Studies have shown that duct leakage depends on the method of duct fabrication, method of sealing, workmanship, and static pressure differential. An equation that describes leakage as a function of leakage class and static pressure is presented in the "Duct Design" chapter of the 1993 ASHRAE Handbook. This equation is used to calculate the leakage rate through a unit of duct surface for constant duct static pressure. However, the static pressure of a leaking duct does not remain constant. This process is described by a differential equation.

• Accurate-For accurate duct leakage calculations, the duct system is divided into single sections between fittings and the leakage rate and pressure loss for each section calculated by the weighing factor method.


• Approximate-For most applications, duct leakage can be calculated by approximate formulas based on the average static pressure in a duct section.

Leakage calculation requires dividing the system into sections between each fitting.

This paper, the fourth in a series on T-method duct design, discusses the theory of calculating air leakage from/into a single duct to incorporate duct leakage into the optimization and simulation calculation procedures.

Units: Dual