Performance studies on solar concrete collectors

Abstract

This article presents performance studies on solar concrete collectors used for providing domestic hot water. Although they are less efficient, such collectors integrated with building structures are likely to be more cost effective than conventional flat-plate collectors using metallic absorber plates. The collectors are made up of thin concrete slabs with a network of PVC (polyvinyl chloride) tubes embedded inside the concrete. A layer of galvanized iron wiremesh on either side of the PVC tubes provides the necessary reinforcement to the concrete. The top of the slab in painted black and glazed, while the back insulation is made out of autoclave cellular concrete. Collectors with tube spacing varying from 6 to 15 cm have been cast and tested for different flow rates and inlet fluid temperatures. Of the collectors tested, it has been found that the collector with a pitch of 6 cm gives the best performance at a flow rate of 0.02 l/s per square meter of collector absorber area. Typically the daily efficiency of such a collector is about 37% for an inlet temperature of about 50°C, daily solar insolation of 23.8 MJ/m 2 and an average ambient temperature of 34°C. The pressure drop across the collector has also been measured and is found to be less than that of a conventional collector. Concrete strength measurements show that the wiremesh reinforcement provides sufficient strength to withstand handling stresses.