Electrochromic (EC) glass darkens in response to the application of low-voltage DC current to reversibly control sunlight and maintain view, while reducing building energy consumption, glare, and harmful ultraviolet (UV) radiation. The initial purchase cost of EC glass may be offset by reduced HVAC capacity, elimination of sunshades and/or internal shading, as well as diminished need for artificial lighting. Long-term savings may be gained from decreased energy use.
Multiple, microscopically thin layers of ceramic materials are sputter- coated on glass substrates to create EC glass. Lithium ions and electrons migrate through these stacked layers when voltage is applied, darkening the coating. This tint absorbs and reradiates solar energy, reducing solar heat gain coefficient (SHGC) and saving energy. When positive and negative poles are reversed, the coating stack returns to its "clear" state.
After coating, EC lites are fabricated into low-U-Factor insulating glass units (IGUs) that are connected by wires to their power supplies, sensors, and software that manually or automatically control the state of EC lites; clear, partially-tinted or fully tinted.
In a 10-year partnership with Minnesota-based SAGE, Wausau has completed a number of successful projects incorporating EC glass. The growing portfolio includes:
- Twin Lakes Elementary School (pictured)
- Lawrence Berkeley National Laboratory (pictured)
- Southern California Edison Irwindale Center
- National Renewable Energy Laboratory
- SAGE Manufacturing Facility
EC Product Characteristics
Even when it's warm and sunny, it takes several minutes for EC glass to darken fully or to clear. Control algorithms help ensure consistency between large lites and small lites in their darkened and clear states.
EC glass has a characteristic amber color in its "clear" state. In its tinted state, EC glass is typically blue-green. Color can be affected by tinted substrates or by coatings on other glass surfaces within the IGU.
IGU spacers are ½-inch, dark bronze, stainless steel and a 13/16-inch, black silk-screened obscuration band on the #2 surface "hides" the spacer on all four sides from the exterior. Warranty on the entire EC IGU is five years.
Glazing, Wiring and Control Systems
When factory-glazed, EC glass is installed and sealed with "pigtail" wires and connectors, which are secured within the glazing pocket or other frame cavity, for field attachment to drop wires and controllers. EC low-voltage control system wiring must conform to the requirements for a National Electrical Code® Class 2 circuit, and is activated by UL-listed power supplies.
Projects utilizing EC glass follow a construction process similar to other high-end glass products, with the added complexity of electrical wiring and controls. Remember to allow time in schedules for the EC supplier and the project's electrical engineer to review, coordinate and approve wiring diagrams and control system plans.
Applications engineering issues include:
- Wiring path within the window framing
- Controling wiring "bundle" size
- Protecting wiring during shipment and installation
- Routing of wires through adjacent substrates
- Labeling of wires for proper attachment
System commissioning after installation ensures proper operation and calibration.
In the future, standalone, wireless, photocell-powered controllers for individual EC lites may be available.
Other Types of Switchable Glass
All switchable or controllable glazing is not EC glass. Other types of dynamic glass include:
- Thermochromic glass, which darkens in response to elevated temperature,
- Photochromic glass, which darkens in response to outside light levels,
- Privacy glass, which switches to a translucent state, or
- Suspended particle devices, which tint and clear similar to EC glass, but are based on UV-sensitive organic coatings, and typically do not provide the level of SHGC reduction that EC offers.
The use of EC glass supports even the most ambitious
and zero-energy building goals, while significantly enhancing occupant comfort.
If you would liketo discuss applications engineering for specific projects in detail, Wausau's market managers are available for architectural support and can be reached at email@example.com, firstname.lastname@example.org, email@example.com,