Duct Design Calculator
Quickly estimate duct friction & fitting losses with this premium layout.
| Material | Shape | L (mm) | D1 (mm) | D2 (mm) | Flow (L/s) | FD | VD | VAV | Flex | 90° | 45° | Dbl 90° | Grille | Loss (m) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Overall Duct Loss: | 0.000 | ||||||||||||||
Global Custom K Overrides (optional)
How to Use This Calculator
- Add a Row: Click the Add Row button to begin entering a new duct segment.
- Select Material & Shape: Choose the material (e.g., Galvanized Iron, Steel) and shape (Rectangular or Circular). The hydraulic diameter and friction factor will automatically adjust.
- Enter Dimensions: Input the length and cross-sectional dimensions of the duct in millimeters. For circular ducts, only Diameter 1 is required.
- Input Airflow: Specify the airflow rate in Liters per second (L/s). The calculator will determine the air velocity and pressure drop for the straight run.
- Add Fittings: If your segment contains dampers, VAV boxes, elbows, or grilles, enter the quantity of each. The calculator will automatically apply standard ASHRAE K-factors.
- Customize K-Factors (Optional): If you have manufacturer-specific K-factors, expand the Global Custom K Overrides panel and enter your custom values.
- Review Results: The individual row loss is shown on the right. The Overall Duct Loss and detailed airflow metrics (Velocity, Reynolds Number, Friction Factor) will display in the Results Summary at the bottom.
- Print Report: Use the Print button to generate a clean, formatted report of your duct design for documentation.
How It Works (Engineering Principles)
This calculator is built on fundamental fluid mechanics and methodologies outlined in the ASHRAE Handbook. It computes pressure losses through a combination of the following principles:
- Darcy-Weisbach Equation: Used to calculate the frictional pressure drop along straight duct runs. It considers the duct’s length, hydraulic diameter, internal surface roughness (based on the selected material), and the kinetic energy of the moving air.
- Colebrook-White Approximation: Calculates the friction factor (f) in turbulent flow regimes (Reynolds Number > 2300) based on the relative roughness of the duct material.
- Dynamic Losses (K-Factors): Pressure drops through fittings (elbows, dampers, diffusers) are calculated using the velocity pressure method. Default K-factors are based on standard industry guidelines but can be overridden globally.
- Continuity Equation: Air velocity is calculated dynamically based on the inputted volumetric flow rate and the computed cross-sectional area of the duct.
Note: Calculations are performed assuming standard air properties at typical indoor conditions (Density ρ ≈ 1.21 kg/m³, Kinematic Viscosity ν ≈ 1.5 × 10⁻⁵ m²/s).