Theoretical evaluation of energy performance achieved by cool paints for dense urban environment
Résumé
In this paper a case study of building cooling-load reduction in a street canyon is studied. According to Synnefa (2005) and Levinson et Al (2006) ``cool'' paintings can be designed with a specific high reflectance and emittance in the entire solar spectrum (UV, VIS, NIR). Extensive studies showed that their surface temperatures are lower than that of traditional coatings. A parametric study is undertaken in the aim to assess the optimum properties values to achieve the best energetic balance over a complete year in a specific location. The examined paintings and their optical properties are chosen from a non-exhaustive bibliography about these new materials. The performance of this technical solution applied to street surfaces is calculated through a tool considering the climate and urban structures interactions. Microclimate at street scale is coupled with the building envelope and indoor environment thanks to a zonal model (Bozonnet 2005). The phenomena modelled and responsible for the heat and mass transfers are prevailing winds, thermal radiation, thermal transfers between the indoor environment and the envelope. The basis of the zonal model is modified to focus on the main parameters such as emissivity, reflectivity, surface orientations, height to width ratio, and load reduction efficiency according to the painted surface (wall, sidewalk, roof, one painted street canyon side). The assessed effects on temperature reductions can make these paintings a cheap means for energetic renovation in order to mitigate the urban heat-island effect.