1. What is the AHU CFM Calculation?

The CFM (Cubic Feet per Minute) calculation for Air Handling Units (AHU) determines the required airflow to meet a specific cooling load based on the temperature difference between supply and return air.

2. How Does the Calculator Work?

The calculator uses the CFM equation:

Where:

• \( CFM \) — Airflow in cubic feet per minute
• \( Cooling\ Load \) — Total cooling capacity needed in BTU per hour
• \( \Delta T \) — Temperature difference between supply and return air in °F
• 1.08 — Constant that incorporates air density and specific heat

Explanation: The equation calculates how much air needs to be moved to achieve the desired cooling effect based on the temperature difference.

3. Importance of CFM Calculation

Details: Proper CFM calculation ensures efficient HVAC system operation, adequate cooling capacity, and proper air distribution throughout the space.

4. Using the Calculator

Tips: Enter cooling load in BTU/h and temperature difference in °F. Both values must be positive numbers for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is the 1.08 constant in the formula?
A: It's derived from the product of air density (0.075 lb/ft³) and specific heat (0.24 BTU/lb-°F) multiplied by 60 (minutes/hour).

Q2: What's a typical ΔT for AHU systems?
A: Most systems operate with ΔT between 15-20°F for comfort cooling applications.

Q3: How does altitude affect the calculation?
A: At higher altitudes, air density decreases, so the constant should be adjusted (typically becomes smaller).

Q4: Can this be used for heating calculations?
A: Yes, the same formula applies for heating, though typical ΔT values may differ.

Q5: What if my system uses variable air volume?
A: This calculation gives the design CFM; VAV systems will modulate airflow based on actual load.