Sacramento, CA (August 1995)- The Shade Tree Program was initiated by the Sacramento Municipal Utility District (SMUD) in 1991 with the objective of reducing summer air conditioning loads by planting trees to shade residential buildings. A secondary objective of the program was to create an urban forest that would help mitigate heat island effect, or the increase in summer outdoor temperatures caused by urban development.
The Shade Tree Program is implemented by SMUD through the Sacramento Tree Foundation, a nonprofit organization that has been contracted by the District to provide a comprehensive and long-term program in tree planting, managements, education, and citizen participation.
By the end of 1994, nearly 170,000 trees had been planted through the program, representing over one-third of the program’s long-term goal of 500,000 trees within the next decade. Under the District’s current strategic plan, the goal of the Shade Tree Program then shifted from planting a specified number of trees to focusing on the goal of shading homes to reduce summer cooling loads.
The Shade Tree Program Impact Evaluation report examines the energy and demand impacts of the program based on information from a variety of research activities completed in 1994 and 1995. In December 1994, information on tree siting and mortality rates were collected by SMUD and Sacramento Tree Foundation staff through on-site surveys of over 300 residential sites at which trees had been planted through the program from 1991 to 1993. In addition, the USDA Forest Service’s Center for Urban Forest Research was contracted to analyze the load impacts of shade trees using computer simulation models of tree shade patterns and the resulting impacts on building energy use.
Key finding include:
* The initial estimate of 109 kWh savings total was found to be 4-6% too low.
* 23% of trees died or were missing within the first three years, with long-term estimates at 43%.
* Trees grew faster than estimated, which contributed to cost-effectiveness analysis.
* Due to less than ideal tree siting, 87% of the cooling savings were lost during the winter months when shading increased heating loads.
Suggested improvements to the program include:
* Stricter tree-siting guidelines could improve program cost-effectiveness by least 8-28%.
* Long-term mortality rates could be cut to 30% through better education and more on-site visits, increasing the programs effectiveness by 18%.
Additional indirect energy benefits of the Shade Tree Program resulted from the effect of trees as wind breaks, which reduced infiltration of unconditioned outside air into buildings. Non-energy benefits of the program included improving the region’s air quality, enhancing aesthetics and quality of life in the region, and improving property values of program participants.
Shade Tree Program Impact Evaluation Full Report
Sacramento Municipal Utility District (SMUD)
Sacramento Tree Foundation