Research And Application Of Thermal Comfort In Hangzhou Green Avenue

With urbanization increasing,the natural underlying surface of the city has been changed.The balance of material and energy near the ground in the urban area has been destroyed,which has led to environmental problems such as the heat island effect,seriously damage the physical condition and thermal comfort of urban residents.As the basic building block of urban outdoor space,the urban green avenues are the most closely related to residents in urban road types.Through the study of the thermal comfort of green avenue in Hangzhou,the optimization application strategy of green avenue is proposed.Accordingly,the microclimate environment in green avenue and the overall thermal environment quality of the city both can be improved.This paper mainly uses two methods to study the thermal comfort of the avenue:field measurement and simulation.Field measurement method:in this method,seven green avenues in a typical and similar external environment in the main urban area of Hangzhou were selected.At the end of July,the microclimate factors in the street:air temperature and relative humidity,black ball temperature,wind speed,and solar radiation intensity were measured.In order to avoid a single deviation of the evaluation indicators,wet bulb globe temperature?WBGT?,mean radiant temperature(T_mrt)and physiological equivalent temperature?PET?were all used as thermal comfort evaluation indicators.The simulation method:using ENVI-met to simulate 6 common street trees,and then other tree species with better improvement in thermal environment were obtained.Through Sketchup and Eco-tect to simulate the different orientations of different green avenues,the shading effect caused by the planting distance of the street trees is changed,and the optimal planting distance of different street trees is obtained at different orientations.The results show:compared with the control point,the WBGT,T_mrt,and PET in the green avenue are significantly reduced,and the thermal environment is significantly improved.The street orientation and aspect ratio in the green avenue structure have a significant impact on the thermal environment.In the same orientation of the green avenue with same street trees,the linear regression equation of the aspect ratio and WBGT is:WBGT=-1.605X+33.341?X is the aspect ratio H/W,the same below?;The linear regression equation for the aspect ratio and the mean radiant temperature?Tmrt?is:Tmrt=-2.35X+40.285;The linear regression equation for the aspect ratio and the physiological equivalent temperature?PET?is:PET=-1.1X+36.01.Considering orientation of green avenue,the thermal environment from the N-S is better than the E-W trend,and the contribution of orientation to the thermal environment is better than the aspect ratio.According to the measured results,it is suitable for the Hangzhou area in summer,and the tree species that provide better heat and comfort is Platanus acerifolia.The order from superior to inferior is:Platanus acerifolia>Cinnamomum camphora>Sapindus mukorossi.According to the simulation results,considering the thermal comfort evaluation index,the order from superior to inferior of the tree species is:Pterocarya stenoptera>Platanus acerifolia>Koelreuteria bipinnata>Albizia julibrissin>Ligustrum lucidum>Ginkgo biloba.In the planting distance simulation,when adult Platanus acerifolia is used as the street tree,the optimal plant distance is 8m.In all orientation of the green avenues,the shade area can cover the intercropping area and reduce the strong sunshine in the avenue.In the NE-SW oriented avenue,the planting distance can be appropriately expanded to 10m,which can ensure the continuous shade during the strongest time of sunshine in a day.In the avenue with adult Cinnamomum camphora as the street tree,the optimal plant distance is 6m,which is suitable for all orientation of the green avenues;when the green avenue is NE-SW,the planting distance can be appropriately expanded to 8m.Conclusion:In the optimization of green avenue structure,choosing the N-S direction as much as possible,and increasing the street aspect ratio is important.In tree species optimization,umbrella-shaped trees with high plant height,large crown width and high leaf area index,such as Platanus acerifolia,Pterocarya stenoptera,Koelreuteria bipinnata,and Albizia julibrissin,can be selected to enrich the types of street trees in the green avenue.In plant spacing optimization,the continuity of the shading in the strong sunshine period is ensured according to the simulation results.The research results can not only provide a scientific basis for the optimization strategy of the pedestrian tree in the avenues of Hangzhou and even East China under the principle of“people-oriented”,and improve the scientific of urban avenues construction,but also better guide the planning and design of street green space in urban green space system.The study provides residents with a more comfortable and safe urban thermal environment,achieving sustainable development.