Development of a zonal model to assess indoor climate and damage risks to art works in church buildings

Most of the degradation of works of art in historic buildings is caused by unfavourable indoor climate conditions. The most important works of art receive invasive conservation treatment, called direct action, but this treatment is very expensive. To avoid invasive conservation treatments and ensure that works of art are protected for now and for the future, indirect action to mitigate the deterioration process is necessary. This holds that exposure to unfavourable indoor climate conditions should be avoided, as far as is compatible with its social use. To assess the preservation conditions and decide upon retrofit or climate control measures properly, it is necessary to take typical conditions in monumental historical buildings into account in indoor climate simulations. The presence of moisture in heavy building walls and the occurrence of hygrothermal gradients (stratification) in the often very large interior volumes due to the limited control by (older) climate installation systems need to be taken into account. 
This paper examines to which extent the expansion of a BES tool with a simplified stratification model allows to improve the simulation of the indoor climate in historic buildings. The mathematical background of the chosen airflow model, the temperature-based zonal model by Togari, and the added equations for moisture transport are presented. The coupling of the airflow model with the BES-software TRNSYS is explained and a validation of the model is performed to check the correctness of the coupled zonal-BES model. 
Finally the coupled approach is applied to assess the indoor climate problems in an existing case study of a historic church building in which an important panel painting is exhibited. The hygrothermal response of the panel painting exposed to different heating regimes with air heating was studied by coupling the thermal-zonal BES model introduced in this paper with a HAM-model. The moisture buffering of the walls was modelled using an EMPD-model.