While the Netsys program does not consider any additional drop pressure for grilles, etc, the calculation does consider a k value of 1 to account for discharge pressure. This accounts for air coming from a large space to a small space (for e.g. room > duct (supply) or duct > outside (extract).
Velocity Pressure is calculated as follows:
VP = ½ ρV²
VP = Velocity Pressureρ (Rho) = Density of air* V = Calculated velocity in duct section
*approximately 1.2kg/m³, but adjusted for the temperature provided in the System Marker
Consider we have a velocity of 10m/s in a duct section, and an air density of 1.2kg/m³
VP = 0.5 x 1.2 x 10² = 60pa