Quantification Of Shade Distribution And Analysis Of Its Thermal Effect In Pedestrian Environment

During summer daytime,the amount of shade space on sidewalks directly affects thermal comfort of walking pedestrians.Therefore quantization of shade space distribution on the sidewalks plays an important role in analyzing summer thermal comfort in pedestrian environment.In particular,grasping distribution of the shaded space in which the body of a pedestrian is completely in the shade(herein called pedestrian shade space)helps to accurately analyze and evaluate thermal comfort during walking on a sidewalk.It was found that there are almost no research reports related to pedestrian shade space in the literature.Based on the above-mentioned background,this study focused on pedestrian shade space and defined the concept of pedestrian shade space.In the first part of this paper,how to quantify the distribution of pedestrian shade space in urban areas was described,and validation of the proposed quantifying method was discussed through the field study in an urban area.In the second part of this paper,an analysis method for evaluating thermal comfort in pedestrian environment was proposed based on pedestrian shade space,and effectiveness of the proposed evaluation method was validated using the measured data of the field study.Through this study,it attempted to fill the gap in the lack of evaluating thermal comfort of walking pedestrians on the sidewalks.The quantifying method of pedestrian shade space and thermal comfort evaluation method proposed in this study can play a design supporting role and provide scientific basis for city planners to design walking environment and reconstruction plan in the built area.The discussions in this paper include the following four aspects:(1)Development of a method to quantify pedestrian shade space in an urban areaThe first step of the proposed quantifying method is to obtain aerial photography and spatial data of the study area by drones or other means.The second step is to build 3D models of urban buildings and other structure from the captured spatial data,and conduct sunlight analysis based on the 3D models.The final step is to extract distribution data of pedestrian shade space on sidewalks using image processing software.(2)Validation of the proposed quantifying method of pedestrian shade spaceA drone was used to take aerial photographs of an urban area in Nanning(a southern city in China).With the image data processing software,3D scene models were automatically generated from the aerial measurement data.From the above spatial data,it can build the 3D models of main objects such as urban buildings and street trees that affect the distribution of pedestrian shade space.A 3D-model-based sunlight analysis was performed to obtain the shade distribution data in the study area,and then the image processing software was used to extract the shade space where a pedestrian is completely in the shade on the sidewalks.As a result,it validated the feasibility of the proposed method for quantifying the distribution of pedestrian shade space.(3)Development of an evaluation method for quantifying thermal comfort in pedestrian environment based on pedestrian shade spacePedestrian space on a sidewalk can be considered as a combination of shaded space(pedestrian shade space)and unshaded(sunlit)space.Because the ratio of pedestrian shade space has a strong correlation with thermal comfort of a walking pedestrian on the sidewalk,the values of a thermal comfort index(Physiologically Equivalent Temperature)in the above two spaces can be calculated at a time.Then on the sidewalk can be obtained from the correlation between the thermal sensation scale and the thermal comfort index,and thermal comfort on the sidewalk can be quantitatively evaluated in terms of the thermal comfort level.(4)Validation of the proposed method for evaluating thermal comfort in pedestrian environment based on pedestrian shade spaceA case study to validate the proposed evaluation method was conducted by taking an urban area in Nanning as the study object.Using a thermal comfort index calculation tool(Ray Man)and meteorological data for typical summer days in Nanning,the values of PET(physiologically equivalent temperature)in shaded space(pedestrian shade space)and sunlit space on each sidewalk in the study area.Then the overall PET on each sidewalk was calculated according to the ratio of the pedestrian shade space on the sidewalk.By comparing the calculated overall PET with the thermal sensation scale for Nanning,it can be obtained the thermal comfort level on each sidewalk at a time on a typical summer day.As a result,it was found that thermal comfort in pedestrian environment can be quantitatively evaluated based on the distribution data of pedestrian shade space.The results show that when people walk in the pedestrian shade space,the physiological equivalent temperature is generally in the comfort value range.However,when the temperature is high and the scattered solar radiation is strong,the human body will still feel thermally uncomfortable.