by Maurizio J. Maso, AIA
Among the many new materials and systems currently available to architects and interior designers, electrochromic technology applied to glass offers exciting possibilities. Think of it as transition lenses for buildings, which can lighten or darken based on the seasonal position of the sun, time of day or weather conditions. It can also be automated or adjusted manually. Each glass pane is individually wired and controlled through an internet protocol (IP) address, providing a greater level of adaptability to glass facades. Electrochromic glass also offers an energy efficient alternative over high performance static glass and interior and exterior shading devices such as blinds and shades.
HuntonBrady Architects is evaluating the different electrochromic glass products available for applications in projects. Our workplace and commercial design group is working closely with United Technologies Industries on their new Center for Intelligent Buildings under construction in Palm Beach Gardens, Florida. We specified Sage Glass electrochromic glass on the East and West elevation, where solar exposure is most difficult to control.
How does it work?
A thin electrochromic layer is placed on the inner surface of an insulated glass assembly in a very precise and challenging manufacturing process. The layer's composition includes metal oxide and lithium particles. The layer is charged with low voltage current displacing the lithium ions from one side of the layer to the other, which makes the glass either darker or lighter. Commercially available systems have preset tinting stages that range from clear to almost completely opaque.
Electrochromic coatings are either organic or inorganic. Organic coatings have faster transition times and better coloring, but shorter durability. They are already used commercially. For instance, aircrafts such as the Boeing 787 Dreamliner allow passengers to control the glass tinting of each window without using shutters. Inorganic coatings are more stable and durable, and the preferred coating for use in building construction.
Evaluation
Electrochromic coatings were developed in the mid-1960s but due to the complexity of manufacturing, commercial production has only been available for approximately six years. As exciting as this new technology is, it is still in the commercial development phase and will hopefully be further refined. New live research and development has produced significant advances including:
Good solar heat gain coefficient (SHGC). This measures the portion of solar energy that enters the building.
Improved uniformity of color.
Good visible light transmittance in the clear stage.
Faster transition times between light and dark tint stages
Opportunities for improvement
The solar heat gain coefficient (SHGC) in the clear stage is almost as efficient a high performance static glass. The SHGC improves in the tinted stages at the expense of transparency, which is very low. In the tinted stages the glass appears very dark. From the exterior looking toward the building in the tinted modes. Color is another opportunity for improvement. Even though advances have been made in neutralizing the inherent yellow color of the electrochromic coating, current products still display a yellow tint, particularly in the clear stage. Some products add a blue tinted glass layer which neutralize the yellow tint, again at the expense of visible light transmittance. Finally, cost has come down considerably, nevertheless it is significantly higher than high performance, low emissivity (low-E) glass, an industry standard.
The technology is exciting and offers a dynamic alternative to static glass. In time, improved performance, added color choices and lower costs will make smart glass gain market acceptance and market share worldwide. As with other high technology products, the question to owners and architects is "when do we jump in?” I believe that given the right project, that time is now.