Study On The Correlation Between Tree Leaf Temperature And Exterior Wall Surface Temperature

Tree is a common representative vegetation near buildings.It has important effects on the environment such as cooling,humidifying and carbon sequestration.The main factors affecting tree species selection and spatial allocation include cultural customs,landscape requirements and economic benefits.However,the impact of tree on the thermal environment is ignored.It results that the huge cooling and energy-saving effect is difficult to play and ecological benefits is wasted.Therefore,this paper studies the law of tree leaf temperature change in summer and the law of correlation between tree leaf temperature and wall temperature.This study consists of two parts.In the first part,using the UAV infrared thermal imaging camera to capture the photos of tree leaf temperature in summer.Four common trees Osmanthus fragrans,Cinnamomum camphora,Acer palmatum and Aesculus chinensis Bunge were taken as objects in Donghu campus of Zhejiang Agriculture & Forestry University.The law of tree leaf temperature change in summer was discussed.In the second part,taking the exterior facade of the teaching building and its adjacent objects as the object,the temperature of external facade,the leaf of tree(Osmanthus fragrans),the grassland and the cement ground were measured respectively.Using the statistical correlation analysis and linear regression analysis,the law of correlation between facade temperature and adjacent surface temperature was discussed.The results shows as follows:(1)From the four directions of east,west,south and north,during the day from 9:00 to 11:00,the tree leaf temperature on the east side was the highest and the the west side was the lowest,with a difference of 1 ~ 7?.From 11:00 to 16:00,the west side leaf temperature was the highest,and the other three sides of the leaf temperature had no obvious law,but the difference between the highest and the lowest was about 7?.From 19:00 to 21:00,the leaf temperature of four trees in the four directions showed no obvious law.From the three levels of upper,middle,and lower,during the day from 9:00 to17:00,the upper leaf temperature was the highest,the lower was the lowest,and the temperature difference was within 5?.From 19:00 to 21:00,the temperature of upper,middle and lower leaves showed no obvious law,but the temperature difference was within 1?.(2)The four kinds of trees generally have the following rules.From 9:00 to 18:00,the average temperature of the leaves was higher than the air temperature,and the temperature difference was about2?.From 19:00 to 21:00,the air temperature was higher than the average leaves temperature,and the temperature difference was about 1?.From 9:00 to 21:00,the facade temperature was always higher than the average leaves temperature and air temperature.Two kinds of evergreen trees,the average leaves temperature of Cinnamomum camphora with small leaf area was lower than that of Osmanthus fragrans with large leaf area.The transpiration rate of Cinnamomum camphora is faster,and its ability of cooling and humidifying is stronger.Two kinds of deciduous trees,the average leaves temperature of Acer palmatum with small leaf area.was lower than that of Aesculus chinensis Bunge with large leaf area The transpiration rate of Acer palmatum is faster,and its ability of cooling and humidifying is stronger.Therefore,the leaf area is an important factor affecting the leaf temperature.(3)In the summer,the heat radiation transfer between the external facade and the adjacent ground objects was completely the same,which was,the heat transfer from the facade surface to the Osmanthus fragrans leaf surface and the grassland.Then the cement ground transferred the heat to the facade surface.The correlation between the facade temperature and the surface temperature of the adjacent ground objects was low and medium in sunny morning,but medium and high at other times in sunny days and cloudy days in summer.Fitting the linear equation between them,it was found that the influence weight of different adjacent ground objects on the facade temperature were different in different time periods.The stronger the solar radiation intensity,the greater the effect of leaf temperature on facade temperature.(4)In the winter,except for sunny afternoons,the heat radiation transfer law between the facade surface and the adjacent objects was the same as in summer.The correlation between the facade temperature and the surface temperature of adjacent objects was high in the sunny morning,afternoon and cloudy afternoon,medium and high in sunny night and cloudy morning,and medium and low in cloudy night.Fitting the linear equation between them,it was found that the effect of leaf temperature on facade temperature was not significant.The above research results can lay a foundation for the establishment of the tree leaf temperature model and the analysis of the influence of adjacent objects such as trees on the thermal radiation of external facades of buildings and the influence of indoor cooling and heating energy consumption.That can provide a theoretical basis for optimizing the greening method of trees around the building.