(06/21/21) BATON ROUGE, La. — Many people think of an air conditioner as something that circulates cool air through their home, but what it really does is remove heat and moisture from the air. So, an understanding of how heat enters the home is the key to choosing the most cost-effective ways to cut summer utility bills, while staying cool and comfortable, said Claudette Hanks Reichel, LSU AgCenter housing specialist and director of LaHouse.
According to an analysis by the Florida Solar Energy Center, the main sources of heat gain in homes during the summer, in order of greatest to smallest, are:
1. Windows (solar heat gain through glass)
2. Duct system (air leaks and absorbed heat)
3. Roof and attic
4. Internally generated heat (appliances, electronics, cooking, bathing, etc.)
5. Air infiltration (outside air leaking into the home)
“Although the amount of heat gain from each source varies among houses and lifestyles, the top five tend to offer the greatest opportunity to save money and stay cool in Louisiana’s hot and humid climate,” Reichel said. She offered advice to keep homes cool during summer’s heat.
1. Shade windows. Sun-control strategies can provide the greatest bang for the buck. An exterior shading strategy should be used for any glass that receives direct sunshine or heat radiating from pavement. Interior window treatments like blinds help but are not nearly as effective as exterior or glass solar control.
Solar screens, or shade screens, are an inexpensive, do-it-yourself strategy that can block up to 70% of solar heat while preserving the view. The screening fabric is easy to install in aluminum screen frames with a spline. The energy savings can surpass the cost in one or two summers.
Solar films (heat control film applied to the interior side of glass) are available with a range of properties to serve a home’s needs. A solar heat gain coefficient (SHGC) under 0.4 (meaning it admits 40% and blocks 60% of radiant heat) and a visible light transmittance (VT) of 0.5 or greater is optimal. The lower the SHGC the better; the higher the VT the better. Do-it-yourself kits are available, but take a bit of finesse to avoid air bubbles.
If planning to install new windows, choose units that are Energy Star certified. Energy Star windows for the southern region will have an SHGC of 0.25 or lower.
Landscaping is a great way to shade both glass and walls as well as add value to a home. Awnings are another good option with aesthetic benefits, but they are costlier.
2. Test and improve ductwork. In a typical home, ductwork might lose 30% or more of its cooling, which costs money. This is due to ducts in most homes in the south being in the hottest part of a home: the attic, which tend to be quite leaky. Leaky ducts mean both air conditioning the outdoors and causing a home to draw in hot, humid outdoor air to make up for the leaked air.
It’s a great investment to have ducts leak-tested by a trained professional with specialized equipment, then have all leaks sealed with mastic tape rather than duct tape. It is also helpful to add duct insulation when feasible and improve its layout to correct tight bends and crimps.
3. Block attic heat. If a home has a vented attic, it can become much hotter than the outdoor temperature. To combat this, find and seal air leaks in ceilings, around chimneys and any other bypasses. This can also reduce dust in a home. If space permits, increase attic floor insulation to R-38.
If the air conditioner and ducts are in the attic, a radiant barrier system can reduce the heat-up of ductwork and the attic by blocking radiant heat from the hot roof. This can be a do-it-yourself project by stapling reinforced foil radiant barrier to rafters, shiny side down.
Powered roof vents are not recommended. They not only use energy but can also create a suction in the attic that pulls air from the living space into the attic. That can result in higher energy bills because the attic is being cooled with the conditioned air.
4. Produce less heat indoors. In general, every three kilowatt-hours of energy saved in the home can reduce the need for cooling by one additional kWh, saving energy and money two ways.
Leaving computers, TVs, lights and even ceiling fans on add heat needlessly. Ceiling fans can save energy by keeping a home cooler at higher thermostat settings, but they waste energy if are left on in unoccupied rooms. Turning everything off when not needed costs nothing. If that seems like a difficult habit to enforce, install and use timers or motion sensors.
When replacing appliances, look for the Energy Star label. Investing in high efficiency pays off. Refrigerators and freezers are especially important because they run — and give off heat — continuously.
Replace incandescent light bulbs with LEDs or compact fluorescent lamps (CFLs). They have a higher price tag, but use about one-fourth the electricity, produce one-fourth the heat and last 10 to 20 times longer — thus staying cooler and saving money in the long run.
Consumers should also think about ways to reduce heat-making activities. This can be accomplished by cooking with a microwave oven and outdoor grill. Waiting for full loads to run the dishwasher is also a good way to save, as is using less hot water for laundry and showers.
5. Cool more efficiently. Last but not least, air conditioning systems should be professionally cleaned and serviced to keep them running as efficiently as possible. Changing the air filter as recommended on its label is important. A dirty filter that restricts air flow causes a big loss of efficiency.
When it’s time to replace an air conditioner, investments in a Seasonal Energy Efficiency Ratio (SEER) of 14 to 16 or an Energy Star qualified model should be made, as is making certain it is sized correctly. Bigger isn’t necessarily better. An oversized air conditioner cools the space too quickly, resulting in short cycles that do not dehumidify adequately. An oversized unit also will cost more to buy and more to operate, and it will not last as long.
To learn more about energy-saving, resilient and healthy home improvements, visit the LSU AgCenter LaHouse Resource Center and its website, www.lsuagcenter.com/LaHouse. The LaHouse Resource Center near the LSU campus is an educational showcase of solutions for the Gulf region’s climate and natural hazards. Also, check out the LaHouse YouTube channel at www.youtube.com/myLaHouse, and get timely tips by following www.facebook.com/mylahouse.