Effect of aging and soiling on the solar reflectance of high-albedo roofing materials

High-albedo roof coatings (or “Cool coatings”) show potential to aid reflecting solar irradiation from the sun on the surface of building roofs, which in turn keeps the surface temperature of the roof low. This subsequently reduces the heat transferred into the building. However, the high-albedo surface could deteriorate overtime and gradually lose its reflectance due to the accumulation of dirt. This paper aims to investigate the effect of soot, as one of the major environmental elements that causes surface reflectance loss, on how it affects the solar reflectivity of cool coating on roof over time. In this study, cool coatings were applied on 3 different substrate materials which are common roofing construction materials; concrete, bare aluminum and coated aluminum. A laboratory setup was developed to investigate the wet deposition of soot on the surface of the material, from which a linear correlation was observed with decreasing solar reflectance and increasing soot concentration. At a soot concentration of 10 mg/m², an average drop of 15.6% in solar reflectance was observed across the 3 substrates. To identify how periods of rain would be able to wash off soot deposited on the surface of the coating, and hence restoring reflectivity of the surface, another setup was developed to mimic the rainy conditions in Singapore. The soiled surfaces was exposed to an equivalent of 3 months of extreme rainfall in Singapore, which saw an average increase in reflectivity of 5.5% from the soiled state.Bachelor of Engineering (Mechanical Engineering