Calculator Inputs
Formula Used
- Volume = length × width × height
- CFM = (Volumeft³ × ACH) ÷ 60
- m³/h = Volumem³ × ACH
- With safety = airflow × (1 + safety%/100)
- CFM = velocityfpm × areaft²
- m³/h = velocitym/s × aream² × 3600
- Design basis = chosen method (or max of both)
- Diffusers = ceil(design airflow ÷ diffuser capacity)
Note: Cleanroom performance depends on filtration, heat loads, layout, and controls; treat this tool as a sizing starting point.
How to Use This Calculator
- Select a unit system and the method your project requires.
- Enter room dimensions, then set target ACH or velocity and area.
- Add a safety factor and diffuser capacity for distribution estimates.
- Choose a pressure regime to estimate return/exhaust airflow.
- Press Calculate Airflow; download a CSV or PDF report.
Example Data Table
| Scenario | Room (L×W×H) | Target | Safety | Estimated Supply | Estimated Diffusers |
|---|---|---|---|---|---|
| ISO 7, mixing | 6 m × 4 m × 3 m | 80 ACH | 10% | ≈ 6,336 m³/h | ≈ 8 (850 m³/h each) |
| Unidirectional zone | 4 m × 3 m × 3 m | 0.45 m/s × 1.5 m² | 15% | ≈ 2,795 m³/h | Depends on terminal unit sizing |
| Support corridor | 10 ft × 8 ft × 10 ft | 20 ACH | 5% | ≈ 280 CFM | ≈ 2 (150 CFM each) |
Examples are illustrative; actual designs should follow your governing standard and project specs.
Cleanroom airflow sizing links construction choices to measurable performance checks. Use the notes below alongside the calculator outputs.
Airflow as a compliance driver
Airflow supports particulate control by diluting and transporting contaminants to filters. Typical screening ranges are often cited, such as ISO 7 at roughly 60–150 ACH and ISO 8 at about 20–60 ACH. Always follow your specification, because process loads, occupancy, and zoning can shift targets.
Choosing between ACH and velocity sizing
The air-change method scales airflow with room volume, while the velocity method sizes flow through a defined opening or filter bank. Unidirectional zones often target approximately 0.30–0.50 m/s at the filter face. If you select both methods, the higher result is a conservative design basis.
- Example data: 6 × 4 × 3 m room = 72 m³ volume.
- At 80 ACH, supply = 72 × 80 = 5,760 m³/h.
- With 10% safety factor, design supply ≈ 6,336 m³/h.
Balancing supply, return, and pressure control
Pressure regime influences how much air is returned or exhausted relative to supply. A positive room may return about 90% of supply to allow a controlled bleed. A negative room may exhaust about 110% to maintain inward leakage. Use project-specific setpoints and verify leakage paths.
Diffuser distribution and terminal sizing
After estimating total airflow, distribution quality becomes the next risk. The diffuser count estimate divides design airflow by a nominal terminal capacity, then rounds up. Confirm the selected terminal meets throw, noise, and face-velocity limits. More locations can improve uniformity. Iterate after ceiling layouts and equipment penetrations are finalized.
Commissioning checks and documentation
During commissioning, sum measured terminal flows to confirm total supply and compute achieved ACH from actual airflow and room volume. Compare results to the design basis, then record final balancing values and filter details for turnover and requalification planning.
FAQs
1) What does ACH mean in a cleanroom?
ACH is air changes per hour. It describes how many room volumes of air are supplied each hour, based on total supply airflow and room volume. It is commonly used as a sizing and verification metric.
2) When should I use the velocity method?
Use velocity × area when airflow is defined through a filter bank, opening, or unidirectional zone. It is helpful when specifications state a face velocity target rather than a room ACH requirement.
3) Why does the calculator add a safety factor?
A safety factor adds margin for leakage, future load growth, balancing tolerance, and operational variability. It helps avoid undersizing early in design. Keep it reasonable and align it with your project’s commissioning expectations.
4) How do I choose diffuser capacity?
Use the manufacturer’s rated airflow for the diffuser or terminal unit at your expected static pressure and noise criteria. If only a rough estimate is available, pick a conservative value and refine it during detailed design.
5) How does pressure regime affect return or exhaust?
Positive rooms often return slightly less than supply to create a controlled outward bleed. Negative rooms often exhaust more than supply to pull air inward. The exact ratio depends on leakage paths, door operation, and control strategy.
6) Does higher airflow always mean a cleaner room?
No. Cleanliness also depends on filtration efficiency, airflow pattern, turbulence, process emissions, and housekeeping. Excess airflow can raise energy use and drafts without improving performance if the airflow pattern is poorly distributed.
7) Can I use this tool for retrofit balancing?
Yes. Enter the measured supply airflow to estimate achieved ACH and compare it with targets. Treat results as a screening step, then validate with field measurements, pressure checks, and any required particle testing.