Cavity walls consisting of an outer leaf, a cavity and an inner leaf are a widespread building enclosure configuration because of their good performance regarding rain tightness. To increase the drying potential, open head joints are typically provided in the brick outer leaf, creating cavity ventilation. Even though this cavity ventilation has a limited effect on the drying out of the brick veneer, it can significantly reduce the moisture levels inside the cavity. This might be crucial when the brick veneer is combined with, for example, a wooden load-bearing wall. A reliable prediction of the cavity moisture levels is hence essential. However, previous studies showed that the ventilation rate in the cavity is highly fluctuating in both magnitude and direction. That is why most numerical models simplify cavity ventilation by neglecting it, replacing it by an equivalent resistance, assuming a constant air change rate and so on. This article verifies common assumptions in numerical models to incorporate cavity ventilation behind a brick veneer cladding, by confronting the simulations with detailed field studies. The results showed that for walls exposed to driving rain and solar radiation, most simplified one-dimensional simulations do not suffice to predict the moisture content in the cavity in a reliable way. Only with two-dimensional simulations, incorporating the airflow in the cavity, a good agreement with the in situ measurements was obtained. Furthermore, the two-dimensional models showed to be able to capture the moisture gradient along with the height of the wall rather precisely.

中文翻译：

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模拟砖单板覆层背后的水分条件：通过现场测量验证常见方法

由外叶、空腔和内叶组成的空腔墙是一种广泛使用的建筑围护结构，因为它们具有良好的防雨性能。为了增加干燥的可能性，通常在砖外叶中提供开放式头部接缝，从而形成空腔通风。尽管这种空腔通风对砖饰面干燥的影响有限，但它可以显着降低空腔内的水分含量。例如，当砖饰面与木质承重墙结合时，这可能是至关重要的。因此，对型腔湿度水平的可靠预测是必不可少的。然而，先前的研究表明，腔内的通风率在大小和方向上都有很大的波动。这就是为什么大多数数值模型通过忽略它来简化腔体通风，假设换气率恒定等，用等效电阻代替它。本文通过对模拟进行详细的现场研究，验证了数值模型中的常见假设，以将空腔通风纳入砖饰面覆层后面。结果表明，对于暴露在强降雨和太阳辐射下的墙壁，大多数简化的一维模拟不足以可靠地预测空腔中的水分含量。仅通过二维模拟，将空腔中的气流结合起来，才能获得与原位测量值的良好一致性。此外，二维模型显示能够相当精确地捕捉水分梯度以及墙的高度。本文通过对模拟进行详细的现场研究，验证了数值模型中的常见假设，以将空腔通风纳入砖饰面覆层后面。结果表明，对于暴露在强降雨和太阳辐射下的墙壁，大多数简化的一维模拟不足以可靠地预测空腔中的水分含量。仅通过二维模拟，将空腔中的气流结合起来，才能获得与原位测量值的良好一致性。此外，二维模型显示能够相当精确地捕捉水分梯度以及墙的高度。本文通过对模拟进行详细的现场研究，验证了数值模型中的常见假设，以将空腔通风纳入砖饰面覆层后面。结果表明，对于暴露在强降雨和太阳辐射下的墙壁，大多数简化的一维模拟不足以可靠地预测空腔中的水分含量。仅通过二维模拟，将空腔中的气流结合起来，才能获得与原位测量值的良好一致性。此外，二维模型显示能够相当精确地捕捉水分梯度以及墙的高度。结果表明，对于暴露在强降雨和太阳辐射下的墙壁，大多数简化的一维模拟不足以可靠地预测空腔中的水分含量。仅通过二维模拟，将空腔中的气流结合起来，才能获得与原位测量值的良好一致性。此外，二维模型显示能够相当精确地捕捉水分梯度以及墙的高度。结果表明，对于暴露在强降雨和太阳辐射下的墙壁，大多数简化的一维模拟不足以可靠地预测空腔中的水分含量。仅通过二维模拟，将空腔中的气流结合起来，才能获得与原位测量值的良好一致性。此外，二维模型显示能够相当精确地捕捉水分梯度以及墙的高度。