A new prototype window can absorb heat in winter and reflect it in summer, as an energy-saving alternative to central heating and air conditioning.
Researchers at the University of Pittsburgh have created their ultra-thin ‘smart glazing technology’ that can potentially line existing windows in the home.
The glazing — made of chemical compounds — can switch its atomic arrangement to either reflect or absorb light from the sun depending on the seasons.
Thermal energy from the sun’s infrared rays is absorbed and re-emitted as heat into a room during winter, or reflected away to cool down rooms in the summer.
If marketed, the ‘smart window’ technology could reduce the energy usage of an average home by up to a third, according to experts.
They call it ‘efficient’, ‘aesthetically pleasing’ and crucial for the successful adoption of green technology in the face of climate change.
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Thermal energy from the sun’s infrared rays is absorbed and re-emitted as heat into a room during winter, or reflected away to cool down rooms in the summer
The fabricated smart windows are shown in both states, showing that the transmitted visible light changes very little
‘The major innovation is that these windows can change according to seasonal needs,’ said study author Nathan Youngblood, assistant professor of electrical and computer engineering at the University of Pittsburgh.
‘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.’
The film is made up of a stack of materials less than 300 nanometres thick, with a very thin active layer made of ‘phase change’ materials that can absorb the invisible wavelengths of the sun’s light and emit it as heat.
That same material can be ‘switched’ so that it turns those wavelengths of light away instead.
‘Importantly, visible light is transmitted almost identically in both states, so you wouldn’t notice the change in the window,’ Youngblood said.
‘That aesthetic consideration is critical for the adoption of green technologies.’
The glazing works by switching from an ‘amorphous’ arrangement of atoms to a ‘crystalline arrangement’, upon the application of heat.
In an amorphous arrangement, atoms are quite irregularly arranged, but the switch to a crystalline arrangement of its atoms makes the atoms bunch up much more tightly, which allows them to reflect heat away.
The switch is triggered in a fraction of a second by a ‘transparent heater’ that’s part of the multi-layer glazing.
When it is cold, the infrared rays from the sunlight are harvested and transformed into building heat to cut heating costs.
If it is warm, the new glass can switch state to reflect the heat and reduce the need for air conditioning.
But the material could even be adjusted so that, for example, 30 per cent of the material is turning away heat while 70 per cent is absorbing and emitting it, allowing for more precise temperature control, such as during spring and autumn.
Researchers estimate that using these windows – including the energy required to control the film – would save 20 to 34 per cent in energy usage annually compared to double-paned windows typically found in homes.
Usually, the thermal and optical properties of current windows are ‘set’ into glass coating as part of the manufacturing process.
Glass with a higher reflectivity property or a solar control coating lets in noticeably less natural light and vice versa.
Usually, the thermal and optical properties of current windows are ‘set’ into glass coating as part of the manufacturing process (stock image)
In order to create and test their prototypes, the researchers worked with University of Oxford spin-out firm Bodle Technologies, which is based near Kidlington.
Bodle Technologies specialises in ultra-thin reflective films that can function as displays by controlling colour and light.
‘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.’
The work has been published in the journal ACS Photonics.