What formula do you use to determine duct airflow velocity?

What formula do you use to determine duct airflow velocity?

• A. Velocity (FPM) = Duct Area (sq ft) × Airflow (CFM)
• B. Velocity (FPM) = Airflow (CFM) / Duct Area (sq ft)
• C. Velocity (FPM) = (Airflow × Fluid Density) / Friction Factor
• D. Velocity (FPM) = (Duct Length / Diameter) × Airflow

Answer: (B)

To determine duct airflow velocity, the correct formula is derived from the relationship between airflow in cubic feet per minute (CFM) and the cross-sectional area of the duct in square feet. The formula states that velocity in feet per minute (FPM) is equal to airflow divided by the duct area. Using this relationship, you can see that velocity is a measure of how fast the air is moving through the duct, and it is influenced directly by both the amount of air passing through and the size of the duct. If the airflow (CFM) increases while the duct area remains constant, the velocity will also increase. Conversely, if the duct area increases while airflow stays the same, the velocity will decrease. This principle is fundamental in HVAC design, as it helps in determining if the air speed is appropriate for the system, ensuring efficient operation and comfort. Understanding this calculation aids in selecting the right duct size and airflow necessary for effective heating and cooling.

To determine duct airflow velocity, the correct formula is derived from the relationship between airflow in cubic feet per minute (CFM) and the cross-sectional area of the duct in square feet. The formula states that velocity in feet per minute (FPM) is equal to airflow divided by the duct area.

Using this relationship, you can see that velocity is a measure of how fast the air is moving through the duct, and it is influenced directly by both the amount of air passing through and the size of the duct. If the airflow (CFM) increases while the duct area remains constant, the velocity will also increase. Conversely, if the duct area increases while airflow stays the same, the velocity will decrease.

This principle is fundamental in HVAC design, as it helps in determining if the air speed is appropriate for the system, ensuring efficient operation and comfort. Understanding this calculation aids in selecting the right duct size and airflow necessary for effective heating and cooling.