Experimental determination of comfort benefits from cool-roof application to an un-conditioned building in India

Increasing roof reflectance reduces absorption of solar radiation, roof surface temperatures, and heat flux in the building interior. At the building level this leads to savings in air-conditioning energy consumption and increase in indoor comfort. At the macro level it helps in mitigating Urban Heat Island effect and reduces net solar radiation absorbed by the earth, lowering local air temperature and pollutant formation, and reducing global warming. Various studies have demonstrated energy savings in buildings using cool roofs. However, there are not many studies on the indoor comfort benefits of cool roofs for unconditioned interior spaces, especially in India. A study was performed on an un-conditioned, institutional building in a composite climate in India. Monitoring was performed for a period of six months (Jan – Jun, 2012) on two adjacent sections of continuous concrete roof surface, one of which had been previously coated with a white paint coating. The measured shortwave band-averaged (0.3-3 micron) solar reflectance was 0.28 and 0.57, for the uncoated and coated surfaces, respectively. The increased reflectivity reduced the seasonal average indoor air temperature and heat flux by 1.07oC, and 14.4 W m-2, respectively, with peak reductions of 1.38oC and 18.3 Wm-2 in April, 2012. This increased the number of adaptive comfort hours by 80 hours (about 8%), providing a significant improvement in human comfort.