Equivalent wall method for dynamic characterisation of thermal bridges

Abstract

Although there are specific rules in the standard ISO 10211 for the characterization of thermal bridges, they are mainly focused on steady state calculations to obtain the linear thermal transmittance (Ψ) or the temperature factor at the internal surface (fRsi). These parameters are respectively indicators of the additional heat flow and the risk of internal surface condensation of thermal bridges. However, in the calculations of building energy demand the dynamic thermal aspects of the envelope take a very important role. Moreover, a high percentage of the envelope is influenced by thermal bridges. Therefore it is necessary to take into account the implicit inertia of thermal bridges for accurate calculations. This paper presents a methodology based on thermoelectric analogy to calculate an equivalent wall of three homogeneous layers, which have the same dynamic thermal behaviour as the thermal bridge. Furthermore, each thermal bridge is associated with an influence area within the envelope, so that they can be easily implemented in building energy simulation programs where the heat flow is usually considered one-dimensional.