Impacts of trees-grass area ratio on thermal environment, energy saving, and carbon benefits

Abstract

Rapid urbanization potentially increases the diversity of building morphological characteristics (e.g., heights), causing urban ecological environment problems, such as urban heat islands, energy loss, and carbon emissions. Greenery (e.g., trees and grasses) can alleviate urban environmental problems, further improving the benefits of cooling effect, energy saving, and carbon emission reduction. With limited land resources, it is significant to effectively combine multiple greeneries and quantitatively optimize the greenery design. This paper designed the trees-grass area ratio (TAR) and explored its effect on the benefits at the community scale. The ranges of 0–90% TARs were considered in the communities as well as three building heights. A low-cost computational fluid dynamics (CFD) method of volumetric source term (VST) was proposed to simulate the thermal environment. Energy performance simulation of buildings was performed. Results indicated that the VST method can reduce computing costs by up to 81% compared with the traditional simulation. Air temperature (T), energy consumption (E), and carbon emission (Ce) decreased with increasing TAR in three types of communities. Carbon sequestration (Cs) linearly increased with increasing TAR. When the TAR was 90%, the maximum reduction of T, E, and Ce were 6 °C, 17.3%, and 20%, respectively. Furthermore, the quantified relationships between TAR, building height, and benefits were proposed. This work can serve as a guideline for the optimal design of urban ecological environment.