Decision framework to select moisture reference years for hygrothermal simulations

Abstract

The dominant degradation agent in facades is exposure to moisture. Damages resulting from long-term moisture exposure are typically evaluated through hygrothermal simulations. These simulations are computationally expensive. Therefore, a Moisture Reference Year (MRY), i.e. one year representing the moisture stress of the climate, is often used instead of simulating damages with the long-term climate itself. Usually, the methods to select MRYs were developed for specific wall types and damages. Up to now, no guideline exists to select one of these methods for particular cases. Therefore, we evaluated 21 existing MRY methods, and we developed a decision framework on how to select appropriate climate data for hygrothermal simulations. This paper presents the comparison between long-term simulations and simulations using MRYs for solid masonry walls in Brussels. The wall assemblies are analysed with and without interior insulation for 16 parameter variations each. A number of MRYs are able to represent the risk on freeze-thaw damage and wood decay, but the best performing MRYs vary between the different damages. Further, the decision framework consists of 5 levels, with each level requiring less computational power at the cost of its precision. It is recommended to perform long-term simulations whenever possible. Second best is to select an MRY with respect to a long-term simulation for a reference case. For large studies, a climate-based MRY accounting for the expected damage mechanisms could be considered as a first estimate of the results. In this study, the decision framework was successfully tested for solid masonry walls in Brussels.