project team wants to make sure the coating reflects the majority of the sun’s non-useable energy reducing the amount of heat passing into buildings, but still appearing clear to the human eye. Optical testing will continue until the scientists are satisfied with the coating’s performance.
Chao, Julia. “Berkeley Lab Scientists Developing Paint-on Coating for Energy Efficient Windows | Berkeley Lab.” News Center. Berkeley Lab, 25 Feb. 2016. Web. 27 Feb. 2016.
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