Standards for air speed in ducts (Duct Velocity)

Article details

Standards for air speed in ducts (Duct Velocity)

according to the guidelines of

It is not specified as a single fixed number, but is divided according to the type of use. (Application) and acceptable sound level

(Noise Criteria) In principle Duct design has a balance between 2 factors:
 * Low Speed (Low Velocity): Reduce noise, reduce friction. (Fan energy saving) but the pipe will be large. Waste of installation space
 * High Velocity: Small pipe saves space and material costs. But it's louder and uses more power from the fan.
Summary of recommended wind speed values (Recommended) and maximum values (Maximum) according to the ASHRAE manual for low velocity systems (Low Velocity Systems) are as follows:

1. Air speed in supply air ducts.
| Building type | Pipe location | Recommended speed (Recommended) | Maximum speed (Maximum) |
| Residential | Main Ducts | 700 - 900 FPM (3.5 - 4.5 m/s) | 1,000 FPM (5 m/s) |
(Residences) | Branch Ducts | 600 FPM (3 m/s) | 800 FPM (4 m/s) |
|  | Return air pipe (Return) | 600 FPM (3 m/s) | 800 FPM (4 m/s) |
| Commercial building/school | Main Ducts | 1,000 - 1,300 FPM (5 - 6.5 m/s) | 1,500 FPM (7.6 m/s) |
(Schools/Offices) | Branch Ducts | 600 - 900 FPM (3 - 4.5 m/s) | 1,200 FPM (6 m/s) |
|  | Return air pipe | 800 FPM (4 m/s) | 1,000 FPM (5 m/s) |
| Industrial factories | Main Ducts | 1,200 - 1,800 FPM (6 - 9 m/s) | 2,500 FPM (12.7 m/s) |
(Industrial) | Branch Ducts | 800 - 1,000 FPM (4 - 5 m/s) | 1,800 FPM (9 m/s) |

2. Wind speed through various equipment (Equipment Face Velocity)
The choice of air velocity across the face of the device is very important. Because if it's too fast, it may cause water to splash (Carryover) or reduce filter efficiency.
 * Outdoor Air Intakes/Louvers: 500 FPM (2.5 m/s) to prevent rainwater splashing in.
 * Air filters (Filters): 250 - 300 FPM (1.25 - 1.5 m/s) for fine filters, 500 FPM (2.5 m/s) for coarse filters.
 * Cooling Coils: 400 - 500 FPM (2.0 - 2.5 m/s) should not exceed 550 FPM to prevent water from the drain tray from being blown away by the wind.
 * Air distributors (Diffusers/Grilles): Depending on the blowing distance (Throw) and sound (NC), generally at 400 - 800 FPM at the distributor neck.
Design Considerations
 * Noise: If the area requires a lot of quiet (such as a recording studio, bedroom, library), you should use a speed value in the "recommended" range or lower.
 * Pressure loss (Static Pressure Loss): The higher the speed, the greater the Friction Loss, causing the need to use a fan with higher Static Pressure, which consumes more power.
 * Return Air: Should always be designed to have a lower speed than the air duct. This is to reduce noise that may be more easily transmitted back to the usable area.
HVAC Duct Design using ASHRAE & StandardsNoise that may be transmitted back to the operating area is easier.HVAC Duct Design using ASHRAE & Standards