Analysis of fluid flow and heat transfer characteristics in multiple glazing roofs with a special emphasis on the thermal performance

Abstract

This study aims to investigate the effect of air layer thickness, glass coating emissivity and number of panes on the flow and heat transfer characteristics in glazing roof and evaluate thermal performance of glazing roof in terms of overall heat transfer coefficient and inner surface temperature. A conjugate heat transfer analysis including radiative heat transfer is conducted considering different emissivity values and air gap values available in the market for double, triple and quadruple pane windows. Computational results show that a progressive improvement is achieved by adding more panes or decreasing surface emissivity. However, increasing air layer thickness may promote heat transfer considerably which defeats the purpose. The-best thermal insulation performance is achieved with-the air gap width of 9 mm for all the cases considered while the poorest performance is obtained with the gap width of 6 mm or 15 mm depending on the number of panes. By using quadruple pane windows, coating the glass surfaces with low emissivity materials and optimizing air gap, the U-value can be reduced down to 0.77 W/(m2 K) providing a great amount of energy saving potential (up to 71%). Besides, the inner surface temperature of window approaches to the indoor temperature which enhances thermal comfort.