Experts Discuss Risks Versus Rewards of ‘Surface 4 Low-E Coatings’

Window technology experts Jim Larsen, director of technology marketing for Cardinal Glass Industries, and Tracy Rogers, the director of industry relations and advanced technology for Quanex, provided commentary and perspective on “Surface 4 Low-E coatings,” pinpointing benefits and risks that might be associated with the technological advancement for window systems, during a recent industry meeting.

According to Larsen, there is a thermal “performance gap” with double- and triple-pane window systems despite technological advancements, which he elaborated upon during his session portion, “Roomside Glass Surface Coatings – An Optimization of Double Pane,” at the recent annual Windows and Door Manufacturers Association (WDMA) Technical Conference.

Larsen said double-pane glass units have peaked when it comes to thermal performance; low-E coatings, argon gas fills and the use of a warm-edge spacer are the main options in terms of high insulation. The common response to hitting the glass ceiling with double-panes appears to be triple-pane units, but he said the difficulty with this system lies in the installation into conventional windows because it often requires a “significant redesign.”

Now the question, he said, becomes: How do manufacturers “bridge the performance gap?”

Larsen said the partial answer is to place a low-E coating on the room-side surface of the glass of an “optimized double-pane (low-E and argon fill).” He suggested that doing this, however, means a higher risk of condensation in cold weather because the coating “reduces radiant heat transfer from room to glass surface [and] improves [the] window U-factor [to] about 0.03 btu/hr•ft²•°F …” Ultimately, he said the room-side glass is cooler, which increases the chance of low levels of insulation, an excess of water vapor in the building structure that can result in peeling paint or mold.

According to Larsen, to reap any reward from the low-E coating, manufacturers need to factor in the risks of condensation without sacrificing major redesigns to window systems. References to make this analysis include “Typical Meteorological Year (TMY) weather data for climate evaluations, and past window performance for real-world humidity levels,” he said.

During Rogers’ portion of the session, “The Effects of #4 Surface Low-E Coatings on Fenestration Condensation Resistance,” he discussed the increased risk of a loss of condensation resistance that might occur when using Surface 4 low-E among “insulating glass configurations of a variety of coating and spacer constructions.”

” … This specific performance improvement configuration can create a lesser performing system that can lead to confounding problems including water and ice damage to the fenestration system and the wall surround,” said Rogers.

He added, however, that while there are factors that might cause condensation levels, there also are technological improvements.

“Primarily, condensation resistance in window systems stems from the functions of components within the window system and insulating glass system so it’s not an average of the entire performance-it’s very discreet based upon how conductive individual components are,” Rogers said. “Obviously the more conductive a giving component is from the warm to the cold side could potentially short-circuit the thermal performance of the system and create a localized cold spot, lowering localized surface temperatures and allow for condensation to form.”

Rogers said many consumers will look at a high-performance window system and consider the high-quality U-factor but fail to realize the associated risk of increased condensation issues. He said some assume that to combat high condensation levels, the humidity within a building structure should be lowered but this would not result in “good quality air.”

In terms of advancements that may help, Rogers said using warm-edge spacers with low-E coatings can help to reduce the risk of condensation.

“The whole focus here is not to say that anything is bad, not to say that there is a problem- it’s just to raise awareness,” Rogers said. “If you’re looking into using these types of technologies, you have to understand the potential implication that you might have. The focus there is that you’re putting time into a product because you want to improve the U-factor, you want to sell a high-performance window system and you’re … promoting it as a high-performance window system with the potential of seeing condensation on the glass. How is that going to be construed in the marketplace? You just want to ensure these types of issues are considered when designing these systems.”

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