Development of numerical model for determination of pressure equalization in facades during wet conditions

Many building components rely on pressure equalization to achieve a good performance in respect to watertightness. Guidelines on geometrical constraints derived from numerical models and experiments are widely spread, but it appears these are only valid for dry conditions. To evaluate the impact of rain on the pressure equalization in facades, a generic experimental setup was built and results were compared with simulations. Two types of deficiencies, 4 mm and 8 mm diameter circular holes, were subjected to sinusoidal pressure loading with varying mean pressures, amplitudes, frequencies, airtightness levels, and water spray rates. A semi-implicit numerical model based on mass balance and ideal gas law was developed and validated against the results for dry conditions. Monte-Carlo sensitivity analysis on simulated pressure equalization highlights the importance of accurate leakage characterization for validation, and normally distributed input parameters entail negative skewness in the results. The difference between the measured pressure equalization in wet conditions and simulations for dry conditions shows a clear correlation with the simulated pressure equalization. As a result, the effect of a water runoff film on the pressure equalization can be accounted for in the numerical model by means of a power function. Simulations for dry conditions may overestimate pressure equalization during rain events significantly. Furthermore, the impact and importance of pressure equalization for facade design was evaluated for 6 building components. An analysis of facade components such as precast concrete panels, two types of masonry brick walls, spandrels, windows and curtain wall systems, indicates that current construction practice and guidelines render inadequate to obtain good pressure equalization.

Publication year:2020

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