Exterior shading. Rather than trying to control light from the inside, it has become popular to look at exterior design strategies. These have included things like adding fixed shades, shutters, or awnings to a building façade which can help reduce solar gain, but are very limited based on the angle of the sun in the sky. They can also require considerable design effort and expertise to have them effectively integrated into a building so they perform as intended without blocking views or too much light. They are usually rather expensive items not only for their initial cost, but also in terms of their life-cycle costs of production, maintenance, replacement, and disposal. Since they are usually fixed in place, they do not adjust to changing light conditions from weather or from adjacent buildings/terrain.

High-performance glass. There have been a series of advancements in glazing technology in recent years that allows for the selection of glass that has different thermal and light transmittance properties. These have been important and useful in the design of many buildings, but the reality is that once the particular glass is selected and installed, it is a fixed or “static” solution. Static solutions are permanently clear or tinted or reflective regardless of changing seasons or sunlight conditions—and cannot respond to changing conditions. This static trait means that either interior or exterior shading will likely be desired in many cases for separate control. It also means that any one window will likely strive for an average condition or a worst case condition and thus not be able to effectively address the range of conditions associated with heat gain, glare, and damage to materials.

Given the need to keep the benefits of glazing and overcome the limitations of conventional control strategies, a number of emerging technologies have been applied to glazing that provide “dynamic” rather than “static” control options. Simply defined, dynamic glass can respond to changing light conditions by clearing or darkening as light levels change. Some examples include photochromic or thermochromic glass that respond to UV light or heat and tint accordingly. This type of dynamic glazing requires no electricity and has been used most commonly in products like eyeglasses, causing them to darken in bright light and clear in less light.

A different type of dynamic glass is privacy glass. Specifically designed for interior applications, privacy glass generally requires 110 volts of AC electricity and is a laminated glass with organic compounds placed between the layers. In either case the glass is made clear when the electricity is turned on and resorts to its natural obscured state when the power is turned off. Privacy glass is for situations that require total privacy and is not typically for solar control.

The Electrochromic Glazing Breakthrough

The one active dynamic glazing technology specifically designed for building envelope applications is referred to as electrochromic (EC) glazing. This rapidly growing technology uses a series of thin, non-organic ceramic and metallic films deposited onto the surface of glass that are electrically charged to regulate both light and heat through the glass. Unlike SPD or LCD glazing, however, the amount of electricity used is dramatically less, typically at less than 4 volts DC and less than 10 milliamps. Further, the electric charge is only needed to tint the glass, since the natural state of EC glazing is clear. Through variable tint control settings, electrochromic glazing preserves the human benefits of abundant sunlight, views, and connection to the outdoors but without the associated issues and environmental penalties. This makes it one of the most promising forms of dynamic glazing available today for exterior applications.

EC glazing is made from panes of conventional float glass that are sputter coated with ceramic layers of metal oxides. The processes are proprietary to the manufacturers, but are similar to the way low-e glass is produced. In most cases, nanotechnology is used to control layers to a very fine degree. The total thickness of all the layers of an electrochromic coating is commonly less than 1/50th of the thickness of a human hair. When an electronic voltage is applied across the coatings, ions travel between layers, where a reversible solid state change takes place, causing the coating to tint and absorb light. Reversing the polarity of the applied voltage causes the ions to migrate back to their original layer, and the glass returns to its clear state.

The coated panes of glass are fabricated into insulating glass units (IGUs) using another piece of glass (clear, tinted, or laminated) and a stainless steel spacer. These IGUs can be fashioned into windows, skylights, and curtain walls, making advanced electrochromic glazing as easy to specify and install as conventional “static” windows. An electronic control system is integrated with the installed glazing and can be customized depending on the needs of the project. The glazing can be controlled by an automated control system, a Building Management System (BMS), or manually using wall switches, or in various combinations of those methods. Most of the tinting occurs in 7 to 15 minutes, depending on glass size and temperature of the glass. Faster tinting can occur in smaller panes and/or warmer temperatures.

The beauty of the installed system is that since the glass itself is controlling solar light and heat, there is no need for exterior or interior shading or other solar devices to be built, purchased, or installed. Therefore, it integrates easily into any design, and into ordinary construction processes.