Whether it is winter or summer, trees can help you save energy at home.
Shade for Savings
Did you know that only 17% shade over your house during the day translates to a savings of 10 dollars a month on your power bill? Additionally, increasing that same shade to 50% will decrease your power bill by an additional $20 per month. For those without trees, it takes time to plant a tree and generate this shade. However one study estimates that within 5 years of planting you can realize a 3% energy savings and by 15 years that savings can increase to 12%. So whether you have shade or are looking to generate some tree shade, read-on to learn the key to success: Put the right tree in the right place.
The Cooling Effect of Trees:
Trees naturally cool the environment. Through the process of transpiration, similar to that of evaporation, trees lose water vapor from their leaves. This allows not only for minerals and water to move throughout the tree, but also has a cooling effect on trees and their surrounding environment. It is similar to our process of perspiring and how it cools our skin.
One study estimated that the net cooling effect of a young healthy tree would be equivalent to 10 room-size air conditioners running for 20 hours a day. By contrast concrete, asphalt and other impervious surfaces in the urban environment absorb heat, causing for this heat to build up and dissipate even well after dark. As a result cities tend to be several degrees warmer than the surrounding countryside. This is referred to as the Heat Island Effect. However, there is hope for the urban environment by introducing trees and putting them to work. Urban trees can not only mitigate higher urban temperatures but reduce cooling and even winter heating bills.
Planting Trees for Summer Shade:
Radiant energy from the sun heats home surfaces such as walls, roofs and windows forcing air conditioners to work harder. This drives energy consumption and power bills up. While good insulation will help mitigate this problem, shade from surrounding trees can further conserve energy, especially for older homes with outdated or limited insulation.
Selecting deciduous trees, or trees that lose their leaves during winter, is ideal for energy conservation. These trees will provide shade during hot summers and only minimal shade during cold winter months when the sun’s heat is desirable. The key to maximizing energy conservation is carefully placing trees to provide shade to the home from morning and afternoon sun.
To protect from morning and afternoon sun plant trees to shade east and west facing walls and windows. For both east and west plantings select a combination of small and large trees. Small trees will providing shade during early morning and late afternoon when the sun’s angler is low on the horizon. By contrast the larger trees with a mature height of 25 feet or more will provide coverage in both late morning and early afternoon when the sun is higher in the sky.
Trees should also be located on the south and southwest sides of the house to provide summertime roof shading. These trees should have high spreading crowns capable of shading the roof. Avoid smaller trees or trees with excessive lower branches in this location as it will cause excessive shade during winter months, even if deciduous.
Planting trees to shade the air conditioner unit can also conserve energy. Trees and their branches should be at least several feet away from the units to allow for easy airflow. Restricting this flow will reduce the efficiency of the unit.
To avoid conflicts and damage to your home plant larger trees at least half of their mature width from the base of your home. For example, if a tree's estimated mature width is 40 feet, plant it at least 20 feet away from your home. Closer to the home smaller trees and shrubs that will cause less conflicts can be planted to shade the home until larger trees mature and begin providing shade.
Planting for Winter Energy Conservation:
Blocking cold winds is the biggest contribution trees can make towards energy conservation in winter. Winter winds can force cold air into holes or cracks in walls or frequently opened doors. It is estimated that 11% of America’s energy use goes into heating and cooling homes and 53% of that goes directly to heating.
A well-designed windbreak can reduce heating costs by 10% to 25%. Windbreaks work by reducing wind speed and divert air up and over homes. Breaks should be planted perpendicular to the prevailing winter winds, this likely means planting on the west, northwest and north sides of the home. However local conditions and weather patterns should be reviewed to select the best planting locations.
The greatest wind reduction occurs between 2 to 5 times the height of the windbreak downwind. This means if you if you expect your trees in the windbreak to achieve a height of 30 feet, it should be planted between 60 to 150 feet from the home they are sheltering. In smaller yards this may not be possible, however, the breaks will still be effective, just to a lesser degree.
For effective windbreaks, select trees that have crowns that extend to the ground and are evergreen (meaning they keep their leaves all winter). These trees should be planted relatively close together to ensure their crowns meet. This distance can ranger from 6 feet for smaller or narrow crowned trees to 15 feet for larger trees. Planting design can be in a straight line, curved or in groupings. If you live in areas with sever winds like hurricanes, groupings are advisable.
Selecting the Right Trees for Success:
Selecting trees that are disease and pest resistant is important to growing a long-term urban forest. This is especially important when planting windbreaks that might be composed of a single species. Additionally, homeowners should strongly consider selecting wind tolerant species as these trees will be close to the home and their failure during storms could cause significant damage.
Avoid the temptation to plant fast growing trees as they are generally short lived, have weaker wood fiber making them more susceptible to wind, snow or ice damage. Trees should be planted in groupings when possible, as they are more wind tolerant than in individual plantings.
Remember to look up and avoid planting trees under or next to power lines. Utility conflicts will lead to power outages or trees being trimmed in unsightly ways by utility companies. Avoid planting trees to close to sidewalks or driveways. Over time roots may damage these structures leading to potential root conflicts. For most medium to large trees plant them at least 10 to 15 feet from these structures.
By: Beau Brodbeck, Auburn University and Sharon Jean-Philippe, University of Tennessee.