Calculator Inputs
Example Data Table
| Scenario | Method | Inputs | Adjusted Flow | Notes |
|---|---|---|---|---|
| Workshop bay | ACH | 8×6×3 m, 6 ACH, safety 10% | ≈ 316.8 L/s (671 CFM) | Good for general dilution ventilation. |
| Site office | Per Person | 12 people, 10 L/s-person, safety 10% | ≈ 132.0 L/s (280 CFM) | Use code-driven rates for occupancy types. |
| Duct check | Duct | 400 mm, 4.0 m/s, safety 10% | ≈ 553.1 L/s (1,172 CFM) | Verify velocity limits for noise and loss. |
Formula Used
1) ACH method
Metric: Q(m³/h) = V(m³) × ACH, then Q(m³/s) = Q(m³/h) ÷ 3600.
Imperial: Q(CFM) = V(ft³) × ACH ÷ 60.
2) Per person method
Metric: Q(L/s) = People × Rate(L/s-person).
Imperial: Q(CFM) = People × Rate(CFM/person).
3) Per area method
Metric: Q(L/s) = Area(m²) × Rate(L/s-m²).
Imperial: Q(CFM) = Area(ft²) × Rate(CFM/ft²).
4) Duct velocity method
Metric: Q(m³/s) = A(m²) × v(m/s).
Imperial: Q(CFM) = A(ft²) × v(ft/min).
Adjustment factors
Qadjusted = Qbase × Outdoor% × Diversity% × (1+Safety%) ÷ System%.
Fan power estimate
Power(W) ≈ Q(m³/s) × ΔP(Pa) ÷ η. Use total static pressure and combined efficiency.
How to Use This Calculator
- Select your unit system and the calculation method.
- Enter room, occupancy, area, or duct inputs as needed.
- Set outdoor air, diversity, and safety to match your scenario.
- Add delivery efficiency if air is lost before reaching the space.
- Optionally enter static pressure and fan efficiency for power.
- Press Calculate to see results below the header.
- Use the download buttons to save CSV or PDF records.
Airflow targets for active construction zones
Ventilation design on site often starts with dilution. Air changes per hour (ACH) suits dusty bays, basements, and temporary enclosures where contaminants mix through the room. Higher ACH improves removal but increases fan size and energy. For cutting or solvents, add local capture and keep slight negative pressure to limit migration. Record the selected ACH and check practical constraints like access and filter loading.
Occupancy and area-based sizing
When people and comfort dominate, per-person and per-area rates provide a clear compliance trail. Rates are commonly tied to space type (site office, welfare unit, meeting room) and expected density. Use this calculator to compare approaches in consistent units before fixing a design flow.
Duct velocity checks and practical limits
The duct method converts area and velocity into flow for quick feasibility checks. As velocity rises, friction losses and noise increase, and temporary duct runs become harder to support. Test circular or rectangular options early; if velocity is excessive, increase size or split into parallel branches.
Adjustment factors that reflect real delivery
Outdoor-air fraction distinguishes total supply from true fresh air. Diversity accounts for partial use, while safety margin covers uncertainty, leakage, and filter clogging. System delivery efficiency increases the required fan flow when losses occur before air reaches the occupied zone.
Energy and documentation with example data
Fan power is estimated from flow, static pressure, and efficiency: Power ≈ Q × ΔP ÷ η. Example data: 8×6×3 m at 6 ACH with 10% safety gives about 316.8 L/s (≈671 CFM). A 400 mm duct at 4.0 m/s with the same margin gives about 553.1 L/s (≈1,172 CFM). Confirm supply and make-up air paths, then verify with airflow readings during commissioning. Use measured pressure to refine power estimates later. Export CSV or PDF for inspection packs.
FAQs
1) Which method should I use first?
Start with ACH for temporary enclosures and dusty tasks. Use per-person or per-area when comfort and occupancy rules dominate. Use the duct method to confirm your selected duct size can carry the target flow.
2) What does Outdoor Air (%) change?
It converts total supply flow into true fresh air. If only 30% of the supply is outside air, set Outdoor Air to 30%. The adjusted target then reflects the fresh-air portion rather than total circulation.
3) Why include System Delivery (%)?
Long runs, leaks, poor distribution, or filters can reduce delivered airflow. System Delivery increases the required fan flow so the occupied zone still receives the intended ventilation after losses.
4) Is the fan power result exact?
It is a first-pass estimate using total static pressure and overall efficiency. Use it for early sizing and cost comparisons. Final selection should come from the fan curve, motor data, and measured system resistance.
5) How do I pick velocity for duct checks?
Choose a velocity that balances size and noise. Higher velocity reduces duct size but increases pressure loss and sound. If calculated velocity is too high, increase duct dimensions or split flow across multiple ducts.
6) What safety margin is reasonable?
Use a margin to cover uncertainty, filter loading, and future changes. For stable setups, 5–10% can be enough. For dusty or variable work zones, consider 10–20% and validate during commissioning.
7) Can I use the exports for reporting?
Yes. The CSV is convenient for spreadsheets and logs. The PDF provides a compact, printable summary for method statements, client signoff, and inspection packs, including the selected method and key results.