Heat-reflective coating for low-cost, energy-efficient windows

It has been estimated that 10% of the total energy utilized in buildings across the U.S. can be attributed to window performance, costing building owners around $50 billion every year, yet the increasing cost of retrofitting windows or replacing them with an energy efficient coating seem to be a major hindrance. Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) of the U.S. Department of Energy (DOE) are currently working to address this issue with creative chemistry, which is a polymer heat-reflective coating that can be painted on at a fraction of the cost. "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. 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", says Raymond Weitekamp, Scientist, Berkeley Lab. The team of scientists from Berkeley Lab are receiving part of a $3.95 million award from the DOE’s Advanced Research Projects Agency–Energy (ARPA-E) to develop this new product. The multi-institutional team is headed by researcher Garret Miyake at the University of Colorado Boulder, and also includes Caltech and Materia. A number of retrofit window films with spectral selectivity are commercially available, but they can only be installed with the help of a professional contractor, which is a barrier for several building owners. A cost-effective option could expand adoption and result in annual energy savings of 35 billion kilowatt-hours, reducing carbon dioxide emissions by 24 billion kilograms annually, the equivalent of removing 5 million cars off the road. The Berkeley Lab technology relies on a material known as a bottlebrush polymer, which contains a single rigid chain of molecules along with bristles from the sides. This unique molecular architecture provides it with some exceptional properties, for instance it does not entangle easily. Weitekamp is partnering with Berkeley Lab’s Steve Selkowitz, a chief expert on building science and window technologies, and Arman Shehabi, a specialist in examining energy use of buildings, to develop a scalable and cost-competitive product. Their target cost is $1.50 per square foot, one-tenth the current market cost for energy efficient retrofit window coatings that are commercially installed One prevailing technical challenge is to enhance the accuracy of the material so that the reflection of infrared light does not cause the visible light to become hazy or scattered. This allows the coating to reflect a huge amount of the sun’s energy, reducing the amount of heat passing through a building, while still being visible to the eye. Selkowitz will examine the coating’s performance using the cutting-edge windows testing facilities at Berkeley Lab. Shehabi plans to develop lifecycle assessment models and building simulation models to understand how this new technology would influence the usage of energy in buildings, and how to maximize energy savings. He will also be using technoeconomic models to observe things such as, payback period and manufacturing considerations.