Studies Of Greening's Effects On Outdoor Thermal Environment

Greening has important effects on the outdoor thermal environment quality and the pedestrian thermal comfort. However, there lack enough systemic studies for a long term, including that how plants affect the thermal environment around them, how to describe and simulate these effects, and what the reasonable evaluation indexes are. In order to solve these problems, some studies are carried out in this thesis.Firstly, a lot of filed experiments were carried out to understand the effects of plant greenings on the thermal environment and the different characteristics among them.Secondly, a general 3-D radiation simulation system is developed, which could realize an accurate radiation calculation when non-transparent objects and half-transparent objects exist together. Using it, the short-wave and long-wave transmission processes inside the canopy of plant, including reflection, absorbsion and transmission, could be predicted accurately. Combined with the radiation system, the 3-D canopy flow simulation models, the heat and moisture transportation models of canopy, and the heat conduction calculation of ground and building surfaces with finite difference method, a general simulation platform is developed for predicting and evaluating the outdoor thermal environment when plant greening exists.Thirdly, an EMGT (Equient Micro Global Temperature) method is developed to describe the radiation filed and the radiation sensation of pedestrian when long-wave and short-wave radiations exists together. A precise method to calculate WBGT index directly with environment parameters is built on. Based on series comparison studies of different indexes applied into same outdoor thermal environment conditions, an assessment index system with WBGT and SET are proposed to evaluate the thermal safety and comfort of outdoor thermal environment, and corresponding simplified calculation formulas for them are developed. Finally, with lots of numerical experiments, some important parameters such as reflection ratio, evaporation ratio of underlaying surfaces are studied. The results show that simply improving reflection ratio could not always improve the thermal environment. In most situations, tree planting has better effects on improving the thermal environment compared with other plant configurations. However, it's still related with some factors such as what the evaluation duration is, and the existence, orientation of the building complex. Also, the different configurations for same kind of plant greening (for example street-tree planting) could result in different effects on the outdoor thermal environment. And the ESVQ (Effective Shading Vegetation Quantity) is proposed to optimize the greening design for better thermal environment.The work of this thesis lays a foundation of accurate prediction and comprehensive evaluation of the outdoor thermal environment, and lets it possible to guide greening planning and design by simulation to improve the outdoor thermal environment.