As wind-driven rain (WDR) is one of the most important moisture sources for a building envelope, a reliable prediction of the WDR and runoff load is a prerequisite to assess the durability of building facade components. Current state-of-the-art Heat Air and Moisture (HAM) models neglect the influence of runoff. This study contributes to research efforts to develop models that combine state-of-the-art HAM models with a runoff model. It incorporates excess water that is present at the surface of the material in the form of a runoff layer. Available models for runoff on porous materials are however insufficiently validated. Therefore the experimental part of the present study focuses on collecting a dataset containing WDR intensities and corresponding runoff flow rates on the southwest facade of a medium-rise building.

For experimental analysis, four modules with known cladding material with incorporated WDR and runoff gauges were mounted on the facade. The gauges are linked to pressure sensors measuring the supplied WDR and runoff every 10 seconds. The dataset is supplemented with detailed meteorological measurements. The results of a first measurement campaign and a comparison between measurements and numerical results of a runoff model for a single rain event point out that future WDR simulations should report impact angle and speed of WDR to allow estimates of splashing and bouncing of WDR on building facades. It was also found that the current runoff models by Blocken & Carmeliet (2012) and Van den Brande et al. (2013) can also be improved by including surface adhesion of water.

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download the full conference paper from the proceedings: nordic2014-tvandenbrande.pdf

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