Combining High-Performance Windows with Insulating Shades
In your June issue, it is recommended that cellular shades not be used [with high-performance windows] until more is known because modeling found temperatures exceeding 200°F and this might affect window seals (see “Making Windows Work Better,” EBN June 2011). Although I champion the research Peter Yost is doing, I disagree with this statement. The great majority of modeled conditions were well below the 150°F range. This is not to say that the air between the shade and the glass was not hotter, as it certainly was. That is what cellular shades do—insulate to save energy and create comfort—so they create a pocket of air where the temperature is higher (in summer) or lower (in winter). Millions of cellular shades have been sold across the U.S. for the last 20 years, and there is not a single reported instance of a window failure created by the shades. No one questions that a vast amount of energy is being wasted out of windows—particularly in winter in the Northeast. From Peter’s research to date, there is no better window covering than cellular shades for insulating against heat loss, and its power is more significant than even anticipated. – Gordon Clements, President Gordon’s Window Décor Editor’s response: You are right; our cautionary language regarding the combination of high-performance cellular shades (particularly with sidetracks) or low-e storm windows with low-e double-glazed windows should have been much more carefully stated. The benefits of these two high-performance window attachments likely outweigh the risks, especially if steps are taken to mitigate the risks associated with their full deployment during the summer. Simply raising or lowering the shade or storm a bit to eliminate the full seal can allow enough air circulation to significantly reduce the heat build-up between the attachment and the double-glazed unit—with, of course, some reduction in energy performance. On the other hand, it is disappointing to see how little the window and window attachment industries have done to resolve this issue by way of research and subsequent guidance. I applaud businesses such as Gordon’s Décor, which has invested its own time and money in better understanding how its products perform. But the industries as a whole are largely reactive rather than proactive when it comes to potential negative interactions between high-performance attachments and glazing.
November 1, 2011
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EBN: Feature - June 2011