1. What is a Pressure Drop Calculator?

Definition: This calculator estimates the pressure loss (ΔP) in ductwork based on airflow rate, duct size, and length.

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

2. How Does the Calculator Work?

The calculator uses the Darcy-Weisbach equation:

Where:

• \( \Delta P \) — Pressure drop (inches water gauge)
• \( f \) — Friction factor (dimensionless)
• \( L \) — Duct length (feet)
• \( D \) — Hydraulic diameter (inches)
• \( \rho \) — Air density (lb/ft³)
• \( V \) — Air velocity (ft/min)

Explanation: The calculation accounts for friction losses in the ductwork based on airflow characteristics and duct dimensions.

3. Importance of Pressure Drop Calculation

Details: Proper pressure drop estimation ensures adequate airflow throughout the system, proper fan selection, and energy-efficient operation.

4. Using the Calculator

Tips: Enter the airflow in CFM, duct size in inches, and duct length in feet (default 100 ft). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical acceptable pressure drop?
A: For most HVAC systems, 0.1 to 0.3 in wg/100 ft is considered acceptable.

Q2: How does duct shape affect pressure drop?
A: Round ducts have lower pressure drop than rectangular ducts at equivalent flow rates.

Q3: What factors increase pressure drop?
A: Higher velocities, smaller ducts, longer runs, and surface roughness all increase pressure drop.

Q4: How do I reduce pressure drop in my system?
A: Increase duct size, reduce length, minimize fittings/elbows, and maintain smooth interior surfaces.

Q5: Does this calculator account for fittings?
A: No, this calculates straight duct only. Add 20-50% for typical fitting losses.