Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento

Abstract

Tree shade reduces summer air conditioning demand and increases winter heating load by intercepting solar energy that would otherwise heat the shaded structure. We evaluate the magnitude of these effects here for 254 residential properties participating in a utility sponsored tree planting program in Sacramento, California. Tree and building characteristics and typical weather data are used to model hourly shading and energy used for space conditioning for each building for a period of one year. There were an average of 3.1 program trees per property which reduced annual and peak (8 h average from 1 to 9 p.m. Pacific Daylight Time) cooling energy use 153 kWh (7.1%) and 0.08 kW (2.3%) per tree, respectively. Annual heating load increased 0.85 GJ (0.80 MBtu, 1.9%) per tree. Changes in cooling load were smaller, but percentage changes larger, for newer buildings. Averaged over all homes, annual cooling savings of $15.25 per tree were reduced by a heating penalty of $5.25 per tree, for net savings of $10.00 per tree from shade. We estimate an annual cooling penalty of $2.80 per tree and heating savings of $6.80 per tree from reduced wind speed, for a net savings of $4.00 per tree, and total annual savings of $14.00 per tree ($43.00 per property). Results are found to be consistent with previous simulations and the limited measurements available.