مطالعات شبیه سازی عددی اثرات الگوهای مختلف پوشش گیاهی در آسایش حرارتی عابر پیاده در فضای باز

Vegetation has positive effects on the outdoor pedestrian comfort and thermal environment. Throughout the three numerical simulation experiments and a presupposition of a same total leaf area for all greening cases, the differences of vegetation patterns on the pedestrian thermal comfort have been studied with an evaluation index as (Standard Effective Temperature) SET . Firstly, in comparison with grass and shrub patterns, greening with tree does not always have better effects for improving pedestrian thermal comfort in summer in all directions around buildings. The reasons include the relatively negative function of tree to decrease the wind velocity and the hourly change of the sun's location. However, if considering the average SET around the pedestrian space, greening with tree is still better than others are. Secondly, the difference for the three vegetations for pedestrian comfort is affected by the arrangements and orientation of buildings. Thirdly, there is an optimized pattern with a lower SET distribution for the configuration of trees (including the shapes and arrangements) around buildings. In this situation, the average SET in the pedestrian space has a slight difference and should be carefully compared for better outdoor pedestrian comfort.

Vegetation has important effects on outdoor pedestrian comfort. The effects of different vegetation patterns on thermal comfort have been compared based on the numerical simulation studies with SPOTE. Three kinds of different comparisons are carried out in this paper with a presupposition that the total leaf areas for all the plants in different cases are the same. Moreover, including the vegetation selection of tree, grass or shrub, different building orientation and different configurations of tree are simulated and compared. From the simulated results, some conclusions could be drawn as follows. Firstly, the greening pattern with a tree is not always effective in improving the pedestrian thermal comfort in summer in all directions around buildings or compared with the average value on the site. The important reason is that the total leaf area is the same for the three cases, and for the grass greening mode it could reduce solar heat released by the ground and prevent higher surface temperature of the road or soil, and the average air temperature and SET would not be higher than that for the tree case. Moreover, for the shrub or tree case, since the total leaf area is the same, the shaded area of the outside ground would be less than that for the grass case. Moreover, it is not only due to the disadvantage of tree for the decrease in air velocity, but also because the pedestrian space could not be over-shaded by the canopy of the tree due to the hourly change of the sun's location. However, if the average effects are considered, greening with tree is still better than the other cases. Secondly, when the arrangements and orientation of buildings and incoming wind are changed, the same planting pattern for the improvement of the outdoor comfort should be re-evaluated. Last but not the least, there is a corresponding optimized pattern for the tree arrangements around buildings, especially when the outdoor space comfort on the south and west sides are more important. At this situation, the average pedestrian comfort value should be carefully used to evaluate different tree configurations since the average differences of SET in different cases are very small, the decreased value of SET on south and west sides are more important. Compared with the daily parameters used in the simulation cases, there are worse climate situations with higher air temperature and humidity in summer for mega cities in China recently. If the wind direction and the velocity changes, more numerical simulations should be carried out to check if the conclusions drawn above could be changed or not. Moreover, in the future, the analysis above should be qualified as tentative conclusions subject to the experimental verification