EnergyWise House: Building a Smarter, More Efficient Window

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Modern windows take advantage of multiple materials. Here, a wood casement window's exterior is sheathed in vinyl for weather resistance and reduced maintenance. On the interior, the exposed wood can be painted or stained. Credit: Andersen Corporation Homeowners love windows — the light they bring, the views they frame, the feel they give to homes. Energy experts hate windows — the heat they bring, the heat they drain, the added energy consumption they cause. The race is on to develop the technology that will allow builders to incorporate windows and homeowners to place them wherever they want without fear of skyrocketing energy costs. Low-e Coatings Windows have continued to improve over the years, first with insulated glass units that provided a buffer zone of air between two panes of glass to reduce the heat loss incurred by single pane units during cold weather. Improvements continued with the advent of low-e or low emissivity coatings. These microthin metallic coatings reflect heat, sending it back where it came from. Low-e coatings significantly improve the thermal quality of insulated glass units, helping homes to stay warmer in the winter and cooler in the summer. Adding argon or krypton gas fill between these coated panes adds to the insulative properties of the window unit. At the high end of available window technology is spectrally selective coatings. The coatings are applied to the panes of glass to reduce heat gain by blocking selected rays from entering the home. This enhancement to low-e coated glass helps further reduce heat loss from inside and heat gain from outside. It also serves to protect furniture and fabrics within from sun bleaching. With gas-filled, spectrally selective coated glass in a well-constructed insulated glass unit, the R-value of a window can approach that of a well-insulated wall. Still, short of drawing the shades or awnings, beating sun challenges all windows and causes solar heat gain that can compromise any energy budget. New Window Technology Companies are now researching technologies that will allow maximum visible light to enter the home while blocking the rays that cause heat buildup within the home. Enter switchable windows that respond with a flick of the switch to darken, lighten, or almost completely block the sun from entering living space. Technology already exists to bring switchable privacy glass (SPG) to homes, but these windows don't block heat gain or ultra violet (UV) light penetration. SPG changes from clear to milky white when switched, which allows light to enter the interior space while the view is blocked from outside. Marvin Windows brought this technology to the residential market, but was forced to abandon it due to failures. "The quality of the glass and reject rate became frustrating for both our supplier and us and were hurting sales," says Anthony Head, Regulatory Product Planner for Marvin. With Marvin's longstanding commitment to quality, durability, and a 20-year warranty, they had no choice but to discontinue the line. "There's still quite a bit of it operational in the field," Head says. "We continue to monitor this technology today in our advanced research area. The most promising technology seems to be glass that isn't a privacy glass, but is a variable tint type of glass." Exclusive EnergyWise House Video Report Philips Products Marquee 9000 Windows - Philips Products Marquee 9000 Series windows offer an innovative design comprised of 3 pieces of insulating glass, with two sealed airspaces filled with Argon gas. When combined with Low-E glass, these windows provide an energy efficiency increase of up to 90 percent over the average Low-E, Argon-filled vinyl window on the market. Solar heat gain coefficients are also improved by up to 40 percent with Philips' unique insulated vinyl windows. Philips' insulating glass package is up to 1 1/2 inches thick, compared with the 3/4 inch to 7/8 inch packages of other vinyl windows, and comes in a variety of styles and finishes. Watch Video!

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