The use of a zonal model to calculate the stratification in a large building

In the past, many churches were raised and in a church building no heating no heating system was installed, except a simple individual coal or peat stove, which could be rented by the churchgoers. The thick high stone walls of the church alleviated the fluctuations of the ambient air temperature and relative humidity. Accordingly, the indoor climate in the church building was quite stable. After the Second World War the living standard of the people increased and the increased prosperity also led to higher comfort demands in churches. As a consequence, many “local” heating systems were often replaced by rugged air inlets, designed to quickly heat the space to increase the thermal comfort. These were designed and operated without taking the effect of the fluctuating temperature and relative humidity on the artwork in the church into account. Consequently, the many artworks in the church building like the organ, the pulpit and the panel paintings are also exposed to this changing climate, leading to faster deterioration or even to damage. Evaluating the conservation conditions for the artworks in a large space requires knowledge of the stratification in temperature and humidity inside a large space that occurs during heating. The use of Computational Fluid Dynamics (CFD) is probably the most suitable method to predict the airflow pattern, but it is quite time consuming and requires a powerful computer. As an alternative a zonal model is a suitable method to predict the airflow in a large space in a simplified way. These models can be linked to a BES- software in which each zone is assumed to be perfectly mixed. By this coupling, the influence of the airflow on the temperature distribution and vice versa can be calculated, in order to judge the thermal comfort and preservation conditions in one zone. This paper presents the coupling of the existing thermal zonal model of Togari with the BES-software TRNSYS. In addition a moisture preservation equation was added to the thermal zonal model to predict the vertical relative humidity gradient in a large space. Further the model also was extended with a EMPD-model to include the moisture buffering of the walls in a simplified way.