Abstract

The most common technology available for harnessing solar energy is flat-plate solar collectors and photovoltaics. Among the various parameters affecting the energy performance of solar collectors, convective heat losses depend greatly on the effect of wind and its cooling effects. Knowledge of wind heat transfer coefficient hw, is required for the estimation of upward losses from the outer surface of flat-plate solar collectors. Furthermore, the wind speed at the location of the collector should be known.
A series of velocity measurements have been conducted at the Concordia University Building Aerodynamics Laboratory to assess the optimum location of a flat-plate solar collector on the roof of a building model. Wind velocity measurements were performed at nine different locations above the roof and for three different wind directions (0°, 45°, and 90°). The building was assumed to be on an open country simulated upstream terrain. A series of additional cases with the model surrounded by different adjacent structures of variable height were also tested. The forced convective heat transfer coefficient hw was correlated against the measured local wind speed Vloc and direction. The study found that local velocities on different roof locations can vary up to 62% for the same wind direction.
An analytical approach of a performance simulation model has been used to calculate the efficiency and the useful heat gain of a flat-plate single-glazed collector. The analysis has been conducted for hypothetical days with constant wind velocities and directions but also for an example actual day, typical of random wind velocity values. The wind impact on a flat-plate solar collector’s performance characteristics when placed on different locations of the roof of a building model was assessed. It was estimated that for a typical sunny day, thermal energy gains can be 17% higher on windward than leeward locations.