Conserving energy with plants nc state extension publications gas 85 octane


Never before has the demand for energy been as high — and never before have homeowners become so increasingly aware of the energy savings possible with landscaping. Although it is not possible to control temperature, wind, and other natural elements, certain landscape practices can help modify the climate in and around the home.

By placing trees, shrubs, vines and landscape structures properly, homeowners can reduce the energy required to keep homes comfortable during winter and summer. Along with the reduction of energy bills, a well-planned landscape adds beauty, interest and increased property values.

Although homeowners have intuitively used landscaping to save energy for many years, we are only beginning to realize the magnitude of the savings possible. According to one government study, winter heating bills may be reduced by as much as 15 percent, while summer cooling energy needs may be cut by as much as 50 percent.

• heat conduction – conduction of heat through materials of which the house is built. Controlling the temperature difference and air movement between inner and outer surfaces of walls, floors and ceilings is the best opportunity for reducing heat conduction. Heat conduction represents up to 50% or more of the total heat exchange between a home and the outside environment;

• solar radiation – heat is transmitted into homes by penetration of the sun’s rays. Up to 90% will be transmitted into the living area if rays are received perpendicular to a single pane. Sunlight will be increasingly reflected by the glass as the sunlight departs from the perpendicular.

The role of landscape vegetation in conserving energy varies with the different microclimates across North Carolina. In the cooler, northwest areas of North Carolina, where enormous amounts of energy are consumed in winter heating, control of air infiltration is paramount. Hotter southeastern areas place more emphasis on use of shade to control heat conduction and reduce the need for summer air-conditioning. Three basic landscape applications which have proven to save energy are: (1) the use of shade trees, (2) windbreaks, and (3) the use of foundation plants.

Deciduous trees provide summer shade, then drop their leaves in the fall. This allows the warmth of the sun to filter through their bare branches in winter and helps warm the home. If a home can be situated to take advantage of shade from existing trees on southeast and west exposures, energy expended to cool the house can be reduced.

If there are no existing trees, the owner can select and place trees that ultimately will provide shade. The temptation is to plant the fastest growing species available. However, this is usually a poor choice for several reasons. Trees that grow at more moderate rates usually live longer, are less likely to break in wind and ice storms, and are often more resistant to insects and diseases.

A carefully selected and planted tree with a moderate growth rate often will respond to good care by increasing its rate of growth. Recommended shade trees for North Carolina would include: Red Maple, Sugar Maple, Pecan, Birch, White Ash, Ginkgo, Honeylocust, Sweetgum, Tulip Poplar, Blackgum, Sycamore, White Oak, Red Oak, Willow Oak, Water Oak, Bald Cypress, Linden, Zelkova, River Birch, and Hickory.

Smaller trees such as Crape Myrtles and Dogwoods can be planted closer to the house and used for shading walls and window areas. Since they are deciduous, they will provide shade during the summer and allow light and sun to penetrate during the winter season (see HIL-621, The Use of Small and Intermediate Size Trees in the Landscape).

Another way to reduce energy consumption with trees and shrubs is to provide shade for the outside protection of a split system air conditioner. A study by the American Refrigeration Institute shows that shading of this type can reduce the temperature inside the home as much as 3°F. However, shrubs planted near the compressor should not obstruct the air flow or access for service. In addition to reducing energy consumption, screening outdoor air conditioning equipment with plantings enhances the esthetic value of the home.