from Alliance for Community Trees, July 2013
As summer peaks and temperatures heat up across the U.S., it’s time to revisit the value of trees for shading homes, businesses, and neighborhoods—as well as conserving energy. Cities are typically 2° to 10° F warmer than their rural surroundings. This marked increase in city temperatures is known as the urban heat island effect and it adversely affects health. Strategically placed trees can deliver cooler cities—and cleaner air. For example, just three or four shade trees located strategically around a house can cut summer cooling costs by 30 percent to 50 percent.
According to Reducing Urban Heat Island Basics, on a hot, sunny summer day, the sun can heat dry, exposed urban surfaces, like roofs and pavement, to temperatures 50 to 90°F (27 to 50°C) hotter than the air, while shaded or moist surfaces—often in more rural surroundings—remain close to air temperatures. And more U.S. deaths are attributed to high temperatures than to any other weather related event.
The urban heat island effect is responsible for 5 percent to 10 percent of peak electric demand and as much as 20 percent of population-weighted smog concentrations in urban areas are due to air-conditioning use alone. Heating and cooling homes accounts for nearly 60 percent of residential electricity usage in the United States. It’s also estimated that warming trends will increase air-conditioning use by 3 percent to 8 percent.
But energy conservation is as simple as planting trees. Trees that shade the house during summer can lower air conditioning bills by blocking the sun from the windows, exterior walls and roof. According to a recent article by Dan Gill, LSU AgCenter Horticulturist, air conditioners cooling a fully shaded house have been shown to work only half as hard as those in a house that has walls and roof exposed to the sun.
Gill cites other research reports that show shade trees will reduce heat gains by 40 percent to 80 percent, depending upon their placement and density. A shade tree is a much better energy saver than an interior blind or curtain. Gill outlines how to evaluate where to plant trees and selecting the best type and size of tree to create needed shade to reduce energy costs and improve air quality.
According to Gill, “deciduous trees that drop their leaves during winter are generally the best choice. These trees let the sun shine on the house in the winter when the sun’s added warmth is welcome. Then, they grow leaves during summer and provide shade when it’s needed.”
Trees are most effective when they’re planted on the southwestern and western side of the house, shading the house from the most intense sun during the hottest part of a summer day.
To landscape for energy conservation, Gill suggests focusing on the proper placement, number and type of trees. He advises that “Generally, medium-size trees, those that grow 30 to 55 feet tall, are suitable as primary shade trees in average-size urban lots. These are large enough to shade your house.”
- Reducing Urban Heat Islands Compendium of Strategies: Trees and Vegetation
- Energy Saving Potentials and Air Quality Benefits of Urban Heat Island Mitigation
Primary source material thetowntalk.com