Suspended Particle Device (SPD) Windows

This electrically controlled film utilizes a thin, liquid-like layer in which numerous microscopic particles are suspended. In its unpowered state the particles are randomly oriented and partially block sunlight transmission and view. Transparent electrical conductors allow an electric field to be applied to the dispersed particle film, aligning the particles and raising the transmittance. Typical visible transmittance (VT) and solar heat gain coefficient (SHGC) ranges for the film alone are VT=0.22–0.005 or 0.57–0.12 and SHGC=0.56–0.41 or 0.70–0.50, respectively, with near instant switching times (less than one second). The SHGC switching range is more limited than electrochromic windows (see below). The device requires about 100 volts AC to operate from the off state (colored) to the on state (near transparent) and can be modulated to any intermediate state. Power requirements are 0.5 W/sf for switching and 0.05 W/sf to maintain a constant transmission state if not off (the most colored, cobalt blue state). With research, the operating voltages could get down to about 35 volts AC. New suspensions are also under development to achieve several different colors (green, red, and purple) and to affect up to a 50% change in solar transmittance. Manufacturers state that these laminated glazings can be fabricated in up to 4-by-8-foot sheets and can be offered in both curved and flat shapes. Long-term durability and solar-optical properties have not been independently verified. Products are now entering the market, but cost remains an issue.


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