Characteristics of ventilation channel and ventilation efficiency assessment: A case study of main built-up area in Guangzhou

This paper attempts to explore the feature and efficiency of the ventilation channel in the main built-up area of Guangzhou, one of the four first-tier cities in China. Building groups were simplified and then the centerlines of open areas were sketched out, and finally proceeded to the identification of the ventilation channels. Data of hourly wind direction and velocity of the year 2016 were used. Indicators based on GIS for measuring the physical and thermal properties of ventilation channels were proposed, which facilitate the analysis of the characteristics of the ventilation channels and the evaluation of their efficiency. The results show that: (1) There are 2451 potential ventilation channel centerlines at a 40-m resolution, when composed, 142 meet the standard of ventilation channel. The total ventilation area reached 96.49 km2, accounting for 21.59% of the study area. (2) Centering around the Pearl River New Town, the potential ventilation network in the study area presents dense-sparse-dense concentric characteristics, and inclines slightly to the northeast direction. The ventilation area of the old town is relatively limited. The width-height ratio of ventilation channel in the Pearl River New Town is 6.54 while in wetland area it reaches the highest to 74.43, illustrating that width-height ratio among different districts varies greatly. Green lands and waters cover more than 90% of the ventilation area of the peripheral region outside the main urban area. (3) According to the similarity in spatial distribution of direction efficiency, there exist three patterns: spring, summer and autumn/winter. In line with the seasonal variation rule of efficiency, three categories of ventilation channel are classified: perennial paths, seasonal paths, and communication paths. The result of seasonal ventilation efficiency assessment shows that autumn outperforms winter which outperforms spring which outperforms summer (autumn > winter > spring > summer). (4) Regarding retardation degree, the contribution of overpassing bridge is two times and ever higher than that of street trees. The maximum retardation in the study area is 4.70 m3/m2 and most of the high retardation values concentrated west of the study area, especially around Sanyuanli where high-density overpassing bridges exist. © 2021, Science Press. All right reserved.