Shelterbelts help cut heating costs

In the past decade there has been an increasing interest in landscape design for energy conservation. In energy conservation landscaping the primary aims are to control wind and sun. In western Canada the first line of defence for energy savings is protection from the cold winter winds by the use of shelterbelts. Research shows that properly designed shelterbelts can reduce the heating cost of a typical farmhouse by as much as 30 per cent.

The Prairie Farm Rehabilitation Administration conducted a two-year study comparing heating costs in a well sheltered farmyard with those in a completely unsheltered one. The study was done in the winters of 1981-82 and 1982-83 near Indian Head, Saskatchewan, using two identical, electrically heated trailers kept at 72F. The study found that the sheltered trailer used 27 per cent less electricity than the exposed trailer.

By correlating the heat loss characteristics of the test trailers with those of a typical farmhouse, an estimate of expected heating savings for an average farmhouse was determined. For an oil heated one-story bungalow with a heated, full concrete basement and a main floor area of 1,200 square feet, the savings work out to $587 per season on the basis of the current 1986 fuel oil price of $0.38 a litre. The heating cost for a completely exposed house of the above type with medium quality insulation and air-tightness typical of construction used between 1950 and 1975 was calculated to be $3.204. The 27 per cent saving reduces this cost to $2.347.

The study found that the savings were directly proportional to the average wind speed in the sheltered location, which means that the primary benefit of shelter is in reducing wind induced air leakage. Heating costs were reduced by 1.2 per cent per kilometre/hour (km/hr) of the average open wind speed. In the Regina plains area, where the average wind speed is 22.3 km/hr, seasonal savings of 27 per cent could be expected; for areas with higher winds the savings would be proportionally greater.

The above results were based on an average wind reduction and density on each of the four sides. The north belt, which has two outside rows of conifers and three inner rows of deciduous trees, was rated as dense. The west belt had two rows of shrubs, one row of deciduous trees and one closely spaced row of conifers; the east belt had a double row of conifers. Both of these belts were rated as moderately dense. The south belt consisted of deciduous trees and shrubs and was relatively open; it was rated as having a light density. The test shelterbelt was a good quality enclosure but less than ideal, having degrees of protection ranging from fair to good depending on wind direction.

By correlating heat loss with wind direction, the effect of differences in shelter density could be detected. It was determined that the dense north belt reduced wind speeds by 83 per cent. In other words, a 40 km/hr wind would be reduced to 7 km/hr in the lee of the shelter, translating into a 1.45 per cent reduction in heat loss per km/hr open wind speed. For the light density belt on the south side the corresponding values were a wind reduction of 52 per cent and a heat loss reduction of 0.82 per cent per km/hr open wind speed. The moderate density belts on the east and west sides reduced wind speed by an average of 70 per cent and resulted in an energy saving of 1.25 per cent per km/hr open wind speed.

Theoretically then, if a shelter was constructed to provide dense protection in all directions with no access openings a benefit of 1.45 per cent per km/hr of exposed wind velocity could be expected. This would be 20 per cent better than the shelter tested and could result in energy savings of more than 30 per cent overall. Such a shelter might be somewhat difficult to achieve and perhaps impractical from a ventilation standpoint. Nevertheless, with proper design and choice of species, savings greater than the test results are possible.

The best design for shelterbelts and windbreaks depends on the use and exact location of the site. However, in most of Canada the prevailing winds are from the northwest, therefore, the maximum protection should be on the north west. A five-row shelterbelt on these two sides consisting of an outside row of shrubs, a double row of deciduous trees and a double inner row of conifers with staggered spacings is the ideal design for protection from both wind and blowing snow. The wind is deflected up and over the shelterbelt, creating a well protected zone in the lee of the belt. The zone of maximum protection extends outward five times the height of the trees. If space is at a premium, fewer rows may suffice, but the use of conifers and other densely branched species is essential for winter protection.

Since south and east winds are generally warmer than north and west winds, it is considered sufficient to have moderate protection on the east and desirable to leave the south open or restricted to rows of shrubs and deciduous trees. More openness to the south permits maximum solar gain in the winter and allows for summer ventilation of the farmyard or living area.

Buildings should be about 100 ft. away from the inner row of trees to avoid the accumulation of snow that can occur immediately inside the belt. Of course, specimen plants can be planted closer to the buildings for addition protection and attractiveness.

Openings in shelterbelts should be designed to avoid creating a wind tunnel effect. If possible the belt should be continuous on the north and west; any openings on these sides should be perpendicular to prevailing winds and positioned on an angle so that wind is not allowed direct access. Trees and shrubs can also be planted around the openings to baffle the winds and keep the snow from piling up in laneways.

Design for an Energy Conscious Future

It would be interesting to speculate from the study as to the overall conservation value of shelterbelts that have been established since the policy of tree distribution was initiated for prairie settlers in 1902. No doubt the accumulated benefits are considerable. The economic incentive of reduced heating costs is additional to known benefits of reduced snow clearing, reduced heat loss by open housed animals and protection of farm buildings. While most farms have at least some naturally treed areas or planted shelterbelts protecting their yard, the full potential benefit from tree planting is far from being realized. The results of this study will help in the design of new shelterbelts or the improvement of existing shelterbelts which can provide maximum protection and improved energy conservation value.

Energy conservation is a growing concern. Current studies confirm what fuel oil dealers have known all along, farms with shelterbelts use considerably less fuel. Long term average savings of $122 per month, based on a seven month heating season calculated at current prices, are indicated by test results. The time to begin planning for an energy conscious future is now.