Numerical evaluation of the thermal performance of different types of double glazing flat-plate solar air collectors

Highlights: • Different types of double glazings are applied into FPSAC. • The thermal performance of three double-glazing FPSACs is evaluated. • Vacuum-glazing FPSAC exhibits the best thermal performance. As the main source of heat loss of flat-plate solar air collectors (FPSACs), single glazing cover reduces the thermal performance of FPSAC. This situation becomes serious when the ambient temperature is low or the inlet temperature is high. A double glass cover with good thermal insulation is a good solution. This work aims to investigate the thermal performance of double glazing FPSAC at low ambient temperature and high inlet temperature. The thermal performance of four FPSACs with single glazing (Model 1), double glazing filled with air (Model 2), double glazing filled with argon (Model 3), and vacuum glazing (Model 4) as the glass cover at different ambient temperatures, different heat transfer air (HTA) inlet temperatures, and different HTA volume flow rates are studied and compared. Result demonstrates that Models 2, 3, and 4 have better thermal performance at low ambient temperature and high inlet temperature compared with Model 1. When the inlet temperature is 65 °C and ambient temperature is −10 °C, the thermal efficiencies of Models 2, 3, and 4 are 1.65, 1.72, and 2.29 times higher than that of Model 1, respectively. The efficiency factor and total heat loss coefficient of Model 4 are 0.62707 and 2.21745, respectively.