A quasi-steady state implementation of air convection in a transient heat and moisture building component model

摘要

For many years, the coupled heat, air, and moisture (HAM) transport through multilayered building components has been an important research topic. As a result, a great number of numerical simulation tools have been developed to asses and predict the hygrothermal behaviour of building enclosures. But, while the literature shows that air transport has a significant impact on the heat and moisture response of light weight constructions, only few existing heat and moisture transport models include air flow as an active mass component. One of the reasons is the different time scale of air transport compared to the other transported quantities and the resulting difficulties in achieving acceptable simulation performance. The current article presents a quasi-steady state airflow model implementation in an existing transient HAM-model. The air transport is described as Darcy flow in porous media including a body force term to capture natural convection. One particular aim is the prediction of significant effects such as overlaying buoyant and externally driven air flow on the hygrothermal behaviour of building envelope components with sound simulation performances. Furthermore, the article includes an evaluation of the model for which three validation cases from the literature are used to show the applicability and limitations of the presented approach.