Simulation Study On Summer Microclimate Environment Of Urban Streets In Xi’an

As an important carrier of people’s outdoor activities,urban streets have been paid more and more attention to improve the microclimate environment which affects human outdoor thermal comfort under the premise of meeting the function.In urban streets,due to the different changes of street space forms such as trend,height width ratio,interface opening,shade space form,tree species selection and planting mode,the microclimate environment and human comfort in the streets are affected differently.This paper takes the urban streets of Xi ’an as the research object,and through the simulation results obtained by relevant software,compares and analyzes the distribution of air temperature and sunshine environment in various street Spaces,so as to judge the difference of influence of different shade space types in the streets on the microclimate environment and human body comfort in summer.From the perspective of landscape architecture,this paper tries to put forward some Suggestions for the design of shady space in different levels of urban streets.Specifically,the following work has been carried out:(1)Research on the current situation of urban street space in the second ring road of Xi’an city.In this paper,90% of the street cross-section space in the second ring road is investigated,and the street cross-section space is described by the spatial form factors such as trend,sidewalk width,roadway width,height width ratio,tree shade space and tree species.On this basis,the common street Valley space forms and shade space types in the main,secondary roads and branch roads in the second ring road are quantified and counted,and the common combination forms of street Valley space and shade space in different levels of urban streets are put forward.(2)Selection of microclimate environment simulation software and verification analysis of simulation accuracy.In this paper,ENVI-met is selected to simulate the daily change of air temperature in the street in summer,ECOTECT is selected to simulate the distribution of sunshine environment in the street in different periods,and the basis of selecting the two software is given.Taking the east-west street of Xi’an city-Qing Nian Road and the North-South Street-Shuang Ren Fu as examples,the sunshine environment and thermal environment in the street on that day were simulated and compared with the measured sunshine environment and air temperature on that day.(3)Construct the simulation conditions of urban streets.Based on the survey results,the common trend,height width ratio and shade space types of Xi’an city streets are sorted out,and the ideal street model is established based on the control variable principle.Among them,the urban main road with a width of 45-60 m is mostly shallow /standard street Valley,and the shade space has a "continuous arch" / two "single arch" closed type,"two lines" / "three lines" open type,with a total of 16 Street models established;the urban main road with a width of 35-45 m is mostly shallow / standard street Valley,and the shade space has a "continuous arch" closed type,"two lines" open type,with a total of 12 Street models;the shade space has a width of 25-35 m There are usually shallow / standard / deep Street valleys in urban secondary trunk roads,and most of the shade spaces are "single arch" closed type and "two line" open type,with a total of 12 Street models;most of the urban branch roads with a width of 15-25 m are standard / deep Street Valley,and most of the shade spaces are "single arch" closed type and "two line" open type,with a total of 8 street models.(4)Simulation analysis of microclimate environment of urban streets in summer.For the period with strong solar radiation intensity in summer(9:00-18:00),by describing the sunshine environment in the street section space,the distribution of air temperature in the section space and the daily change process of temperature at the height of 1.5m on both sides of the sidewalk,this paper analyzes the characteristics of microclimate environment in different grades of urban streets in summer,so as to judge that the main,secondary and branch roads in Xi’an are affected by different trends,height width ratio The influence of different shade spaces on the sun shading and air temperature in the street is different.(5)Analysis of the regulating effect of shade heat comfort in urban streets.According to the evaluation method that the research group has put forward,the shade shading effect is evaluated by the comfortable District of street section space,and the shade cooling effect is judged by the difference between the maximum air temperature obtained from the air temperature simulation result and the air temperature of meteorological station.Based on the difference of shading and cooling in the shade space,this paper analyzes the control effect of different shade spaces on pedestrian comfort in the main,secondary and branch roads of the city.To sum up,this paper proposes some design Suggestions for the tree-shaded space in some urban streets of Xi ’an based on the purpose of effectively reducing air temperature,speeding up heat dissipation in streets,effectively shielding the pedestrian space on both sides from the sun,and improving human comfort.The first choice of urban main roads is "continuous arch" closed type,followed by two "single arch" closed shade space;On both sides of the road tree should crown shade thick;Among them,the canopy width of south-north street roadway should not be closely lapped with the buildings on both sides.The urban secondary trunk road and branch road can choose "single arch" closed type and "two lines" open shade space.On both sides of the road tree crown can be selected to cover the pavement;On both sides of the road trees and buildings can be closely overlapped,the canopy above the roadway should not be overlapped.