Robust moisture reference year methodology for hygrothermal simulations

Abstract

Hygrothermal models allow designers to evaluate the hygrothermal performance of building envelopes. A key question in hygrothermal modeling however remains in the proper selection of representative exterior moisture conditions, i.e. a moisture reference year. A Climatic Index combining wind-driven rain load and potential evaporation is developed allowing considering the effect of climatic variability on the performance of the building envelope. The proposed Climatic Index combines thus both the wetting load and evaporation potential. This index is suitable for the evaluation of the level of moisture damage risk of wall assemblies where typical moisture problems are mainly caused by rainwater uptake or ingress.The Climatic Index is determined for four cities in Switzerland. The hygrothermal performance of the assemblies is simulated and evaluated using a hygrothermal indicator, called the RHT Index. A clear correlation between Climatic Index and RHT Index is found. However, the moisture reference year selected based solely on a 10% level criterion of the Climatic Index may not correspond to the year with the most significant moisture damage risk. Therefore, a new procedure is proposed which combines a first selection of three years around the 10% level criterion, followed by a careful comparison of these years based on hygrothermal simulations and selection of the year with the largest RHT Index as moisture reference year. The combination of Climatic Index and RHT Index from hygrothermal simulations allows for the selection of moisture reference years that are around the 10% level, but excluding the ambiguity.