Investigation of Cool Roof based on Reflective Paints, Evaporative Cooling and Shading

Abstract

In this study, three different approaches are investigated for keeping the roof cool and reducing the heat flow inside a building located in Kanpur, India. In the first approach, various reflective paints are investigated and their performance degradation over a year is examined along with the cost-benefit analysis. In the second approach, the roof surface is kept wet and due to water evaporation, the roof was kept cool. In the third approach, the effect of shading on the rooftop surface temperature is studied. It is observed that without any cooling, the rooftop temperature can rise about 20°C above the ambient air temperature. The application of white acrylic paints can reduce this temperature rise to about 5-7°C. However, after a year due to degradation, this temperature rise is about 10-12°C. Using evaporative cooling the rooftop temperature can be lowered even below the ambient air temperature by about 3°C. However, this approach will require active management of the system and consumption of water. The cost for the first two approaches is estimated to be about 5-6 Rs./sq.ft with a payback time of 2 years. Shading can reduce the temperature rise to about 5°C. Structures meant for other purposes such as photovoltaic panels can serve the additional benefit of cooling the roof. Shading seems to be a robust and low-maintenance option and cost analysis of structures meant primarily for shading the roof needs to be explored.