Evaluierung der Effizienz von IR-remittierenden Beschichtungen

Abstract

Coatings reflecting solar energy, so-called "cool" coatings, attract high interest inscience and technology due to their ability to save energy for cooling of devices and constructions covered by such coatings. Of a special interest are new applications of cool coatings in automotive industry due to the possibility for saving energy on air conditioning and reduction of emission of C02. lt is of relevance to apply solar light reflecting coatings for E-mobility cars considering their limited energy resources. Reduction of surface temperature can be achieved by increasing solar reflectance and thermal emission of energy. in order not to restriet the colour range, the solar reflectance in the near infrared (NIR) range is most important, which covers one half of the power of the total solar irradiation. Special NIR reflective and NIR transparent pigments are emerging into the market that can be incorporated in coating materials. lnvestigation of the heat transport by IR reflective coatings du ring solar irradiation of the surface gives a possibility to simulate heating of a substrate exposed to sun. This can be applied for Simulation of heating of a car body by the solar radiation. Cool paint material compositions were developed and prepared by dispersion of IR reflective pigments in the base coat material applied in automotive industry. A special set-up was developed to analyse the effect of IR reflective coatings on heating of a substrate under solar irradiation. One of the most important tasks in the application of IR reflective coatings is their characterisation and correct selection of pigments. To evaluate cool coatings, usually the value of Total Solar Reflectance (TSR) is used. The TSR value is calculated by integration of the reflectance spectra. Considering that the "cooling" effect of coatings is aimed in decreasing temperature of the substrate, changes in temperature of the substrate during coatings exposure to solar light were analysed. The kinetics was investigated based on the temperature profiles against time. The heat uptake by cool coatings was compared with that by carbon black coatings imitating absolute black body. Cool and carbon black containing coatings with and without a clear coat were evaluated to investigate the effect of clear coats related to conventional coatings in automotive industry on the heat uptake. lt is proposed to evaluate the "cooling" efficiency by the amount of heat taken up by cool coatings compared to coatings filled with carbon black. A new method for the evaluation of the efficiency of IR light reflective coatings was developed and discussed. The efficiency of some commercial pigments was evaluated using the proposed approach