Wind Tunnel Assessment of the Wind Velocity Distribution on Vertical Façades

Building integrated photovoltaic/thermal (BIPV/T) systems serve two purposes – generate electricity and heat ambient air using absorbed solar energy. High wind velocity reduces the efficiency of unglazed transpired solar collectors (UTC). Indeed, wind flow on the collector’s surface reduces the useful heat transferred to the plenum air by effectuating convection losses and suction in the pores; thereby outflow from the plenum behind the collector. The present study measured the detailed wind speed distribution in front of a building wall by means of wind tunnel experiments. It was observed that indeed heat losses from the solar wall and hence, its thermal efficiency was influenced by wind direction. Assuming that the reference velocity acts uniformly throughout the surface, results in an overestimation of convective losses and underestimation of UTC thermal efficiency. The importance of using actual velocity distribution in building simulation has been discussed.