Quantifying the Benefit of Venting Glazed Spandrels to Reduce Breakage and Control Moisture

While venting glazed spandrels is cited to be a benefit to control heat buildup, several instances of spontaneous glass breakage in spandrel insulated glazing units, attributed to thermal stress, have been reported in vented spandrel cavities used with an opacifier on the inside glass surface. The implication is that if venting is not an effective solution to reduce thermal stress and the associated need for higher strength glass, then it is desirable not to vent to avoid dirt buildup on the inside glass surface as it cannot be cleaned. The benefit of venting or weep holes must also be evaluated in terms of condensation risk and damage.

The objective of this paper is to address questions related to the real need to vent spandrel sections to control heat buildup. This paper covers a field study that includes monitoring spandrel sections with a combination of single- and double-glazing, three different venting scenarios, and both clear- and opacified-glass scenarios. The data collected will be used to calibrate 3-D thermal and CFD simulations. The computer simulations will allow for cross-validation of the field monitoring data and broaden the relevance of the findings through the investigation of other conditions including different spandrel designs, venting scenarios, and climates.

The field monitoring suggests that venting the spandrel cavity has little to no impact on reducing thermal stress in clear-glass double-glazed spandrel sections, and a limited impact in clear-glass single-glazed spandrel sections. With the higher solar absorption associated with an opacifier coating, venting shows even less impact on reducing thermal stress, with some data suggesting an adverse effect. Also, in the temperate climate of this field study, the condensation risk was found to be very low regardless of the venting configuration. Based on these preliminary results, there is reason to question the need to vent double-glazed spandrel sections. The 3-D thermal and CFD model is currently being calibrated and findings will be presented in a subsequent paper. Preliminary simulations results show good agreement with the field monitoring data.

Author: Julien Schwartz, Patrick Roppel, Stephane Hoffman, Neil Norris

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