Improved estimates of tree-shade effects on residential energy use

Tree-shade alters building cooling and heating loads by reducing incident solar radiation. Estimates of the magnitude of this effect, and how it is influenced by urban forest structure (e.g. tree size and location), are difficult due to the complexity inherent in tree-sun-building interactions. The objective of this paper is to present a simplified method for making these estimates appropriate for neighborhood and larger scales. The method uses tabulated energy use changes for a range of tree types (e.g. size, shape) and locations around buildings (lookup tables), combined with frequency of occurrence of trees at those locations. The results are average change in energy use for each tree type that are not explicitly dependent on tree location. The method was tested by comparison to detailed simulations of 178 residences and their associated trees in Sacramento, California. Energy use changes calculated using lookup tables matched those from detailed simulations within +/-10%. The method lends itself to practical evaluation of these shading effects at neighborhood or larger scales, which is important for regional assessments of tree effects on energy use, and for development of tree selection and siting recommendations for proposed energy conserving planting programs. (C) 2002 Elsevier Science B.V. All rights reserved.