This paper challenges the common thinking within the window industry by discussing the practical application of a pressure equalized insulated glass unit (IGU) within exterior building envelopes and introduces the dynamic computer simulation model that was created to model the expected performance. The pressure equalization technology is currently envisioned as being retrofit into in-situ IGUs that exhibit visible signs of failure. Pressure equalized IGUs utilize a special device that equalizes the insulated glass cavity pressure with the exterior of the IGU under specific pressure differentials. These pressure differentials are caused by external environmental factors. By equalizing the pressure, the stresses impacting the IGU sealant material that are typically encountered within the current IGU designs are reduced, resulting in an IGU that is significantly more resistant to seal failures. Due to the exchange of air between the interior and the exterior of the IGU, the pressure equalization technology is not currently compatible with IGUs that use fill gases other than air. This consideration is less important when the technology is applied to existing failed IGUs in the field as the fill gases will have previously dissipated as the interior humidity level of the unit has increased to the point of failure of the unit.

To better understand the complex physical, thermal and moisture dynamics in failed IG systems, a software tool (WinSim, which was developed for EnviroClear Technologies by The Moisture Group Incorporated and is the proprietary property of EnviroClear Technologies) was developed. The physics behind the complex interactions taking place within insulated glass units are well known and documented, however there did not exist a simulation model that incorporated the scientific and climatic data to dynamically model the moisture conditions within these systems. In addition to the International Organization for Standardization (ISO) 15099 calculations, the model also includes dynamic interior and exterior moisture loads, a micro-climate subsystem at the sealant failure location, the effect of convection within the IGU and the impact of the desiccant. WinSim takes hourly climatic data from approximately 50 cities in the United States and Canada and allows the user to “build” the IGU to be modeled from a database containing hundreds of standard glazing components (or custom entered characteristics). WinSim produces raw data, charts and animated movies that dynamically model the thermal and moisture transport in clear glass regions on an hourly basis for both system incorporating the pressure equalization technology and standard failed IGU’s.

Variations of the pressure equalization technology have also been deployed in field trials to determine their performance within a real-world setting. The field trials have performed as predicted by WinSim, however a more detailed and rigorous instrumentation of the test IGUs will be required in order to fully validate and calibrate the WinSim outputs.

The results have shown that incorporation of the pressure equalization technology has increased the moisture tolerance of IGU units, reducing and most of the times eliminating the occurrence of condensation on the IGU glass surfaces. It is expected that subsequent generations of the technology can be climatically tuned to further improve the performance of a Pressure Equalize IGU within specific climatic zones. Of particular interest is that WinSim also demonstrates that a Pressure Equalized IGU does not require the presence of a desiccant to manage the appearance of condensation within the interior cavity and indicates that it may be possible to manufacture Pressure Equalized Insulated Glass Units that do not incorporate desiccant within the spacer system.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings X – December 2007

Units: Dual