A new form of smart window made from a porous nanocrystal structure is capable of selectively blocking either light or heat depending on the level of electric potential applied to it.

The energy efficiency of human-occupied built environments could receive a dramatic boost from the development of a new form of smart window that is capable of more nuanced adjustment of its physical qualities in response to electrical stimulus.

The smart window developed by researchers from the Cockrell School of Engineering at the University of Texas at Austin marks a significant advance upon similar, preceding technologies in its ability to affect light and heat differently, permitting more flexible control of the indoor environment.

Prior efforts to create energy efficient smart windows invariably resulted in materials whose transparency levels varied, resulting in a, fixed positive relationship between the amount of light and heat allow to passed through. This meant that when more light was allowed to pass through more heat would enter, and vice versa.

The new smart window produced by Delia Milliron dispenses with this limitation, using a special coating to permit external illumination to penetrate while still stopping the entry heat, or impeding the entry of light while enabling heat to pass through.

The key to the smart window's heightened functionality an electrochromic glass that is permeated with indium tin oxide nano crystals. The glass consists of a single porous network that responds in a variable way to the amount of electrical voltage applied to it, and selectively altering its ability to block light or heat.

Diagram of interaction of the window material with heat and light

Diagram of interaction of the window material with heat and light

The smart window is capable of high levels of opacity when adjusted to hinder illumination, blocking as much as 80 per cent of visible light as well as 90 per cent of near-infrared light.

Another advantage of the glass is its ability to switch modes with far greater speed than its predecessors. While other materials might take hours to adjust their physical qualities, the University of Texas smart window is capable of undergoing alteration within just minutes.

According to Milliron the smart window is cost-effective and ready for commercial deployment, with the team of researchers now working on finding economical production methods.

"Sophisticated dynamic control of sunlight is possible," said Milliron. "We believe our deliberately crafted nanocrystal-based materials could meet the performance and cost targets needed to progress towards commercialisation of smart windows."