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TECHNOLOGY AND YOU

Window film blocks UV rays and saves energy

Q: The afternoon sun blasts in our windows. It literally bakes us, fades our furniture and pushes up our air-conditioning costs. How effective are the new do-it-yourself clear summer/winter window films? - H. E.

A: Installing window film, either low-cost do-it-yourself or professionally-installed film, is your best solution to block the sun's intense heat and 99 percent of the ultraviolet (UV) fading rays. Many of the new nearly-clear summer/winter films are barely noticeable once installed. Some have warranties up to five years, but last even longer.

Even if you already have efficient double pane windows, installing these new films makes sense. The nearly-clear films can be applied to single or double pane windows without problems. Avoid installing the older-technology darkly tinted films on double pane windows. They can cause the glass to get warm and the airtight seal between the panes to prematurely leak.

In addition to comfort improvement, there are hidden savings of installing window film. Although you only notice the fading of your furniture and carpeting, the sun's UV rays slowly break down the material fibers too. Installing film lowers your air-conditioning costs and reduces the utility's peak electricity demand to moderate future rate increases.

All window films also increase the shatter resistance of glass. In areas prone to damage by tornadoes, hurricanes or children, this is a real plus. If the glass breaks, the pieces hang together for safety. Special extra-heavy clear security films make it difficult for burglars to break through.

Do-it-yourself year-round window film is simple to install. You just need a sharp knife, a spray bottle, soapy water, a squeegee and about 20 minutes. First clean the indoor window surface thoroughly with diluted soapy water. Courtaulds Performance Films now has a new solution to dissolve the adhesive if you have old film to remove first or you choose to later remove the film.

Cut a piece of the film to a size slightly larger than the window. Peel off the film backing to expose the adhesive. Wet the adhesive side of the film with a spray bottle and place it against the window. Squeegee out the air bubbles and trim the film around the edges.

True summer/winter window films have the same type of low-emissivity (low-e) coating as on new expensive high-tech replacement windows. This blocks radiant heat loss through your windows in the winter as well as heat gain in the summer. As you begin to apply the film yourself, you can immediately feel the heat reduction.

To achieve these super-efficient properties, a microscopically-thin, invisible layer of metal atoms is deposited on the polyester film surface. It is far too thin to see. It is transparent to energy in the visible light range, but opaque to energy in the UV or infrared heat range. When this film is applied to the window, the view is distortion-free.

Although most of the window films look similar in the home center store, there are significant differences among them in summer heat rejection and winter heat savings performance. It is important to compare several key performance factors for the films. Do not just buy the cheapest brand on sale.

Total solar energy rejection (TSER) factor is important when comparing summer heat rejection. The higher the number, the more heat and UV rays it blocks. A related factor is the shading coefficient (SC). It compares the overall net

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

Copyright 1996 James Dulley

18 ILLINOIS COUNTRY LIVING AUGUST 1997


benefit in blocking summer heat gain. A lower number blocks more heat.

The visible light transmission (VLT) factor determines how dark the film is and the amount of glare from the window. A lower number is darker. Keep in mind that film always looks darker before it is installed. The emissivity factor affects year-round utility bill savings and comfort in the winter. A lower number is better.

Since the sun is high in the southern sky near noon and early afternoon, direct heat through south-facing windows can be blocked by a large roof overhang. Another option is building a simple window flower box/sun shield. The flower box has opaque sides and a clear plastic top to block the fading UV rays. A do-it-yourself exterior vertical-sliding sun shade can also be effective.

Write for Utility Bills Update No. 732—a buyer's guide of year-round do-it-yourself (plus a sample piece) and professional residential window films listing TSER, SC, emissivity, VLT, tint colors, prices, installation instructions and instructions for making a flower box/sun shield and sun shade. Please include $2 (with checks payable to Jim Dulley) and a business-size SASE, and send to Jim Dulley, Illinois Country Living, P.O. Box 3787, Springfield, IL 62708. To read previous columns, go to http://www.dulley.com.

18 ILLINOIS COUNTRY LIVING AUGUST 1997


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