Thermochromic coatings for buildings: Preparation and assessment of potential energy savings

Cool coatings show high solar reflectance and thermal emittance and have proved to decrease the energy consumption of buildings by reducing solar heat gains. However, previous studies have demonstrated how the effect of cool coatings is limited or counterproductive during cold seasons when free solar heat gains are reflected away too. Thermochromic pigments, with their ability to change their solar reflectance at different temperatures, could reduce the heating penalties during winter while keeping the benefits of lowering the cooling demand during summer. In this work, four different thermochromic pigments have been used to create basic building paints, and their solar reflectance, thermal emissivity, and the SRI have been evaluated. A significant change of the reflectance of the four paints was registered in the visible range, with a maximum variation of 0.37. The near-infrared reflectance was high during both colored and colorless phases; therefore, a high solar reflectance was registered even in the colored phase. To evaluate the potential energy benefits of thermochromic paints, an office building in downtown Toronto (Ontario) and the surrounding area have been modeled in Energy Plus. Four scenarios have been simulated with conventional, cool, and thermochromic coatings applied on the roof and facades of the building. Thermochromic paints have provided an 8.9% decrease in the cooling demand while limiting the heating penalties to 1.7%, compared to the 2.6% resulted using cool coatings. Despite the limited heating penalties, the overall annual energy demand of the case study building was similar, as the prolonged and severe winter of Toronto nullifies the benefits obtained during the cooling period. Similar results were obtained when the inter-building effects were taken into account. However, the evaluation of the climate change impact evaluated using a future weather file proved the beneficial effect of thermochromic paints in a more temperate climate.