Electrochromic Sun Control Coverings for Windows

The 2 billion square meters (m2) of building windows in the United States cause a national energy drain almost as large as the energy supply of the Alaskan oil pipeline. Unlike the pipeline, the drain of energy through windows will continue well into the 21st century. A part of this energy drain is due to unwanted sun gain through windows. This is a problem throughout the country in commercialbuildings because they generally require air conditioning even in cold climates. New commercial windows create an additional 1600 MW demand for peak electric power in the United States each year. Sun control films, widely used in new windows and as retrofits to old windows, help to mitigate this problem. However, conventional, static solar control films also block sunlight when it is wanted forwarmth and daylighting. New electrochromic, switchable, sun-gain-control films now under development will provide more nearly optimal and automatic sun control for added comfort, decreased building operating expense, and greater energy savings. Switchable, electrochromic films can be deposited on polymers at high speeds by plasma enhanced chemical vapor deposition (PECVD) in a process that maybe suitable for roll coating. This paper describes the electrochromic coatings and the PECVD processes, and speculates about their adaptability to high-speed roll coating.