Volume 34, Number 4, April 1999

 

Great Performances

Evolving Concepts in Glass Performance

by Tim Singel

Glass has changed in nearly every way imaginable since the early Egyptians used it for decorative purposes. Today, glass provides form as well as function, including aesthetic appeal, energy efficiency, daylighting, safety and security. High-performance glazing packages, which usually incorporate low-E coated glass, now account for as much as 40 percent of all windows sold annually. This number is up from less than 10 percent only a decade ago.

While the shift in North American demand for low-E products is significant, consider the European analogy. Following the Energy Conservation Regulation of 1995, low-E penetration rose from less than 15 percent, to more than 90 percent in the German prime window market. Almost overnight, low-E became a standard product, and since 1996 has dominated sales of architectural glass. This radical change in glass performance concept/application was the result of a legislative initiative, based upon financial return and an interest in energy conservation. Admittedly, we cannot ignore the dramatic difference between United States and European energy costs. However, all of the elements that stimulated low-E propagation in Central Europe exist in the United States today.

Several factors are driving demand for high-performance glass packages in the North American marketplace. Fundamentally, all factors point to a single phenomenon—heightened consumer awareness. Fueling this heightened awareness are:

The very definition of high performance also has changed significantly. Today, the use of spectrally selective low-E products and laminated glass are commonplace. More and more residential and commercial applications include solar management tints and coatings, in addition to climatically-oriented low-E. These combination configurations represent the customization that a full-service supplier is capable of providing. Manufacturers of these glass elements continue to introduce new products that are designed to address an age-old problem—the unwanted flow of energy.

To oversimplify the concept, energy (heat) travels from where it’s hot, to where it’s not. As an industry, we have addressed the three methods by which energy travels. With the advent of insulating glass, we reduced the heat lost due to convective transfer. Next, we enhanced insulating glass with the evolution of spacer materials. This slowed down the heat that travels conductively between the inside and outside of a window system. Add to the equation low conducting inert gases such as argon or krypton, and the window system begins to behave like a barrier instead of a gateway. The third form of heat transfer has been addressed through the use of low-E glass. Radiative heat transfer, or heat that has been absorbed by a body (human or structural), and then released or re-radiated can be minimized by incorporating a low-E coating into the window system. While the industry debates issues such as positive or negative impact of passive heat gain (under scrutiny by no less than three industry committees), it is clear that low-E glass offers the benefit of energy savings in all North American climates.

By following the evolution of low-E products, it is fairly easy to understand why the use of these products continues to escalate. Early low-E product designs were relatively simple. The primary objective of the first low-E products was to provide better thermal performance than clear glass—and they did. In retrospect, that single dimensional approach failed to address a significant problem. Much of North America must deal with excessive solar heat gain for at least a portion of the year. With this important element in mind, our industry pushed onward in low-E design and introduced the first in an ongoing series of multidimensional, spectrally-selective products. In addition to offering advantages that include thermal and solar control, these new designs also provide ultraviolet protection. While spectrally-selective low-E designs continue to evolve, it is important to appreciate where we are today. We have reached the point of diminishing returns in our pursuit of lower emittance products. For example, while breaking the .04 barrier may sound impressive, if unprecedented thermal performance doesn’t result, have we added value?

I feel the future of high-performance glass packages is in the package. Enhancements in thermal performance will come from new and enhanced configurations of coated and uncoated glass products, improved spacer systems, and new thinking in air space management. Ultraviolet performance is, and will continue to be addressed by glass coating technology and through the use of laminated glass. Solar performance, offering the greatest potential for enhancement, will evolve through the use of standard and high-performance glass tints and advancements in coatings technology.

Now, perhaps more than ever before, it is critical that the relationship between window manufacturer and supplier, or specifier and manufacturer be based on open dialogue regarding application objectives. It is also clear that in choosing a supplier partner for glass products, breadth and depth of capability are critical. Technologies that once were exclusive to automotive, appliance, optical, commercial or residential construction are converging at an ever increasing rate. Is the criteria that was used to select your present supplier applicable to your future needs?

Tim Singel is coated products manager for Guardian Industries Corp., based in Auburn Hills, MI.


USG

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