Investigation on the use of hygrothermal modelling for paper collections

Dynamic simulation is increasingly adopted in the preventive conservation of cultural heritage as an advanced method to investigate strategies for mitigating the climate-induced degradation. The conservation of paper collections is strongly interrelated with the relative humidity of the air, as organic-hygroscopic materials act as buffers on relative humidity fluctuations while being vulnerable to moisture-induced damage. In the dynamic simulation of the microclimate within library and archival storage facilities, it is thus fundamental to include the hygrothermal interaction between the building and its hygroscopic content. The hygroscopic behaviour of paper collections can be modelled by hygrothermal tools such as those of the HAM-family (Heat, Air and Moisture), used to simulate simultaneous heat and mass transfers through porous envelope materials. This research aims at investigating the use of the HMWall model coupled with the software IDA ICE (Indoor Climate and Energy) to simulate of the 1-D heat and moisture transfer through a single wall made of paper. A literature survey was carried out to collect the available hygrothermal properties of modern and historical papers. Sensitivity analysis was used to identify the most relevant hygrothermal parameters in the simulation of moisture gradients across the paper wall. Moreover, the number of sub-layers in the paper wall model was found to significantly affect the internal distribution of moisture gradients. The use of the HMWall model was then tested in the simulation of the hygroscopic behaviour of a single paper wall in both steady-state and transient conditions. Finally, a simplified model able to preserve the accuracy of the results was proposed with the purpose of reducing the computation effort that a high-resolution model could involve if implemented in whole buildings. This study represents the first step towards the application of the HMWall model for the simulation of the indoor climate of library repositories.