The pair collected data in the summer of 2007. They used aerial photography to collect data on the trees surrounding the 460 houses based on three factors: crown size, distance from the house, and aspect relative to the house. They then collected electrical billing data from the Sacramento Municipal Utility District and water use data from the city of Sacramento. They found that trees providing shade on the west and south sides of the houses reduced summertime electricity consumption by 5.2%, and that east-side trees had no effect, since they cast shade on the house during the cool morning, when the A/C is turned off. To the researchers’ surprise, though, north-side trees within 6.1 meters of the house had a converse affect, increasing summertime electricity use by 1.5%. Donovan and Butry hypothesized that trees close to the house may reduce the cooling effect of the wind, slow the release of heat at night, or cause more lighting to be used in the house.
Gavin Nachbar is a freelance writer. His specialty is covering recent and relevant scientific studies.
For more information:
Donovan, Geoffrey and David T. Butry. “The value of shade: Estimating the effect of urban trees on summertime electricity use.” Energy and Buildings. January, 2009. To read the full study, go to: linkinghub.elsevier.com/retrieve/pii/ S037877880900005X
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