University College London (UCL) researchers have announced that a combination of thermochromatic coating and nano-scale engineering have created an innovative new window design could reduce cleaning costs and even heating bills by up to 40%.

The surface of the prototype contains cone-shaped nanostructures that trap air and only allow a miniscule amount of water to contact the glass. In essence, rain will turn into balls upon striking the glass and roll off, removing dirt at the same time.

With normal window glass, raindrops linger and roll down, leaving residue.

According to the lead UCL researcher, this self-cleaning capability will make the window highly attractive to the owners of high-rise buildings, as the cost of cleaning windows exceeds the cost of installing them after five years have passed.

An extremely thin (under 10 nanometres) vanadium dioxide film coats the glass, providing a barrier that keeps thermal radiation in during cold weather and, during hot spells, prevents infrared radiation from infiltrating the building. Vanadium dioxide is a material that is both inexpensive and in abundance, unlike the silver or gold-based film that energy-saving windows presently use.

The technology was developed with assistance from the Engineering and Physical Sciences Research Council.

Researchers say that a third important benefit is the coating’s ability to reduce glare inside the building. The nano-scale ridges in the surface provide the windows with the same anti-reflective capabilities found in the eyes of moths and other animals that survive by hiding from predators.

The film reduces the amount of light reflected inside the building to less than 5%, which is substantially lower than the 20 to 30% attained by other prototype windows coated with vanadium dioxide.

Dr Ioannis Papakonstantinou, who is the research leader at UCL, said that this project represents the first time that a nanostructure has been integrated with a thermochromic coating.

He explained that the nanostructure, which is bio-inspired, intensifies the coating’s thermochromics properties. The result is a smart window that cleans itself and is high-performing.

The team at UCL have estimated that the windows could lower heating costs by up to 40%, with the actual amount depending on the building’s latitude. They say that high-rise office buildings in particular will benefit from the technology.

Dr Papakonstantinou said that due to the difficulties involved in the process, the cost of cleaning a high-rise’s windows during its first five years would be the same as their original installation costs.

He said that the new glass could significantly reduce this expenditure. There is also the advantage of lower energy costs and heightened employee productivity due to reduced glare. As more glass is integrated into modern architecture, windows will need to be as low-maintenance as possible.

Talks are now in progress with glass manufacturers to make the prototype commercially available.

The challenge will be to expand the scope of both the nano-manufacturing production scale and the vanadium dioxide coating process. UCL says that if industrial manufacturers back the process, the new windows could reach the market in under five years.