Windbreaks and Shade Trees save Energy, Money, and the Environment
Planting trees around homes is an ancient concept used to conserve home energy use. Windbreaks, which consist of rows of trees placed perpendicular to prevailing winds, were greatly used in the Midwest to protect exposed houses, livestock, and crops from severe winds. The use of shade trees was especially emphasized during the 1970s to combat the energy crisis caused by Arab oil embargoes.
The recent concern over global warming has made tree planting and energy conservation important issues again. The global warming problem is thought to be caused by industrial and automotive emissions of greenhouse gases, such as carbon dioxide, to the atmosphere as well as from the clearing of tropical forests for agriculture.
Many scientists believe that a historical buildup of greenhouse gases in the atmosphere is trapping more of the sun’s energy once it reaches the earth. The result has been a slow rise in the earth’s temperature by about 0.5°C (1°F) over the past century. Many computer models now predict a 0.3°C (0.5°F) temperature rise over the next decade. The results of such changes in the earth’s temperature could be severe.
Scientists believe that changes in rainfall patterns, increases in global sea level, and a general shift in climates may be imminent. The use of planted windbreaks and shade trees can combat this problem on two fronts. First, trees consume carbon dioxide and produce oxygen, thus reducing the amount of carbon dioxide in the atmosphere.
Second, the strategic location of trees can reduce home energy use and, therefore, reduce the number of greenhouse gases produced by energy utility companies. Since residential heating and cooling represents about 11 percent of total U.S. energy use, windbreaks and shade trees may offer significant energy savings.
If windbreaks and shade trees could reduce heating and cooling energy needs by 10 percent at the residential level, total U.S. energy demand would be reduced by about 1 percent. Such savings seem minor, but when multiplied by millions of households, the overall reduction in utility emissions of greenhouse gases could be important.
The incentive to homeowners to plant windbreaks and shade trees is based on their potential to save money from subsequent energy reductions. Winter heating bills may be reduced by 15 percent while summer cooling needs may be reduced by 75 percent in certain types of homes. This publication is meant as a guide for homeowners interested in utilizing windbreaks and shade trees for energy savings. The material includes sections on how energy savings are accomplished, how to properly build and locate windbreaks, and how much windbreaks will cost and save the typical household.
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Home Heat Exchanger
To take full advantage of the effects of trees, how homes gain or lose heat must be understood. Heat exchange in a home occurs through three major processes: air infiltration, heat conduction, and sunlight transmission through windows. Air infiltration is the passage of outside air through cracks around doors and windows or other home openings.
Outside air is forced or drawn through these openings by the wind on the outside of the home or by temperature differences between inside and outside air. Wind on the outside of the home will replace indoor air with an equal amount of outdoor air.
Depending on the outside temperature, this process may cause undesirable temperature changes in the house. Temperature differences between inside and outside can also create a natural circulation of air in the home. Warm interior air will rise and escape the house through openings near the roof while cool air is drawn into the home through lower house openings.
This process is known as the “chimney effect” (Figure 1). Air infiltration due to the chimney effect and from wind exposure often occur simultaneously. But the chimney effect often is most important in winter due to the large temperature differences between inside and outside air.
The combined effect of wind and temperature differences may cause air within a home to be completely changed several times per hour. Properly placed trees can reduce air infiltration by reducing wind velocity in the vicinity of the home. However, a large, dense forest near the home may also reduce exterior air temperatures and tend to increase air infiltration by the chimney effect in winter.
Heat conduction is the transmission or loss of heat through home construction materials. Different construction materials conduct heat differently depending on their thermal conductivity, thickness, and surface area. Most walls and ceilings are composite layers of materials and are effective in reducing heat conduction by trapping air within or between the layers.
Windows are less effective at stopping heat conduction unless a double-pane-style window is used with an air layer sandwiched between two panes of glass. Control of the temperature difference between inner and outer surfaces of walls, ceilings, and floors offers the best opportunity for reducing heat conduction. The inner surface temperature is largely controlled by the interior air temperature. One method of conserving energy in winter is to lower the interior temperature, reducing the difference in temperature between inside and outside surfaces.
The outer surface temperature of a home is controlled by the outside air temperature, wind velocity, and solar radiation, as well as by the amount of heat being conducted through the material. Trees can reduce the amount of sunlight reaching the outer surfaces of the home and thereby reduce the temperature difference between inner and outer building surfaces in summer when the heat is rapidly being conducted into the home. However, in winter, solar heating of the building’s exterior surfaces can be beneficial in reducing rates of heat loss. Winter shade from trees would interfere with this beneficial heating.
