A PQ-Formulation for Ventilation Duct System Flow Analyses

A formulation to analyze ventilation duct system airflows employing, as the basic unknowns, the flow rates in the channel sections and the static pressures at the channel section ends is presented. This approach is called the PQ-formulation and the corresponding system equations are called PQ-equations. The system equations in the PQ-formulation are the engineering Bernoulli equations for the channel sections, the inlet and outlet pressure jump equations at the inlet and outlet nodes, the continuity equations at the junctions and the pressure jump equations at the junctions. The nonlinear system equations are solved by the Picard method using a relaxation factor. The linearizations employed in the Picard method are described. Special additional themes are the treatment of the updating of junction coefficients and the use of a so-called balancing factor for checking convergence. Numerical demonstration results are given in some example cases.