Growing summer energy conservation through residential tree planting

Abstract

Energy conservation strategies are now at the forefront of electrical utility demand-side management planning. Residential shade trees extenuate the heating of buildings in the summertime by intercepting insolation and by evapotranspirative cooling of their immediate surroundings. By modifying location-specific climate data and tree growth characteristics, we adapt the Sacramento Municipal Utility District's (SMUD) Tree Benefits Estimator for application in Toronto, Canada. We then use our tool to model the air conditioning energy conservation savings delivered by 577 trees planted in Toronto backyards between 1997 and 2000. In urban residential neighbourhoods, where houses are closely spaced, the energy conservation benefits of planting a tree depend on species, on pre-existing canopy, and on placement of the tree with respect to distance and orientation from buildings. Study trees contributed 77,140kWh (167kWh/tree) of electricity savings as of 2009, 54.4% of which was due to shading of neighbouring houses. Twenty-five years following planting, we estimate that each study tree will have delivered, on average, between 435 and 483kWh in energy conservation benefit. Our findings indicate that residential tree-planting programmes in densely settled urban areas should not focus exclusively on location-driven strategic planting to yield large energy conservation benefits. Instead, we argue that priority should be given to selecting planting locations that will maximize tree survival as neighbourhood energy conservation benefits of a tree that achieves mature stature often outweigh the homeowner-specific benefits of a strategically planted tree.