The dynamic modelling of air humidity behaviour in a multi-zone space

Single-zone dynamic modelling of air humidity can fairly account for most moisture transfer processes in single-zone buildings. However, such models cannot truly represent air humidity behaviour in most building since they have distinct interior partitioning of their volumes. A dynamic model to describe the air humidity behaviour and to determine its variations in a multi-zone space is proposed. The model accounts for boundary conditions variation from one zone to another, the different zonal interaction with the outdoor environment and the individual zonal functional and physical characteristics. The model accounts for both diffuse moisture transfer and convective moisture transfer due to inter-zonal air movement. A multi-cell air flow model that accounts for individual zone air flow, air flow through the envelope in each zone and the inter-zonal air flow is incorporated. Air humidity within each zone is determined through a simultaneous solution of a set of linear algebraic equations using time dependent humidity parameters. A discrete time interval approach was used since most moisture transfer processes are not continuous in nature. A case study on a six-zone building space is presented to demonstrate the air humidity behaviour in a multi-zone space as well as to examine the effect of the influencing parameters such as wind speed and direction, air leakage characteristics, indoor moisture generation, surface condensation, inter-zonal air temperature variation, and building materials absorption and desorption. The results also showed the uniqueness of individual zones air humidity behaviour and its dependence on its relative location along the building air humidity flow path.