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.