Coupling of Solar Reflective Cool Roofing Solutions with Sub-Surface Phase Change Materials (PCM) to Avoid Condensation and Biological Growth

Cool roofs are effective solutions to counter the overheating of building roofs, inhabited spaces below and urban ar- eas in which buildings are located thanks to their capability of reflecting solar radiation. Nonetheless, the relatively low surface temperatures that they induce can cause condensation of humidity and leave the surface moistened for a long time during the day, thus, promoting the growth of bacteria, algae and other biological fouling. This can cause a quick decay of the solar reflective performance. Biological growth is countered by surface treatments, which may be toxic, forbidden in many countries and may vanish quickly. It can also be countered by lowering the thermal emittance and thus decreasing heat transfer by infrared radiation and consequently leading to night undercooling. However, this can decrease the performance of cool roofs. An alternative approach, which is ana- lyzed in this work, is to embed in the first layer below the cool roof surface a phase change material (PCM) that absorbs heat during the daytime and then releases it during nighttime. This can increase the minimum surface temperatures, reduce the occurrence of humidity condensation and biological growth. In this work, preliminary results on the coupling of a cool roof surface with a PCM sublayer are presented. Results are obtained by carrying out a theoretical investigation on commercial materials and taking into account the time and patterns of evolution of the environmental conditions.