Effects of urban geometry on thermal environment in 2D street canyons: A scaled experimental study: Fid-Bau Portal

Effects of urban geometry on thermal environment in 2D street canyons: A scaled experimental study

Chen, Guanwen / Charlie Lam, Cho Kwong / Wang, Kai / Wang, Boguang / Hang, Jian / Wang, Qun / Wang, Xuemei

Abstract Changes in urban geometry significantly alters the urban microclimate. Suitable urban geometrical layouts can effectively improve the urban thermal environment to achieve a more sustainable and healthier city. A quantitative assessment of the relationship between the urban geometry and thermal environment is essential to provide scientific guidance for better urban and building design. Hence, we performed a scaled outdoor measurement to investigate the diurnal variations in air, and west and east wall temperatures within two-dimensional (2D) street canyons. We adopted the daily average temperature $\overline{T}$ , daily temperature range DTR, and hottest time $t_{m a x}$ to describe the diurnal temperature characteristics. The influence of aspect ratios was considered (building height/street width, H/W = 0.5, H = 0.5 m, and H/W = 1, 2, 3, 6, H = 1.2 m). Canyon air experienced a smaller $\overline{T}$ and DTR compared with the east and west walls. With an increase in the aspect ratio, no significant difference was observed in the $\overline{T}$ of canyon air. The east and west walls of H/W = 2, 3, and 6 experienced lower $\overline{T}$ (26.1–26.9 $°C$ ) and smaller DTR (11.7–18.4 $°C$ ) than those of H/W = 0.5, 1 ( $\overline{T}$ =26.7–28.7 $°C$ and DTR = 16.0–26.1 $°C$ ). A higher phase lag of $t_{m a x}$ occurred between H/W = 0.5, and H/W = 6. As the aspect ratio increased, the differences in $\overline{T}$ , DTR, and $t_{m a x}$ between the east and west walls decreased. This study improves our understanding of how urban morphology influences urban thermal environment and provides meaningful references for urban planning. Such high-quality experimental data can be used to validate and further improve numerical simulations and theoretical models.

Highlights • Diurnal temperature variations within 2D street canyons are studied in SOMUCH. • Impact of aspect ratios (H/W = 0.5, H = 0.5 m; H/W = 1, 2, 3, 6, H = 1.2 m) is evaluated. • FFT is applied to obtain more generalized daily temperature characteristics. • Wider street exhibits larger daily temperature range (DTR) and earlier hottest time. • Not all diurnal temperature characteristics vary linearly with the aspect ratio.