Seite - 53 - in Water, Energy, and Environment - A Primer

and speed of transmission control (complete switching can take several minutes). Many different electrochromic window options at different price points for buildings are now available, and active R&D efforts are underway. One recent advance is the development of reflective, rather than absorptive, windows which switch between transparent and mirror-like. Electrochromic windows are an attractive energy efficiency measure because (a) they can block heat (infrared radiation) in the summer, reducing air conditioning loads, and (b) allow infrared radiation to pass into buildings in the winter and reduce heating loads (windows account for about 30% of building energy load). This also reduces utility peak load demands. Tunable electrochromic windows also serve to reduce lighting loads when adequate natural light is available, reduce glare, provide privacy without the need for blinds and curtains, and reduce fabric and art fading by blocking ultraviolet radiation. Other important applications include use in automobile windows, sunroofs and rear view mirrors, in aircraft (e.g., the Boeing 787 Dreamliner uses electrochromic windows in place of pull down window shades), and as internal partitions in buildingswith the ability to switch screens anddoors fromclear to private. Given that EC windows have been under development for many years, their obvious ability to block or transmit wavelengths of light as needed, and their many applications, why hasn’t greater use of such windows become a standard part of building construction? The simple answer is cost. NREL looked at this issue in its December 2009 report entitled ‘Preliminary Assessment of the Energy-Saving Potential of ElectrochromicWindows in Residential Buildings’ and compared the cost of low-e argon-filled windows with that of EC windows and concluded that ‘…EC windows would have to reach a price point of approximately $20/square Energyoptions 53