Volume 9, Issue 3 - March 2008

Eye on Energy

Let Green Be Your Guide
Developing Energy-Efficient Windows for the Future
by Ric Jackson

Green is more than a trend. It’s here to stay. In the building industry, you can feel the momentum. An increasing number of consumers are seeking sustainable building products to help make their homes environmentally friendly. For window manufacturers and sellers, this movement translates into significant opportunity. To meet the growing demand for green products is to contribute to the sustainability of our planet—and your business.

Two main camps have emerged for measuring a product’s green qualities: composition and conservation. Composition is concerned with the materials that make up a product, or the process and energy that go into manufacturing the product—including recycled or environmentally friendly materials. Conservation looks at products from the standpoint of how their performance may help to save energy or protect the environment over their useful life. Windows fall into this latter category. For purposes of defining windows as an energy-saving appliance, we will consider them to have green potential.

What can your company do to produce the most marketable, energy-efficient window possible? It’s a vital question, because when homeowners think green, they often think of windows first. Windows can account for between 10 and 25 percent of the total energy consumption for heating and cooling an average home. Homeowners want energy-efficient windows that will help the environment provide greater comfort and save them money.

If you sell and market to the southern climate zones, where cooling energy makes up more of the total household energy bill, you will need to focus on the effects of solar heat gain coefficient (SHGC). For each 0.10 reduction in SHGC, there is an average corresponding reduction in energy load of 4 MBTUs per home-year* by reducing the amount of solar energy (infrared) that can enter through the window. The opposite change of 0.10 increase in SHGC in the northern heating zone allows more heat energy into the home, saving up to 4 MBTUs per home-year, which can reduce carbon dioxide pollution by more than one ton per year. 

In the northern heating and cooling climate, the impact of U-value improvements is larger than the effect of the SHGC changes. For every 0.05 U-value improvement (decrease), we see approximately 5 MBTUs reduction in energy consumption—or approximately 1.5 tons of carbon dioxide potential reduction.

The most recent proposed changes to the Energy Star® program (see the February 2008 issue of DWM, page 16), demonstrate the importance of optimizing SHGC and U-value of windows to help save energy. Saving energy also reduces carbon dioxide pollution, creating an opportunity to promote the green benefits of windows.

The choices you make in window construction carry U-value and SHGC consequences. Glass options can reduce U-values of the total window by up to 0.17, going from clear float to an emissivity of 0.18 in a typical vinyl window; triples with krypton can reduce that U-value by another 0.10, or down to 0.15. The choice of insulating glass spacer also can have an impact by as much as 0.04, going from aluminum spacer bar to the lowest-conductivity non-metal spacer. Now consider that each 0.01 U-value improvement in a window can save approximately 400 pounds of carbon dioxide per year in a typical home—and hundreds of dollars a year to the homeowner.

As homeowners choose energy efficiency in their windows in increased numbers, window fabricators have important choices to make. Let green be your guide.

* U-value simulations were performed by Enermodal Engineering Limited using Window 5.2 and Therm 5.2 as per NFRC 100, and NFRC 500, 2001 on December 23, 2003. Energy savings were calculated using Resfen 5.0 and climate locations in Tampa, Fla., and International Falls, Minn. 

Ric Jackson is director of marketing and business development for Truseal Technologies Inc. He can be reached at rjackson@truseal.com. The views and opinions expressed in this article do not necessarily reflect those of this magazine.



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