| dc.description.abstract | Urbanization has changed the original underlying surface, transforming natural vegetation into an artificial impermeable surface, greatly affecting energy balance and material exchange near the ground, and creating a unique urban climate. The morphology of cities can have a significant impact on local microclimates, which in turn affects the thermal comfort of the region. The relationship between urban thermal comfort and urban morphology is complex and multifaceted. Urban street canyons, as the basic unit of urban form, have a significant impact on indoor and outdoor microclimate, human thermal comfort, and energy consumption of urban buildings. Understanding this relationship is important for designing sustainable and livable cities. Previous research has focused on small areas such as neighborhoods and parks due to the large data sample size, with limited research on urban street canyon areas. This study aims to explore the distribution of thermal comfort in urban street canyons, based on existing research on the estimation model of mean radiation temperature and the acquisition of bulk data and calculation. In the Xi'an area, research was conducted on the verification and optimization of the estimation model and the impact of urban form on the distribution of thermal comfort in street canyons with the following results:
(1) In quantifying outdoor thermal comfort in urban areas, the mean radiant temperature (MRT), which objectively reflects the multi-spectral radiation heat flux from the environment, is taken as the starting point, and a predicted model for mean radiant temperature considering the influence of vegetation is proposed. The model is compared and verified using field measurement data, and the results show that the improved MRT prediction model has a good consistency with the observation results. Compared to the prediction model that only considers a single impermeable surface, the RMSE is increased from 5.15 °C to 3.87 °C, and the R2 of the model is increased from 0.72 to 0.74, which can better reflect the trend of MRT and is more suitable for complex and changing urban streets.
(2) Considering the large amount of data within the study area, the outdoor thermal comfort index UTCI (Universal thermal climate index), which is more applicable, is selected, and a calculation process for batch acquisition of urban street canyon thermal comfort is developed through self-programming, combined with the improved average radiant temperature prediction model. This process is used to obtain the distribution of thermal comfort at 35,763 street canyon sample points in the main urban area (inside the ring expressway) of Xi'an during a typical high temperature heat wave period in 2021.
(3) The average UTCI spatial-temporal distribution in Xi'an was obtained through spatial interpolation, and the results showed that the urban morphology had a significant impact on the distribution of street thermal comfort. In the densely populated city center, the thermal comfort was significantly better due to the mutual shading of buildings and vegetation compared to highways and out-of-town main roads.
(4) Using the number of uncomfortable hours as an indicator to evaluate street thermal comfort, the influence of street direction and width on the distribution of street thermal comfort was studied. The results showed that the hourly change in street thermal comfort during the high temperature heat wave mainly depends on the solar trajectory, and the differences in thermal comfort levels between different streets are not significant. The streets facing north and south had significantly higher street thermal comfort than the east and west ones from 10:00 to 12:00, but the difference was not significant at other times. Overall, the number of uncomfortable hours is mainly concentrated between 10:00 and 17:00.
(5) The distribution of two basic urban form parameters (building density and average building height) in the main urban area of Xi'an (inside the ring expressway) was obtained and analyzed, and the distribution of street thermal comfort in the main urban area of Xi'an (inside the ring expressway) was studied in combination with the calculation of thermal comfort. The results showed that the correlation between building density and street thermal comfort is relatively high, especially for the north-south direction, showing a high negative correlation. Although the average building height has a low correlation, it also shows a similar pattern.
Keywords: thermal comfort, urban morphology, panorama images, street canyon. | |