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Hygrothermal modeling and evaluation of freeze-thaw damage risk of masonry walls retrofitted with internal insulation

机译：内装保温砌体墙的湿热模拟和冻融破坏风险评估

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For historical buildings with a worth-preserving appearance, internal wall insulation can be the only possible solution to improve the building energy efficiency. However, the application of an internal insulation layer changes significantly the hygrothermal performance of the building envelope. For masonry walls, such intervention may lead to freeze-thaw damage of the brickwork. In this study, a hygrothermal model is developed. The model takes into account moisture and heat transport in porous medium and tracks the occurrence of freezing and thawing in function of pore size distribution and as well as the ice content. Freezing and melting of water in porous medium is implemented based on the theory of freezing point depression, as freezing temperature of water in porous medium depends on pore size, i.e. water in the smaller pores freezes at temperatures lower than 0 degrees C. The numerical model results are compared with a porous medium freezing experiment and good agreement is found. Traditional hygrothermal assessment uses the number of zero crossings on a Celsius scale as the number of freeze thaw cycles. We propose a method that uses the number of actual ice growth and melt cycles as an indicator more accurately accounting for the freeze-thaw process. In addition, we develop an index, called FTDR Index, to assess freeze-thaw damage risk. We perform simulations of uninsulated and internally retrofitted masonry walls using two Swiss climatic conditions. The study clearly shows increase of freeze-thaw cycles and ice content after internal retrofitting in both climates. Thus, FTDR Index increases after internal retrofitting. (C) 2017 Elsevier Ltd. All rights reserved.
机译：对于具有保值外观的历史建筑，内墙绝热可能是提高建筑能效的唯一可行解决方案。然而，内部绝热层的应用显着改变了建筑物围护结构的湿热性能。对于砌体墙，这种干预可能导致砖砌的冻融破坏。在这项研究中，建立了一个湿热模型。该模型考虑了多孔介质中的水分和热传递，并根据孔径分布和冰含量跟踪冻结和解冻的发生。多孔介质中水的冻结和融化是基于凝固点降低理论进行的，因为多孔介质中水的冻结温度取决于孔径，即较​​小孔中的水在低于0摄氏度的温度下冻结。数值模型将结果与多孔介质冷冻实验进行比较，发现吻合良好。传统的湿热评估使用摄氏尺度上的零交叉数作为冷冻解冻循环数。我们提出了一种方法，该方法使用实际冰的生长和融化循环的次数作为指标来更准确地说明冻融过程。此外，我们开发了一个称为FTDR指数的指数，以评估冻融损坏的风险。我们使用两种瑞士气候条件对未隔热和内部翻修的砌体墙进行模拟。该研究清楚地表明，在两种气候下进行内部改造后，冻融循环和冰含量都增加了。因此，在内部改造后，FTDR指数会增加。 （C）2017 Elsevier Ltd.保留所有权利。

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