WINDOW TECHNOLOGIES: Advanced
Gasochromic windows produce a similar effect to electrochromic windows, but in order to color the window, diluted hydrogen (below the combustion limit of 3%) is introduced into the cavity in an insulated glass unit. Exposure to oxygen returns the window to its original transparent state. To maintain a particular state, the gap is simply isolated from further changes in gas content. The optically active component is a porous, columnar film of tungsten oxide, less than 1 micron thick. This eliminates the need for transparent electrodes or an ion-conducting layer. Variations in film thickness and hydrogen concentration can affect the depth and rate of coloration.
Visible transmittance can vary between 0.10–0.59 with a SHGC range of 0.12–0.46. Transmittance levels of less than 0.01 for privacy or glare control are possible. An improved U-value can be obtained with a triple-pane, low-E system (since one gap is used to activate the gasochromic). Switching speeds are 20 seconds to color and less than a minute to bleach. The gas can be generated at the window wall with an electrolyser and a distribution system integrated into the facade. Gasochromic windows with an area of 2-by-3.5 feet are now undergoing accelerated durability tests and full-scale field tests and are expected to reach the market in the near future.