Evaluation of economic and thermal performance of closed loop solar hybrid air and water heating systems for Indian climates

Abstract

Water heating collectors lead to problems like leakage and corrosion on many occasions. Air heaters, generally, are free from corrosion and leakage is not a severe problem. Moreover, the use of plastics has reduced the price of air heating collectors. Using low cost plastic air heating collectors available in the local market, three hybrid solar air and water heating systems have been developed and studied in detail. In this paper, we derive generalized performance equations of the HWB type. Explicit expressions are obtained for the collection efficiency in terms of design parameters (system efficiency factor and overall heat loss coefficient) for air and water heating systems. The utility of the performance equations has been verified with the help of experiments conducted and a transient thermal model developed with open loop cycle and closed loop cycle. A simple techno-economic analysis is carried out for a daily consumer hot water demand with time for 400 l. at 70°C desired temperature with a storage tank of 360 l. capacity. It is found that the hybrid solar water heating systems made of locally available plastic air heaters with air/water heat exchanger are less expensive and free from corrosion and leakage problems and are more suitable than conventional air water heating systems in their performance, both technically and economically, for domestic use.