Sunlight transmission through windows can also transmit heat into homes. If sunlight is received perpendicular to a single-pane glass surface, up to 90 percent will be transmitted into the home. Although sunlight can pass through the glass, the heat produced inside the home cannot escape.
Thus, the net effect of sunlight transmission is the heating of the inside of the house. The size, position, and type of windows at home relative to the position of the sun in summer and winter greatly influence the role of sunlight in-home heat exchange. Many homes are being designed to capture greater amounts of radiant energy from the sun.
In these homes, radiant energy is absorbed and used to heat water or air. Trees around a home can be used to influence sunlight transmission by blocking sunlight from windows during midday, which is desirable in summer.
The potential role of trees in-home energy conservation in Pennsylvania varies between summer and winter seasons due to shifts in the importance of heat exchange processes. In winter, air infiltration becomes the major heat exchange process and the use of trees to reduce wind velocity is most important. Shading in winter reduces the already small amount of beneficial solar heating at this time of year.
In summer, air infiltration accounts for small heat gains in the home due to the relatively small temperature differences between inside and outside air. Heat conduction and transmission of sunlight predominate in summer and the use of trees to shade the exterior surfaces and windows is most important. Shading by trees in the summer reduces the amount of sunlight absorbed by the home.
One observer in New Jersey noted that the exterior surface temperature of a shaded, wood-sided home was 9°C (16°F) cooler than similar unshaded surfaces in June. Such reductions in exterior surface temperatures can lower the exterior-interior temperature differences substantially and thereby reduce the rate of heat conduction into the home. Without air conditioning, differences in heat conduction will cause differences in interior air temperatures.
In a mobile home shaded by trees, interior temperatures were up to 11°C (20°F) less than in an unshaded trailer during mid-day. Maximum temperatures in the shaded trailer occurred up to 3.5 hours later than at an open site. Cooling of interior air to tolerable levels also occurred sooner at the shaded site. When a home is air-conditioned, trees can save energy. In Alabama, where the need for air conditioning is greater than in Pennsylvania, the results of one study indicated that shaded mobile homes had annual electricity bills ranging from $45 to $100 less than unshaded mobile homes.
Differences in electric bills prevailed even when homes averaged only 20 percent of their roof shaded per day. In a Pennsylvania study, the energy required for air conditioning a mobile home was estimated to be 75 percent less in a grove of tall deciduous trees than in an open, unshaded site. Sunlight on the shaded mobile home was only one-tenth of that in the open.
Providing shade appears to be the only important effect of vegetation on home energy conservation in summer. Trees will reduce wind velocity and air infiltration rates in summer, but the effect on heat gains to a home in Pennsylvania will be small. Small, open groves of trees common around homes in urban and suburban areas will generally have little effect on air temperature. Trees that provide shade in summer may be detrimental in winter if solar heating of the home is interrupted.
In a dense red pine plantation in Pennsylvania, which reduced solar radiation by 75 percent in winter, heating energy needs for a small trailer were estimated to be 12 percent greater than at an unshaded site. Here any benefit from reduced wind velocity was completely offset by reduced solar heating of the trailer.
Energy consumption for trailer heating in a deciduous grove was up to 8 percent less than for a similar trailer in an open site. Even though the deciduous grove reduced wind velocities by 40 percent in winter, solar radiation was also reduced by 37 percent by the leafless tree canopy. Thus it appears that trees around a home can reduce wind velocity, but heat energy savings will not occur if the dwelling is heavily shaded at the same time. Vegetation arrangements that reduce wind velocities around homes but do not shade homes will produce the greatest energy savings in winter.
Windbreaks located considerable distances from a building can reduce wind velocities without shading it. Research in Pennsylvania indicated that up to 15 percent of heat energy savings are possible using windbreaks. Most of these savings resulted from reduced wind velocity and, therefore, reduced air infiltration in homes downwind from the windbreak. The effects of windbreaks are greater at higher wind velocities.
Savings will increase with the amount of reduction in wind velocity affected by the windbreak. Savings also will be greater for loosely constructed homes. It should be remembered, though, that windbreaks have almost no effect on air infiltration during calm days.
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Tips for homeowners
A perfect arrangement of trees that can provide all year round energy savings is to have windbreaks that reduce the speed of wind in winter, along with a variety of trees that shade your home during summer. The difficulty in achieving this ideal arrangement is contingent upon the vegetation that is already on the property as well as the possession of a sufficient amount of land.
The land that was located in the forest usually contain enough trees to allow for the desired layout fairly quickly. However, when houses are constructed on agricultural land that has been cleared most of the required trees and shrubs have to be planted.
