The Partnership for Advancing Technology in Housing (PATH)
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Summary
Electrochromic windows can block the glare of the sun or provide instant privacy with the flip of a switch. Electrochromic windows are part of a new generation of technologies called switchable glazing-or "smart" windows-which change the light transmittance, transparency, or shading of windows in response to an environmental signal. Electrochromic windows change from transparent to opaque or shaded by an electric signal. Potential uses for electrochromic technology include privacy, daylighting control, and solar control in windows and skylights, making traditional window shades and blinds obsolete.
Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the U.S. Department of Housing and Urban Development (HUD/FHA), The Partnership for Advancing Technology in Housing (PATH), or any PATH-affiliated Federal agency or private company. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.
Details
A variety of electrochromic technologies and media have been developed. One type, developed by Lawrence Berkeley Laboratory, consists of transparent outside layers of electrically conductive film that has inner layers which allow the exchange of ions. When a voltage is applied across the outer conductive layers, ions move from one inner layer to another, causing a change in tinting of the electrochromic material. Reversing the voltage causes the window to become clear again. The windows can have variable light transmittance during operation, from 5 to 80 percent. This type of electrochromic glazing has "memory" and does not need constant voltage after the change has been initiated. Further, it can be tuned to block certain wavelengths, such as infrared (heat) energy.
Another electrochromic technology is called suspended particle display (SPD). This material contains molecular particles suspended in a solution between the plates of glass. In their natural state, the particles move randomly and collide, blocking the direct passage of light. When switched on, the particles align rapidly and the glazing becomes transparent. This type of switchable glazing can block up to about 90 percent of light.
The National Renewable Energy Laboratory (NREL) has developed a switchable glazing based on electrochromic technology that switches from clear to tinted based on the amount of sunlight it receives. This type of window can be used for controlling unwanted heat in skylights and windows without an electrical hookup.
While not considered a true electrochromic window by some, one U.S. window manufacturer has introduced a residential window with a liquid crystal glazing that switches from clear to milky white. The windows do not significantly reduce the amount of light transmission, but only the transparency of the windows. This type of glazing, however, increases the cost of windows by about $90 per square foot of glass and requires a steady current when keeping the glass in the clear mode.
Installation
Installation is more complicated than ordinary windows since electrochromic windows require an electrical source and switch. When electrochromic windows are introduced, they will likely require installation by a licensed electrician.
Benefits/Costs
The Solar Energy Industries Association claims that "smart" windows can save as much as 50 percent of a building's energy use. In the summer months, electrochromic windows can block ultraviolet rays and radiant heat from direct sunlight passing through windows and skylights. This helps lower cooling loads by reducing solar heat gain. They can also help slow the fading of interior furnishings by blocking out the sun's ultraviolet rays. Electrochromic windows offer the flexibility of control not available in photochromic or thermochromic windows-windows that turn opaque when exposed to light or warm temperatures. Electrochromic glazing technologies are expected to be relatively expensive when initially commercialized, but decline in cost as the technology and manufacturing process matures.
Limitations
Electrochromic films require an electrical hookup that is not required for other types of solar-control window films. The durability of some electrochromic films, particularly liquids, is still not known. Work continues on development of a compound that improves durability, is less costly, and solves technical problems related to the ion-storage layer. One commercially-available system is used primarily for office interior partitions.
Code/Regulatory
In residential buildings, electrical devices operating from line voltage current must be listed with an approved testing agency. One commercially available product requires that wiring be performed by a qualified electrician, a power conditioner be used, a junction box be located within six feet of the window, and wiring pass through a ground fault circuit interrupter.
Availability
Electrochromic technologies are available for license to manufacturers. There are currently no U.S. manufacturers that are producing a true electrochromic window. Liquid crystal "privacy" glazing is available in the United States, for residential use.
Contact(s)
Do you have a specific question about this technology and/or its 'real life' applications? Try the contacts listed below:
Energy Efficiency and Renewable Energy Clearinghouse
P.O. Box 3048
Merrifield, VA 22116
800-363-3732
www.eren.doe.gov
National Renewable Energy Laboratory
1617 Cole Blvd.
Golden, CO 80401-3393
303-275-3000
www.nrel.gov/buildings/windows
Research Frontiers Incorporated
240 Crossway Park Drive
Woodbury, NY 11797-2033
888-SPD-REFR (773-7337)
Fax: 516-364-3798
www.refr-spd.com
SAGE Electrochromics Inc.
2150 Airport Dr.
Faribault, MN 55021
(507)-333-0078
Fax: 507-333-0145
www.sage-ec.com |
