Landscaping for Energy Conservation
Until alternate forms of energy become inexpensive and widely available, heating and cooling costs are going to continue eating up a large portion of our monthly budgets.
While it may take some time to fully experience the benefits of energy-conservative landscaping, the long term benefits may well be worth it. Trees, shrubs, vines, and man-made structures can modify the climate around your home to reduce heat gains in summer and heat losses in winter.
Over time, investing in green landscaping can reduce your heating bills as much as 25 percent and summer cooling bills by 50 percent or more.
Here are six factors to consider for energy-efficient landscaping.
1. Air Infiltration
Air infiltration is the passage of outside air driven by the wind through cracks around windows and doors. This forces an equal amount of interior air out of the home through openings that face away from the wind.
In winter, air-filtration can represent up to half your total heat loss on the windiest, coldest days. Fortunately, properly placed plants can reduce air infiltration by reducing wind velocity near the home.
The amount of heat conduction depends on the insulating property and thickness of your building materials, the surface area available for heat flow, and the temperature difference between inner and outer surfaces. Landscaping can help reduce this heat conduction.
Exterior surface temperatures are controlled primarily by the outside air temperature, wind velocity and solar radiation. In summer, trees and shrubs can reduce the amount of solar radiation reaching the outside surfaces of a home, and thus reduce heat conduction into the house. In the winter, blocking cold winter winds will reduce conductive heat loss.
3. Solar Radiation
Large expanses of east- or west-facing windows will admit undesirable solar radiation in the summer, while large south-facing windows can help heat a home in winter. Planting vegetation around your home can regulate solar radiation during different seasons of the year.
Strategically planted greenery along your home's sunny borders will shade south-facing roofs and walls that receive the most direct midday sun. You also can place plants to shade east- and west-facing walls that receive direct sunlight.
4. Planting Shade
If you live in a region with a great deal of sun, plant deciduous trees (those that lose their leaves each fall) in an arc on the east, southeast, south, southwest, and west sides of your home. Plant shade trees based on their mature height, shape of tree crown, position of the sun, desirable views, and roof and wall height. Remember, small trees grow faster than large trees and will provide early protection. Taller trees should be planted so they won't shade smaller trees when they reach maximum height.
Summer shade for a south-facing roof generally depends on overhanging tree crowns. You'll want to plant shade trees as close to the home as practical so the crowns absorb the maximum sunlight. Select a species that won't easily break and promptly remove diseased or damaged limbs.
In colder climates, planting trees for maximum summer shade can reduce your home's winter sun exposure by up to one third. However, the winter sun is typically less than 45 degrees above the horizon, so tree trunks will provide the most shade. For this reason, it's best to plant shade trees along the southern edge of your home. Remember to prune the lower trunk for maximum solar heating in winter. You may need only two or three large deciduous trees with well-developed crowns.
Also, trees aren't the only way to create energy-saving shade. Consider covering east- or west-facing walls with vines or shrubs.
5. Wind Protection
Windbreaks can save you up to 25 percent in heating costs. Evergreens planted upwind will divert cold winds away from your home. The optimum distance for reducing wind velocity is about one to three times the tree height. However, a windbreak can provide reasonable protection at a distance of six-times tree height.
Because windbreaks can lead to snow drifts, extend a row of trees 50 feet beyond the ends of the area being protected. Where space is limited, a single row of evergreens should do it. However, up to five rows of several evergreen species is more effective for larger properties. If you're planting several rows of trees, leave at least six feet between trees. Remember to consider the mature shape of the tree and how it will ultimately grow.
Because it takes time to establish an effective windbreak, you might want to construct a fence with an open weave pattern until trees reach their optimum heights.
Windbreaks have the additional advantages of protecting your privacy and improving the aesthetics of your home. Some greenery also will attract wildlife and provide them with winter protection and food.
6. Landscape Plan
Before you begin planning, it greatly helps to develop a scaled sketch. Measure the height of your home, and create a plan using one-quarter inch for each foot. Mark compass directions, doors, solar collectors, windows and other glass areas. Observe how the sun and wind affect your home during a winter storm through snow-drift directions and patterns. Sketch in windbreaks to block this wind flow.
Next, you'll want to check out sun exposure during different seasons. How does the light strike the house between 9 a.m. and 3 p.m. in the winter and summer? Incorporate into your plan measures to reduce this exposure.
To determine the best vegetation for your home, consult with your county Extension agent.
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