Modeling the Effect of Trees on Energy Demand for Indoor Cooling and Dehumidification Across Cities and Climates

Abstract

Increasing urban tree cover is a common strategy to lower urban temperatures and indirectly the building energy demand for air-conditioning (AC). However, urban vegetation leads to increasing humidity with potential negative effects on the AC dehumidification loads in hot-humid climates, an effect that has so far been unexplored. Here, we included a building energy model into the urban ecohydrological model Urban Tethys-Chloris (UT&C-BEM) to quantify the AC energy reduction effects of trees in seven hot cities with varying background humidity. A numerical experiment was performed simulating various urban densities and tree cover scenarios in the city-climates of Riyadh, Phoenix, Dubai, New Delhi, Singapore, Lagos, and Tokyo. The relative contribution of tree shade, air temperature reduction, and humidity increase on the AC energy reduction was further quantified. We found that well-watered trees provide the largest average summer AC energy reduction of −17% in the hot-dry climate (Riyadh, Phoenix). As tree shade is the dominant factor leading to the AC energy reduction in all city-climates, humid cities also show an average summer AC energy reduction ranging from −6% to −9%. However, increasing humidity is affecting AC dehumidification loads, especially under higher ventilation rates in humid climates and in these cities, AC energy reduction is most efficient with up to 40% tree cover. Additionally, we found that trees effectively reduce peak AC energy consumption due to higher shading effects in those hours. These results can inform urban planning strategies to maximize reduction in the AC energy demand using urban trees.