A new method to estimate the periodic temperature distribution underneath a slab-on-ground structure

The objective of this study was to create a method to estimate the temperature distribution at the fill layer underneath a slab-on-ground structure of a heated building. It concerns the typical Finnish slab-on-ground structures, where the footing wall extends above the surrounding soil surface. According to the field measurements and a series of numerical modelling performed in this study, there are three boundary temperatures having an effect on the temperature distribution underneath a slab-on-ground structure: the internal, the external and the subsoil temperature. Later, a relation between the numerically determined static-state weighting factors of these three boundary temperatures and the interrelations of the theoretical thermal transmittance values of the adjoining structural layers is detected. Based on these observations a new semi-analytical method for the estimation of temperature distribution along the fill layer underneath a slab-on-ground structure in periodic conditions is developed. The method applies the superposition principles, where the annual mean boundary temperatures form a basic steady-state temperature distribution and the amplitudes of the external and internal temperatures contribute periodic seasonal alterations.