Experimental and numerical study of heat transfer from a window with an internal Venetian blind

Abstract

For windows with internal shading devices, accurate calculations of the thermal transmittance, solar heat gain, and window surface temperature require knowledge of the heat transfer by ventilation between the room and the unclosed cavity formed between the glazing surface and the shading devices. In this study, experiments and numerical analyses (CFD) were conducted to evaluate the effects of the blind slat angle and temperature difference pattern on the airflow characteristics and heat transfer. For the airflow rates near the glass surface and the blind surface in the cavity, the airflow rates were larger as the temperature difference increased but were not significantly affected by the blind slat angle in neither experiment nor CFD. Comparing the results between the heat transfer of the experiment and CFD, the CFD trend was in line with that of the experiment. The convective heat transfer from the glass and the blind seemed to be unaffected by the slat angle. The method to estimate the heat transfer by ventilation from the unclosed cavity to the room, presented in this study, seemed to be viable. These results provide fundamental knowledge regarding window energy and surface temperature calculations for the models that have spacing between glass to shading more than 100 mm.