Linköping University Electronic Press

Unglazed transpired solar collectors are usually mounted on the side of the building that receives the most sunlight. It is a fan-assisted system; whereby air is drawn through the holes into the plenum and the warm air is then ducted into the building. The primary reason for using the unglazed transpired metal plate as the solar collector is not only to absorb the solar heat but also to reduce the convection heat loss. These in return will have higher heat exchange effectives and heating efficiency. Though many research have been carried out to study the Nusselt number correlations; heat exchange effectiveness; wind effects and pressure drop; yet only hand full of research that involved heat transfer study that including the vertical airflow in the plenum. This paper is to assess the heating performance of this system through experimental tests which involve the study of temperature rise along the vertical air flow in the plenum. Results show that the temperature of the air flowing vertically is increasing gradually from the bottom to the top of the plenum. This is contrast with the previous studies which assumed that the temperature of the air in the plenum is constant and same as the outlet air temperature at the top of the plenum. The temperature rise is increasing with solar radiation intensity. Temperature rise along the plenum contributes between 30 to 60% of the total temperature rise at a constant suction velocity. On the other hand; temperature rise is decreasing with suction velocity. Values of temperature rise along the plenum are between 30 to 50% of the total temperature rise for suction velocity of 0.03 to 0.05 ms^-1 at 600Wm^-2 of solar radiation. Therefore; this study has proved that heat transfer of vertical airflow in the plenum has a crucial heating effect.

Keywords: Unglazed transpired solar collector; Air heating; Solar façade