A numerical study on the role of leakage distribution and internal leakages under unsteady wind conditions

The existence of air leakages in a building has been very clearly stated as an important reason for energy loss. The decrease in the efficiency of the mechanical ventilation has also been clarified. The global demand for achieving nearly zero-energy buildings makes the uncontrolled leakage paths even more undesired. Despite the fact that steady state measurements of in- and exfiltration rates offer a simple and easy way of estimating the airtightness level of an eclosure, a supplement to those methods might be imposed.
While a significant amount of studies points out the key role of the ‘artificial’ unsteady conditions to the actual leakage rates of a building, there are only few that discuss the influence of natural unsteady phenomena. In this context, the correlation between the dynamic characteristics of the wind and the leakage numbers of a building, should be more studied. Computational Fluid Dynamics (CFD) could be employed in order to investigate the role of the air flow mechanisms.
In the current numerical study, unsteady wind conditions are performed around an one-storey building-model of size 5m x 10m x 3m. Variable leakage areas Aleak around windows are simulated and solved in a transient mode aiming to investigate the role of the distribution of the leakages under natural conditions. A ratio (0 ≤ α ≤ 1) that represents the portion of leakages (distribution) per surface is employed and the infiltration rates respect to this ratio are shown. Different situations of the enclosure volume (from the perspective of internal wall airtightness) are assumed in order to investigate the influence of the latter to the infiltration rate of the building’s envelope. The impact of the internal leakages is proven and the importance of controlling them is discussed.