Near-infrared reflective coatings for cool roof applications

Cool roofs can mitigate the growing Urban Heat Island effect as well as the increasing energy consumption for air conditioning. By reflecting the solar radiation very efficiently the amount of energy absorbed by the building can be minimized making the interior of the building cooler.

White roofs are already able to reflect high amounts of solar energy. As many homeowners prefer nonwhite roofs, there is a need for cool colored roofs. The purpose of this project is to develop coatings for tiles which reflect high amounts of invisible near-infrared (NIR) sunlight while keeping the same spectral response of traditional tiles or being transparent in the visible region. Taking into account that the sun emits about 58% of its energy as NIR radiation, a significant improvement in building passive cooling can be achieved, even for dark colors.

In particular, this project deals with the preparation and investigation of NIR reflecting coatings by adding appropriate “cool” nanopigments. This pigments could be new inorganic colored nanopigments, which offer improved NIR-reflecting capabilities while keeping the optical properties in the visible spectrum unchanged. Another kind of promising particles for that purpose could be highly doped transparent conductive oxides (TCOs), which are transparent to visible light but still NIR-reflective.

The desired properties are planned to be achieved by tuning the crystal size and distribution of selected nanostructured oxides, as well as by choosing suitable doping materials and ratios. The developed coatings are examined for their IR reflectance properties, surface temperature and the thermal emission to evaluate the effect of different pigments/particles, binders and coating thicknesses. The results are compared to coatings prepared with commercially available pigments.