Authors: Pei-Jung Liu, Ying-Ming Su
With the rapid development of urban areas, urbanized population in developed countries are over 85 ％ nowadays. Urban heat island has deteriorated in cities around the world. The factors affecting both the occurrence and intensity of heat island can be classified into two categories. The first category is meteorological factors including wind speed, direction, humidity and cloud cover; the second category is urban design such as the density of built up areas and urban block width ratio. Several studies have already proven that fine urban wind environment can decrease the effect of urban heat island efficiently and improve the quality of the environment. Outdoor ventilation is an important factor for having both a healthy and a livable urban environment. Recent studies have analyzed the influence of urban geometry on micro-climate, including analyzing the influence of urban block width and building height on the direction and velocity of wind. Urban design regulates the building geometry and block width ratio; those design parameters shape good and comfort ventilation. With the use of urban design, it has become an important strategy for creating a favorable wind environment. In this study, different factors including block size, building width, block width ratio and wind direction were used to discuss the potential effect on ventilation. Typical Taiwanese blocks were used as the subject of this study through simulation. The wind field was measured by the environmental testing equipment, Testo480. Evaluation of block size, building width, block width ratio and wind direction was made under constant floor area with the help of Simulation CFD (Computational Fluid Dynamics) to adjust research methods for optimizing regional wind environment. The result of this study indicates building width has an influence on the efficiency of outdoor ventilation; improvement of the efficiency of ventilation with large block width is also shown. This study finds out that there exists a close relationship between block width, H / D value and PR value. Furthermore, this study shows a significant relationship between block geometry and outdoor comfortableness.
Keywords: Urban ventilation path, Ventilation efficiency indices, CFD,Urban parameters, Urban Designm