IGMA: October 2012
By Helen Sanders
Advances in dynamic glazing
By Helen Sanders
Dynamic glazing is one of the more exciting innovations occurring in the glass industry today.
Dynamic glazing is one of the more exciting innovations occurring in the glass industry today. The technology is evolving quickly, and promises to deliver significant benefits to the energy efficiency, cost and interior environment of buildings where it is used. I had a chance to address an industry group on this topic at the IGMA Performance and Innovation in Insulating Glass Educational Seminar in Las Vegas that took place right before GlassBuild.
Dynamic glazing refers to glazing elements that change their transmission properties in response to such external stimuli as heat, sunlight, gas or electricity. Respectively, these four types are referred to as thermochromic, photochromic, gasochromic and electrochromic.
Thermochromic laminated glass incorporates a PVB interlayer with a low-E coating on the third surface. It darkens as it heats up. Thermochromic insulating glass sandwiches the PVB between two panes on the exterior side of the unit and puts the low-E coating on the inside pane, the fifth surface. It can achieve a VLT range from 50 to 10 per cent and an SHGC range from 0.32 at 25 C to .2 at 65 C.
Electrochromic glazings come in four subtypes: polymer-based, monolithic ceramic, suspended particle devices and liquid crystal devices.
LCD glazing is used for privacy applications as it becomes completely opaque when activated rather than simply reducing transmissions. The LCD interlayer consists of a layer of electrolytes sandwiched between two conducting layers. When high-voltage AC current is applied, the electrolyte crystals line up, allowing light to transmit. When the current is off, the crystals float randomly and completely diffuse light.
SPD dynamic glazing is mechanically similar to LCD designs, except reactive particles are suspended between conductors instead of electrolytes. In its off state, the unit is tinted. As higher levels of AC voltage are applied, the unit achieves different tint conditions until, at the highest level, it is apparently clear. SPD modulates visible light with only a small effect on SHGC. Its big advantage is the speed with which it can switch transmission characteristics. VLT can range from 50 to 0.7 per cent, and SHGC can range from 0.61 to 0.37.
Polymer-based electrochromics are presently only made in Europe. The system consists of a laminate of two glass plys each containing a transparent conducting oxide and electrochromic electrode or counter electrode respectively, with a special polymer in the middle that is both conductive and acts as an adhesive laminate. When DC current is passed through the conductors, electrons pass through the polymer, causing a polarity shift that darkens the unit. When used in an IGU, VLT ranges from 50 to 15 per cent and SHGC ranges from 0.38 to 0.12. These designs require an edge seal on the laminate portion.
Monolithic ceramic electrochromic designs allow the active dynamic layers to be deposited on the back of a single sheet of glass rather than sandwiched as a laminate interlayer between two sheets. As in polymer-based designs, an ion-transmitting middle layer separates two electrodes and two conductors. In this case, however, the middle layer is a ceramic rather than a polymer. Framed into an IG unit, monolithic ceramic glazing can be combined with argon gas fills as required to achieve VLT ranges from 62 to two per cent and SHGC ranges from 0.47 to 0.09.
Dynamic glazing promises to open up architectural options by eliminating the need for increased HVAC, sunshades, low-E IGUs and automated blinds. Architects will have a chance to meet energy efficiency requirements at affordable cost while delivering improved views and more comfortable living and working environments.
Helen Sanders is the vice-president of technical business development for Sage Electrochromics and an IGMA board member. She chairs the IGMA’s Emerging Technology and Innovation Technical Committee.