Glass Coatings Continue to Advance Performance and Possibilities

By Ellen Rogers

The development of low-E coatings in the 1970s was a game changer for architectural glass. It provided a means for builders, developers, architects and specifiers to use an abundance of glass, while keeping occupants comfortable and without concern of increased energy costs. Glass also become clearer, as in the past, it often had to become darker to provide the same comfort and performance. Low-E coatings, however, were an early step toward reducing the amount of ultraviolet and infrared light that passed through glass while still maintaining visible light transmittance (VLT). And that was just the beginning. With subsequent advances in higher performing products came a drive in the codes for even better glazing products. And today, it’s quite likely that no new building would meet codes without the use of coated glass.

Glass coatings have evolved to not only offer improved energy performance, but are also clear and more transparent. And, they continue to advance, paving the way for future developments.

Changes and Trends

Today’s coated glass has come a long way since the early days of low-E. Technologies have continued to evolve and there are hundreds of options for individual locations and climate zones, as well as aesthetics.

“The glass world has been dominated by the Magnetron Sputtering Vapor Deposition (MSVD) coating realm,” says Nathan McKenna, director of marketing and innovation with Vitro Architectural Glass (formerly PPG). “[MSVD products] dominated the technology and development, and part of that is every time the code changed you needed a higher performance glass… to reach those numbers in the climate zone.” He explains that within the codes, it’s the Solar Heat Gain Coefficient (SHGC) and U-value that have become increasingly stringent.

That’s leading the charge on the commercial side, because coatings have gotten better,” he says. “The trends have gone from having to use dark glass to get the performance, to now achieving it with clear glass because the coatings have gotten better,” he adds.

According to Tim McKittrick, the sector manager for thin film photovoltaics at Pilkington, architects are focusing on thermal performance of glass coatings—maximizing daylight transmission while minimizing solar heat gain and having good U-value performance.

“Thermal performance is the most important feature of coated glass. Whether that’s achieving excellent U-values in heating dominated regions or attaining low SHGCs in cooling dominated regions, the comfort of the occupants and the associated energy costs of maintaining that comfort are the key factors for commercial buildings.”

Alissa Schmidt, architectural design and technical services manager with Viracon, points out that while the general idea of high light transmittance combined with solar performance to optimize a building’s energy efficiency isn’t new, there’s been an increased focus on balancing the two.

“As a result, coating development has been highly focused on pinpointing specific light transmittance and SHGC requirements,” she says.

While coatings have advanced to become increasingly high performance, they have also evolved aesthetically. Leigh Anne Mays, eastern regional architectural manager, with Guardian Glass, says the changes and developments in coatings follow a similar trend as the fashion industry.

“Architects want to change. They don’t want the same glass color palettes,” she says. “Right now we’re seeing more interest in gray/blue, but they want a subtle appearance, in the mid-reflectivity range. They’re looking for something to give a little more shimmer but not overwhelming.”

Kristen Petersen, architectural design specialist with Viracon, agrees that gray is trending.

“Architects love gray, so there’s definitely a shift to wanting the gray/neutral colored coatings while avoiding the green tint of some of the higher performing coatings,” she says. “Using low-iron glass is very popular to help reduce some of the green tint.” However, she says even with coatings that have a neutral gray appearance, “I think there will still be demand for something even more neutral gray, without having to use a tinted substrate and lose that reflectivity that gives the vibrant appearance.”

Another architectural trend has been the increasing demand for bigger sizes of glass, which means companies have had to change their operations to accommodate coating larger sizes. Yago Martinez, AGC Interpane’s business development manager for North America, says he has seen a lot of demand for jumbo-sized coated glass and, with that, has come improved quality and consistency in the coating process.

“Previously, there was not a huge requirement when it came to consistency. Now there are means to keep tighter control over color consistency.”

Mays agrees.

“The last ten years have seen a lot of tweaks and improvements to products and processes. We’ve seen tempering ovens change to accommodate the coatings and they’ve gotten better,” she says. “A lot has happened to streamline the process and make it more efficient to get a better quality product to the market.”

Continual Improvement

While VLT, SHGC and U-Value are important performance criteria for coatings, there is not a one-size-fits-all option. What’s right for one project in one region may not work for another building somewhere else. Schmidt points out that building-specific criteria is being added to the general key performance criteria.

“A building may require a coating with low exterior reflectance due to its orientation and surroundings. A different building may need a bird-collision mitigation treatment in addition to the coating. A one-size-fits-all coating solution is becoming less and less common,” she says.

Marni Windschitl, architectural design associate, also with Viracon agrees that the most important performance features of coated glass are dependent upon a number of considerations, in particular, location.

“The owner/consultant/architect should work with a glass fabricator to make sure the performance goals are met based on energy calculations,” she says. “The orientation of the building (North/South/East/West) also comes into play when determining performance requirements. Almost all commercial buildings are cooling dominated; selecting a coating with a low SHGC is always a good idea.”

