Optic-energy performance improvement of exterior paints for buildings

Several strategies to mitigate urban heat island (UHI) phenomenon have been proposed or developed, such as highly reflective envelopes of buildings and urban paving. The reduction of the temperature of a surface exposed to sunlight can be obtained by improving urban materials' solar reflectance. Directional reflective materials, and in particular retro-reflective (RR) materials have been proposed in addition to traditional diffusive cool materials. Previous studies investigated the performance of commercially available RR sheets that were typically used for street signs. The present study is aimed at investigating the performance of RR materials for building application. An exterior paint typically used in Italian cities has been provided with glass beads with different sizes. The angular reflectance of one diffusive and two retro-reflective samples is examined at three different wavelengths. The diffusive behavior is kept by the diffusive sample for the three wavelengths. The retro-reflective behavior is kept by the RR samples for low angles of incidence, for the three wavelengths. For high angles of incidence (greater than 60°) the retro-reflectivity is lost by the RR samples. The experimental characterization showed that RR materials could be effectively applied as coatings on building envelope, in order to reduce the energy trapped within the urban canopy and thus to reduce the UHI effect. Further investigations are foreseen to propose a process to produce industrial retro-reflective materials for building application.