Natural ventilation assessment in typical open and semi-open urban environments under various wind directions

Five semi-open roof types are studied: Walls being hung above street roofs (coverage ratio λa = 100%) at z = 1.5H, 1.2H, 1.1H ('Hung1.5H', 'Hung1.2H', 'Hung1.1H' types); Walls partly covering street roofs (λa = 80%) at z = H ('Partly-covered' type); Walls fully covering street roofs (λa = 100%) at z = H ('Fully-covered' type). They basically obtain worse UCL ventilation than open street roof type due to the decreased roof ventilation. 'Hung1.1H', 'Hung1.2H', 'Hung1.5H' types are better designs than 'Fully-covered' and 'Partly-covered' types. Greater urban size contains larger UCL volume and requires longer time to ventilate. The methodologies and ventilation indices are confirmed effective to quantify UCL ventilation.