Production is beginning for a new window coating that automatically adjusts to control solar gain through windows. Raven Windows, made by Denver-based RavenBrick, are made with a special nanomaterial coating which makes the windows responsive to outdoor temperature. The Raven Windows act as "an intelligent window filter that automatically blocks solar heat when the outside temperature is too hot, while delivering solar heat inside when the outside temperature is cold."
The Raven Window material is a thermo-reflective coating that is applied to the inside surface of the outer pane of glass in a double-glazed window assembly. The material is somewhat like glasses that darken when you step outside into brighter conditions. Although darker, the material is more thermally reflective, so that heat is kept out of the building during hotter times of year, but is transparent, and lets heat and light through when the temperature is colder. Better yet, unlike some other technologies, the transformation is automatic, and requires no electricity or controls.
With Raven Windows, the most reflective state of the glass has a solar heat gain coefficient (SHGC) as low as 0.03, meaning that only 3% of the solar energy passes through the window, which helps cut down the need for air conditioning, but those windows can also adjust during cold weather to allow as much as an SHGC of 0.35.
Like low-E windows, this is a coating applied to one surface of the glass in a double pane window, although the performance of this material is like low-E on steroids. However, "because smart windows and low-E save energy by completely different mechanisms, their effects are complementary and thus their savings can be added together." It is possible to have windows that have the Raven Windows coating, as well as having low-E.
The company's information suggests a retail cost of $25 per square foot for the material and assumes that payback can be achieved within 5-8 years with these windows. One of the first installations of these windows is for executive offices in the new National Renewable Energy Laboratory (NREL) in Colorado.
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