On parallel operation of fans

The paper presents a method for distinguishing unstable operating points in ventilation networks with fans operating in parallel. Several concepts of ventilation systems and their characteristics were applied. The analysis of local stability of equilibrium points of the system of ordinary differential equations describing unsteady incompressible flow in a simplified network ventilated by 2 fans in parallel, leads to formulation of a simple condition of stability. Some graphic examples of construction of ventilation systems characteristics are presented. Results of calculations were graphed to show time variations of flow quantities and pressure during transients caused by the loss of stability.