Design of energy efficient buildings is the quickest way to reduce energy consumption. The skin of the building acts as a barrier between the indoor environment and the outdoor environment. The thermal performance of a building depends upon the façade design to a large extent, ranking second to the local climatic characteristics. Potential for energy conservation exists in all building typologies, but it becomes more of a concern in energy intensive buildings such as airconditioned offices and shopping malls. This paper discusses the significance of the Overall Thermal Transfer Value (OTTV) controls as a means of enhancing energy efficiency of buildings. OTTV is a measure of heat gain into the building through the building envelope. It also acts as an index for comparing the thermal performance of buildings. The objectives and need for OTTV controls are discussed. The parameters used in calculating OTTV and therefore the need to customize OTTV calculations based on the location of the building are analyzed. The paper also discusses the OTTV standards in countries such as Singapore, Malaysia, Jamaica and Thailand. The application and calculation of OTTV for a case study building is demonstrated. The paper discusses the limitations of OTTV standards, its significance and relevance, and concludes that OTTV is one of the means of achieving energy efficiency of air conditioned buildings.

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In a hot-humid tropical climate, indoor thermal performance can be enhanced by comfort ventilation. Indoor ventilation depends upon building opening size. But risks involved in providing openings include ingress of mosquitoes and insects which thrive in the tropical climate. A practical and prevalent option to prevent insects in ventilated dwellings of the tropical, hot-humid city of Chennai, India is through the use of fly screens. Fly screens, when used over openings, prevent a certain quantum of solar radiation and wind from entering inside the rooms. Reduced direct solar radiation prevents the indoors from heating up, while reduced wind movement prevents the cross ventilation. Therefore, it is important to know the indoor thermal performance of ventilated rooms in the presence of fly screens with changing opening sizes. The criterion to evaluate indoor thermal performance in this paper is indoor air temperature. The aim of this research is to investigate the influence of fly screens on openings with varying sizes, in a naturally ventilated dwelling in the hot-humid climate of Chennai, India, during the summer period. The results of the study show that fly screens raise the indoor air temperature when openings are in the range of 100% to 35% of the room floor area. There is no significant change in the indoor air temperature when the opening sizes are less than 30% of the room floor area.