Experimental study of wind effects on unglazed transpired collectors

• Local wind velocities on a façade integrated UTC were measured in a wind tunnel.
• Wind velocities and convective heat loss across a UTC area are not uniform.
• Local velocities that affect UTCs are influenced by wind direction and surroundings.
• Maximum convective heat losses were found for winds at 45° to the UTC surface.
• An increase of 2 m/s in the wind speed reduces UTC efficiency by about 20%.

High wind velocity affects the performance of unglazed transpired collectors (UTC); indeed, wind flow on the collector’s surface reduces useful heat transferred to the collector fluid by effectuating convection losses and suction in the pores and thereby outflow from the plenum. Wind does not impinge uniformly on all points on a large area; the velocity distribution depends on wind direction and surroundings of the concerned area. The paper describes an experimental and analytical parametric study to assess the effect of wind on UTCs. Velocity measurements obtained using wind-tunnel experiments were applied to analytical models of UTC performance evaluation and were found to influence UTC performance. The assumption that a reference wind speed acts uniformly throughout the UTC area, as opposed to the more realistic non-uniform distribution, resulted in the overestimation of heat exchange effectiveness up to 50% and underestimation of convective heat transfer coefficients up to 20%. The importance of using actual velocity distribution, as opposed to an assumed uniform velocity distribution in building simulation, has been discussed.