Cut Your Utility Bills : Window Awnings Help Save Energy

Q. Dear Jim: I have always liked the appearance of wood windows awnings. The salesman told me installing them can also save a lot of energy. Do they really save much energy, and which awning choices are best? - William B.

Answer : Dear William: The awning salesman was not just blowing smoke to get a sale.Installing window awnings can significantly reduce the cooling energy usage in your home. There are also other benefits such as reduced fading of furniture, drapes, and carpeting, as well as protection of primary windows from the sun and severe weather. The same UV rays that fade your furniture also slowly degrade window frame materials over time. The reduction in air-conditioning electrical usage results from the blocking of the direct radiant heat from the sun through windows. Studies by the University of Minnesota found installing window awnings can reduce cooling energy needs by 21 percent in Phoenix, 17 percent in St. Louis, and 24 percent in Boston.

Even though the percentage savings is highest in a northern area such as Boston, the total dollar savings is greater in a warm climate because the overall air-conditioning costs are much higher. The actual savings you realize depend upon the overall energy efficiency of your specific home, the amount of natural shading from trees, orientation of the windows to the sun, etc. Awning energy savings is greatest during the hottest hours of the afternoon when the sun is most intense. Awnings can reduce the peak electricity load for the utility company’s electric generation, so there is less chance of brownouts and other problems from excessive electricity demand.

Cutting peak electricity demand can also reduce longterm electricity rate increases by delaying the need for building new electricity generating plants. For many businesses, their utility rate depends somewhat on their peak energy usage. By reducing this peak, their electric bills can be reduced substantially. In the future, I believe some homeowners’rates may also be dependent upon their peak electricity usage. There are many window awning options available. The first decision to make is if you wantfixed or adjustable awnings. They both are equally effective during the summer to reduce your peak electricity usage in mid-afternoon. The advantage of adjustable awnings is the level of shading can be changed throughout the day and various seasons. Fixed and adjustable ones are available in all aluminum or fabric over an aluminum frame.

Adjustable fabric awnings offer better protection from severe weather because some can be lowered to be almost flat over the window opening. They can also be raised to expose most of the window glass. The maximum projection from the wall for an adjustable aluminum awning is fixed by the frame and the down arm length. To open them, the aluminum awning slats roll up above the frame and the hinged arms swing upward. The advantage of aluminum is its strength and its resistance to degradation from the sun’s UV rays.

Sideless awning designs,called Venetian awnings, are effective for true south-facing windows because the most intense sun’s rays come from overhead. Actually, just a relatively short flat board over the window, such as a large roof overhang, is effective at blocking the sun over these windows. If you need to block the late afternoon sun at those south-facing windows, install hood style awnings with sides. For casement windows, hip-style awnings provide clearance for the window sash to swing open outward.

Proper sizing (projection length from the house wall) of window awnings is important for blocking the summer sun and for allowing the winter sun to shine through the windows for free passive solar heating. This is particularly true if you install fixed awnings, instead of adjustable ones, because their shading cannot be changed. The orientation of the window to the sun also affects the proper awning sizing because the sun is lower in the sky during early morning and late afternoon.

If you still remember some of your high school geometry, you should be able to calculate the size of awning needed for various windows in your house. The latitude angle for your area determines how high the sun is in the sky and its angle of incidence on your windows. The sun’s height also varies throughout the day and seasons. You can find the sun location for various regions, seasons, and times of day in most basic solar energy books. If you are not a math wiz, just make some test awnings with cardboard to determine the proper size.

By James Dulley

Source : http://bluestemelectric.com/documents/Document_ID_389.pdf

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