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Smart windows block up to 70% heat, without blocking views

Sustainability Matters

November 10, 2021

New energy-saving material, developed by researchers from the Nanyang Technological University, Singapore (NTU Singapore), helps control heat transmission without blocking views.

The material for electrochromic (EC) windows operates at the flick of a switch and is said to help block up to 70% of infrared radiation, a major component of sunlight that emits heat, while allowing up to 90% of visible light to pass through, according to the researchers.

It features nanostructure and comprises advanced materials like titanium dioxide (TiO2), tungsten trioxide (WO3), neodymium-niobium (Nd-Nb), and tin (IV) oxide (SnO2), and can be coated onto glass window panels. When activated by electricity, users would be able to ‘switch on and off’ the infrared radiation transmission through the window.

The invention is claimed to be 30% more effective in regulating heat than commercially available electrochromic windows and is cheaper to make due to its durability.

Light, heat and durability

Electrochromic windows currently available on the market are only effective in blocking visible light, not the infrared radiation, which means heat continues to pass through the window, warming up the room, according to NTU researchers. These windows work by becoming tinted when in use, reducing light from entering the room. The performance of the electrochromic component in these windows tends to degrade in three to five years.

Commercially available electrochromic windows usually have a layer of tungsten trioxide (WO3) coated on one side of the glass panel, and the other, without. When the window is switched on, an electric current moves lithium ions to the side containing WO3, and the window darkens or turns opaque. Once switched off, the ions migrate away from the coated glass, and the window becomes clear again.

NTU’s technology went through rigorous on-off cycles in lab tests to evaluate the material’s durability. The properties of the window retained stability, blocking more than 65% and demonstrating potential for long-term use in sustainable buildings, according to the researchers.

“By incorporating the specially designed nanostructure, we enabled the material to react in a ‘selective’ manner, blocking near infrared radiation while still allowing most of the visible light to pass through whenever our electrochromic window is switched on. The choice of advanced materials also helped improve the performance, stability and durability of the smart window,” said lead author of the electrochromic window study, Associate Professor Alfred Tok of the NTU School of Materials Science and Engineering.

The new electrochromic technology may help conserve energy that would be used for the heating and cooling of buildings and could contribute to the future design of sustainable green buildings, according to the research team.

Next generation smart windows

With an aim to improve their smart window technology, the NTU team created a switch system that helps to control conducted heat, which is the heat from the external environment.

The patented NTU switch comprises magnetic carbon-based particles and thin films that are good conductors of heat. When the switch is turned off, conducted heat cannot transfer through the window. When switched on, the heat will be allowed to pass through the glass window.

When integrated with the newly developed electrochromic material, the team’s smart window can control two types of heat transmission: infrared radiation and conduction heat, which is the main mode of heat transfer through matter.

Image credit: ©stock.adobe.com/au/Sergey Nivens