When calculating the duct pressure using the Darcy-Weisbach equation for the sum of C-coefficients where ΣC0, errors are introduced into the duct leakage calculation if the local resistances are not located individually. These errors can be avoided if a system is divided into sections between fittings. This makes practical sense only if local resistance coefficients are relatively large. If resistance coefficients are small, static pressure in a duct can be assumed to be an average of static pressures in the sections. [Tsal, Part IV; 1998]
In general, duct leakage should be included in the objective function when optimizing the life cycle cost of a duct system. A new methodology was developed by ASHRAE to add duct leakage to the T-Method previously developed for duct simulation [Tsal et al., 1998]. Incorporating duct leakage in the T-Method involves simulating leakage as an additional imaginary section with zero length for each actual duct section. It should be noted that the majority of duct systems are not one section but a tree where the number of terminal sections is greater than the number of trunk sections. [Tsal, Part V; 1998]
