Duct Sizing methods
Duct Sizing methods
(OP)
I know of these 3 methods that are used in the industry.
1.Equal friction method
2. Static regain method
3. T method
But have also heard many saying "Constant velocity" method.
Is this another name for the Equal friction method.
1.Equal friction method
2. Static regain method
3. T method
But have also heard many saying "Constant velocity" method.
Is this another name for the Equal friction method.





RE: Duct Sizing methods
RE: Duct Sizing methods
RE: Duct Sizing methods
RE: Duct Sizing methods
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Duct Sizing methods
That must be hell to calculate.
B.E.
RE: Duct Sizing methods
RE: Duct Sizing methods
RE: Duct Sizing methods
When using the equal friction method, does the velocity remain more or less the same across the entire length of the duct (atleast the main branch)
RE: Duct Sizing methods
1. Constant Velocity - used in dust extraction etc. Need, say 15m/s duct velocity to maintain particle removal. You set the wheel to 15m/s at the velocity window and read duct size from the V flow.
2. Equal Friction - Very common method of rough sizing supply air etc ductwork. Eg. Use, say 0.8 Pa/m for all duct runs. You set the wheel to 0.8 Pa/m at the friction window and read duct size from the V flow.
RE: Duct Sizing methods
Which means all these three methods are entirely different and are based on applications. But i guess the ductulator has no provision for the Static regain method. Can you suggest the application and methods used for Static regain. Do u suggest a software that i can use for Static regain.
RE: Duct Sizing methods
Static regain method—a method of duct sizing in
which duct velocities are systematically reduced,
allowing a portion of the velocity pressure to
convert to static pressure and offsetting duct
friction losses
Velocity reduction method—a method of duct
sizing in which arbitrary reductions are made in
velocity after each branch or outlet
Total pressure method—a method of duct sizing
that allows the designer to determine all friction
and dynamic losses in each section of a duct
system (including the total system)
Equal friction method—a method of duct sizing in
which the duct friction loss (pressure drop) value
is used constantly throughout the design of a low pressure
system.
Of the four methods of duct sizing listed
above, the equal friction method is the one most commonly used in light
commercial and residential low-pressure systems.
For residential and light commercial duct systems,
the design criteria normally used are pressure drops
of 0.10 in. w.g. (inches of water gauge) for the supply
side of the system and 0.05 in. w.g. for the return
RE: Duct Sizing methods
The additional method, u mentioned about Total pressure was very new to me. Thanks once again for a god description.
RE: Duct Sizing methods
If you were using constant velocity the 2000 CFM branch would be 20" diameter.
RE: Duct Sizing methods
If you know both static and velocity losses, it will keep you from using high-loss fittings and high velocity flow (noise).
Total pressure is also the only way to analyze an existing duct system to identify problems. It also will allow you to construct pressure gradient diagrams for the whole system.
Specifying fans by total pressure will also allow you to get the fan you want from suppliers and not a cobbed-up substitution.