Air inﬁltration calculation and measurement
Typical air leakage paths in a house are illustrated in Figure 3.1. In general, the air leakage rate through a building envelope is dependent on: (i) the size and distribution of leakage paths; (ii) the ﬂow characteristics of the leakage paths and (iii) the pressure difference across the leakage paths. To evaluate the air ﬂow through a building component or envelope it is essential
that all these three inﬂuencing factors be known or can be determined by one of the methods described later in this section. The main concept of air leakage estimation is based on the mass balance of air across the whole building envelope. The air ﬂow through a building component or envelope is very complex, but an estimate of the ﬂow rate may be made using one of two basic equations depending on the type of opening present. These are the equations for fully turbulent ﬂow and the equation for laminar or transitional ﬂow.