A potentially revolutionary new type of smart window – developed by University College London – could cut window-cleaning costs in tall buildings, while reducing heating bills and boosting worker productivity.
The smart windows were developed by University College London (UCL) with support from the Engineering and Physical Sciences Research Council (EPSRC).
Prototype samples reportedly confirm that the glass can deliver three key benefits:
- Self-cleaning: the window is ultra-resistant to water, so rain hitting the outside forms spherical droplets that roll easily over the surface – picking up dirt, dust and other contaminants and carrying them away. This is due to the pencil-like, conical design of nanostructures engraved onto the glass, trapping air and ensuring only a tiny amount of water comes into contact with the surface. This is different from normal glass, where raindrops cling to the surface, slide down more slowly and leave marks behind.
- Energy-saving: the glass is coated with a very thin (5-10 nanometre) film of vanadium dioxide which during cold periods stops thermal radiation escaping and so prevents heat loss; during hot periods it prevents infrared radiation from the sun entering the building. Vanadium dioxide is a cheap and abundant material, combining with the thinness of the coating to offer real cost and sustainability advantages over silver/gold-based and other coatings used by current energy-saving windows.
- Anti-glare: the design of the nanostructures also gives the windows the same anti-reflective properties found in the eyes of moths and other creatures that have evolved to hide from predators. It cuts the amount of light reflected internally in a room to less than 5%– compared with the 20-30% achieved by other prototype vanadium dioxide coated, energy-saving windows.
Project leader, UCL’s Dr Ioannis Papakonstantinou explained: “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 ground-breaking glass could be especially well-suited to use in high-rise office buildings.
Papakonstantinou continued: “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 new window concept towards commercialisation. The key is to develop ways of scaling up the nano-manufacturing methods that the UCL team has specially developed to produce the glass, as well as the vanadium dioxide coating process.
Depending on the team’s success in securing industrial interest, smart windows could begin to reach the market within around 3-5 years.
Papakonstantinou added: “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 to deliver the triple benefit of lower energy use, less light reflection and self-cleaning, without significantly affecting aesthetics.”
Professor Philip Nelson, Chief Executive of EPSRC said: “This project is an example of how investing in excellent research drives innovation to produce tangible benefits. In this case the new technique could deliver both energy savings and cost reductions.”