New technology makes "Smart Windows" even smarter
"Smart windows", made out of "smart glass" allow users to control the amount of light let in and ultimately save costs for heating, air-conditioning, and lighting.
Improving on this technology, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have designed a new material to make smart windows even smarter by applying a new window coating, which will essentially have a major impact on building energy efficiency.
"In the US, we spend about a quarter of our total energy on lighting, heating and cooling our buildings," says Delia Milliron, a chemist at Berkeley Lab's Molecular Foundry who led this research.
The material is a thin coating of nanocrystals embedded in glass that can dynamically modify sunlight as it passes through a window. Unlike existing technologies, the coating provides selective control over visible light and heat-producing near-infrared (NIR) light, so windows can maximize both energy savings and occupant comfort in a wide range of climates.
The technology hinges on an electrochromic effect, where a small jolt of electricity switches the material between NIR-transmitting and NIR-blocking states. This new work takes their approach to the next level by providing independent control over both visible and NIR light. The innovation was recently recognized with a 2013 R&D 100 Award and the researchers are in the early stages of commercializing their technology.
Independent control over NIR light means that occupants can have natural lighting indoors without unwanted thermal gain, reducing the need for both air-conditioning and artificial lighting. The same window can also be switched to a dark mode, blocking both light and heat, or to a bright, fully transparent mode.
At the heart of the technology is a new "designer" electrochromic material, made from nanocrystals of indium tin oxide embedded in a glassy matrix of niobium oxide. The resulting composite material combines two distinct functionalities—one providing control over visible light and the other, control over NIR—but it is more than the sum of its parts. The researchers found a synergistic interaction in the tiny region where glassy matrix meets nanocrystal that increases the potency of the electrochromic effect, which means they can use thinner coatings without compromising performance. The key is that the way atoms connect across the nanocrystal-glass interface causes a structural rearrangement in the glass matrix. The interaction opens up space inside the glass, allowing charge to move in and out more readily.
The paper is published in the journal Nature.
Read more at the Berkeley Lab News Center.
Window image via Shutterstock.