An alternative way to maintain a cool house or reduce air-conditioning use is natural (or passive) cooling. Passive cooling uses non-mechanical methods to maintain a comfortable indoor temperature.
The most effective method to cool your home is to keep the heat from building up in the first place. The primary source of heat buildup (i.e., gain) is sunlight absorbed by your house through the roof, walls, and windows. Secondary sources are heat-generating appliances in the home and air leakage. Specific methods to prevent heat gain include reflecting heat (i.e., sunlight) away from your house, blocking the heat, removing built-up heat, and reducing or eliminating heat- generating sources in your home.
Reflecting Heat Away Dull, dark-colored home exteriors absorb 70% to 90% of the radiant energy form the sun that strikes the home's surfaces. Some of this absorbed energy is then transferred into your home by way of conduction, resulting in heat gain. In contrast, light-colored surfaces effectively reflect most of the heat away from your home.
The most effective method to cool your home is to keep the heat from building up in the first place. Installing a radiant barrier Radiant barriers are easy to install. It does not matter which way the shiny surface faces - up or down. But you must install it on the underside of your roof - not horizontally over the ceiling. and the barrier must face an airspace.
For your own comfort while in the attic, install the radiant barrier on a cool, cloudy day. Use plywood walk boards or wooden planks over the ceiling joists for support. Caution: Do not step between the ceiling joists, or you may fall through the ceiling.
Staple the foil to the bottom or side of the rafters, draping it from rafter to rafter. Do not worry about a tight fit or small tears in the fabric; radiant transfer is not affected by air movement. The staples should be no more than 2 to 3 inches (5 to 8 centimeters) apart to prevent air circulation from loosening or detaching the radiant barrier. Use a caulking gun to apply a thin bead of construction adhesive to the rafters along the seams of the foil barrier. This will make the installation permanent. Roofs
About a third of the unwanted heat that builds up in your home comes in through the roof. This is hard to control with traditional roofing materials. For example, unlike most light colored surfaces, even white asphalt and fiberglass shingles absorb 70% of the solar radiation. One good solution is to apply a reflective coating to your existing roof. Two standard roofing coatings are available at your local hardware store or lumberyard. They have both waterproof and reflective properties and are marketed primarily for mobile homes and recreational vehicles. One coating is white latex that you can apply over many common roofing materials, such as asphalt and fiberglass shingles, tar paper, and metal. most manufacturers offer a 5-year warranty.
A second coating is asphalt based and contains glass fibers and aluminum particles. You can apply it to most metal and asphalt roofs. Because it has a tacky surface, it attracts dust, which reduces its reflective somewhat. Another way to reflect heat is to install a radiant barrier on the underside of your roof. A radiant barrier is simply a sheet of aluminum foil with a paper backing. When installed correctly, a radiant barrier can reduce heat gains through your ceiling by about 25%. (see box for information on installing a radiant barrier.)
Radiant-barrier materials cost between $0.13 per square foot ($1.44 per square meter) for a single-layer product with a kraft-paper backing and $0.30 per square foot ($3.33 per square meter) for a vented multiflora product with a fiber- reinforced backing. The latter product doubles as insulation. Walls
Wall color is not as important as roof color, but does affect heat gain somewhat. white exterior walls absorb less heat than dark walls. and light, bright walls increase the longevity of siding, particularly on the east, west, and south sides of the house.
Windows
Roughly 40% of the unwanted heat that builds up in your home comes in through windows. Reflective window coatings are one way to reflect heat away from your home. These coatings are plastic sheets treated with dyes or thin layers of mental. Besides keeping your house cooler, these reflective coatings cut glare and reduce fading of furniture, draperies, and carpeting.
Two main types of coatings include sun-control films and combination films. Sun-control films are best for warmer climates because they can reflect as much as 80% of the incoming sunlight. Many of these films are tinted, however, and tend to reduce light transmission as much as they reduce heat, thereby darkening the room.
Combination films allow some light into a room but they also let some heat in and prevent interior heat from escaping. These films are best for climates that have both hot and cold seasons. Investigate the different film options carefully to select the film that best meets your needs. Note: do not place reflective coatings on south-facing windows if you want to take advantage of heat gain during the winter. The coatings are applied to the interior surface of the window. Although you can apply the films yourself, it is a good idea to have a professional install the coatings, particularly if you have several large windows. This will ensure a more durable installation and a more aesthetically pleasing look.
Landscaping is a natural and beautiful way to shade your home and block the sun. Blocking the Heat Two excellent methods to block heat are insulation and shading. Insulation helps keep your home comfortable and saves money on mechanical cooling systems such as air conditioners and electric fans. Shading devices block the sun's rays and absorb or reflect the solar heat.
Insulation
Weatherization measures - such as insulating, weather stripping, and caulking - help seal and protect your house against the summer heat in addition to keeping out the winter cold. For more information on weatherizing your home, see the energy efficiency and renewable energy clearinghouse (EREC) fact sheet caulking and weather stripping and the U.S. Department of Energy (DOE) fact sheet insulation. The attic is a good place to start insulating because it is a major source of heat gain. Adequately insulating the attic protects the upper floors of a house. Recommended attic insulation levels depend on where you live and the type of heating system you use. for most climates, you want a minimum of R-30. In climates with extremely cold winters, you may want as much as R-49. again, check the DOE fact sheet insulation on how to determine the ideal level of insulation for your climate.
Wall insulation is not as important for cooling as attic insulation because outdoor temperatures are not as hot as attic temperatures. also, floor insulation has little or no effect on cooling.
