La prestazione ottico-radiativa nel tempo dell'involucro edilizio: esposizione naturale in ambiente urbano, e invecchiamento e sporcamento accelerato in laboratorio - Building envelope's optical-radiative performance over time: natural exposure in urban environments, and accelerated weathering and soiling

Ageing processes as material weathering, dirt deposition and biological growth, modify the optical and radiative response of building envelopes. Weathering and soiling are generally not considered in building energy simulation standards and the solar reflectance values of building surfaces at initial time are generally utilized during the whole simulation time. Herein we present the results of a natural exposure programme in Roma and Milano. We exposed 7 single-ply roofing membranes, of which we measured the UV-Vis-NIR reflectance at time zero, and at 3, 6, 12, and 18 months of ageing. For high albedo membranes (initial solar reflectance greater than 0.80), after 18 months years of natural exposure in Milan, we observe absolute losses of solar reflectance in average equal to 0.20, and of 0.17 in Roma. We set up a modified procedure for accelerated weathering and soiling, starting from the protocol developed by Lawrence Berkeley National Laboratory (LBNL) and that is able to reproduce the UV-Vis-NIR natural exposure spectra to within 0.02 for most of tested products.