Fluid Material Controls Light and Heat Passage in Windows

Windows are essential for allowing both light and heat into a space, but there are situations where you may not want both simultaneously. Recently, engineers from North Carolina State University (NCSU) have created a novel material that enables windows to effortlessly transition between three distinct modes.

The innovative dynamic windows have the capability to alternate between three distinct modes: a standard transparent mode that permits the entry of light and heat, a mode that obstructs heat while maintaining transparency to light, and a tinted mode that partially blocks light but not heat. This feature ensures that users are well-equipped to adapt to varying seasonal needs.

Tungsten Oxide in Electrochromic Dynamic Windows

The crucial element in this process is a substance known as tungsten oxide, a common component in electrochromic dynamic windows. Typically transparent, tungsten oxide darkens and restricts light when subjected to an electrical signal, making it suitable for windows that can adjust their tint as needed.

However, in the recent research conducted by NCSU, scientists uncovered a remarkable additional capability. By introducing water, tungsten oxide transforms into tungsten oxide hydrate, introducing an additional setting when utilized in electrochromic windows.

Tungsten Oxide Hydrate’s Phases in Action

When in the off state, it maintains its transparency to both light and heat, making it an ideal choice for dreary winter days when maximizing both is essential. When introduced to some electrons and lithium ions, the material goes through a sequence of phases. Initially, it starts by blocking infrared light (felt as heat) while still remaining transparent to visible light.

Eventually, as more electrons enter the material, it shifts into a dark phase where it obstructs both visible and infrared light, which is perfect for the summertime.

The precise reason behind tungsten oxide hydrate’s behavior in this manner remains uncertain. However, the NCSU scientists have a working hypothesis. According to Jenelle Fortunato, the first author of the study, “The presence of water in the crystalline structure makes the structure less dense, so the structure is more resistant to deformation when lithium ions and electrons are injected into the material”

Understanding the “Cool” and “Dark” Phases of Tungsten Oxide Hydrate

Our hypothesis is that, because tungsten oxide hydrate can accommodate more lithium ions than regular tungsten oxide before deforming, you get two modes. There’s a ‘cool’ mode, in which the injection of lithium ions and electrons impacts the optical properties but doesn’t cause structural change yet, absorbing infrared light. And then, after the structural change occurs, there’s a ‘dark’ mode that blocks both visible and infrared light.

While there are numerous dynamic window technologies in progress, it’s not common to find a system with such a wide range of modes. When multiple modes are offered, they often necessitate bulkier configurations. However, in this instance, because only one material is needed, it should maintain the glass thickness and energy requirements at approximately the same level as traditional tungsten oxide windows.

Delia Milliron, one of the co-corresponding authors of the study, stated, “The discovery of dual-band (infrared and visible) light control in a single material that’s already well-established in the smart windows community may expedite the development of commercial products with enhanced capabilities.”

Read the original article on: New Atlas

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