关键词: 天津, 原租界街区, 设计因子, 热环境, 热舒适

Abstract: Population growth and the gradual expansion of urban areas have led to the gradual deterioration of the urban outdoor thermal environment in summer. Tianjin experiences a semi-humid monsoon climate in the warm temperate zone, and has four distinct seasons, including a hot and humid summer, with a historical maximum temperature of 41.6℃. The heat-island effect in downtown Tianjin is gradually increasing and expanding. The original nine concession blocks are mostly important tourist attractions in Tianjin, which have large annual passenger flows. Therefore, the thermal environment of the Tianjin concession blocks in summer must be focused on. This study explores the differences in the thermal environment among the five typical former concession blocks, and determines the relationship between design factors, the thermal environment, and thermal comfort in these blocks. In addition, the relationship between block design factors and thermal comfort is systematically and quantitatively analyzed from the perspectives of block planning, spatial form, and the detailed design of buildings, streets, and landscapes. Based on the analysis results, corresponding improvement strategies were put forward for existing concession blocks, and relevant suggestions for similar block designs were proposed to design a better thermal environment. This is expected to provide some theoretical basis and practical guidance to improve the thermal environment after the reconstruction of existing concession blocks and implement a low-rise block design in Tianjin. Field measurements were used to obtain the thermal environmental parameters of five concession blocks. The air temperature and relative humidity were measured using a HOBO-MX2302A instrument; the instantaneous wind speed was measured using the KIMO AMI310 instrument; the black ball temperature was measured using the HQZY-1 instrument; and the street surface temperature was measured using the Fluke Ti400 infrared thermal imager. Furthermore, the physiological equivalent temperature (PET) was calculated using the Rayman software, developed by Matzarakis’s team in Germany. Since different blocks were measured on different days, the nearest weather station to the test area was chosen as the reference point, and the differences in the value of each physical quantity were analyzed. According to the analysis, the average PET increment of the former British concession block, with large vegetation coverage, is the lowest in comparison to the weather station, at only 1.20℃. The former Austro-Hungarian concession blocks, with low plant coverage, have the highest average PET increment, reaching 8.50℃. In addition, the relationship between the design factors and PET was quantitatively analyzed from the perspectives of the block design planning indicators, spatial form, and detailed design. Some conclusions could be drawn: (1) with respect to planning indicators, the greening rate of the block ranges between 0%~40%，and the PET decreases by 1.30℃ for every 10% increase in the greening rate, and increases by 1.15℃ for every 10% increase in the street percentage. (2) In terms of spatial morphology, the PET increases by 1.26℃ for every 0.10 increase in the sky-view factor (SVF) at the measuring point; the PET of the street at 49° east is the lowest. Further, its PET decreases by 0.15℃ for every 10% increase in the street aspect ratio. (3) In terms of the design details, plants, colonnade spaces, and building shading construction could reduce the outdoor temperature to a certain extent. The improvement effect of plants on PET differs due to its trimmed shape, and the difference between the same tree species can reach 1.60℃. Finally, the relationships among the block design factors, thermal environment, and thermal comfort, as well as the adjustment effect of design factors on the microclimate were clarified in this paper. Next, some specific strategies for environmental improvement were proposed based on the current scenario. In summary, relevant suggestions for the Tianjin similar block design were proposed in this paper, from the perspective of improving summer thermal comfort: (1) the greening rate of the block should not be less than 20.0%, and preferably be higher than 50.5%, and the percentage of hard streets should be less than 43.6%, with an optimum around 30.0%. (2) the SVF value of the measuring point should be as low as possible and less than 0.397; when the street orientation ranges from 49° to 56° east, the thermal environment is better than that in other orientations; the street aspect ratio should be controlled between 0.624 and 1.100. (3) In terms of the design details, plant selection and pruning shapes need to be considered. More colonnade spaces should be designed, along with overhanging building facades or overhanging roofs, and sun-shading structures with shade. Further, the water landscape can improve the thermal environment in open spaces, according to particular local conditions.

Key words: Tianjin, former concession blocks, design factors, thermal environment, thermal comfort