Researchers at the University of Oxford have collaborated with industry experts to develop an adaptable smart window technology that could reduce the energy usage of an average home by up to a third as part of the EPSRC (WAFT) Wearable and Flexible Technologies Collaboration.

One solution from University of Delaware has been the addition of methyl salicylate but this is more difficult to manufacture.

The Oxford solution has been to create a new glass with spectrally tuneable low-emissivity coating that uses a phase change material to control the amount of heat that comes into the room from the window, without affecting the quality of the light so that the thermal energy from the sun’s infrared rays is absorbed by the glass and re-emitted as heat in the winter using transparent electrical heaters in the glass substrate or in the summer reflected away to cool the room so that the windows can change according to seasonal needs. The team built a prototype with an active chalcogenide-based phase change material so the new glass can adapt to the temperature, to save energy and the active phase change material is adjustable – for example, 30 percent of the material is turning away heat while 70 percent is absorbing and emitting it – for more precise temperature control.

Current the low-emissivity glass or low-E glass used in today’s double-glazed homes and offices is inert, using a nano-thin metallic reflective coating that reflects the UV and infrared waves in sunlight to reduce heat transfer through the glass and this glass is not as responsive.

Importantly, visible light is transmitted almost identically in both states, so you wouldn’t notice the change in the window because aesthetic consideration is critical for the adoption of green technologies.

They absorb near-infrared light from the sun in the winter and turn it into heat for the inside of a building. In the summer months, the sun can be reflected instead of absorbed.

Harish Bhaskaran, professor at Oxford’s Department of Materials, who led the research and the WAFT consortium, said ‘Although significant future research is necessary before this technology can be commercialised, the results show that the concept is very promising and with further research can achieve very good efficiencies.’

Oxford spin-out Bodle Technologies developed the phase change material scaled down for the prototype. ‘This work demonstrates yet another interesting optoelectronic application of phase change materials with the potential to significantly improve our everyday life,’ said Peiman Hosseini, CEO of Bodle Technologies.’I believe this technology should be part of any future holistic policy approach tackling climate change.’

Read the full paper – ‘Reconfigurable Low-Emissivity Optical Coating Using Ultrathin Phase Change Materials’ – in ACS Photonics.

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