(continued)

One can also imagine situations where the desires for view, energy savings, and visibility may conflict with each other. Then a "smart" controller would have to optimize for competing conditions, always subject to the occupant's manual override.

Unlike the all-or-nothing solution of interior drapes, electrochromic glazing can darken and lighten gradually in response to gradually changing conditions. And even in its most colored state, it permits views to the outside, which is healthy for occupants, both ergonomically and psychologically.

This adaptation to diurnal changes in daylight availability saves energy in two primary ways. It reduces the need for electricity-consuming lighting. And it reduces the load to the cooling system that would otherwise be increased by the lights and the incoming solar radiation. This is especially significant in commercial buildings, where lighting and cooling are by far the biggest energy consumers.

Another advantage of this system is that it reduces glare from direct sunlight and bright exterior sources, which would otherwise cause visual discomfort and make it hard to see work surfaces, especially computer screens. Also, use of electrochromic glazing potentially reduces a building's electricity consumption in the middle of the day, taking advantage of utility companies' custom of charging higher rates during hours of peak usage.

Although research into "switchable" glazings has been going on for many years—and is now familiar in the form of day/night positions of rear-view mirrors in cars — this technology is not yet commercially available for large-area applications.

Large-area glazing, such as would be needed in office buildings, can be obtained for about $1000 per square meter, plus the cost of integrating the controlling electronics with the rest of the building's control systems. The LBNL researchers expect that such products will come to the mainstream marketplace in 3-5 years and that their cost will ultimately drop to about $100 per square meter.

To help advance this promising technology into the marketplace, LBNL is leading a U.S. Department of Energy-funded program to understand and resolve the many applications-related issues. The first full-scale office tests were recently completed in California.

In test rooms, in an office building in Oakland, the glazing was combined with a layer of low-e tinted glass. As a result, the overall light transmissivity of the assembly varied between 11 percent, when switched to the darkest, and 38 percent at its lightest.

The researchers expect that when the electrochromic glazing is mass-produced for the marketplace, there will be a greater range of difference between darkest and lightest states, and that more neutral colors will be available. They also expect that smarter automated controls will be developed but that occupant controls will always be available to override them.

If this technology does become widespread, we can expect it to change the appearance of commercial architecture. Because these glazings change gradually in response to external and internal conditions, it is likely that there will be noticeable differences in color and opacity between different areas of a large, glazed facade. Those seeking a uniform facade may forego the energy benefits or look for ways to mask these differences. On the other hand, architects who relish the idea that buildings reflect their environments will surely seek imaginative ways to celebrate the differences.

The testing described here was conducted by Eleanor Lee, Dennis DeBartolomeo, and Stephen Selkowitz, of the Lawrence Berkeley National Laboratory's Building Technologies Department. A technical description of their testing is available at the LBNL Web site. The research was sponsored by the U.S. Department of Energy's Office of Building Technology, State and Community Programs.

B.J. Novitski is managing editor for ArchitectureWeek and author of Rendering Real and Imagined Buildings.

Before sunlight strikes the window in the morning, the glazing is switched to its clearest (38% transmissivity) and the electric lights are on at 80% of full power. Photo: Eleanor Lee/LBNL As soon as direct sunlight enters the room, the glazing begins to darken and the lights dim quickly to 30% of full power. Photo: Eleanor Lee/LBNL Within a few minutes, the glazing has achieved its darkest state (11% transmissivity) and the lights are dimmed back up somewhat, to 42% of full power, to compensate. Photo: Eleanor Lee/LBNL The colored state of electrochromic windows is switched by a system that also dims electric lights up and down, all triggered by a photosensor. Image: Eleanor Lee/LBNL   Click on thumbnail images to view full-size pictures.