August 2008
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| February 2008 |
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The Problem - Anne Perkins, Director of RDI's Home Ownership Programs, has been on a quest to find ever more energy efficient windows for each home we build. She spent two days walking the exhibitor floor at the International Builders' Show (IBS) in Orlando, FL this past February, talking with every window company she could find. All of them had focused their marketing on warm climates with attention given to lowering the Solar Heat Gain Coefficient (SHGC) and not to lowering the U-value of the windows. We cold climate people are looking for a high SHGC along with a low U-value. If the Visible Light Transmission (VLT) can be high, so much the better.
The Solution - Upon her return Anne, and Robb Aldrich of Steven Winter Designs, energy systems engineer for the Wisdom Way Solar Village, started researching windows in more depth. Ultimately, they were able to work with Paradigm Windows, the window supplier for RDI’s ENERGY STAR homes for several years, to devise a way to increase the SHGC on their double pane window up to 0.36 (from 0.29) , while lowring the U. value from 0.28 to 0.26. RDI chose to use these windows on the south face of the walls. At the same time, Paradigm had developed a triple pane window with a very low U. value of 0.18; RDI chose to install those windows in the north, east, and west faces of the village.
Heat Mirror & krypton gas on left;
low-E and argon gas on right*
The triple-paned windows used on the North, East and West orientations at WWSV will show results similar to the window on the left.
*These infrared photographs show the difference between double pane windows with Heat Mirror and krypton gas, versus low-E and argon gas. The Heat Mirror is a low-emissivity (low-E) coated film suspended between two panes of glass.