1. What is Volumetric Air Flow Rate?

Definition: This calculator determines the volumetric flow rate of air in gallons per minute (GPM) equivalent based on velocity and cross-sectional area.

Purpose: It helps HVAC engineers, mechanical designers, and technicians calculate air flow rates for duct systems and ventilation applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Volumetric flow rate (GPM)
• \( V \) — Velocity of air (ft/s)
• \( A \) — Cross-sectional area (ft²)
• \( 448.83 \) — Conversion factor (ft³/s to GPM)

Explanation: The formula converts the product of velocity and area (which gives ft³/s) to gallons per minute (GPM).

3. Importance of Air Flow Rate Calculation

Details: Accurate flow rate calculations are essential for proper HVAC system design, ensuring adequate ventilation and energy efficiency.

4. Using the Calculator

Tips: Enter the air velocity in ft/s and the cross-sectional area in ft². Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why use GPM for air flow?
A: While CFM is more common for air, GPM equivalent helps when comparing with liquid systems or certain industrial applications.

Q2: What's a typical air velocity in ducts?
A: Typically 800-1200 ft/min (13.3-20 ft/s) for main ducts, lower for branch ducts.

Q3: How do I find cross-sectional area?
A: For round ducts: \( A = \pi \times r^2 \). For rectangular ducts: \( A = width \times height \).

Q4: Why the 448.83 conversion factor?
A: It converts cubic feet per second to gallons per minute (1 ft³/s = 448.83 GPM).

Q5: Can I use this for liquid flow?
A: Yes, the same formula applies to incompressible fluids like water when using proper units.