CFM Calculation For AHU

Air Handling Unit Airflow Formula:

\[ CFM = \frac{BTU/hr \times 1.08}{\Delta T} \]

CFM:

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1. What is CFM Calculation For AHU?

CFM (Cubic Feet per Minute) calculation for AHU (Air Handling Unit) determines the airflow rate required to meet specific heating or cooling loads. This calculation is essential for proper HVAC system design and sizing.

2. How Does the Calculator Work?

The calculator uses the AHU airflow formula:

\[ CFM = \frac{BTU/hr \times 1.08}{\Delta T} \]

Where:

\( CFM \) — Cubic Feet per Minute (airflow rate)
\( BTU/hr \) — British Thermal Units per hour (heating/cooling capacity)
\( \Delta T \) — Temperature difference across the coil (°F)
\( 1.08 \) — Constant derived from air density and specific heat

Explanation: The formula calculates the airflow needed to transfer the specified amount of heat energy given the temperature difference across the air handling unit.

3. Importance of CFM Calculation

Details: Accurate CFM calculation ensures proper HVAC system performance, energy efficiency, and occupant comfort. Undersized systems struggle to maintain temperatures, while oversized systems cycle frequently and waste energy.

4. Using the Calculator

Tips: Enter BTU/hr (heating or cooling capacity) and ΔT (temperature difference across the coil). Both values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What does the constant 1.08 represent?
A: The constant 1.08 is derived from the product of air density (0.075 lb/ft³) and specific heat of air (0.24 BTU/lb-°F) multiplied by 60 minutes.

Q2: What is a typical ΔT for AHU systems?
A: Typical ΔT values range from 15-25°F for cooling applications and 30-70°F for heating applications, depending on system design.

Q3: How does CFM affect system performance?
A: Proper CFM ensures efficient heat transfer, adequate air distribution, and maintains designed temperature differentials across coils.

Q4: Can this formula be used for both heating and cooling?
A: Yes, the formula works for both heating and cooling calculations, though typical ΔT values differ between applications.

Q5: What factors affect CFM requirements?
A: CFM requirements depend on building load, space usage, occupancy, equipment efficiency, and desired temperature conditions.