= Effective opening area for pressure-driven ventilation
{title2=$q=A_e\sqrt{\delta p/\rho}$}
An effective opening area may absorb both the discharge coefficient and the factor of two in an orifice law. If $A_e=\sqrt2C_dA_{\rm geom}$, its discharge is $q=A_e\sqrt{\delta p/\rho}$. Two equal openings carrying the same flux share the total <pressure> drop, so $q^2=A_e^2\Delta p/(2\rho)$. They do not share equal drops when an internal volume source makes their fluxes unequal. State the effective-area convention before comparing numerical factors in <natural ventilation> models.
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