Enhancement of natural ventilation rate and attic heat gain reduction of roof solar collector using radiant barrier

Presented in this paper are the experimental results on natural ventilation flow rate enhancement and attic heat gain reduction of a roof solar collector equipped with a radiant barrier (RB). Investigation was conducted using an open ended inclined rectangular channel with an RB. The RB was used on the lower plate while the upper plate was heated with constant heat flux intensity. The channel dimensions are 1.5×0.70×0.19 m. The slope of the channel was fixed at 30° from horizontal plane. Four heat flux (190.5, 285.7, 380.9 and 476.2 W m−2) and five air gap space (3, 5, 7, 9 and 11 cm) were considered. Data analysis was made to determine the free convection heat transfer coefficient and induced airflow rate using two dimensionless parameters, viz., Nusselt number (Nu) and Reynolds number (Re). The Nu and Re   were correlated as a function of Rasin30 and channel aspect ratio defined as the ratio of air gap space to the channel length. The relations obtained were as follows: Nu=0.371Nu=0.371(Ra sin 30)0.2223(S/L)−0.0469 and Re=191.68(Rasin30)0.1213(S/L)-0.085.When compared to a conventional roof solar configuration with gypsum board on the lower part, it was observed that the use of RB increased convective heat transfer and airflow rate by about 40–50%, thereby increasing heat transfer reduction through the lower plate by about 50%. The developed correlations are useful for the design of such open-ended channels like the roof solar collector for passive ventilation of houses.