The windbreak should be located away from the house in the direction of predominant winds. In Pennsylvania the winter wind comes mostly from the northwest and west. The trees' rows should be placed perpendicularly towards this direction. Topography, as well as structures in the local area could redirect the wind in such a way that the wind direction within the vicinity of the house can be very different. A look at drifting snow could serve as a way of determining the current direction that winds blow around the house (Figure 2.).
The windbreak's position should be located upwind of the home by 50-200 feet, the ideal distance is 100-150 feet. To avoid the problems caused by snow drifts, you should plant trees that are at the minimum of 50 feet from the driveway or the home. If possible the trees must extend for 50 feet beyond the edges of the area to protect the area.
A small lot often requires cutting down on the distance to the home as well as how long the windbreak runs. There is no reason to consider installing additional windbreak trees in the event that vast areas of dense forest are already within the required distances. The layout and the composition of the windbreak will depend upon the available space on the property, as well as the plant species and the size of the trees that are available.
Local ordinances may limit species and their locations. If space is restricted only a single line of trees may be enough. However five rows of various evergreen species are more efficient. The rows on the outside, both upwind and downwind should be trees that have dense, low-growing growth like white Colorado blue or Serbian Douglas fir, spruce and white fir.
The rows to the right should be larger, faster-growing trees like white, red, Austrian pineas well as the hemlock and Norway spruce. White pine is suggested to be planted only to the south of Blue Mountains and east of the Susquehanna River because the white pine weevil can be found both to the west and north of the area.
Colorado blue spruce, and Douglas fir are both suggested as a solution for the south. All spruces and one of the firs can be utilized to the west and north. Most spruces , except for Colorado blue spruce are not well-adapted to the climate of the southeast region of Colorado (figure 3.).
Spacing between one, two and three-row windbreaks ought to be six feet between trees. If there are more than four rows spacing, it ought to be eight feet. Rows should be between 10 and 12 feet from each other, with trees being planted in a staggered order. If space is available and faster, more complete protection is desired, the two or three rows of fast-growing trees can be planted 15 feet in front of the windbreak permanent.
Hybrid poplar Lombardy poplar or Japanese larch ought to be spaced four feet from each other in rows, or 6 feet with staggered arrangements when two rows are planted. They can grow to 10-15 feet tall in five years and should only be considered as a temporary plant. They should be removed after 10 years, so that they don't hinder the development of the permanent plants.
Lombardy poplar is best viewed as a tree with a short lifespan because of fungal diseases. Dimensions and options of plant materials include transplants, seedlings containers, trees that are grown in containers, or trees dug using the help of a ball of soil covered with burlap (B&B).
Seedlings are the cheapest but they are the slowest to grow Container plant or B&B trees are more expensive in cost and established faster and increase in size. Transplants are priced moderately in terms of cost in terms of establishment, price, and rate of growth. The species of tree that is a windbreak can be bought from commercial nurseries.
Property owners must be aware of local ordinances that restrict planting close to boundary lines, or prohibit the plantation of specific species. The early spring is generally the best time to plant. It is true that B&B tree can also be established in fall if they receive the proper winter-time maintenance. The container plants are able to be planted anytime the soil isn't frozen. The preparation and maintenance of the site for planting are suggested to ensure optimal growth.
In competition with the vegetation like grass, weeds or woody plants need to be eradicated through cultivating, cutting herbicidal treatment or a combination. The soil test will determine the degree of soil acidity and the levels of nutrients should be adjusted to ensure proper growth and establishment. The recommendations for fertilizer and lime usage will be provided with the results of the soil test.
Assistance with planning and setting up windbreaks can be requested from the local extension office as well as Conservation District Office. A list of commercial nurseries that sell trees and planting materials as well as soil testing kits are readily available at the county extension offices. Many commercial nurseries offer guidance on choosing of trees, their planting, and the care of trees. The estimated cost of plant stock is determined by the size of the tree as well as windbreak's size calculated based on the 150-foot windbreak.
This length of windbreak could protect the structure or home 50 feet long and extend 50 feet to the building's end (Table 1.). Care and protection are required. Once the windbreak trees have been planted, they should be kept safe and in an optimal and vigorous growth condition. It is particularly important to shield weaker branches against damage or slow growth.
Elimination of animals, pets as well as children is required when trees are getting established. The competing vegetation, such as grasses, weeds, as well as brush should be kept from expanding trees. Although mowing is effective, it's not 100% effective but mowed plants can still deprive the trees of nutrients and moisture. The recommended chemical herbicides, if used correctly are safe and effective against the majority of annual grasses and weeds without harming trees. Proper pruning is sometimes needed as trees grow.
Multiple tops must be cut in order that one terminal leader grows at the base of the tree. Multiple tops can allow the trees to easily be damaged in snow or ice storms. The trees that die or become severely damaged must be replaced in the next year, so that holes do not form in the screen.
