Investigation of heat transfer associated with support structures in large glass walls

The heat transfer characteristics of window glass panes, supported by mullion structures, are considered. Windows usually consist of approximately 85% glass and 15% supporting structures by area. However, because supporting structures may have high thermal conductivities, they may strongly influence the heat transfer through windows. Sometimes condensation may also occur inside the window causing aesthetically undesirable effects. Hence, an understanding of heat transfer mechanisms through windows is desirable. In this work a physical model is suggested in which a hypothesized one dimensional heat transfer is investigated in two parts. One part deals with heat transfer through the supporting mullion while the second part deals with heat transfer through the glass panes. The analysis is done using the theory of extended surfaces combined with radiation. Dimensionless parameters are introduced to enable designers to understand and use the results in practical applications. If mullion/glass wall structure is considered as a combined unit, some modifications are required for achieving efficient heat transfer. These include alteration of cross section geometry, use of alternative materials or the addition of a thermal barrier. Numerical examples are worked out to enable comparison of the theory with published experimental work. They are found to compare favorably. On this basis, some design suggestions are given