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Landscaping For Energy Efficiency

Summary: This section will give you some landscaping tips that will help you save energy and money year-round, including climate and site considerations, design and planning, and tree and shrub selection. Are you looking for cost-effective yet eye-pleasing ways to lower your energy bills? Planting trees, shrubs, vines, grasses, and hedges could be the answer. In fact, landscaping may be your best long-term investment for reducing heating and cooling costs, while also bringing other improvements to your community. A well-designed landscape will:

  • Cut your summer and winter energy costs dramatically.

  • Protect your home from winter wind and summer sun.

  • Reduce consumption of water, pesticides, and fuel for landscaping and lawn maintenance.

  • Help control noise and air pollution.

Landscaping Saves Money Year-Round: Carefully positioned trees can save up to 25% of a household's energy consumption for heating and cooling. Computer models devised by the U.S. Department of Energy predict that the proper placement of only three trees will save an average household between $100 and $250 in energy costs annually.

On average, a well-designed landscape provides enough energy savings to return your initial investment in less than 8 years. An 8-foot (2.4-meter) deciduous (leaf-shedding) tree, for example, costs about as much as an awning for one large window and can ultimately save your household hundreds of dollars in reduced cooling costs, yet still admit some winter sunshine to reduce heating and lighting costs. Landscaping can save you money in summer or winter.

Summer: You may have noticed the coolness of parks and wooded areas compared to the temperature of nearby city streets. Shading and evapotranspiration (the process by which a plant actively moves and releases water vapor) from trees can reduce surrounding air temperatures as much as 9 degrees F (5 degrees C). Because cool air settles near the ground, air temperatures directly under trees can be as much as 25 degrees F (14 degrees C) cooler than air temperatures above nearby blacktop. Studies by the Lawrence Berkeley Laboratory found summer daytime air temperatures to be 3 degrees F to 6 degrees F (2 degrees C to 3 degrees C) cooler in tree- shaded neighborhoods than in treeless areas. A well-planned landscape can reduce an unshaded home's summer air-conditioning costs by 15% to 50%. One Pennsylvania study reported air-conditioning savings of as much as 75% for small mobile homes.

Winter: You may be familiar with wind chill. If the outside temperature is 10 degrees F (-12 degrees C) and the wind speed is 20 miles per hour (32 kilometers per hour), the wind chill is -24 degrees F (-31 degrees C). Trees, fences, or geographical features can be used as windbreaks to shield your house from the wind. A study in South Dakota found that windbreaks to the north, west, and east of houses cut fuel consumption by an average of 40%. Houses with windbreaks placed only on the windward side (the side from which the wind is coming) averaged 25% less fuel consumption than similar but unprotected homes. If you live in a windy climate, your well-planned landscape can reduce your winter heating bills by approximately one-third.

Landscaping for a Cleaner Environment: Widespread tree planting and climate-appropriate landscaping offer substantial environmental benefits. Trees and vegetation control erosion, protect water supplies, provide food, create habitat for wildlife, and clean the air by absorbing carbon dioxide and releasing oxygen.

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Figure 117: Buildings and Trees are Natural Partners: Deciduous trees planted on the south and on the west sides will help keep your house cool in the summer and allow sun to shine in the windows in the winter.

 

The National Academy of Sciences (NAS) estimates that urban America has 100 million potential tree spaces (i.e., spaces where trees could be planted). NAS further estimates that filling these spaces with trees and lightening the color of dark, urban surfaces would result in annual energy savings of 50 billion kilowatt-hours -- 25% of the 200 billion kilowatt-hours consumed every year by air-conditioners in the United States. This would reduce electric power plant emissions of carbon dioxide by 35 million tons (32 million metric tons) annually and save users of utility-supplied electricity $3.5 billion each year (with an average of $0.07 per kilowatt-hour).

Also, some species of trees, bushes, and grasses require less water than others. Some species are naturally more resistant to pests, so they require less pesticides. Another alternative to pesticides is integrated pest management, an emerging field that uses least-toxic pest control strategies. One example is to introduce certain insects such as praying mantises or ladybugs to feed on-and limit populations of-landscape-consuming pests.

Certain grasses, such as buffalo grass and fescue, only grow to a certain height -- roughly 6 inches (15 centimeters) and are water thrifty. By using these species, you can eliminate the fuel, water, and time consumption associated with lawn mowing, watering, and trimming. Also, recent studies have found that gasoline-powered mowers, edge trimmers, and leaf blowers contribute to air pollution.

