Hygrothermal simulation challenges: Assessing boundary condition choices in retrofitting historic European buildings

This study explores the influence of uncertain boundary climate conditions on the hygrothermal performance of an internally insulated historic masonry wall using numerical simulations. The research compares diverse internal and external climate data sources to evaluate their reliability. A pre-validated hygrothermal simulation model serves as the benchmark for comparing simulated data with actual monitoring data. An array of climate data sources, including adaptive indoor climate models defined in the EN 15026 and UNI EN ISO 13788 standards, Typical Meteorological Years, and ground weather station data are considered. The core assessment parameters are temperature and relative humidity values beneath the insulation. Unexpectedly, the findings reveal that external climate conditions have a minor influence on the simulation results. Conversely, internal climate conditions significantly impact the outcomes, causing substantial variations. These implications underline the criticality of selecting an appropriate indoor climate model and moisture load class. The incorrect choice can lead to substantial errors, with peak relative humidity values predicted by the models varying in a range greater than 15 percentage points of relative humidity. In conclusion, the study reveals that utilizing Typical Meteorological Years and adaptive indoor climate models still yields excellent results, despite the inherent uncertainties. Moreover, this study emphasizes the importance of carefully selecting suitable indoor climate models to enhance the accuracy of hygrothermal simulations in historic buildings and underlines the need for future research focused on developing more precise guidelines for identifying the correct moisture load classes.