3.5.1. System Characteristic Curve

Each system has its own characteristic curve (also called resistance parabola) and can be determined more or less exactly by precalculations, so that the course of the characteristic curve can be marked with sufficient accuracy (see figure 3.5.1.). For almost all plant components occurring in practice (turbulent flow systems), the pressure decrease or increase changes with the square of the volume flow. A system characteristic curve can therefore be easily calculated according to the formula:

 p_{II}=p_I\cdot\left(\frac{q_{V,II}}{q_{V,I}}\right)^2

Note: Most flow resistances are"p_d" -proportional , that is, the losses increase quadratically with the volume flow ratio. However, since various systems contain filter resistors, their linear resistance behavior - pressure drop change with linear volume flow ratio - must be taken into account.

The system characteristic curve describes the consumption or the usable air capacity provided by the fan impeller.

Figure 3.5.1.: Plant characteristic curve