T-Method duct design, Part V: duct leakage calculation technique and economics.

The procedure of incorporating duct leakage into the T-method simulates leakage as an additional parallel section with zero length for each duct section. The assumption that additional air leakage creates additional system resistance is wrong. Leakage always reduces, not increases, system resistance. How fan power consumption changes due to leakage depends on the fan performance curve.  Methodology was developed to add duct leakage to the T-method previously developed for both the design and simulation of duct systems. It is shown that in most cases the sealing of ductwork is economical. Duct sealing is not recommended when electricity cost is less than 2¢/kWh and sealing cost is greater than $1.5/m2. A simple rule is: the higher the system cost, the greater the need for ductwork sealing.