Lien De Backer

Evaluation of the diffusion coefficient and sorption isotherm of the different layers of early Netherlandish wooden panel paintings

The preservation of early Netherlandish panel paintings gets a lot of attention as they are an important part of the cultural heritage of the lower countries. Indoor humidity fluctuations are the main cause for mechanical damage of these artworks. To estimate the risk of mechanical damage, the intention of the authors is to model the moisture transport in the artwork related to a simulated indoor climate. Because the hygrothermal response of the panel is controlled by the vapour permeability of the wood and the barrier effect of different material layers on top and on the back of the wooden panel, hygric material characteristics of all layers are needed to perform reliable simulations of the local moisture content gradients in the object. In the literature, several values were presented which were used to model the mechanical behaviour of the panel painting. The driving potential in these studies is the moisture content of wood. However, for the coupling of a HAM tool, which predicts the moisture transport in the object, with other simulation tools (BES, CFD, etc.), it is more straightforward using one unique and material-independent driving potential in both tools, such as vapour pressure. The conversion of characteristics presented in the literature using vapour pressure instead of moisture content is not straightforward as information about converting the characteristics is missing. Another difficulty is that the obtained quantitative results in the literature are valid for a specific application method. Consequently, it is disputable whether these characteristics may be applied to early Netherlandish panel paintings. Therefore, the main goal of this study is to measure the moisture properties of early Netherlandish panel paintings. The desired characteristics were determined using inverse modelling of a 1D moisture transport and finding the best fit between the calculated diffusion process and the measurements.

A strategy for modelling typical indoor climates in historic buildings : moisture buffering of massive walls and stratification by heating

Artworks in historical church buildings degrade due to indoor conditions that are not optimal to preserve artworks. Building Energy Simulation (BES) tools are useful and powerful tools in making decisions of different retrofitting designs to improve the indoor conditions. However, to make a more detailed assessment of the preservation conditions, it is important to take typical conditions in historical church buildings into account in the simulation model. Two of them are the buffering capacity of the heavy thick walls and the stratification during heating. Although BES-tools, based on the well mixed assumption, are adequate for the prediction of an average temperature and relative humidity in small rooms, it cannot predict detailed temperature and airflow distributions within each room. To provide a more realistic representation of thermal and hygric conditions in a church building, in this paper a simplified method is suggested to take into account the stratification during heating in combination with the moisture buffering.