Trees are nature’s air conditioners. Through a process called, evotranspiration, trees convert water into cooling vapor which is released into the air. Some trees even release chemicals called terpenes into the atmosphere which helps thicken the clouds above them and bounce light and heat away. The right tree planted in the right place not only cools the air outside, but can significantly lower the temperature inside a building. A tree can shade your house or business, the surrounding pavers and even HVAC and pool units, resulting in more efficient use of energy.
Strategically placed trees and shrubs can reduce the temperature of surrounding air by as much as nine degrees, so trees are a great "low tech" solution to reducing utility usage and costs.
The trick is to select the right type of tree and then to position it and maintain it in just such a way that it produces the optimal cooling effect. Here are some considerations to help you shade most effectively. (Source: Florida Power & Light, Landscape Planning book)
- Choose the location for your shade tree based on careful consideration of seasonal sun angles. For example, to minimize the impact of the strong summer sun, plant shade trees on the east and west sides of your home. The reduces exposure during early morning and late afternoon hours. They should be close enough to the building to cast a shadow over it during periods of high sun exposure.
- In general, trees should be placed to shade, but not block views or create safety hazards.
- Choose drought-resistant, Florida-friendly trees with large spreading or round canopies. Trees with full crowns are best for summer shading. Their high branches allow greater visibility below the branches and do not block the flow of cooling summer breezes.
- Avoid topping trees or over-pruning which can harm the tree and negate the positive effects of correct placement.
- Consider planting deciduous trees (that lose their leaves in the winter) that will shade the house in the summer but allow the sun's rays to penetrate the home in slightly cooler winter.
- Remember that trees cannot provide shading on the roof when the sun is directly overhead. The roof need not be totally shaded to achieve excellent energy-saving results. Air conditioning costs can be reduced as long as the roof is properly insulated and partially shaded during the day.
- Closer to the building, you can also use smaller bushes at the base to insulate it from the sun, and also climbing, clinging vines such as bougainvillea can protect walls from direct solar radiation.
- Use trees to shade air conditioning equipment. They may be better options than trellises and other fence-like structures, and even better than shrubs or bushes. Studies show up to a 10 percent increase in air conditioning efficiency in homes where the air conditioning equipment is properly shaded, as long as the landscaping does not interfere with equipment's air flow. However, studies conducted by the Florida Solar Energy Center at the University of Central Florida, showed little energy efficiency gain from fronting units with small plantings, and that structures or bushes placed too close to an HVAC unit can impede air flow and reduce unit efficiency by trapping hot air released by the unit. Shading HVAC with a large tree is much more effective, especially when combined with placement of the HVAC on the north side of a building.
- Other hotspots around the home which can benefit from shade are patios, driveways and sidewalks. They absorb heat during the day and radiate it long after the sun sets. Deciduous trees planted on the west side of the pavement can reduce this heat build-up.
You can read more about the benefits of using landscaping to reduce energy usage by clicking on the Department of Energy's Landscaping infographic at right.
These pages about "Landscaping to Conserve Energy" are excerpted from FPL's print booklet on Landscape Planning. The advice is specific to our climate, and to the position of the sun and direction of winds in various seasons.
The National Arbor Day Foundation offers a comprehensive brochure on utilizing trees to reduce energy consumption. Keep in mind when reading the brochure that the information is written to be relevant to all interested parties, and as such, some of the advice may be more geared to those who deal with winter conditions. Nevertheless, there are lots of good tips in the bulletin. Just be sure to fact check with FPL's information.
Energy.gov website is full of practical tips for reducing your energy usage. This part of the site focuses on using trees and other landscaping to cool, insulate and shade your home so that you use less and save more. You can also download the full Landscaping Infographic pictured above.