WINDOW TECHNOLOGIES: Advanced
The emerging concept for the window of the future is more as a multifunctional "appliance-in-the-wall" rather than simply a static piece of coated glass. These facade systems include switchable windows and shading systems such as motorized shades, switchable electrochromic or gasochromic window coatings, and double-envelope window-wall systems that have variable optical and thermal properties that can be changed in response to climate, occupant preferences and building system requirements. By actively managing lighting and cooling, smart windows could reduce peak electric loads by 20–30% in many commercial buildings, increase daylighting benefits throughout the United States, improve comfort, and potentially enhance productivity in homes and offices. These technologies can provide maximum flexibility in aggressively managing demand and energy use in buildings in the emerging deregulated utility environment. They can also move the building community towards a goal of producing advanced buildings with minimal impact on the nation's energy resources.
The ideal window would be one with optical properties that could readily adapt in response to changing climatic conditions or occupant preferences. Researchers have been hard at work on new glazing technologies for the next generation of smart windows. After many years of development, various switchable window technologies are now in prototype testing phases and should be commercially available in the near future. As with other window technologies, the architect will need to understand these new systems in order to specify them properly.
There are two basic types of switchable windows—passive devices that respond directly to a single environmental variable such as light level or temperature, and active devices that can be directly controlled in response to any variable such as occupant preferences or heating and cooling system requirements. The main passive devices are photochromics and thermochromics; active devices include liquid crystal, suspended particle, and electrochromics.