In case the C-value of a VAV box is known, it can be converted into a corresponding Vn value as both are linked by Δpnom.
Formulas are linked by Δpnom
${\dot{V}}_{\text{nom}} = C \bullet \sqrt{\mathrm{\Delta}p_{\text{nom}}}$ and $V_{n} = \sqrt{\frac{300\ \lbrack Pa\rbrack}{\mathrm{\Delta}p_{\text{nom}}\lbrack Pa\rbrack\ }}$ $\rightarrow V_{n} = C \bullet \frac{\sqrt{300\ \lbrack Pa\rbrack}}{{\dot{V}}_{\text{nom}}}$
Example for a box with C = 57.2 and Vnom = 900 m3/h:
$$V_{n} = C \bullet \frac{\sqrt{300\ \left\lbrack \text{Pa} \right\rbrack}}{{\dot{V}}_{\text{nom}}} = 57.2\frac{\left\lbrack \frac{m^{3}}{h} \right\rbrack}{\left\lbrack \sqrt{\text{Pa}} \right\rbrack} \bullet \frac{\sqrt{300\ \left\lbrack \text{Pa} \right\rbrack}}{900\ \left\lbrack \frac{m^{3}}{h} \right\rbrack} = 1.1$$
In this case, set Vn = 1.1 which corresponds to a Δpnom = 248 Pa.