Introduction
Duct design methods are presented in the 1997 ASHRAE HandbookFundamentals. Three methods are presented: equal friction, static regain, and the Tmethod.
As nonoptimizationbased methods, the equal friction method is widely used for lowpressure system in most buildings.
The Tmethod, introduced by Tsal et al. (1988), is the only optimizationbased method, described in the 1997 ASHRAE Handbook Fundamentals.
I wrote a macro for EXCEL spreadsheet for the calculation of the systems duct with equal friction and Tmethod.
You can compare the results of the two methods.
For the definition of the variables used in the Excel sheet see ASHRAE fundamental book.
Rules for numbering of the trunks / branches
You must enumerate the network hydraulically disadvantaged. The network consists of trunks. In each trunk the air flow rate is constant. It begins with the trunk with great air flow up to the trunk with smaller air flow ( see figure 1 ).
fig.1
Subsequently be numbered branches from those that branch off from the trunks to reach higher up than those in the lower reach (see figure 2).
In addition to number the branches must be inserted in the trunk which they refer ( see figure 3 ).
If it is necessary to calculate a network with a T must insert a truncated length equal to the fictitious example to 0.1m (see figure 4).
From a branch can not start another branch (see figure 5).
fig.5
Excel example figures
For the Excel example i referred to the duct network following (see fig.6).
fig.6
References

Tmethod duct optimization with Excel
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