New model for the hygrothermal calculation of condensate on the external building surface

By means of new hygrothermal models, which include long-wave radiation effects, the temperature drop of the surface below ambient conditions by long-wave emission at night and the resulting condensation can be calculated for external thermal insulation composite systems (ETICS). The most essential condition for microbial growth (esp. algae or mould) is a sufficient amount of moisture on the surface. Thus, the question to be answered is, whether a hydrophobic coating leading to lower water absorption of the render, is of advantage concerning the risk of microbial growth. With a capillary active render system the condensed water may be drained below the surface and is therefore not available for micro-organisms. Up to now, hygrothermal models can calculate the transient water content in the materials of a building, but not the moisture on the surface. Now a new model is developed and validated with laboratory experiments and field tests. For the future, this new tool will help to develop a new render with optimal hygric behavior.