Modeling of Heat Transfer through Multilayer Walls of a Building, in Stationary and Non-stationary Regimes


In order to perform the calculations regarding the energy efficiency of a building, one of the stages is to deter-mine the thermal resistance of the building elements. This quantity depends on the temperature difference and on the heat flow that crosses them. A possible approach to this calculation is the numerical one, where, depending on the existing or imposed by the regulations environmental condi-tions, these quantities can be accurately determined, whether the materials of these elements are homogeneous or inhomogeneous, linear or nonlinear. In this paper, the calcu-lation method based on the numerical calculation using the finite volumes method is presented. As an example, the study focuses on the analysis of a multilayer exterior wall. The temperature conditions to which it is subjected corre-spond to the normal operating conditions during the winter, as they are provided by the regulations in force in Romania. The stationary case was firstly analyzed, considering the constant ambient temperatures inside and outside the build-ing. Subsequently, a non-stationary thermal field analysis was performed, taking into account the variation in tem-perature over the course of a day, during the winter period. The algebraic equations resulting from the discretization of the problem equations were implemented in a program cre-ated in MATLAB. The obtained results were compared with those offered by a specialized calculation program for the thermal fields, which uses the finite element method, Quick-Field Professional. The calculation of errors proved a good correspondence between the obtained values. images