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No single recipe for efficiency

With increasing mainstream media coverage of climate change and global warming, it should come as no surprise that consumers are increasingly aware of energy efficiency. Unlike energy-efficient appliances that can be considered efficient in any area the country, energy-efficiency requirements for windows vary depending upon in which part of the country they will be installed. “There are different requirements for the exact same window in different climates,” explains Jeffrey Inks, vice president of codes and regulatory affairs with the Washington, D.C.-based Window & Door Manufacturers Association. 

“Window manufacturers are constantly looking for ways to evolve their products to make them more energy efficient,” Inks says. “That can be challenging because windows have so many functions. It’s not just energy efficiency. You must be able to accomplish that, while at the same time ensuring you have proper operability, proper size, fall protection and protection against natural hazards, particularly in hurricane-prone regions.”

Energy efficiency often comes down to the correct combination of U-factor, solar heat gain coefficient and visual transmittance. Because this can be complicated to evaluate, however, many consumers rely on Energy Star, which simplifies the window selection process by identifying which windows are highly efficient for the region in which they will be installed. 

“Science is an amazing thing. We are always learning,” Inks says. Windows have advanced from single-pane to dual-pane to coatings that protect against heat penetration and heat loss. “Window evolution has been a progression of single-pane, double-pane, double-pane with low-e coatings, double pane with gas fill; then you get into triple-pane or double-pane with multiple coated surfaces. When you look at a double- or triple-pane window, you generally see an aluminum thermal break in it.” Thermal break technology continues to advance as a window’s performance relies on the frame, including what material is used and how it is insulated and sealed. 

Driven by codes

Inks says the national model building codes such as the International Energy Conservation Code establish  minimum energy performance requirements for new construction, which also are applicable to window replacement. Different jurisdictions, however, may adopt different versions of the same building code. “One jurisdiction may have enforced the 2003 edition of the International Energy Conservation Code while another may have the 2006 edition enforced while another one may have enforced the 2009 or 2012 version,” Inks explains.

“The latest edition always has the most stringent building requirements, which is driven by the notion that every time we revise the energy code we should shoot for a goal of making it more energy efficient than the previous version. That’s the same concept with Energy Star. The criteria for that often is related to market penetration; it’s a trigger for evaluating what is necessary.” 

When updating codes and enforcing energy efficiency, Inks notes it’s important to ensure performance requirements aren’t outpacing the ability to produce a cost-effective product with reasonable return on investment. WDMA worked with Energy Star in its Energy Star Version 6.0 for residential windows, doors and skylights to ensure the requirements met the aforementioned criteria. “The objective in working with them, and what we accomplished, was to raise the bar for Energy Star to where you have more efficient windows and qualification criteria, but not set it so stringent that its cost would position the product outside the financial reach of most consumers.” The next version of Energy Star will take effect Jan. 1, 2015, except for in the northern part of the U.S., where it will take effect Jan. 1, 2016. 

“There’s a combination of factors constantly being worked together in codes. It really depends on what area you’re in, the type of window you’re manufacturing, and the type of framing and spacer materials,” Inks says. “There are so many factors; it’s not just the glass itself. There’s no single recipe. It’s a challenge, but manufacturers are stepping up to the plate.”