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Measuring Facility for Light Transmittance and Diffusion of Condensation or Rain Covered Glazing Materials
J.G. Pieters, I.V. Pollet and S.M. De Clercq
University of Ghent, Department of Agricultural Engineering Coupure Links 653, 9000 Ghent, Belgium
Abstract
To investigate the effect of water drops on the light transmittance and diffusion of glazing materials, a new experimental unit was built. A light-tight double climate room (hot box/cold box), equipped with a temperature and humidity control system, as well as with a rain simulator, allows for the controlled production of condensation or artificial rain drops on any glazing material. By means of a parallel light source inside the cold box and an integrating sphere in the hot box, it is possible to measure the light transmittance for several glazing materials, for the several phases of the condensation/rain and evaporation process, and for several orientations of the material under investigation: vertical or inclined. Replacement of the integrating sphere with a movable photocell allows for the determination of the light diffusion by condensation or rain drops.
Preliminary results for experiments on a polyethylene film pointed out that the presence of condensation without run-off gave rise to a decrease of the light transmittance by about 25% at normal incidence. When compared to the transmittance curves for dry materials, those for wet materials were found to be less steep for incidence angles up to 60°.
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