Energy Manager

Control & Automation
FEATURE – New Insulated Glazing Technologies Pose an Exciting Future

July 11, 2012 - New requirements for windows, embedded in everything from the 2012 IECC (International Energy Conservation Code) which calls for U-factors down to 0.32 to Energy Star upgrades and the DOE’s R-5 (U = 0.20) window program are clear evidence of the trend toward higher performance expectations.

July 11, 2012

To meet the increasing pressure for more energy-efficient windows, many improvements to the performance of double-glazed products have taken place over recent years—notably:

• Advanced “triple-silver” spectrally-selective low-emissivity (low-E) coatings
• Inert gas infills, usually argon or the more expensive yet more highly insulating krypton
• “Warm edge” spacers that reduce heat flow around the edges of IG units

But, IG (insulated glazing) technology is evolving to achieve even more.

• Enhanced Low-E Glass – promising technical approaches to improve low-E coatings include creating a more durable silver layer through treatment with plasma during growth, modification of the surrounding oxide layers and variation in silver alloy composition.
• Triple Glazing – many think of triple versus double glazing as subject to the law of diminishing returns, but newer triple-glazed designs and tighter performance requirements can make it viable in less frigid climates as well. By specifying low-conductivity spacers, gas filling, thermally enhanced frames and two lites of very low-E glass, manufacturers can produce triples with U-values as low as 0.15 (R-7). Other versions feature a thin film-like material in place of the center layer of glass.


The Next Big Thing: Dynamic Glazing
After many years of being no more than a niche, the “smart window” market now seems ready to take off, according to market research firm NanoMarkets, LC.

“Smart Windows” equipped with “dynamic glazing” allow building occupants to manually or automatically control a window to change from clear to dark to meet the optimal solar control requirements of the day or season. Dynamic glazing technologies include electrochromic, photochromic and thermochromic variations on a similar theme.

Electrochromic glass can be darkened or lightened (i.e., have their transparency dynamically changed) electronically, literally with the flip of a switch. This capability allows for the automatic control of the amount of light and heat that passes through the windows.

There are several types of electrochromic technologies including Polymer Dispersed Liquid Crystal (PDLC) and Suspended Particle Device (SPD) systems and vacuum glass coated with multilayer electrochromic coatings. Each has its benefits and disadvantages.

Other variations on the smart window theme include:

• Self-Cleaning Windows – offering more convenience than energy savings, the technology behind these glazings is a thin layer of TiO2 coating that has both photocatalytic and hydrophilic effects. The photocatalysis effect breaks down organic dirt on the glass to form mainly CO2 and water. The hydrophilic properties prevent droplets from forming on the coating because the water spreads out into an almost uniform film.
• Liquid Crystal Windows – used for privacy control, they do not provide energy savings.
• Thermochromic Windows – which have a thin plastic film inserted into the IG assembly that becomes opaque (self-tints) when a specific temperature is reached. This glazing is probably best suited for skylights, rather than view windows.
• Photochromic Windows – responds to changes in light, much like sunglasses that darken in bright light.

The Future
Research efforts are seeking to develop cost-effective window products with U-factors between 0.10 – 0.20 and with a range of SHGCs for all applications. Of particular interest are novel transparent insulating materials, such as aerogels, Vacuum Insulated Glazing (VIG) and Building Integrated Photovoltaics (BIPV) that capture the light from the sun and turn it into energy via a system of optics and photovoltaic (PV) cells placed within the air cavity of a standard IG unit.

Even further “out there” are several types of microstructured glazing materials under development—including holograms, microlouvers, and liquid crystals—and three-dimensional light redirecting systems. Other futuristic coated glass innovations for IGs could include the same technology used in smart phones or tablets, enabling touch screen functionality to control a room’s temperature, turn on the lights, check our email or convert large bay windows into big-screen TVs.

By AAMA (American Architectural Manufacturers Association) Glass Material Council

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