IASUR Conference 2014 ○ c International Alliance for Sustainable Urbanization and Regeneration Natural ventilation in High-Rise Residential buildings in Hot and Humid Climate: Malaysia as a Case Study Tareq G. FAREA PhD Student, Faculty of Built Environment, Universiti Teknologi Malaysia. Department of Architecture, Faculty of Built Environment, 81310 UTM , Johor, Malaysia; tareqgfarea@outlook.com Abubakar D. ISAH PhD Student, Faculty of Built Environment, Universiti Teknologi Malaysia. Dilshan R. OSSEN Associate Professor, Faculty of Built Environment, Universiti Teknologi Malaysia. Saqaff ALLKAFF Associate Professor, Department of Mechanical, Faculty of Engineering & Technology, Multimedia University, Malaysia . Natural ventilation is used as a passive strategy in high-rise buildings to provide the air quality and thermal comfort at the same time saving energy. This study examines the internal lightwell connection to outdoor through different horizontal voids as inlets in high-rise residential (HRR) buildings. A Computational Fluid Dynamics (CFD) technique employing ANSYS Fluent code is used to predict airflow characteristics for alternative ventilation configurations of full-scale building model. The full-scale model was developed in accordance with common configurations of high-rise residential (HRR) buildings in Kuala Lumpur as well as referring to the minimum requirements of Uniform Building By-Law (UBBL). The results show that the existence of a direct connection of the internal lightwell through horizontal void affects the air change per hour (ACH) and thermal comfort in the lightwell space and adjoining units, respectively. Although the existence of double-level voids increases ACH up to 200% along the lightwell, it reduces the air velocity by 78% in both units compared to the lightwell without direct connection. Based on the results of this study a design guideline for naturally ventilated HRR buildings was developed. Keywords: Natural Ventilation, HRR Buildings, Lightwell, Void, CFD 1. Introduction Natural ventilation is the most effective strategy in naturally ventilated buildings (Jiang and Chen, 2002; Kubota et al., 2009; Zhai, 2006). This strategy plays an important role regarding thermal comfort, air quality and thus energy saving (Kubota et al., 2009). In hot and humid climate building configuration is incorporated with a number of different types of lightwells, either in core or the perimeter of the building that allows opening of windows in different directions and thus providing cross-flow ventilation (Givoni, 1998; Nutalaya, 1999) . Building codes in some tropical countries such as Australia, Malaysia, Singapore and Hong Kong emphasized providing all habitable rooms in apartment buildings with natural ventilation. In Malaysia the Uniform Building By-Laws (UBBL) of 1984 regulates the minimum size of sky opening as outlet of internal lightwell as well as its adjoining windows to ensure natural ventilation for those rooms that are far from the external facades. However, UBBL did not stipulate the possible direct connection of the lightwell to outdoor through inlet openings such as horizontal voids which is common in practice (Farea and Ossen, 2013; Farea et al., 2012). Previous studies demonstrate that the lightwell space is subjected to produce suction effect along its space and adjoining indoor spaces (Chiang and Anh, 2012; 5-5 －354－