NIR reflective Paints as an Alternative for Sustainable Façade Renovation

Abstract

Several studies of infrared reflective materials used on opaque envelopes have shown that their application can reduce the surface temperature and the cooling energy needs of buildings and help mitigate the urban heat island effect. Some of these studies were carried out by incorporating near-infrared (NIR) reflective materials on new buildings or as part of new construction systems, considering that one of the simpler and most used façade renovation methods is repainting. In a repainting process, the reflectance could change since the reflectance depends on the interaction between the reflective layer and the substrate. A study was carried out on the reflectance of paints with NIR reflective properties applied on the finishing coat of external thermal insulation composite systems (ETICS), simulating a façade renovation. A black NIR reflective paint was applied in one layer over the existing finishing coat of two ETICS samples: one with a grey mortar colour and another with a conventional black colour. A second configuration was considered by adding an intermediate layer of regularisation with white colour. Traditional black colour and the mortars were applied on a transparent acrylic base as a reference. The samples were assessed with a modular spectrophotometer to assess the total and NIR reflectance and the colour coordinates on the CIELab space. The results showed that the reflectance and colour of the new layer are independent of the colour or type of the first layer in the case of conventional paint. Conversely, the substrate affects the NIR paint performance, where a lighter substrate can help improve the reflectance but can also lead to a more significant colour change. Likewise, the results of the paint over a new white layer resulted in a lower reflectance compared to the reflectance of a single paint layer.