Natural ventilation of attic space for solar heat removal - heat and air flows along lower surface of a roof.

In a hot climate, a large amount of solar heat irradiates on a roof and it is transmitted to an occupied space beneath it through an attic. To interrupt this heat to attain a comfortable condition in the occupied space, ventilation of the attic is an important and effective measure. There are two ways of the ventilation, one is natural and the other is forces ventilation. The former measure should be considered prior to the latter from such reasons as simplicity in practice and power saving. Even though forced ventilation is applied, the natural air movement in the attic should be known to attain intended effect in forced ventilation. In this study, the air and heat movements by natural convection were searched fur with two electrically heated plates in a laboratory. The heat flux on the surface, incline angle of the plates and aperture on the top joint of the plates were variables in the experiments. The velocity and temperature measurement and flow pattern observation indicated that an aperture of an 50 mm or above this is required to evacuate the heat absorbed air and to cool the lower surface of a roof effectively.