 Effective opening area for pressure-driven ventilation

An effective opening area may absorb both the discharge coefficient and the factor of two in an orifice law. If $A_e=\sqrt{2}{C}_d{A}_{\mathrm{geom}}$, 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.