Measuring the Hygroscopic Properties of Porous Media in Transient Regime. From the Material Level to the Whole Building HAM Simulation of a Coated Room

Abstract

Moisture level inside buildings is a key factor influencing the durability of construction, indoor air quality, thermal comfort and energy performance. Numerical simulation can be used to predict the hygric inertia of a room, but reliable material data are needed as inputs for the model.Although the advancement of numerical models for whole building HAM (Heat Air and Moisture) transfer, a general need for more experimental data able to quantify the hygroscopic performance of porous building material remains. Recent benchmark data for validating 1-D HAM simulation models proposed in international projects are based on numerical and analytical data, while well-documented and accurate data are scarce. In IEA Annex 41 new numerical models have been implemented and used to simulate the HAM interaction between indoor air and hygroscopic materials during transient changes in indoor humidity due to internal moisture gains. Some experimental data obtained in dynamic humidity regime are presented in this study. The goal is to validate models that represent the moisture buffering of hygroscopic materials in contact with indoor air,.In order to fit the experimental data with numerical simulation and to determine the most influencing hygroscopic material properties in HAM modeling, a sensitivity analysis on the numerical fitting of measured properties relevant for indoor moisture buffering, such as the water vapour permeability and the sorption isotherm was carried out. Material data have been monitored using a climate chamber device especially designed for this purpose. In Italian buildings, especially dwellings, walls are very often plastered with gypsum plaster for levelling purposes. The gypsum plaster is generally covered with waterborne wall paint for decoration which represents a barrier for the water absorption or desorption. In order to assess the hygric performance of a room in real conditions, the influence of the water transfer properties of the painted gypsum on the whole building HAM dynamic simulation is assessed considering both an uncoated and a coated room using a waterborne paint.