Winter  2003

Warming Up
Completing the Picture with Warm-Edge Technology for IGs In Commercial Windows

by Mike Gainey

Over the past three decades the commercial glass industry has provided architects and construction professionals with tremendous advancements in glass selection. Combining increased performance of U-factor, shading coefficient, solar heat gain coefficient, a variety of light-transmittance properties in products along with a variety of colors and coating options have made glass choices a technical labyrinth.

Glass selection usually has two important components—performance and appearance. Performance is dictated by heating and cooling requirements, which are influenced by a need to comply with building codes. The owner’s desire to reduce energy costs and the architect’s desire to create a comfortable environment can also play a role in performance criteria. 

Appearance and available features in the glass selection process are very diverse. Starting with the glass substrate itself, there is a medley of choices for color, opacity, texture, etching and silk-screening.

While we have identified changes and technical advances for commercial glass, one component that has not changed in 30 years is the type of air spacer used. Commercial glass fabricators have used the same aluminum box spacer without any change in technology. Certain manufacturing practices have changed since the days when fabricators used plastic corner keys and even soldered corners, but the spacer material has remained the same. Currently, the majority of high-performance, commercial insulating glass is produced with rolled-formed aluminum, bent at all four corners, desiccant filled (with one short and one long leg being filled) and are dual sealed with a combination of polyisobutylene (PIB), silicone, polyurethane or polysulfide. Sealants are chosen for moisture-vapor-transmittance (MVT) characteristics along with the ability to hold the glass together in the face of thermal stress, wind loads and deflection. 

Air spacer improvement (warm-edge technology) has become the de facto standard in the residential window business. As is often the case in the glass industry, products are first introduced for residential use—in this case warm-edge spacers—and once they have proven their efficacy, commercial applicators will seek the same technology. All warm-edge spacers provide energy saving benefits. The concern for commercial application is structural stability, since not all warm-edge spacers are known for being structural. 

The “Final Frontier”
Improvements in high-performance glass, along with more energy-efficient wall systems, have driven the focus to what we call the weak link or the final frontier for improvement in the glazing system. That weak link has become the aluminum spacer. The question that needs to be asked is, “Does it make sense to improve the air-spacer material in a thermally improved wall system that uses high-performance glass?” The answer is yes, but with products designed to be structural. 

The Improvement
Utilizing the new Therm 5 (1) and Windows (2) programs, improvements that can be achieved in U-factor performance values are depicted in thermodynamic imaging shown in Figure 1 (see page 15). The improvements come in 
the form of incorporating structural polyurethane along with the aluminum spacer material. Creating a true structural thermal barrier within the aluminum itself by using the pour and debridge method, a process that has been used for nearly 40 years in the aluminum fenestration industry for thermally improved windows and doors.

The Results
One of the most widely used glass products is a double-silver, low-E insulating glass that has a center of glass U factor of .30. Figure 2 shows the impact of changing from an aluminum air-space material to a thermally improved material.

The Benefits
Benefits, as a result of the thermally improved airspace, include higher sight line temperature and increased sight line condensation resistance factor (CRF) as shown in Figure 3. To the end-user this translates into increased comfort, less interior condensation, an improvement in sound transmission control (STC) ratings and a lower energy bill.

The Strongest Link
A warm-edge spacer that incorporates a structural thermal barrier will exhibit 20 percent less deflection than a standard aluminum spacer and is able to withstand more than twice the force-to-failure than an aluminum spacer (743 lbf to 361 lbf respectively).

What is Driving Warm-Edge Technology?
There are a number of reasons why warm-edge technology will become the new standard for commercial insulating glass projects. Reasons include:
• Building codes (national, state and local);
• Department of Energy (DOE);
• ENERGY STAR® for commercial buildings is on the horizon;
• Architects; and
• Consumers.

The DOE raised public awareness with the ENERGY STAR® program and is now in the process of road-mapping energy reduction strategies for commercial buildings. Even the American Institute of Architects has established this creed as a guiding principle “Return to well-established methods of design that conserve energy and natural resources.” The commercial glass industry must now position itself to catch up with warm-edge technology to see dramatic improvements in U-edge value, sight-line temperature, sight line CRF, improvement in STC ratings, overall structural improvement and improvements in the U-factor of the opening. Improvement with new warm-edge air spacer material technology, suitable for the monumental demands of commercial construction, is a way to do just that.

What Are People Saying?
To test the validity of a thermally improved, structurally sound warm-edge spacer, we selected nine architectural firms in Chicago to which the information was presented. These firms are among the largest, most respected firms in the world. We asked them to respond to three questions after the presentation: Does this make sense? Do you understand it? Will you specify a thermally improved, structurally sound air spacer? The response from all nine firms was the same—a resounding yes. Architects and engineers who understand high-performance glass know that one result of using a new glass technology is that the spacer material has become the focal point for energy transfer. Improving the spacer, by using a structural, warm-edge material will allow the architect to complete the picture for commercial projects. The result: a functional, thermally improved glazing system. 

Thermodynamic Imaging U-Factors Sightline CRF

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