PERFORMANCE OF A SOLAR COLLECTOR WITH DIFFERENT GLAZING MATERIALS AND THEIR DEGRADATION UNDER THE CONDITION PREVAILING IN A SOLAR COLLECTOR

The effects of different glazing materials, namely double window glass (DG), single window glass (SG) and polymethyl methacrylate (PMMA), on the performance of a 2m2 solar flat plate collector for air heating have been studied. The decrease in solar transmittance of these covers, measured between 0 and 60-degrees angles of incidence (theta-i), seems to be compensated by the corresponding increase in solar reflectances while the solar absorptances were not so sensitive to the variation of theta-i. Under identical insolation level and ambient temperature, at air flow rates between 0.014 and 0.103 kg/s, the rise in air temperature for a 2m2 collector with DG cover was 1 and 2-degrees-C higher than that of the collectors with SG and PMMA covers, respectively. At 0.100 kg/s (0.05 kg/s m2), the thermal efficiencies of the collectors with DG, SG and PMMA covers were 46.0, 42.0 and 36.5%, respectively. Long term durability of the DG and PMMA systems was poor under the conditions prevailing in a solar flat plate collector. The PMMA fitted with the collector showed a degradation when it was exposed to outdoor conditions. In consequence, the decrease in solar transmittance was a maximum within 3 months, due to the formation of low molecular weight products.