Experimental comparison of evacuated tube solar air heater based on energy and exergy analyses with environmental and economic (4-E) study

For the purpose of low-medium air heating applications like timber seasoning, HVAC, agricultural & food drying, space heating and desalination, there is requirement of hot air. Solar air heaters are the promising systems to satisfy these requirements in a very inexpensive manner. Due to higher efficiency at higher operating temperature and lower cost, evacuated tube collectors (ETCs) are preferred for solar air heating. In this manuscript, the comparative parametric study of two similar sets of evacuated tube solar air heater (ETSAH) is performed. The comparison is based on energy & exergy analyses, and also presents the environmental and economic study (4E analyses). Each set is fabricated using mild steel (M.S.) along with 50 evacuated tubes with total collector area of 8.46 m2. The experimental investigations are made at diverse flow rates, with and without using conventional reflectors. Without incorporating any additional heat storage unit, the system provides average hot air temperature of 76.13 degrees C when average solar intensity was 502.68 W/m(2) during 11 h of operation from 09:00 to 20:00 h. ETC's absorber glass and the M.S. material was observed to have significant energy storage and discharge. The single set of ETSAH has CO2 mitigation of 89.20 tons with 2.05 years of energy payback period, which is significantly low as compared to its 20 years of lifespan. For the optimum system performance the cost of generated hot air is 0.00048 $/kg, which is considerably low.