Adjusting the air balance in a rectangular duct system (Rectangular Duct)

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Adjusting the air balance in a rectangular duct system (Rectangular Duct)

Proper techniques and equipment must be used.So that the air supply at each point will be in the amount as designed.

Especially square pipes are more complicated than round pipes in some points. such as eddies, dead corners, and pressure drops.

Higher if the design is faulty

✅ How to adjust the air balance in a square pipe system.

1. Damper is used in each arm of the pipe.
 • Install a Volume Damper or Balancing Damper (such as a splitter damper or opposing-blade damper).
 • Adjust to balance the air flowing to each point. (not too much or too little)

2. Use Flow Hood or Anemometer to measure at the dispenser head.
 • Measure CFM (Cubic Feet per Minute) at the dispenser head (Diffuser or Grille).
 • Compare with the design value and adjust the Damper to get the closest value.

3. In the case that there is no Damper, use the method of “adjusting the resistance force”.
 • For example, reducing the size of the end of the pipe or adding an Orifice Plate / perforated plate to create less resistance to the airflow at strong wind points.
 • Or increase the length of the pipe / curve to increase the pressure drop.

4. Adjust by “redesign” if the flow is very wrong.
 • For example, the division of wind was not appropriate from the beginning. Or the dispenser is too close to the AHU.
 • You may need to change the supply point. or adjust the new pipe route

📐 Example of a square pipe pattern that is often used in work.

Format Properties
Long straight pipe (Main Duct) distributes the main air, must have a damper separated into arms.
Branch pipe is separated. Need to control the air volume of each arm.
Vertical pipe (Riser) for high-rise buildings, must balance ground and upper floors.
Some Return Air pipe systems must be balanced on the suction side as well.

🔧 Equipment used for balancing
 • Flow Hood – measures the air volume at the dispenser head.
 • Anemometer – measures the air velocity in the pipe.
 • Pitot Tube + Manometer – measures pressure and velocity within a pipe.
 • Balancing Damper – a device for adjusting the air volume.
 • Duct Traverse Tool – for measuring the cross-sectional area of square pipes.