Enter the volumetric air flow rate and the cross-sectional area of the duct into the calculator to determine the air velocity.

Air Velocity Formula

The following equation is used to calculate the Air Velocity.

Vair = AFR / DA
  • Where Vair is the air velocity (ft/s)
  • AFR is the airflow rate (ft^3/s)
  • DA is the air duct area (ft^2)

To calculate air velocity, divide the air flow rate by the duct area.

What is an Air Velocity?

Definition:

An airflow velocity describes the linear speed at which air flows through an enclosed duct.

How to Calculate Air Velocity?

Example Problem:

The following example outlines the steps and information needed to calculate Air Velocity.

First, determine the air flow rate. In this example, the airflow rate is found to be 50 ft^3/2.

Next, determine the air duct area. For this problem, the air duct area is found to be 10 ft^2.

Finally, calculate the Air Velocity using the formula above:

Vair = AFR / DA

Vair = 50 / 10

Vair = 5 ft/s

FAQ

What factors can affect air velocity in a duct?

Several factors can affect air velocity in a duct, including the duct size and shape, the roughness of the duct interior, bends and turns in the ductwork, and any obstructions within the duct. Changes in temperature and pressure can also impact air velocity.

Why is it important to calculate air velocity in HVAC systems?

Calculating air velocity is crucial in HVAC systems to ensure efficient and effective heating, cooling, and ventilation. Proper air velocity ensures that air is distributed evenly throughout a space, helps in maintaining desired temperature and humidity levels, and prevents issues like duct noise and system overload.

Can the air velocity formula be used for any type of duct shape?

Yes, the air velocity formula (Vair = AFR / DA) can be applied to any duct shape, as long as the cross-sectional area (DA) of the duct is accurately calculated. For non-rectangular ducts, the area calculation might be more complex, but the principle of the formula remains the same.