Calculator Inputs
Example Data Table
| Case | Airflow (m³/h) | Diameter (mm) | Total Length (m) | Velocity (m/s) | Pressure Drop (Pa) | Fan Power (W) |
|---|---|---|---|---|---|---|
| Office Supply Run | 2500 | 315 | 24 | 8.91 | 68.73 | 73.43 |
| Workshop Exhaust | 4000 | 400 | 30 | 8.84 | 63.17 | 107.99 |
| Kitchen Extract | 1800 | 250 | 21 | 10.19 | 103.15 | 79.35 |
| Plant Room Vent | 3200 | 355 | 26 | 8.98 | 65.26 | 89.25 |
Formula Used
Pipe area: A = πD² / 4
Airflow conversion: Q(m³/s) = Q(m³/h) / 3600
Velocity: V = Q / A
Reynolds number: Re = ρVD / μ
Laminar friction factor: f = 64 / Re
Turbulent friction factor: Swamee-Jain equation
Velocity pressure: Pv = ρV² / 2
Pressure loss: ΔP = f(L / D) × (ρV² / 2)
Fan power: Power = (ΔP × Q) / η
Suggested diameter: D = √(4Q / πVtarget)
This model gives fast engineering estimates for circular ventilation runs. Real projects should also review leakage, noise, temperature, altitude, dampers, and terminal losses.
How to Use This Calculator
- Enter the required airflow in cubic meters per hour.
- Enter the selected circular pipe diameter.
- Add straight length and equivalent fittings length.
- Set roughness, density, viscosity, and fan efficiency.
- Enter target velocity and optional room volume.
- Submit the form to view results above.
- Review pressure loss, velocity, Reynolds number, and fan power.
- Use the graph to compare alternative diameters quickly.
- Download the result summary as CSV or PDF.
Ventilation Pipe Design Notes
Why sizing matters
Ventilation pipe sizing affects air quality, noise, and energy use. A small pipe raises air speed. That increases friction loss. It also makes the fan work harder. A larger pipe lowers resistance, but it needs more space and material. Good design balances velocity, pressure drop, installation limits, and operating cost.
What this calculator evaluates
This calculator estimates key duct performance values for a circular ventilation run. It converts airflow into velocity. It then checks Reynolds number and selects a friction factor method. After that, it estimates total pressure loss across the straight pipe and fitting allowance. It also estimates fan power from pressure loss, airflow, and fan efficiency.
Why pressure loss is important
Pressure loss is one of the most important ventilation design checks. High loss means higher fan power. High power means higher running cost. It can also reduce delivered airflow if the fan cannot overcome system resistance. By checking pressure drop early, engineers can avoid poor duct selections and oversize fans less often.
How velocity changes performance
Velocity influences noise and system stability. Low velocity usually means quieter operation. Very high velocity often means rumble, hiss, and larger pressure losses. It can also increase terminal imbalance. The target velocity field helps you compare your chosen diameter with a more practical size for steady ventilation duty.
Using the graph for decisions
The diameter sensitivity graph shows how pressure loss and velocity move together. As diameter rises, velocity falls. Pressure drop usually falls sharply too. This trend helps engineers justify a better pipe size during early design, value engineering, or retrofit planning. It is useful for workshops, offices, mechanical rooms, and exhaust runs.
Important design reminder
This tool gives a strong first estimate. Final design should still consider local codes, sound limits, pipe material, temperature, dust loading, leakage class, balancing devices, and fire protection details.
FAQs
1. What does this ventilation pipe calculator measure?
It estimates airflow velocity, Reynolds number, friction factor, pressure drop, fan power, air changes, and a suggested pipe diameter for a chosen target velocity.
2. Is this calculator only for circular pipes?
Yes. The formulas in this file use circular cross section area. Rectangular ducts need equivalent diameter or separate duct formulas.
3. Why do I need equivalent fittings length?
Elbows, tees, dampers, and transitions add resistance. Equivalent length converts those local losses into a simple added length for quick design estimates.
4. What is a good ventilation velocity?
Many comfort systems prefer moderate values, often around 4 to 8 m/s. Industrial systems may run higher. Noise and pressure loss should guide the final choice.
5. Why is Reynolds number shown?
Reynolds number helps identify flow regime. The regime determines how friction factor is estimated and affects the final pressure loss result.
6. Can I use default air density and viscosity?
Yes, for quick indoor estimates. For hot air, cold air, altitude changes, or special gases, enter project-specific properties for better accuracy.
7. Does fan power equal motor size?
No. This result is airflow power adjusted by fan efficiency. Real motor selection also considers drive losses, safety margin, startup duty, and manufacturer data.
8. Should I rely on this result for final construction drawings?
Use it for early engineering checks and option comparisons. Final documents should still be reviewed against project codes, acoustic limits, and full system layouts.