Fertilizing might be necessary If the trees don't have a normal or rapid growth. A year after planting, fertilizer must apply to trees during the month of March or in the beginning of April. The process is repeated every two years at intervals afterward. If a soil test has not been conducted and specific recommendations received, these general guidelines can be followed:
# Apply 5-10-10 Granular fertilizer.
# Spread the seeds in an 8-inch circle that is at least eight inches from the tree's stem for trees that are less than 2 feet tall. Apply 0.25 pounds of mulch to each tree.
* Treat trees that are more than 2 feet tall with a circular strip 12 inches in width under the the branches that are lower.
Use 0.5 pounds of weight to the trees which are taller than 4 feet 2 pounds should be applied for trees that are 6 feet high and 4 pounds to trees that are 8 feet high. The taller trees are recommended to receive 2 pounds for every inch of diameter of trunk. Insect and disease outbreaks tend to be first observed when a portion of the tree's foliage begin to turn brown, reddish or yellowish. A closer inspection will uncover outbreaks of insect or disease before they get too severe.
If the insect or disease that is causing the issue cannot be identified from the home owner, then foliage and twigs must be brought into the office of county extension to be identified. The need for thinning can occur when trees are growing together and could become overcrowded. Injured, weak, or overcrowded trees must be cut off first. This can happen between 12 and 15 years after the planting.
Additional benefits from windbreaks. Many windbreaks are used for other functions besides conservation of energy. Research has proven that trees can be effective in noise barriers when traffic-spurred highways or industrial factories that emit a lot of noise are located close to. Visual screening can also be offered when trees reach between 5 and 6 feet tall. An appropriately planned and maintained windbreak can be visually appealing (Figure 4,).
A properly installed windbreak can be an effective snow-blocker. Windbreaks with multiple rows trap snow in the trees and much more is falling on the protected lee side. The height of the trees and the speed of wind determine the distance to the lee-side the snow falls, but it's usually within two times what the size of trees. Wildlife is the primary benefit of a live windbreak.
Animals and birds are drawn to trees to protect themselves and for food. The songbirds can use a windbreak all year long or during migration. Ringneck pheasants, rabbits squirrels, and others might use the windbreak when they have trees large enough offer shelter.
The design of the windbreak can be altered in the event that the owner is attracted to attracting wildlife. The addition of certain deciduous trees and shrubs could increase the attraction of wildlife, both mammals and birds however it would decrease the effect of wind barriers.
Deciduous plants with proven benefits for wildlife can be planted outside in rows, and conifers in the middle section. considerations Summer shade should be given by big deciduous plants strategically situated near the southern edge of the house. The exact location of the plants is determined by height at which they mature the tree as well as the direction at which summer sun is received.
In Pennsylvania The position of the sun's position in the sky during the summer can vary from around 45 to 75 degrees over the horizon in midday. The trees should extend from the southeast until the southwest corner of the home and should be tall enough to shield the house from these angles. In winter, the leafless deciduous trees must not obscure the roofing of your house. In general, the sun's angle in winter is not more than 45 degrees above horizontal line, and any shading of the house does happen will mostly be caused by trees' trunks.
To this end, only those trees that are needed for shade during summer are to be kept on the southerly side of the house. Trees that are too far from the house to shade the home in summer could cause undesirable shade during winter. Removal of damaged or diseased trees is necessary in order to protect the house by falling debris. The precise location of trees could also be contingent on keeping a pleasing perspective from windows an aesthetic design and appeal of landscaping and the avoidance of overhead cables and pipes that are underground.
Shade trees for summer may be found on homesites with forested areas as long as the developer is able to preserve them during construction. If trees are planned to be planted, the fast-growing poplars are able to be mixed with slower-growing, but more desirable shade trees. Poplar trees may be removed later on as well as bigger B&B trees can be planted to provide permanent shade near the southern end of the house.
Final Effects and Costs
The effect of the final result of vegetation arrangement on the total energy requirements to heat and cool will be dependent on the area and weather conditions, as well as the specifics of the home. Though the possibility of a 75 percent savings in the energy required for cooling could be accomplished by shading during summer cooling, air conditioning is typically not required in many areas of Pennsylvania. But, shade during summer would help make interior areas more comfortable.
In winter, when winds are at a speed typically found in Pennsylvania the windbreaks could help save between 10 and 15 percent off the heating cost The greatest savings coming from loosely built homes. The ultimate cost of creating the summer shade and windbreaks need to be evaluated against the value of energy savings, as well as other benefits for wildlife and environmental. When planting is needed and the cost is long-term. In reality, most homeowners choose to invest in landscaping for their home spending a bit more time dedicated to planning the most effective plant arrangement and species could be worth the investment.