www.sciencetarget.com International Journal of Environment and Sustainability [IJES] ISSN 1927-9566 Vol. 7 No. 2, pp. 41-56 (2018) Analysis of Cool Roof Passive Techniques for Residential Buildings in a Subtropical Humid Climate Megha Jain 1 and Krishna Kant Pathak 2* 1 Department of Civil and Environmental Engineering., NITTTR, Bhopal, India 2 Department of Civil Engineering, IIT (BHU), Varanasi, UP, India Abstract. The objective of this study was to provide the thermal comfort by means of passive cool solar reflective materials which have a high solar reflec- tance and high thermal emittance on the existing roof and thereby reducing the consumption of electrical energy. Experiments were performed by using locally available solar reflective materials to insulate the roofs. In this work, the thermal performance of concrete roof and asbestos sheet roof with and without insula- tion has been analyzed by performing experiments to existing buildings. The re- sults are verified by computer simulation using Computational Fluid Dynamics tools with FLUENT software. The result of using solar reflective paint with high reflective coating shows a fall of 4.8°C in peak hours and saves 303 kWh when considering an energy load with an air conditioner in the summer season, in comparison to non-insulated pitched and flat roof energy loads of residential buildings in Bhopal. An optimum solution of an insulator for both types of roofs is presented. The application is intended for low-rise or medium- rise residential buildings in a subtropical climate like Bhopal. *Correspondence: Keywords. passive cooling, cool roof, thermal comfort, insulators, subtropical climate kkpathak.civ@itbhu.ac.in Introduction Despite the declaration of various schemes, the residential buildings in India have been experi- encing an unusual increase in the frequency of power outage. Figures available with the Central Electricity Authority (CEA, 2016) show that dur- ing the summer of 2016, the peak demand in In- dia was 159,542 megawatt (MW), but only 156,934 MW of it was met. Thus, during last sum- mer, there was a peak deficit of 1.6%. This growth in demand for electricity in the summer is due to the increased use of mechanical equip- ment for thermal comfort (Yeretzian and Visser, 2013). It is concluded in many research papers that one of the ways of reducing energy generation is to reduce the demand for air conditioning (Akbari et al., 1998; Ferreira and Prado, 2005; Yeretzian and Visser, 2013). Engineers and architects should investigate more in researching different passive and active strategies to reach the best possible solution for thermal comfort. This can be done by using less energy and by natural cli- matic control for their buildings instead of rely- ing on machines for cooling which are electricity dependent, and take part in ruining the environ- ment (Yeretzian and Visser, 2013). Mainly in summer, thermal comfort is always the main concern in subtropical climate regions like Bhopal. Passive cooling and natural ventilation have traditionally been two important features in the city of nawabs. To achieve thermal indoor comfort, vernacular architecture can be seen in old monuments of Bhopal. Using insulators with good thermal resistance for roofs, either during the designing and con- struction of the building, or during renovation, are usually more cost-effective and can reduce a considerable amount of the energy that is con- sumed in cooling (Boixo et al., 2012; Synnefa et al., 2007; and Synnefa et al., 2010). Cool roofs by applying insulators in the form of solar reflective