Effects of three landscape treatments on residential energy and water use in Tucson, Arizona

Vegetation can reduce the cooling loads of buildings in hot arid climates by modifying air temperature, solar heat gain, longwave heat gain, and heat loss by convection. However, savings from reduced mechanical cooling may be offset by increased irrigation water costs. In this study, three similar 1 4-scale model buildings were constructed and surrounded with different landscapes: turf, rock mulch with a foundation planting of shrubs, and rock mulch with no plants. Irrigation water use and electricity required to power the three room-sized air conditioners and interior lights were measured for two approximately week-long periods. Electrical energy consumed for air-conditioning by the rock model was 20 - 30% more than for the turf and shade models. Factors accounting for these differences in energy performance include dense shade that substantially reduced solar heat gain for the shaded model, a 16% difference in longwave radiation flux between the rock and turf treatments, and a maximum drybulb depression of 4 °C over the turf compared with the rock. Air-conditioning savings exceeded water costs for shade treatments that were simulated to receive moderate and low amounts of irrigation water. These preliminary findings suggest that the localized effects of vegetation on building microclimate may be more significant than boundary layer effects in hot arid regions.