Novel nanomaterials with high solar reflectance for energy efficient envelope systems.

Abstract

Exposure to weathering conditions requires selecting and applying solutions with appropriate durability to preserve façades without the need for frequent extensive rehabilitation actions. The consequent heat gain from solar radiation exposure accelerates the degradation of the most exposed façade layer, reducing their service life. An attractive solution to mitigate this overheating is the incorporation of functional nanomaterials in the façades finishing coatings, which reflect a part of the solar radiation in the near-infrared region. This solution may have an even higher influence on dark-coloured coatings, whose use has been increasing by architects and final consumers. To design more energy-efficient buildings, applying thermal insulation systems, such as External Thermal Insulation Composite Systems (ETICS), is necessary. These systems experience significant surface temperature fluctuations (amplified by the dark colour application), causing dimensional variations and naturally leading to cracking. Therefore, this Doctoral Thesis proposes a strategy combining these two façade solutions: dark-coloured finishing coatings applied on ETICS, aiming to improve solar reflectance and reduce the surface temperature. The study focused on developing new dark-coloured formulations with reflective nanomaterials, without excessively changing the visual aesthetics. A systematic study of their intrinsic properties was performed to understand and predict the nanomaterials' behaviour and ability to reflect or absorb. Subsequently, a commercial TiO2 Rutile and a newly developed nanocomposite, combining two nanomaterials, were included in a dark-coloured commercial finishing coating for ETICS and the surface properties were evaluated. The thermo-optical properties revealed an overall total reflectance increase for the two samples (15% and 20%) compared to only 12% of the non-modified finishing coating, providing a similar visual aesthetic. The reflectance improvement observed with the incorporation of nanomaterials certainly impacted the surface temperature, as the modified finishing coatings showed better performance and durability, as evidenced in the accelerated ageing test as thermal oscillations responsible for fractures are reduced. From these results, this strategy could emerge as a promising solution for low-cost dark reflective coatings that can be easily applied on building façades