Wind effects on the performance of solar collectors on rectangular flat roofs: A wind tunnel study

Wind induced convection is the main cause of heat loss for roof-mounted solar collectors. In this study the importance of using the actual wind velocity distributions over the whole roof area, instead of a commonly assumed single velocity of a reference location, is addressed through experimental measurements and numerical assessment of the performance of solar collectors placed on different locations over the roof of a typical rectangular building. The measurements were carried out at the Boundary Layer Wind Tunnel of Concordia University, for nine different locations on the roof, three different wind directions and cases concerning both an isolated building and a building with surroundings of various configurations. For the isolated building case, it was found that local velocities on different roof locations may vary more than 60% and the effect of these differences on the performance of solar collectors placed on these locations was assessed. In an attempt to generalize the results, 17 different surrounding configurations were considered. For a typical day in Montreal (with 4-7 m/s average wind speed), it was found that the thermal gains between solar collectors at different locations over the same roof could vary up to 21%.