One of the easiest ways to reduce solar heat gain and subsequent energy costs is as simple as planting a tree. The strategic placement of
trees, known as landscape shading or tree shading, is a technique used to provide shade from the warm summer sun. Unobstructed solar heat can significantly increase indoor air temperature, which will frustrate efforts to keep the house cool. However, appropriate tree placement can reduce indoor temperatures by up to 9° F(12° C) through evapotranspiration — the process by which a plant releases water vapor — as well as the shade provided by the tree.
According to the U.S. Department of Energy (DOE), air temperatures directly under trees can be as much as 25° cooler than air temperatures above nearby blacktop. Also, shade trees can reduce cooling costs by as much as 10%, which is important because the average home devotes almost a fifth of its energy expenditure to cooling.
Researchers from the National Institute of Standards and Technology and the U.S. Department of Agriculture conducted the first large-scale study on landscape shading in 2007. In Sacramento, Calif., 460 houses were studied over the summer to discover whether well-placed shade trees could reduce energy costs, as well as atmospheric carbon. Their specific findings were as follows:
- Trees planted on the west and south sides of a house decreased summertime electricity use, while trees planted on the north actually increased energy consumption. Trees planted on the east side had no effect.
- Fast-growing trees are better energy-savers than slower-growing trees.
- Placement of the trees, particularly their proximity to the house, is a significant factor in their effectiveness as shade trees.
- One great performer was the London plane tree, which can reduce carbon emissions from summertime electricity use by an average of 31% over 100 years.
- The average household energy savings was approximately $25 for the summer. Consider, however, that the trees used in this study cost around $85 each, and each house used many of these trees. In optimal conditions, it will take 26 years for losses from the study to be recouped.
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