Geoola, F., Institute of Agricultural Engineering, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Kashti, Y., Institute of Agricultural Engineering, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel
Peiper, U.M., Institute of Agricultural Engineering, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel

An experimental model greenhouse for investigating of solar radiation transmission and aging of cladding materials in general, and of materials with anti-drop additives in particular, was designed and constructed. The experimental greenhouse comprising 18 identical sections was covered by corrugated polycarbonate sheets (CPS), of different types. The experimental greenhouse was mounted on a turntable and could be turned to compensate for changes in surface azimuth angle of the sun rays, allowing normal solar radiation transmissivity measurements at any time. The intensity of radiation after passing through the material was not uniform and changed over the cross section of the sheets. Therefore the radiation intensity under the sheets was measured continuously while the measuring device (pyranometer) was traveling under the sheets. Comparisons of radiation transmission in a dry state and in a wet state (under condensation) of five types of CPS revealed that all CPS with anti-drop layer have almost the same transmissivity in wet and dry states. The CPS with no anti-drop layer has approximately 10% lower transmission in the wet state than in the dry state of the sheet.