Research On Optimization Strategies For Microclimate And Thermal Comfort In Outdoor Space Of Southwest University In Autumn And Winter

Universities are an important component of urban construction,and their outdoor space utilization rate has greatly increased with the reform of education and teaching.The comfort of campus outdoor space design is particularly important for teachers and students.Reasonable planning not only needs to meet the subjective feelings of teachers and students,but also needs to be scientific.Therefore,the thermal comfort adaptation of campus outdoor space has been widely studied.This article takes five different types of outdoor space measurement points at Southwest University as the research object.Through subjective evaluation survey,on-site data measurement,and ENVI met software simulation,the microclimate characteristics and thermal comfort spatiotemporal distribution patterns of each measurement point in autumn and winter are analyzed,in order to construct an optimization strategy suitable for the microclimate and thermal comfort of university campuses in Chongqing.The conclusion of this article is as follows:（1）A total of 614 valid questionnaires were collected in this experiment（376 in autumn and 238 in winter）.The research results show that the majority of votes on thermal comfort and thermal acceptability are in an acceptable state.In autumn,when it is relatively hot and sunny,people mostly choose to activities in shaded areas such as gardens and squares with high shading.Playgrounds and garden squares with strong sun exposure have lower heat acceptance;In winter,on the contrary,people prefer playgrounds with higher solar radiation for activities,with a stronger shade and coldness under the trees and trees.In addition,the main factors affecting thermal comfort are sunlight and air temperature.（2）The larger the sky visibility factor（SVF）of different outdoor spaces in autumn and winter,the higher the air temperature;The water environment and plant greenery affect the humidity of local areas;The average wind speed at all measuring points in autumn and winter is around 0.5m/s and 0.2m/s,respectively.The magnitude and total amount of wind speed are closely related to the surrounding environment of the measuring points;The overall trend of relative humidity in winter is mainly influenced by solar radiation,and the solar radiation at measuring points with higher shading levels tends to stabilize throughout the day.（3）Concrete brick paving has a good absorption of solar radiation,with the lowest air temperature and relative humidity in autumn.The function of granite paving,lawn paving,and plastic paving in absorbing solar radiation gradually decreases;The plastic field has the best insulation effect in winter,and the lawn paving has a significant humidification effect.In autumn,the planting method of trees and shrubs has a lower temperature of 0.8℃than the planting method of trees and grass.Shrubs have a better cooling effect than lawns,but their humidification effect is not as significant as lawns.In winter,the planting method of trees and grass has25.91W/m2 higher solar radiation than the planting method of trees and shrubs.The planting method of trees and shrubs has the highest temperature,simpler vegetation structure,and lower humidity.（4）The total average values of mean radiant temperature(T_mrt)in autumn and winter are 41.3℃and 8.0℃respectively,and the total average values of physiological equivalent temperature（PET）are 32.3℃and 10.5℃respectively.The thermal comfort level corresponding to most thermal sensations in autumn is"warm",while that in winter is"slightly cool".The overall thermal comfort level of the campus does not appear to be the worst;The microclimate factor that has the greatest impact on PET in autumn is solar radiation,followed by mean radiant temperature,and finally air temperature;Air temperature and mean radiant temperature had the greatest impact on PET in winter,followed by wind speed and humidity,and solar radiation had little impact on PET;For every 20%increase in SVF in autumn,solar radiation will increase by 30.2W/m2,T_mrtvalue will increase by6℃,and PET will increase by 3.8℃.For every 20%increase in winter SVF,solar radiation will increase by 6.4W/m2,T_mrtvalue will increase by 4℃,and PET will increase by 0.17℃.（5）Based on the ENVI-met simulation of the microclimate and thermal comfort of the outdoor space of Southwest University,by comparing and analyzing the measured and simulated values,explore the spatial and temporal distribution differences of microclimate factors and thermal comfort in different spaces,and propose specific improvement strategies from the underlying surface materials,plant planting,structure shading,water and other landscape elements:in autumn,the non shaded site can choose permeable bricks,gravel roads and other pavement materials with greater heat capacity,Choose materials such as dark granite or cement bricks for the walking space in the teaching and living areas,and choose leisure areas or parking lots with weak traffic functions for lawn brick paving or a mixture of brick and grass paving;Choose deciduous trees with appropriate branch height to effectively create a shaded space and avoid the problem of not being exposed to sunlight in winter,ensuring the comfort of the geothermal environment.The selection of trees and shrubs should be comprehensively considered based on the spatial wind environment.If the wind speed on the site is high and affects thermal comfort,consider increasing the number of trees appropriately to resist the wind;If there is no wind on the site or the wind speed is low,which results in low comfort for the crowd,consideration should be given to reducing the planting of trees and selecting shrubs for upwind planting.The relationship between the opening direction of the enclosure of the structure and the prevailing wind direction in the current season;Reasonable drainage or water storage measures should be taken for the water body of the site to correspond to the subjective thermal sensation of different seasons.In summary,based on subjective research,on-site measurements,and analysis of software simulation results,an experimental optimization design was selected for a research area with low thermal comfort at Southwest University.Corresponding improvement strategies were proposed to address the existing problems of the site,and the optimization plan was incorporated into ENVI-met simulation software to calculate PET.The microclimate factors before and after optimization were compared and analyzed with PET,and it was found that autumn air temperature and solar radiation decreased,The increase in relative humidity brings the thermal comfort index closer to the comfort level,further verifying the effectiveness and feasibility of the plan,and providing ideas for optimizing the landscape design of other outdoor spaces at Southwest University.Campus landscape optimization is a comprehensive combination of adjustments within a certain regional range to achieve the effect of microclimate optimization in a certain area.It is not only about optimizing a single landscape element at a single measuring point,but also about the regional nature of microclimate optimization strategies.Therefore,relevant research needs to be further improved.