1. What is CFM Calculation From Velocity Pressure?

CFM (Cubic Feet Per Minute) calculation from velocity pressure is a method used in HVAC and ventilation systems to determine airflow rate. It uses the relationship between velocity pressure and the cross-sectional area of the duct to estimate the volume of air moving through the system.

2. How Does the Calculator Work?

The calculator uses the CFM formula:

Where:

• \( CFM \) — Cubic Feet Per Minute (ft³/min)
• \( A \) — Cross-sectional area (ft²)
• \( VP \) — Velocity pressure (in WG)
• 4005 — Constant derived from standard air density

Explanation: The formula calculates airflow by multiplying the constant 4005 (which accounts for standard air density) by the cross-sectional area and the square root of the velocity pressure.

3. Importance of CFM Calculation

Details: Accurate CFM calculation is essential for proper HVAC system design, balancing airflow in ventilation systems, ensuring adequate air exchange rates, and maintaining indoor air quality standards.

4. Using the Calculator

Tips: Enter the cross-sectional area in square feet and velocity pressure in inches water gauge. Both values must be positive numbers. The calculator will compute the CFM value based on these inputs.

5. Frequently Asked Questions (FAQ)

Q1: What is velocity pressure in HVAC systems?
A: Velocity pressure is the pressure caused by air movement in a duct, measured in inches water gauge (in WG). It represents the kinetic energy of the moving air.

Q2: Why is the constant 4005 used in the formula?
A: The constant 4005 is derived from standard air density conditions (0.075 lb/ft³) and conversion factors. It ensures the formula produces accurate results under standard conditions.

Q3: How do I measure velocity pressure?
A: Velocity pressure is typically measured using a pitot tube connected to a differential pressure gauge or manometer, taking readings at multiple points across the duct for accuracy.

Q4: Can this formula be used for non-standard air densities?
A: The formula assumes standard air density. For non-standard conditions (high altitude, extreme temperatures), correction factors should be applied to ensure accuracy.

Q5: What are typical CFM values for residential HVAC systems?
A: Residential systems typically range from 600-2000 CFM, depending on the size of the home and system capacity. Commercial systems can range from 2000-20,000+ CFM.