Tuneable smart window coating traps heat in winter, reflects it in summer
Windows may be important for letting natural light and warmth into a room, but sometimes they let in too much, or let your artificial warmth out instead. Researchers at Oxford have developed a new smart window coating that can be tuned on the fly to emit or reflect heat from the Sun in different amounts, reducing the energy costs of heating and cooling by up to a third.
The key to the new tech is a chalcogenide-based material that changes phase in response to heat. In cold weather, this material absorbs the infrared rays from sunlight, and emits it into the room as heat. But when it’s hot out, the material can be switched to reflect heat from the Sun back outside, keeping the interior of the building cooler. In both cases, the idea is to reduce the use of climate control, which is one of the biggest guzzlers of energy.
The team also embedded small, transparent heater units into the coating, which activate the phase change material to different degrees. With this setup, the coating can be adjusted on demand to emit or reflect heat at different rates – so, for example, it could be set so 30 percent of the material reflects heat while 70 percent emits it.
No matter which state the material is in, it will still allow the same amount of visible light to pass through. The team estimates that even including the energy required to tune the material, windows fitted with this kind of glass would save a home or building between 20 and 34 percent on energy usage every year, compared to traditional double-glazed windows.
This is far from the only glass coating in development to allow users to choose how much heat makes it through. Past smart windows have used electrochromic materials, tiny mirrors angled so they reflect heat outwards in summer and inwards in winter, or liquid-filled films that keep a room cool during the day and warm overnight.
The team says this new design should be relatively simple and inexpensive to implement, but of course it’s not quite ready for prime time just yet.
“Although significant future research is necessary before this technology can be commercialized, the results show that the concept is very promising and with further research can achieve very good efficiencies,” said Harish Bhaskran, lead researcher on the study.
The research was published in the journal ACS Photonics.
Source: Oxford University