On the evaluation of visual performances of obstructed glass panes

Michele Zinzi, ENEA Ente Nazionale Energia e Ambiente Giuseppe Rossi, IEN Istituto Tecnico Nazionale Galileo Ferraris Paola Iacomussi, IEN Istituto Tecnico Nazionale Galileo Ferraris Giacomo Zangiacomi, Stazione Sperimentale del Vetro

The glass industry is oriented towards the production of always new materials, sometimes to improve the performances of transparent systems, sometimes to improve their aesthetics and building envelopes. Obstructed glazings can be used for both functions, in fact reducing the amount of solar radiation transmitted by the transparent system, they can avoidoverheating and glare for users, as well as lower cooling loads for the air conditioning. At the same time, they can be used by architects for innovative fagade solutions in buildings.

Even if the light and energy performance must be evaluated according to the relevant European and international standards, some more information should be submitted to the public for a more comprehensive evaluation of the product. One important issue is the obstruction of the view through the transparent system cause by the obstructions, which can be printed on the glass or put down on a plastic layer successively laminated between two glass sheets.

In this paper a complete light and visual characterization of some of such innovative products is presented. In particular the angular hemispherical and the bi-directional transmittance are measured with two experimental facilities. The view-through index, as defined in the REVIS project, is calculated. An innovative method, whose methodology is still at a preliminary stage, to evaluate the quality of vision is then presented. Such method is based on the analysis of images collected by CCD detector and successive mathematical evaluation. If after subjective tests this correlation will be enough accurate an alternative and comparable measurement procedure might be proposed.