Plavecsky's Ponderings By Jim Plavecsky
by Jim Plavecsky
May 22nd, 2019

Triple Pane Trifecta

When surface-four low-E coatings came onto the scene a few years ago, offering U-values in double-pane insulating glass (IG) that’s similar to triple-pane, some thought this would bring about a significant decline in the use of triple-pane configurations. But I have to say—while visiting various window manufacturers, I continue to find a strong interest in fabricating windows utilizing triple-pane glass. Triple-pane window platforms offer the trifecta in window performance: U-value optimization, the highest condensation resistance and improved sound attenuation.

U-Value Optimization

Larger air gaps in IG lead to increases in convection, which in turn decreases thermal performance. When air has more space to circulate, it does so, in the process transferring heat. Triple-pane designs create two smaller air gaps, as opposed to a single larger air gap, resulting in less convection and consequently better thermal performance. Also, exotic low-conductivity gases, such as krypton and argon/krypton blends, tend to work their magic in smaller, more confined areas. As a result, triple-pane designs maximize the benefits of those exotic gases. Therefore, U-values can be optimized as two panes of low-E glass are combined with two cavities filled with 99.9% krypton or krypton/argon blends. This maximizes the energy savings for homeowners.

Condensation Resistance

Do you want to actually see the reason why windows allow condensation to form on the inside pane of glass during cold winter months? Then try this experiment: Borrow a thermal imaging camera from a roofing company and take a thermal picture of a window from outside of the house on a cold day. You will see reddish color bands at the edges of glass, as heat is traveling from inside a home through the spacer system and to the outside. Heat travels from where it is hot to where it is not. So, you are seeing an actual picture of heat loss. If the outside lite of glass is warmer in this part of the window, then it means the inside pane is correspondingly cooler in the exact same area. Therefore, any moisture vapor trapped inside the home will condense on the perimeter area of the inside lite of glass, resulting in condensation. Dual-pane windows made with surface-four low-E coatings will show more heat loss in this perimeter area compared to triple-pane windows. For this reason, triple-pane windows excel with higher condensation resistance (CR) ratings. Condensation resistance can be boosted even higher with the use of warm edge spacer systems. The lower the conductivity of the spacer, the higher the CR.

Sound Attenuation

Triple-pane windows also allow window manufacturers to achieve improved (higher) STC ratings, by taking advantage of the science of decoupling. Materials of identical characteristics respond to sound waves in identical ways. So, by combining materials of dissimilar characteristics, sound waves of dissimilar wavelengths are generated. These offsetting wavelengths will “decouple” or cancel out one another, as opposed to those of similar wavelengths which build upon each other, creating amplification.

Triple-pane configurations also allow us to use two different sized air cavities versus the same sized gaps, or two different glass thicknesses. Even two different glass materials, such as conventional versus laminated glass, can be used in triple-pane designs to decouple sound waves, thereby achieving even higher STC values. The result is less sound transmission from passing planes, trains, automobiles, neighborhood kids, lawnmowers and barking dogs.

Sound attenuation will become increasingly important in the future, as density of population increases in urban areas. Homeowners love to enjoy the view outside but don’t necessarily want to hear the associated sounds!

So, even though there are now other avenues to achieve U-values that rival those of triple-pane configurations, triple pane windows can enable window designers to not only optimize U-values but also condensation (CR) ratings and sound transmission classification (STC) ratings as well – a trifecta in the world of window performance!

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