I've been following Sage Electrochromics for a long time. In 2006, BuildingGreen named SageGlass one of our Top-10 Green Building Products. It was the first practical, durable dynamic glazing that worked in exterior façade applications. This week, the company rolled out a new, much-higher-performance product.

By way of context, most glazing is "static." That means it has certain performance properties that remain the same, including visible light transmittance (Tvis), solar heat gain coefficient (SHGC), and U-factor. When specifying windows (or glazings), we try to choose a product with properties that will, on average, provide the needed transparency, control of heat loss, and control of solar heat gain. It's usually a trade-off, because there are times when solar heat gain is desirable and times when it is undesirable.

Dynamic glazings, on the other hand, have properties that can be changed. There are three ways this can happen--none of which are common today. Photochromic glazings change passively based on exposure to sunlight; thermochromic glazings change passively based on temperature; electrochromic glazings change when electric current is applied to a coating on the glass. SageGlass falls into this last category. With the push of a button, a user can switch it from a clear state to a tinted state. The glazing darkens over several minutes and will remain tinted as long as a small amount of current continues to be applied to the electrochromic coating. Once the electric current is discontinued, the glazing slowly reverts to the clear state.

The SageGlass that Environmental Building News reviewed back in 2006 was configured into double-glazed units. When using clear 6 mm glass, double-pane SageGlass has the following properties in clear vs. tinted states, respectively: Tvis – 62% vs. 3.5%; SHGC – 0.48 vs. 0.09; and center-of-glass winter U-factor – 0.29 (the same U-factor clear whether or tinted). By switching the glazing to the tinted state, glare and unwanted solar heat gain can be virtually eliminated--without having to lower interior blinds or exterior shutters.

SageGlass's new innovation is applying this dynamic tinting technology to high-performance triple-pane glazing units. In this configuration, the inner surface of the outer lite (#2 surface in glazing parlance) has the electrochromic coating, and an optional second low-e coating can be provided on the outer surface of the inner lite (#5 surface).

With this triple-pane, low-e version, assuming two half-inch spaces filled with 90% argon gas-fill, the properties are as follows (clear state vs. tinted): Tvis – 52% vs. 3%; SHGC – 0.38 vs. 0.06; and center-of-glass winter U-factor 0.14 (R-7.1). With 95% krypton gas-fill and a thinner 9 mm spacing between lites, the U-factor can be as low as 0.12 (R-8.3).

While there are glazings with lower U-factors, most notably top-performing products from Serious Windows with multiple suspended low-e films and krypton or xenon gas-fill, there are none I am aware of that offer the overall energy performance of Sage triple-glazed low-e, because of the potential to regulate unwanted heat gain.

Don't expect these glazings to start selling like hotcakes. The cost is too high. However, the marginal cost for tinting is offset somewhat by avoiding the need for interior blinds or exterior shading--for applications where that level of control would be provided. A long-term goal of Sage is to be cost-competitive when compared with the combination of conventional glazing and automated blinds.

Sage produces insulated glazing units (IGUs), not windows. In commercial-building applications, these IGUs can be incorporated into curtainwall-façade systems by curtainwalls. Residential applications will depend on partnerships with window manufacturers. (With double-pane SageGlass, Velux was an early partner.) Look for initial application of Sage's new triple-pane, electrochromic glazings for high-performance commercial buildings in locations where individual controllability of glare is needed, such as at workstations.

For more information:

Sage Electrochromics, Inc.

Faribault, Minnesota

507-331-4848

www.sage-ec.comI invite you to share comments on this blog.

Alex Wilson is the executive editor of Environmental Building News and founder of BuildingGreen, LLC. To keep up with his latest articles and musings, you can sign up for his Twitter feeds.

See more on this product in the GreenSpec Guide