During the past few years several different computer models have been developed that can predict the hygrothermal behavior of building walls with different degrees of complexity. A new hygrothermal model has been developed that combines the building envelope parts and the indoor climate. The model is capable of predicting the combined transfer of heat and moisture, including liquid and vapor flow and phase changes of moisture in the porous media and CO Moisture can have several unwanted effects on the durability of building materials, such as rotting, mold growth, corrosion, and deterioration of masonry. Moisture and mold growth in some materials may result in increased emissions and become a health risk. Some of these effects occur only at certain temperatures and moisture contents, which makes it important that the coupling of the energy and moisture transfer equations be done correctly.

The effect of vapor and CO₂ diffusion through building walls on the interior climate and wall moisture contents are presented as functions of ventilation rates for a corner bedroom. Two lightweight wood frame wall structures are investigated, one with and one without a vapor barrier (6-mil PE). The model is verified against small-scale experiments in huts exposed to real environmental conditions. These results are then expanded for a full-scale house using the simulation model.

Results clearly show the importance of diffusion processes on the indoor climate at low ventilation rates. At high ventilation rates, the effect becomes insignificant and the indoor climate in the rooms approach each other, as would be expected.

Units: SI