Self cleaning windows also save energy and cut glare

Smart windows developed by University College London (UCL) with support from the Engineering and Physical Sciences Research Council (EPSRC) could cut window cleaning costs in tall buildings while reducing heating bills and boosting worker productivity.

The windows are said to incorporate nanostructures engraved into the glass that trap air, meaning that only a small amount of water comes into contact with the surface. The water, thus, forms spherical droplets that quickly roll over the surface washing away dirt, dust and other contaminants.

The glass is coated with a 5 to 10nm film of vanadium dioxide which during cold periods stops thermal radiation escaping, preventing heat loss; during hot periods it prevents infrared radiation from the sun entering the building.

The design of the nanostructures also cuts the amount of light reflected internally in a room to less than 5% – compared with the 20 to 30% achieved by other prototype vanadium dioxide coated, energy saving windows. This reduction in glare is claimed to provide a boost to occupant comfort.

UCLs Dr Ioannis Papakonstantinou said: “This is the first time that a nanostructure has been combined with a thermochromic coating. The bio-inspired nanostructure amplifies the thermochromics properties of the coating and the net result is a self-cleaning, highly performing smart window.”

The UCL team calculate that the windows could result in a reduction in heating bills of up to 40%, with the precise amount in any particular case depending on the exact latitude of the building where they are incorporated. Windows made of the smart glass could be especially well-suited to use in high-rise office buildings.

Dr Papakonstantinou explained: “It’s currently estimated that, because of the obvious difficulties involved, the cost of cleaning a skyscraper’s windows in its first five years is the same as the original cost of installing them. Our glass could drastically cut this expenditure, quite apart from the appeal of lower energy bills and improved occupant productivity thanks to less glare. As the trend in architecture continues towards the inclusion of more glass, it’s vital that windows are as low-maintenance as possible.”

Discussions are now under way with UK glass manufacturers with a view to driving this concept towards commercialisation. The key is to develop ways of scaling up the nano-manufacturing methods that the UCL team have developed to produce the glass, as well as scaling up the vanadium dioxide coating process.

Dr Papakonstantinou says: “We also hope to develop a ‘smart’ film that incorporates our nanostructures and can easily be added to conventional domestic, office, factory and other windows on a DIY basis.”

Tom Austin-Morgan

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