Windows of opportunity: ever-improving energy-saving glazings are open to all markets

Building Products, Nov-Dec, 2004 by Linda C. Lentz

There was a time when specifying windows was a simple matter of size, shape, frame material, and budget. The problem was, once installed they did little more than keep out the snow and rain--even ice formed on the inside.

Times changed. Over the past 25 years rising environmental and energy concerns--and mandates--have caused manufacturers to re-invent the proverbial wheel. As a result, the array of products available bears little resemblance to the fenestrations of 30 years ago.

Of course this complicates the selection process considerably. The good news is quality energy-efficient windows have never been easier to purchase--no matter what the project or budget.

For Lake Geneva, Wis., custom builder John Engerman of Engerman Contracting, there are no bad windows any more. "With the information and technology available, all manufacturers are making much better windows than they did 15 or 20 years ago," he says.

To combat vigorous lake breezes yet provide the appropriate look for a private residence he built on Lake Geneva, Engerman used Vetter aluminum-clad wood windows and patio doors with the latest SDL (simulated divided light) technology and argon-filled low-E2 glass, or glazing.

Indeed, aluminum cladding has been embraced by builders and consumers for its reliable performance and low-maintenance characteristics. "It's crisp, stable, and it doesn't expand and contract like other materials," says Engerman. Unfortunately, it is also a good conductor of heat and cold.

To compensate, manufacturers are engineering their newest models with the highest-performing glazings, such as argon-filled low-E2, and other insulating materials. Consequently, products such as Caradco's Tradition Plus and Pella's ProLine double-hung aluminum-clad wood windows meet or exceed the DOE's tough Energy Star requirements.

"Windows are responsible for quite a bit of energy consumption in a home" says Joe Wiehagen, the NAHB Research Center's energy-efficiency senior research engineer. "So if you improve the window technology, the benefit can be huge--not just in energy savings. It can also reduce the size of your heating and cooling system, which is an upfront cost you can take advantage of."

As defined by the DOE, low-E (low-emittance) coatings are highly reflective, transparent coatings applied to the window glazing. Because they are designed to reflect long-wavelength infrared radiation, less heat is transferred through the window either from the home or the outside.

By contrast, the newer low-E2, a spectrally selective or low-solar-gain low-E coating (known under a variety of brand names) reflects the heating energy from the sun (or solar heat gain) to keep homes cooler in hot, sunny climates, particularly in the South and Southwest. Filled with gas--argon or krypton--both become even more thermally efficient, which is de rigueur for colder northern regions.

"Manufacturers must have products that are going to perform with more and more energy codes being put in place by each state," explains Jeff Kliber, brand manager for Vetter and sister company Peachtree. "We try to put products into place that are going to perform in all four NFRC [National Fenestration Rating Council] zones with our highest glazing option possible."

At Peachtree, both the aluminum-clad wood 500 series and more custom aluminum-clad or primed-wood 700 series come standard with the same EasyCare low-E2 glazing, which is an option on the more entry-level vinyl-clad wood 300 series. All, however, are outfitted with a flexible warm-edge spacer system for improved insulation and condensation resistance.

ELEMENTAL ADJUSTMENTS

According to researcher Christian Kohler of the Lawrence Berkeley National Laboratory Window and Daylighting Group in California, "Every insulated glazing [IG] has a spacer on the edge, which acts as a kind of thermal short circuit. Aluminum is common, but manufacturers are experimenting with different designs and materials to improve performance."

Weather Shield's flexible Warm Edge I spacer, for one, is made with a non-conductive material that the manufacturer claims reduces conductivity by more than 50 percent over other warm-edge spacers.

"The technology and design used in Warm Edge I increases the glass temperature, making windows warmer. This insulates the flame and edge of the glass better than metal spacers and aluminum spacer bars and significantly minimizes condensation" explains Peter Lenar, Weather Shield brand manager.

Hurd developed the Energy Plus window with a new warm-edge spacer system in an effort to provide Energy Star-rated extruded aluminum products that don't require a gas-fill. This was done specifically for high-altitude regions where it is necessary to insert a "breather tube" into the glass to prevent damage due to pressure shifts. Although these tubes are crimped and sealed at the site, stopping the release of gas, there's no way to control how much is lost due to varying conditions on jobsites.

"There are two key factors for our Energy Plus unit," says Hurd design manager Paul Surek. "One is the high-thermal composite core placed within the extruded aluminum frame to reduce the amount of cold and heat conduction. The other is our stainless steel Intercept spacer." This channel- or Gshaped spacer adds to the unit's efficiency that, again, reduces metal conduction to make it more thermally efficient. "In addition," Surek contends, "the stainless steel is a better insulating material than aluminum or even other types of steel."