Mays points out that coatings can provide various levels of performance and benefits depending on geographic location.

“In the Northeast/Canada U-value is most important. So [to meet code] you’re also looking at triple glazing and skinny triples and [the aesthetic] has been more of a European style,” she says.

Martinez agrees that U-values are drawing a lot of attention, particularly in cold climate zones.

“Codes are becoming stringent and demanding lower U-values and, in some cases, the only way to achieve [the requirements] is triple glazing,” he says. “But in many cases, the clients don’t want that added cost or weight of triple glazing, so there has been development in room-side coatings, for example.” This type of coating is designed to reflect indoor heat back into the room, helping to improve thermal efficiency. Martinez adds, “They help in achieving U-values similar to triple glazing but with reduced cost/weight.”

Mays says heat gain tends to draw the most attention outside the Northeast.

“But they both [U-value and SHGC] matter depending on where you live. That’s why triple silver coatings are so important; they allow more visible light, but drive down solar heat gain. No one wants to sit in a dark box,” she says.

A Closer Look

Triple silver coatings have seen significant development over the past decade. McKittrick says this has been one of the biggest developments in coated glass.

“Initially, they were single silver based, but have progressed to double silver and now to triple silver based,” he says. “Doing so subsequently improved the selectivity and thermal performance of the solar control insulating glass units.”

Martinez agrees, adding that it’s the silver that gives the glass its selectivity behavior. He explains that selectivity is the ratio between how much light and how much energy goes through the glass. “Newer coatings have a higher selectivity ratio so you can allow more than twice as much light as energy,” says Martinez. “The more silver, the more selective,” he says, adding that it’s not simply a matter of placing a coating of silver upon a coating of silver multiple times.

“[Silver] is expensive and can also give the glass a green appearance. The process is complex because every time you use a silver layer you need to add other layers on  top, and you continue to repeat the layers each time. So if you want to go from single silver to double silver you’re adding five or six layers and you have to keep increasing those to go to a triple silver.”

Mays agrees, adding the silver decouples the light-heat connection. “It’s still connected but it’s not as ‘one-to-one’ as it used to be,” she says.

The first triple silver coatings tended to give the glass a green aesthetic. Mays says that from the first generation of triple silvers, to what’s available today, many process tweaks and changes to improve the clarity have occurred, because architects don’t want green shaded glass.

“Now companies have figured out the different layer stacks to offset that green color and still get high performance,” she says.

And those layers also mean enhanced performance.

“As layers of silver are added to a coating, the coating is more likely to provide higher VLT and lower SHGC than a single or double silver counterpart,” says Schmidt.

Windschitl adds, “Triple silver coatings do a great job of balancing a high VLT, 50% or higher and maintaining a low SHGC, less than a .29. They have a neutral aesthetic and balance reflectivity.”

The Next Generation

Low-E coatings have continued to develop since they were first introduced.
As building codes continue to advance, we can likely expect to see increasingly high-performance glass as well. McKenna says as the environmental impact of building products continues to move to the forefront of importance, programs such as LEED and Net Zero, among others, will become so prevalent that products have to evolve to meet those needs.

“You also have to keep an eye on what the future of work-life really is. Is the commercial office building the future or is it in smaller pockets?” he says. “It’s hard to say, because we don’t know what the commercial office building will look like in the next ten years. It’s hard to predict, but sustainability and green will continue to be important.”

McKittrick adds they are also seeing an increasing interest in carbon neutral buildings. “That means [the use of ] building integrated photovoltaics which often require a coated glass substrate to perform efficiently without becoming objectionable from an aesthetic viewpoint,” he says.

Petersen adds, “I see [coatings] becoming even more energy efficient, with even lower SHGCs. Perhaps coatings that were once our best performers are going to need to perform even better.”

There are also coated glass developments that extend beyond energy performance. Anti-microbial glass, for example, has increased in importance.

McKittrick sees anti-microbial glass coatings as a sector with significant potential. In fact, Pilkington recently introduced an anti-microbial glass product (see page 60).

“Obvious applications include hospitals, retirement homes or any glazed area where the general public is likely to mix and interact with others,” says McKittrick. “Photocatalytic coatings are particularly well suited to these applications, where the interaction of UV light in daylight causes a reaction on the coated glass surface to inactivate viruses and bacteria on the glazed area.”

Other coating developments likely to become more common include growth in bird-friendly glazing, dynamic/electrochromic glass (see page 54) and the incorporation of low-E coatings onto VIG.

The glass industry continues to evolve, but not necessarily at a rapid pace. And for good reasons.

“It’s not a massive step change where one day it’s one direction and the next day another,” says Mays. “That’s because people want tried-and-true tested and a performance guarantee. The industry is cautious, but optimistic in looking at new designs and ways to do things. People want confirmation it works before it’s adopted; it has to be validated. People like that comfort level.”

Ellen Rogers is the editor of USGlass magazine. Follow her on Twitter @USGlass and like USGlass on Facebook to receive updates.

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