HVAC Pressure Drop Calculator

Pressure Drop Formula:

\[ \Delta P = f \times \left( \frac{L}{D_h} \right) \times \left( \frac{\rho \times V^2}{2} \right) \]

Friction Factor (f):

Duct Length (L):

Hydraulic Diameter (D_h):

Air Density (ρ):

kg/m³

Air Velocity (V):

m/s

Pressure Drop (ΔP): Pa

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1. What is an HVAC Pressure Drop Calculator?

Definition: This calculator estimates the pressure loss in HVAC ductwork using the Darcy-Weisbach equation with hydraulic diameter.

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

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \Delta P = f \times \left( \frac{L}{D_h} \right) \times \left( \frac{\rho \times V^2}{2} \right) \]

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 formula calculates the pressure loss due to friction in the ductwork based on system characteristics.

3. Importance of Pressure Drop Calculation

Details: Accurate pressure drop calculations ensure 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 hydraulic diameter?
A: It's a characteristic length used for non-circular ducts, calculated as \( D_h = \frac{4 \times \text{Area}}{\text{Perimeter}} \).

Q2: How do I find the friction factor?
A: For smooth ducts, use 0.02-0.03. For rough ducts, use Moody chart or Colebrook equation based on relative roughness.

Q3: What's a typical air velocity in ducts?
A: Residential systems: 2.5-5 m/s, Commercial: 5-10 m/s, Industrial: up to 15 m/s depending on application.

Q4: Does this include dynamic losses?
A: No, this only calculates friction losses. Add dynamic losses (elbows, fittings) separately.

Q5: How does pressure drop affect system design?
A: Higher pressure drops require more powerful fans, increasing energy costs. Designers aim to minimize pressure drop.