How To Calculate Air Velocity In Duct

Air Velocity Formula:

\[ V = \frac{CFM}{Area} \]

Air Velocity (V):

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1. What is Air Velocity in Duct?

Air velocity in duct refers to the speed at which air moves through a ventilation or air conditioning duct system. It is a critical parameter in HVAC design and maintenance, affecting system efficiency, noise levels, and air distribution.

2. How Does the Calculator Work?

The calculator uses the fundamental air velocity formula:

\[ V = \frac{CFM}{Area} \]

Where:

\( V \) — Air velocity (feet per minute)
\( CFM \) — Cubic feet per minute (air flow rate)
\( Area \) — Cross-sectional area of duct (square feet)

Explanation: This formula calculates the speed of air moving through a duct by dividing the volumetric flow rate by the cross-sectional area of the duct.

3. Importance of Air Velocity Calculation

Details: Proper air velocity is essential for efficient HVAC system operation. Too high velocity causes excessive noise and pressure drop, while too low velocity may lead to poor air distribution and sediment accumulation.

4. Using the Calculator

Tips: Enter CFM value in ft³/min and duct area in ft². Both values must be positive numbers. For rectangular ducts, area = width × height. For circular ducts, area = π × (diameter/2)².

5. Frequently Asked Questions (FAQ)

Q1: What is the typical air velocity range for HVAC ducts?
A: For residential systems: 600-900 fpm; for commercial systems: 1,000-2,000 fpm; for high-velocity systems: 2,000-3,500 fpm.

Q2: How do I calculate duct area for different shapes?
A: Rectangular duct: width × height; Circular duct: π × radius²; Oval duct: more complex calculation using major and minor axes.

Q3: Why is air velocity important in HVAC design?
A: Proper velocity ensures efficient air distribution, minimizes energy consumption, reduces noise, and prevents issues like duct sweating or dust accumulation.

Q4: What happens if air velocity is too high?
A: High velocity increases noise levels, creates excessive pressure drop, reduces system efficiency, and can cause vibration issues.

Q5: How does air velocity affect comfort?
A: Proper velocity ensures even temperature distribution and adequate air changes without creating uncomfortable drafts or noise disturbances.