Although unintentional infiltration of out-side air is not a major contributor to inside temperature, it is still a good idea to keep it out. Outside air can infiltrate your home around poorly sealed doors, windows, electrical outlets, and through openings in foundations and exterior walls. Thorough caulking and weather stripping will control most of these air leaks. Shading Shading your home can reduce indoor temperatures by as much as 20øf (11øc). effective shading can be provided by trees and other vegetation and exterior or interior shades.
Landscaping
Landscaping is a natural and beautiful way to shade your home and block the sun. A well-placed tree, bush, or vine can deliver effective shade and add to the aesthetic value of your property. When designing your landscaping, use plants native to your area that survive with minimal care. Trees that lose their leaves in the fall (i.e., deciduous) help cut cooling energy costs the most. when selectively placed around a house, they provide excellent protection from the summer sun and permit winter sunlight to reach and warm your house. The height, growth rate, branch spread, and shape are all factors to consider in choosing a tree. Vines are a quick way to provide shading and cooling. grown on trellises, vines can shade windows or the whole side of a house. Ask your local nursery which vine is best suited to your climate and needs.
Besides providing shade, trees and vines create a cool microclimate that dramatically reduces the temperature (by as much as (9øf []5øc]) in the surrounding area. During photosynthesis, large amounts of water vapor escape through the leaves, cooling the passing air. and the generally dark and coarse leaves absorb solar radiation. You might also consider low ground cover such as grass, small plants, and bushes. a grass-covered lawn is usually 10øf (6øc) cooler than bare ground in the summer. If you are in an arid or semiarid climate, consider native ground covers that require little water. For more information on landscaping, see the erec fact sheet landscaping for energy efficiency. Planning Your Planting
Placement of vegetation is important when landscaping your home. The following are suggestions to help you gain the most from vegetation.
Shading Devices
Both exterior and interior shades control heat gain. Exterior shades are generally more effective than interior shades because they block sunlight before it enters windows. When deciding which devices to use and where to use them, consider whether you are willing to open and close them daily or just put them up for the hottest season. You also want to know how they will affect ventilation.
Removing Built-Up Heat
Nothing feels better on a hot day than a cool breeze. Encouraging cool air to enter your house forces warm air out, keeping your house comfortably cool. However, this strategy only works when the inside temperature is higher than the outside temperature.
Natural ventilation maintains indoor temperatures close to outdoor temperatures close to outdoor temperatures and helps remove heat from your home. But only ventilated during the coolest parts of the day or night, and seal off your house from the hot sun and air during the hottest parts of the day. The climate you live in determines the best ventilation strategy. In areas with cool nights and very hot days, let the night air in to cool your house. A well-insulated house will gain only 1of (0.6øc). By the time the interior heats up, and the outside air should be cooler and can be allowed indoors.
In climates with day time breezes, open windows on the side from where the breeze is coming and on the opposite side of the house. Keep interior doors open to encourage whole house ventilation. If your location lacks consistent breezes, create them by opening the windows at the lowest and highest points in your house. This natural "thermosiphoning," or "chimney," effect can be taken a step further by adding a clerestory or a vented skylight.
In hot, humid climates where temperature swings between day and night are mall, ventilate when humidity is not excessive. Ventilating your attic greatly reduces the amount of accumulated heat, which eventually works its way into the main part of your house. Ventilated attics are about 30øf (16øc) cooler than unventilated attics. Properly sized and placed louvers and roof vents help prevent moisture buildup and overheating in your attic. For more information on ventilation, see the erec fact sheet fans and ventilation.
Reducing Heat-Generating Sources Often-overlooked sources of interior heat gain are lights and household appliances, such as ovens, dishwashers, and dryers. Because most of the energy that incandescent lamps use is given off as heat, use them only when necessary. Take advantage of daylight to illuminate your house. and consider switching to compact fluorescent lamps. These use about 75% less energy than incandescent lamps, and emit 90% less heat for the same amount of light. For more information on lighting, see the erec fact sheet energy-efficient lighting.
New, energy efficient appliances generate less heat and use less energy.
Many household appliances generate a lot of heat. When possible, use them in the morning or late evening when you can better tolerate the extra heat. Consider cooking on an outside barbecue grill or use a microwave oven, which does not generate as much heat and uses less energy than a gas or electric range.
Washers, dryers, dishwashers, and water heaters also generate large amounts of heat and humidity. To gain the most benefit, seal off your laundry room and water heater from the rest of the house.
New, energy efficient appliances generate less heat and use less energy. When it is time to purchase new appliances, make sure the are energy efficient. All refrigerators, dishwashers, and dryers display an energy guide label indicating the annual estimated cost for operating the appliance or a standardized energy efficiency ratio. Compare appliances and buy the most efficient models for your needs. For more information, see the erec fact sheet a guide to making energy-smart purchases.
Saving Energy
Using any or all of these strategies will help keep you cool. even if you use air conditioning, many of these strategies, may not be enough. sometimes you need to supplement natural cooling with mechanical devices. fans and evaporative coolers can supplement your cooling strategies and cost less to install and run than air conditioners.
Ceiling fans make you feel cooler. their effect is equivalent to lowering the air temperature by about 4øf (2øc). Evaporative coolers use about one-fourth the energy of conventional air conditioners.
Many utility companies offer rebates and other cost incentives when you purchase or install energy saving products, such as insulation and energy efficient lighting and appliances. Contact your local utility company to see what it offers in the way of incentives.
Energy Efficiency and Renewable Energy Clearinghouse Cooling Your Home Naturally DOE/CH10093-221 FS 186 OCTOBER 1994
Cooling Strategies to Consider
We would like to thank The Consumer Information Center for the above information. Please visit their website at www.pueblo.gsa.gov 