Windows have long been a conundrum in the green building world. On one hand, they allow for natural daylighting and a free source of heat when the sun is shining. On the other hand, they also tend to create drafts in the winter and overheat occupants in the summer, both of which overburden the building’s heating and cooling system, wasting energy.
Electrochromic glass solves this problem by tinting to block the sun’s rays at the touch of a button, or based on a pre-set program. Currently, it’s expensive enough that the market for this specialty glass has been limited to high-end, high-profile architectural showpiece buildings–but with the recent announcement that two of the leaders in this technology, Sage and Saint Gobain, are teaming up to lower the cost of production, that could change.
To get a handle on what this could mean for the green building industry, we recently interviewed Jim Wilson, Sage’s Chief Marketing Officer:
EarthTechling (ET): Solar Thermal Magazine has called your product, SageGlass, “the world’s only commercially available, electronically ‘tintable’ window glass.” How was your technology developed? How does it work?
Jim Wilson (JW): SageGlass was developed using nanotechnology-based coatings consisting of five layers of ceramic materials, which have a total thickness that is less than 1/50th that of a human hair. When low voltage is applied, the electrons darken the ceramic coatings. Reversing the voltage polarity causes electrons to return to their original layer, and the glass clears. This solid state electrochromic reaction is controlled through a low voltage DC power supply. When the SageGlass coating darkens, the sun’s light and heat are absorbed and subsequently reradiated from the glass surface to the exterior – much the way low-emissivity glass also keeps out unwanted heat.
SageGlass can be switched from clear to darkly tinted at the click of a button, or programmed to respond to changing sunlight and heat conditions. For example, on hot, sunny days the tint in the windows will darken to reduce glare and block out heat. On cold, cloudy days the windows will clear to allow sunlight and heat to fill the office or home. The electrical switching of tints can be operated manually or integrated into an automated building management system. SageGlass modulates visible light transmission and solar heat gain, and, in the tinted condition, blocks 91 percent of the solar heat gain.