Smart window coating blocks heat, not views

Written by: Andrew Wade | Published:
(Credit: Mario Mendez via Unsplash)

Scientists from Singapore's Nanyang Technological University have developed a transparent electrochromic window material that controls heat transmission without impeding views.

The composite material is intended to be coated onto glass window panels, and when activated by electricity, users would be able to control the level of infrared radiation transmitted through the window, potentially having a major impact on HVAC costs for buildings. The electrochromic material has a specifically designed nanostructure and includes materials such as titanium dioxide (TiO2), tungsten trioxide (WO3), neodymium-Niobium (Nd-Nb), and tin (IV) oxide (SnO2).

Detailed in ACS Omega, the new substance is estimated to be capable of blocking up to 70 per cent of infrared radiation according to experimental simulations. It also allows up to 90 per cent of visible light to pass through, meaning that views through the glass are not compromised, something that is not true of standard electrochromic windows.

Electrochromic windows usually work by becoming tinted when in use, reducing light from entering the room. Commercially available electrochromic windows commonly have a layer of tungsten trioxide (WO3) coated on one side of the glass panel. 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. However, current electrochromic windows are only effective in blocking visible light, so heat continues to pass through the window.

Another perceived drawback of current technology is its durability, as the performance of the electrochromic component tends to degrade in three to five years. In lab tests, NTU’s electrochromic technology was put through on-off cycles to evaluate its durability and results showed the properties of the window retained ‘excellent stability’, blocking over 65 per cent of infrared radiation.

“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," said study lead author, Associate Professor Alfred Tok of NTU’s School of Materials Science and Engineering.

"The choice of advanced materials also helped improved the performance, stability and durability of the smart window.”

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