Window awnings reduce energy usage

 
 
Posted8/7/2021 6:00 AM

Q: I have always liked the appearance of window awnings. The salesman told me installing them can also save a lot of energy. Do they really save much energy and what awning choices are best?

A: The awning salesman was not just blowing smoke to get a sale. Installing window awnings can reduce summertime energy use. There are also other benefits such as reduced fading of furniture, drapes and carpeting, and protection of your primary windows and doors from the sun and severe weather. The same UV (ultraviolet) rays that fade your furniture also slowly degrade window frame and door materials over time.

 

The reduction in air-conditioning electrical usage results from the blocking of the direct radiant heat from the sun through windows and doors. Studies by the University of Minnesota found installing window awnings can reduce cooling energy needs by 21% in Phoenix, 17% in St. Louis and 24% in Boston.

Another advantage of awning energy savings is it is greatest during the hottest hours of the afternoon when the sun is most intense. This reduces the peak electricity load for the utility company's electric generation, so there is less chance of brownouts and other problems associated with excessive electricity demand.

There are many window awning options available. The first decision to make is if you want fixed or adjustable awnings. They both are equally effective during the summer to reduce your peak electricity usage in midafternoon. 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 nearly expose the entire window glass for winter solar heat gain. Fabric awnings using Sunbrella fabrics provide SPF-15 cancer risk protection. Also, ones using GORE Tenara thread are durable and hold up well to UV degradation.

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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 directly overhead. Actually, just a relatively short flat board over the window, such a large roof overhang, is effective at blocking the sun over these windows. If you also 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.

If you are also concerned about security and privacy, select an adjustable awning that can be lowered completely flat against the window. This offers privacy and some protection from break-ins and storm damage to the window glass from flying objects.

Proper sizing (projection length from the house wall) of window awnings is important both for blocking the summer sun and for allowing the winter sun to shine. This is particularly true if you install fixed awnings, instead of adjustable ones, because their shading angle 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 your high school geometry, you can calculate the size of awning needed for various windows and doors. The latitude angle (varies from about 29 degrees for Houston to 45 degrees for Minneapolis) for your area determines how high the sun is in the sky and its angle of incidence on your windows. 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 whiz, just make a "test stick" awning to determine the proper size. Hold the end of a stick against the top of the window frame or wall at the time of day when you need shading. Vary the stick lengths and the angle until its shadow provides the shading you desire. The shades width should extend at least 2 inches on either side of the window.

The following companies offer window awnings: Awntech, (800) 200-5997, www.awntech.com; Craft-Bilt, (800) 422-8577, www.craftbilt.com; Eastern Awning, (800) 445-4142, www.easternawning.com; and General Awnings, (888) 330-3115, www.generalawnings.com.

Q: We use a heat pump year-round in our house. It seems like the room temperatures stay more constant if we run the blower continuously. Does doing this save or waste more electricity overall?

A: There are several factors that determine whether you are saving electricity. If running the blower continuously has improved your comfort to the point you set the thermostat several degrees lower during winter and higher during summer, then you will save electricity.

Also, if you have a variable-speed, ECM (electronically commutated motor) blower, it uses much less electricity than a standard blower motor in the slow-speed mode. Check with your HVAC contractor.

• Write to James Dulley at 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit dulley.com.

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