Optimizing roof insulation for roofs with high albedo coating and radiant barriers in India

•Examined the combined effects of roof insulation, cool roofs and radiant barriers in buildings HVAC energy consumption.•Shift in point of inflexion of roof insulation with high solar reflectivity of roof.•Economic analysis to find the best return of investment for roof insulation.

To make roofs energy efficient, typically two types of techniques are followed: surface treatments (cool roofs, radiant barriers) and thermal property modifications (roof insulation). The interplay between these two techniques has been studied using energy simulations. A single storey, daytime operational, office building of 200 m2 area has been simulated for five climatic zones in India. A total of 88 different roof combinations have been studied for each climatic zone. An economic analysis using Internal Rate of Return has been performed to identify a suitable roof insulation thickness for a roof with high albedo, and radiant barrier combination. The incremental benefits in energy savings reduces by adding insulation after a limit. For a roof with albedo of 0.6 and radiant barrier emittance of 0.2, the optimized roof R-value is 0.49 m2 K/W in hot and dry and composite climates, 0.31 m2 K/W in warm and humid and temperate climates, and 1.02 m2 K/W for cold climates.