7/22/2019 ASHRAE Duct Noise vs Velocity

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ASHRAE

Sound and Vibration Control

Design Rectangular Circular Increased Flow

Main Duct Location RC (N) Duct Duct Circular vs Rectangular

In Shaft or above drywall ceiling 45 3,500 5,000 1.43

35 2,500 3,500 1.40

25 1,700 2,500 1.47

Above suspended acoustic ceiling 45 2,500 4,500 1.80

35 1,750 3,000 1.7125 1,200 2,000 1.67

Duct located within occupied space 45 2,000 3,900 1.95

35 1,450 2,600 1.79

25 950 1,700 1.79

Notes:

1. Branch ducts should have airflow velocities of about 80% of the values listed.2. Velocities in final runouts to outlets should be 50% of the values or less.

3. Elbows and other fittings can increase airflow noise substantially, depending on the type.

Therefore, duct airflow velocities should be reduced accordingly.

Maximum Airflow Velocity, fpm

Table 3 - Maximum Recommended Duct Airflow Velocities

Needed to Achieve Specified Acoustic Design Criteria