Climate, Site, and Design Considerations:

Climate: The United States can be divided into four approximate climatic regions: temperate, hot-arid, hot-humid, and cool. The energy-conserving landscape strategies you use should depend on which region you live in. These landscaping strategies are listed by region and in order of importance below.

  • Temperate:

  • Maximize warming effects of the sun in the winter.

  • Maximize shade during the summer.

  • Deflect winter winds away from buildings.

  • Funnel summer breezes toward the home.

  • Hot-Arid:

  • Provide shade to cool roofs, walls, and windows.

  • Allow summer winds to access naturally cooled homes.

  • Block or deflect winds away from air-conditioned homes.

  • Hot-Humid:

  • Channel summer breezes toward the home.

  • Maximize summer shade with trees that still allow penetration of low-angle winter sun.

  • Avoid locating planting beds close to the home if they require frequent watering.

  • Cool:

  • Use dense windbreaks to protect the home from cold winter winds.

  • Allow the winter sun to reach south-facing windows.

  • Shade south and west windows and walls from the direct summer sun, if summer overheating is a problem.

Microclimate: The climate immediately surrounding your home is called its microclimate. If your home is located on a sunny southern slope, it may have a warm microclimate, even if you live in a cool region. Or, even though you live in a hot-humid region, your home may be situated in a comfortable microclimate because of abundant shade and dry breezes. Nearby bodies of water may increase your site's humidity or decrease its air temperature.

Your home's microclimate may be more sunny, shady, windy, calm, rainy, snowy, moist, or dry than average local conditions. These factors all help determine what plants may or may not grow in your microclimate.

Siting and Design: A well-oriented and well-designed home admits low-angle winter sun, rejects overhead summer sun, and minimizes the cooling effect of winter winds. If you are building a home, pay attention to its orientation.

In the northern hemisphere, it is usually best to align the home's long axis in an east-west direction. The home's longest wall with the most window area should face south or southeast. The home's north-facing and west-facing walls should have fewer windows because these walls generally face winter's prevailing winds. North-facing windows receive little direct sunlight.

You may be able to design and orient your new house to maximize your homesite's natural advantages and mitigate its disadvantages. Notice your homesite's exposure to sun, wind, and water. Also note the location and proximity of nearby buildings, fences, water bodies, trees, and pavement -- and their possible climatic effects. Buildings provide shade and windbreak. Fences and walls block or channel the wind. Water bodies moderate temperature but increase humidity and produce glare. Trees provide shade, windbreaks, or wind channels. Pavement reflects or absorbs heat, depending on whether its color is light or dark.

If your home is already built, inventory its comfort and energy problems, then use the following landscaping ideas to help minimize these problems.

Shading: Solar heat passing through windows and being absorbed through the roof is the major reason for air-conditioner use. Shading is the most cost-effective way to reduce solar heat gain and cut air-conditioning costs. Using shade effectively requires you to know the size, shape, and location of the moving shadow that your shading device casts. Remember that homes in cool regions may never overheat and may not require shading.

Trees can be selected with appropriate sizes, densities, and shapes for almost any shading application. To block solar heat in the summer but let much of it in during the winter, use deciduous trees. To provide continuous shade or to block heavy winds, use evergreen trees or shrubs.

Deciduous trees with high, spreading crowns (i.e., leaves and branches) can be planted to the south of your home to provide maximum summertime roof shading. Trees with crowns lower to the ground are more appropriate to the west, where shade is needed from lower afternoon sun angles. Trees should not be planted on the southern sides of solar- heated homes in cold climates because the branches of these deciduous trees will block some winter sun.

A 6-foot to 8-foot (1.8-meter to 2.4-meter) deciduous tree planted near your home will begin shading windows the first year. Depending on the species and the home, the tree will shade the roof in 5 to 10 years. If you have an air-conditioner, be aware that shading the unit can increase its efficiency by as much as 10%.

Trees, shrubs, and groundcover plants can also shade the ground and pavement around the home. This reduces heat radiation and cools the air before it reaches your home's walls and windows. Use a large bush or row of shrubs to shade a patio or driveway. Plant a hedge to shade a sidewalk. Build a trellis for climbing vines to shade a patio area.

Vines can shade walls during their first growing season. A lattice or trellis with climbing vines, or a planter box with trailing vines, shades the home's perimeter while admitting cooling breezes to the shaded area.

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Figure 118: During the summer, tall spreading trees planted close to the home shade the roof. Broad, shorter trees on the west side block afternoon solar heat. A windbreak on the northwest side can shield the home from prevailing winter winds. A well-designed landscape will cut your summer and winter energy costs dramatically.

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