AGG - 2006 - May/June

Volume 20 • Issue 3 • May / June 2006

The Energy March Forward

Comparing Yesterday's Glass Units
With Today and Tomorrow's Efficient Ones

Since the introduction of sealed insulating glass units, the glass and glazing industry has taken significant strides to provide the very best in energy performance.

While the principle goal is to improve window U-factors, the introduction of insulating glass a few decades ago effectively negated the transfer of heat and cold—much like a thermos bottle—by decreasing the overall U-factor 1.75 W/m2K (0.30 Btu/h ft2F). In doing so, insulating glass welcomed in an era of unprecedented energy savings and innovations in glazing and glass coatings that continues to evolve even today.

Glass manufacturers have since developed certain coatings that give even more unique characteristics to the insulating components of the traditional unit. For example, low-emissivity (low-E) coatings, once reserved for select fenestration projects, are now commonplace in the glazing industry and have afforded U-factor improvements to 0.90W/m2K (0.15 Btu/h ft2F).

Yet, even with performance enhancements such as coatings, either in place or in prototype practice, the fenestration industry is not resting on its laurels. Window manufacturers are still striving to add components to insulating glass to “squeeze” out as much energy efficiency as possible to produce a near-seamless end product.

Breaking the Weakest Link
One of the remaining weaknesses is the spacer utilized to separate the two lites of glass in an insulating unit. Traditionally, the material of choice for spacers has been aluminum; however aluminum is highly conductive—a thermal weak link in the window assembly, even though it is structural and stable. It is necessary to reduce the energy transfer in spacers or to seek other resources to serve as surrogate separators.

Insulating glass manufacturers have responded with the use of several energy-efficient warm-edge spacer materials. For residential structures, materials such as foam, desiccated matrix, steel and plastics serve as substitutes, while stainless steel and thermally-broken spacers are often used in commercial glazing openings. All these products have their individual niche in residential and commercial applications based on structural and code requirements. Additionally, all improve the U-factor of the window unit from 0.05 to 0.18 W/m2K (0.01-0.03 Btu/h ft2F), adding yet another energy and comfort component to the overall unit.

Even structural glazing utilized in today’s high-rise buildings can incorporate energy-efficient structural spacers with often multiple benefits. For example, thermally-broken aluminum spacers not only lead to inherent energy savings, but also provide additional structure for improved compression and deflection against strains and forces inherent in high elevations and large glazing openings.

Glass Coatings Today and Beyond
Glass coatings are yet evolving beyond what is in practice today—to more spectrally-selective coatings that simultaneously improve U-values and indoor comfort.

Perhaps the most interesting technology is the next wave in performance materials. Aerogel is a light, translucent super material used by NASA on the Mars Pathfinder. With its extreme insulating properties—39 times better than fiberglass insulation—it is being researched for use in glazing and windows.

Special glass tints are being tested that have the capability to restrict light waves based on the geographical location of a building, the time of day or the amount of daylight required within a room. Some of these coatings even allow occupants the ability to adjust the settings based on personal comfort preferences.

Additionally, new tech glass is being explored to control the heating and cooling of a building or to control indoor lighting. Such glass turns building lights up or dims them according to the amount of sunlight, or lack thereof, entering the building. Other prototype glass is being developed that provides electricity to the edifice, capturing the sun’s rays and directing the captured energy for use to power a building’s computers, lights and other energy-reliant appliances.

The strategic goal of the Department of Energy in the U.S. is “constructing cost effective net zero energy homes by 2020 and net zero commercial buildings by 2025.” Ultimately, the window will become a net energy provider for the entire building, a far different expectation from the once-believed criticism that windows and doors were the main energy losing component in a building, but also a fair assessment given the advancements that the insulating glass and window and door manufacturers have made and continue to make in their field.

Saint-Gobain Vitrage and Shell to Develop New Generation of Photovoltaic Panel
Saint-Gobain Vitrage, the flat glass business of French glass manufacturer Saint-Gobain and Shell signed a memorandum of understanding the end of February to produce next-generation solar panels.

Shell has developed a new generation of photovoltaic panel based on C.I.S. (Copper Indium Selenide) thin film deposited on glass. This panel does not incorporate silicon wafers. It has been successfully tested and offers record efficiency, especially under low illumination conditions.

Saint-Gobain Vitrage brings to the partnership its knowledge of thin-film layer deposits and glass transformation.

This partnership is designed to strengthen Saint-Gobain's competitive advantages in its technical businesses through innovation, which is consistent with the company's strategy of increasing its research and development effort in the high performance materials and flat glass sectors.

Employing approximately 37,000 people around the world, Saint-Gobain Vitrage had sales of 4.7 billion euros in 2004. It operates in 39 countries and ranks number two worldwide and number one in Europe in the flat glass market.

David J. Mills is president, CEO and vice chairman for the worldwide Azon companies, a supplier of thermal barrier chemicals and equipment used in aluminum window, door, sunroom and curtainwall extrusions and thermally improved, warm-edge spacers used in the manufacture of insulating glass units. Azon USA Inc. is located in Kalamazoo, Mich.