Study on Thermal Environment in Street Canyons

Observations and analysis were carried out to investigate the thermal environments in street canyons in Japan. Air temperature, relative humidity, wind velocity and temperatures of the ground surface and walls of buildings were measured at many locations in north-south and east-west streets in Yokohama City, Japan. Additionally, solar radiation and atmospheric long-wave radiation are measured at the top of a building. Based on the measured environmental factors, the thermal environment inside different street canyons is evaluated by employing the well-known two-node model for the response of a human body to the thermal environment. The radiation attacking the human body is evaluated by the same method of Vu and Asaeda (2000). Human thermal feeling is evaluated using the PMV*.

Results of the analysis using observational data show that although there are large discrepancies in results, for both north-south and east-west streets, street canyons with larger aspect ratio (the ratio between building height and road width) have better thermal environment during the day and worse thermal environment at night. It is difficult to distinguish the difference in the thermal environment for the two kinds of street canyons, but there is a slight trend that the north-south street canyons have better thermal environment during the early morning and later afternoon. However, at noon, there is a clearer dependence of PMV* on aspect ratio for east-west street canyons. Results of numerical experiments, performed by the numerical model with two-dimensional street canyons also confirm these findings. Results of the numerical model also reveal that street canyons with wind blowing along the street have much better thermal environment compared with street canyons with wind blowing cross the street, regardless of street orientation. Thus, in coastal city, with the presence of sea breeze, streets normal to the shoreline have better thermal environment than streets parallel to the shoreline.

References: Vu T.C. and T. Asaeda (2000) Influence of a Park on the Surrounding Urban Thermal Environment. Abstract of the Third Symposium on Urban Environment.