ABSTRACTThe solar air heater (SAH), which utilizes solar energy to satisfy the building’s heating demands, is an important integrated component of the building. However, SAH’s performance isn’t good enough for it to be used in building. Adding roughness component to the effective zone of heat transfer underneath the absorber plate is the most successful and efficient technique to augment the thermal performance of solar air heater (SAH). In this regards, artificial roughness consisting of several Multiple Open Trapezoidal Rib (MOTR) has been devised with intention of capitalizing on the benefits of secondary flows with regard to the improvement of heat transmission. The geometrical parameters of MOTRs such as relative limb length (L/w = 0.2–1.0), Reynold number (Re = 2000–16000), relative rib height (e/Dh = 0.023–0.054), and relative roughness pitch (p/e = 6–12) have been exploited, while relative width ratio (W/w = 6) and angle of attack (α = 60°) are maintained constant in all the set of experiments. The highest augmentation in Nusselt number (Nu) is observed as 6.07 times as that of smooth absorber plate. In addition, following empirical correlations have been developed for Nu & f with accuracy of average absolute deviation of 5.47% and 5.02%, respectively.