Pearl luster pigments as overheating protection in transparently insulated solar façades

Abstract

Transparently insulated (TI) walls are an efficient means to reduce the heating demand of buildings. However, large scale use of TI is still not realized, basically due to overheating problems. Mechanical shading devices are expensive and may malfunction. Furthermore, the lack of acceptance from architects because of the missing color-designability remains an unsolved problem. A promising solution for both mentioned points is a coating of pearl luster pigments on the TI wall. These pigments show an angle-dependent transmittance and reflectance and their color is variable. The pigments are structured similarly to natural pearls, where the color is caused by an interference effect of multiple layers with alternating refractive indices. A model for radiation transfer in the pigments has been derived and verified experimentally. The model can be used to design pigments with tailor-made properties. Based on insolation data from the test reference year for Wuerzburg, Germany (TRY05), the ideal cut-off angle which depends on the latitude has been calculated for a middle-European location, considering direct and diffuse solar radiation. This allows to derive the energy savings potential of TI walls covered with optimized pearl luster pigments. Finally, a 1.6×2.4 m 2 glass cover, equipped with selected pigments, was installed at the ZAE test facility in Wuerzburg. These experiments show that the heat flux into the room in summer is reduced drastically and overheating can be prevented.