Numerical Simulation of Winter Microclimate and Thermal Comfort of an Asymmetric Canyon in the Urban Square Area

Abstract

Variable canyon building morphology and neighborhood configurations affect pedestrian habits and comfort, and cold weather limits pedestrian mobility in the city. The orientation and aspect ratio of a canyon significantly affect the thermal comfort and microclimatic conditions of outdoor pedestrians. This study evaluated thermal comfort and microclimate conditions in an asymmetric canyon (aspect ratio $\lt 0.5)$ within the East Square of Komatsu Station, Japan. The method combines ENVI-met numerical simulations and site measurements to derive thermal comfort ranges at the highest and lowest winter temperatures through the physiologically equivalent temperature (PET) thermal index. The results showed that the optimal comfort zone was on the south side of the E-W canyon, with a higher distribution of thermal comfort levels in the S-N orientation. The mean PET index was $17^{\circ}\mathrm{C}$ at the highest temperature, and it was $4.48^{\circ}\mathrm{C}$ at the lowest temperature. Meanwhile, there is a significant difference between the thermal comfort and mean radiation temperature (Tmrt) between day and night. Interestingly, the thermal comfort index PET distribution showed that the southern side of the seating area was consistent with the winter's optimal horizontal thermal comfort zone. The mean PET index was kept between $9.69^{\circ}\mathrm{C}$ and $11.77^{\circ}\mathrm{C}$, indicating that physiological stress at the moderate cold level in the asymmetric canyon (E-W direction) is challenging to maintain pedestrians' thermal balance and comfort in windy winter weather. As one of the typical urban canyon morphologies, the evaluation results of winter thermal comfort and microclimate in the asymmetric canyon will provide an important reference for the climate-sensitive design and planning of the local urban environment.