Pressure Drop Calculator Air Duct

Pressure Drop Formula:

\[ \Delta P = \frac{f \cdot L}{D_h} \cdot \frac{\rho \cdot V^2}{2} \]

Friction Factor (f):

Duct Length (L):

Hydraulic Diameter (D_h):

Air Density (ρ):

kg/m³

Air Velocity (V):

m/s

Pressure Drop (ΔP):

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1. What is a Pressure Drop Calculator for Air Ducts?

Definition: This calculator estimates the pressure loss in air ducts due to friction using the Darcy-Weisbach equation.

Purpose: It helps HVAC engineers and technicians determine the pressure loss in duct systems for proper fan selection and system design.

2. How Does the Calculator Work?

The calculator uses the Darcy-Weisbach equation:

\[ \Delta P = \frac{f \cdot L}{D_h} \cdot \frac{\rho \cdot V^2}{2} \]

Where:

\( \Delta P \) — Pressure drop (Pascals)
\( f \) — Friction factor (dimensionless)
\( L \) — Duct length (meters)
\( D_h \) — Hydraulic diameter (meters)
\( \rho \) — Air density (kg/m³)
\( V \) — Air velocity (m/s)

Explanation: The equation calculates the pressure loss due to friction as air flows through ducts.

3. Importance of Pressure Drop Calculation

Details: Accurate pressure drop estimation ensures proper airflow, energy efficiency, and correct fan sizing in HVAC systems.

4. Using the Calculator

Tips: Enter the friction factor (default 0.02 for smooth ducts), duct length, hydraulic diameter, air density (default 1.2 kg/m³), and air velocity. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical friction factor for ducts?
A: For smooth metal ducts, 0.02 is common. For rough ducts, it can be 0.03-0.05.

Q2: How do I find hydraulic diameter?
A: For round ducts, it's the actual diameter. For rectangular ducts: \( D_h = \frac{2 \cdot (width \cdot height)}{width + height} \)

Q3: When would air density change?
A: Density varies with altitude and temperature. At higher elevations or temperatures, use lower density values.

Q4: What's a typical air velocity in ducts?
A: Main ducts: 6-12 m/s, branch ducts: 4-8 m/s, residential: 3-5 m/s.

Q5: Does this include dynamic losses?
A: No, this calculates only friction losses. Add 10-30% for fittings and dynamic losses.