EN 15026 specifies the model components to be used in a numerical hygrothermal simulation model for calculating the transient transfer of heat and moisture through building structures. In contrast to the steady-state assessment of interstitial condensation by the Glaser method (as described in ISO 13788), transient hygrothermal simulation provides more detailed and accurate information on the risk of moisture problems within building components and on the design of remedial treatment.
While the Glaser method considers only steady-state conduction of heat and vapour diffusion, the transient hygrothermal simulation models which are composed of the formulae defined in this document also take account of heat and moisture storage, latent heat effects and liquid and convective transport under realistic boundary and initial conditions. The application of such models has become widely used in building practice in recent years, resulting in a significant improvement in the accuracy and reproducibility of hygrothermal simulation.
The following examples of transient heat and moisture phenomena in building components can be simulated by the models covered in EN 15026:
— drying of initial construction moisture,
— moisture accumulation by interstitial condensation due to diffusion in winter,
— moisture penetration due to driving rain exposure,
— summer condensation due to migration of moisture from outside to inside,
— outside surface condensation due to cooling by long-wave radiation exchange,
— moisture-related heat losses by transmission and moisture evaporation.