Modelling of moisture transfer in structures—I. A description of a finite-difference nodal model

Abstract The physical, numerical and computational basis of a 1- 2- or 3-D time-dependent finite-difference nodal model for heat and moisture transfer in buildings is described. The model is designed to be very flexible so as to be able to analyse a wide variety of geometries and circumstances. The solution procedure is fully implicit with non-linear processes such as condensation, radiation and convection being described in terms of an effective conductance at each time step. The model is iterated at each time step to arrive at a good estimate of the updated value of these effective conductances. The performance of this model is analysed in a later paper.