The Influence Of Shade Tree Layout On The Microclimate And Thermal Comfort Within The Courtyard

With the rapid development of the city and the improvement of people's living standard,it is necessary to improve the microclimate performance and thermal comfort of the outdoor environment in urban residential areas for solving the increasing severe problems of urban environment and ecology.The courtyard is a circumscribed area,often enclosed by in facades of the surrounding buildings,playing an important role in urban outdoor space,it is of great significance to improve thermal comfort by adjusting the environmental microclimate through plants.Therefore,this study aims to analyze the effects of plants by courtyard air temperature,wind velocity,wind direction,relative humidity,and universal thermal climate index(UTCI)by simulating the green coverage ratio,planting-tree position and layout pattern with the shading tree layout,providing guidance and advice on courtyard planting design more scientifically and quantitatively,and then to improve the microclimate performance and thermal comfort of courtyard.Combining with the field measurement and numerical simulation was used to analyze the influence of the layout of courtyard shading trees on the air temperature,wind velocity,wind direction,relative humidity and thermal comfort of the courtyard.The main conclusions are as follows:(1)The increase of the green coverage ratio by the shading trees could reduce the average air temperature and average wind velocity of the courtyard,increases the average relative humidity,and improves the thermal comfort of the site.However,as the green coverage ratio gets too large,the average temperature of the site will increase,the average relative humidity will decrease,and the thermal comfort comes worse.When the green coverage ratio is 30 ~ 60%,it generally has better thermal comfort.With the increase of green coverage ratio,the degree of decrease in average air temperature gradually decreases,the degree of increases in average relative humidity gradually increases and the degree of optimization of thermal comfort decreases gradually.(2)Compared with the centralized layout,the distributed layout reduces a larger cooling area size and wind velocity cutting in the cases of each planting position.When the green coverage rate is low,compared with the distributed layout of courtyard shade trees,the thermal comfort of the centralized layout of the courtyard site is better.In the distributed layout,the case that reducing the wind velocity of the courtyard vents by reducing the planting position has better thermal comfort.(3)Different planting positions of courtyard shade trees lead to different effects on air temperature,wind velocity,wind direction,relative humidity and spatial distribution of thermal comfort at the pedestrian height of the courtyard site.Each of the planting position cases obviously reduces the minimum value of air temperature,and increases the maximum and minimum value of relative humidity in the site,consequently the air getting cooler and moister,but has basically no effect on the minimum value of wind velocity in the site.It indeed has a reducing effect on the maximum value of UTCI in the courtyard area.However none of these seem to make any difference to the minimum value.The overall temperature of the site is lower,thermal comfort is better when courtyard shade trees are planted centrally in the center of the courtyard,,.Generally avoid centralized trees in the southern side of the courtyard.(4)When the green coverage ratio is around 30%,no matter where the trees are planted,the thermal comfort of the yard has been improved.Centralized layout which the shaded trees in the central courtyard has a higher level and more area of cooling reduction for UTCI than distributed layout.Courtyard shade trees are planted certainly in the center of the courtyard which has a greatest level and surface of cooling reduction for UTCI.