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New ‘Smart’ Window Material Blocks Rays Without Blocking Views

This material can block up to 70 per cent of infrared radiation while allowing up to 90 per cent of visible light to pass through, expected to help cut the energy needed to cool and heat buildings.

An international group of researchers led by scientists from Nanyang Technological University in Singapore has invented a “smart” window that enables us to enjoy a clear view out of the window while minimising the amount of heat transmitted through. At a flick of a switch, this new energy-saving material can be operated to block infrared radiation but still allow visible light to pass through, effectively reducing the energy needed to cool buildings.

Around 30 to 40 per cent of electrical energy consumed in residential and commercial buildings is devoted to lighting and thermal management systems. In 2019, Singapore consumed 51.7 TWh of electrical energy, 17.5 TWh or 34 per cent of which was used for lighting and indoor cooling. Because approximately 80 per cent of this electrical energy is generated from fossil fuels, reducing the energy needed to cool or heat buildings has become a prerequisite to designing greener, smarter buildings.

To achieve this, scientists have developed electrochromic windows. When in use, these windows become tinted to prevent light from entering rooms. Commercially available electrochromic windows are generally coated with a layer of tungsten trioxide on one side of the glass panel, but not the other. When these windows are switched on, an electrical current moves lithium ions to the tungsten trioxide-coated side, after which the window darkens or becomes opaque. Switching them off causes the ions to migrate away from the coated glass, returning the windows to their original clear state.

However, while these windows can block visible light, they are ineffective in blocking infrared radiation, consequently allowing heat to pass through and warm up rooms. Moreover, the electrochromic component of these windows is also not durable as it tends to degrade within three to five years. Taking note of these limitations, the scientists aimed to create an effective and durable material that improves upon present technologies.

The newly developed material is made up of advanced materials such as titanium dioxide, tungsten trioxide, neodymium-Niobium, and tin (IV) oxide. It has a special nanostructure and was designed to be coated onto glass window panels. Upon activation by electricity, users would be able to “switch on and off” the transmission of infrared radiation through the material. Compared to commercially available electrochromic windows, the invention is about 30 per cent more effective in regulating heat, more durable, and is less costly to make.

“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 study, Associate Professor Alfred Tok of the NTU School of Materials Science and Engineering.

In their laboratory tests, the scientists subjected their electrochromic technology through rigorous on-off cycles to examine its durability. Based on the results, it was established that the window managed to retain remarkable stability as it continued to block more than 65 per cent of infrared radiation. Their tests also showed that the material surpassed current electrochromic windows in terms of cost-saving potential, feasibility, and performance for long-term use in sustainable buildings.

To complement their smart window technology, the team has also created a switch system that can help control conducted heat. The patented switch is made of magnetic carbon-based particles and films that are excellent conductors of heat. When integrated with the newly developed electrochemical material, the smart window will be able to control both infrared radiation and conduction heat.

“By integrating both the new electrochromic material we invented and the patented switch in a window, we can create a smart window with unique capabilities. With the ability to control both infrared radiated heat from the sun and conducted heat passing through the window, we expect this technology to be particularly useful in temperate climates, as building occupants can use it to regulate heat loss or gain according to the needs of the changing seasons, while still enjoying much of the view,” said first author of the study, Dr. Ronn Goei, Senior Research Fellow at the NTU School of Materials Science and Engineering.

Moving forward, the team intends to bring their invention out of the lab and into the market. At present, they have partnered with glass manufacturer iGlass Asia Pacific to conduct more tests and are hoping to incorporate the smart window into its projects to improve efficiency and sustainability. [APBN]

Source: Goei et al. (2021). Nd–Nb Co-doped SnO2/α-WO3 Electrochromic Materials: Enhanced Stability and Switching Properties. ACS Omega, 6(40), 26251-26261.