Beyond Air Changes: How to Evaluate Cleanroom Airflow Performance

Question: Is a high air change rate enough to guarantee good cleanroom airflow performance?
Not necessarily. A cleanroom can have a high air change rate and still experience uneven airflow, stagnant zones, or poor contaminant removal around equipment.
For semiconductor manufacturing, where airborne particles can affect sensitive processes, airflow performance should be evaluated as a complete system - not simply by counting how many times the room air is circulated each hour.

1. Technical Basics: What Really Determines Airflow Performance? Airflow performance depends on several interconnected factors. Air Change Rate (ACH) ACH indicates how many room volumes of air are supplied or circulated per hour, depending on the system and calculation method. It is a useful design parameter, but it does not directly show whether air reaches every critical area effectively. The calculation is: ACH = Supply Airflow Rate (m³/h) ÷ Room Volume (m³) For example, a room measuring 10 m × 8 m × 3 m has a volume of 240 m³. If the measured supply airflow is 12,000 m³/h, the calculated ACH is 50. However, this figure alone cannot confirm that contaminants are being removed efficiently. Airflow Distribution and Dead Zones Air supply and return locations must work together. Poorly positioned equipment, blocked return grilles, and obstacles beneath ceiling filters can disrupt airflow and create recirculation zones. In semiconductor cleanrooms, airflow visualization and, where appropriate, computational fluid dynamics (CFD) can help identify these issues before finalizing the layout. HEPA Filtration Efficiency and Integrity HEPA filters remove airborne particles from the air passing through them. However, overall performance also depends on correct installation, airtight sealing, appropriate airflow, and the absence of filter damage or bypass leakage. A filter's nominal efficiency does not automatically guarantee the cleanliness of the entire room. Airflow Velocity and Direction Unidirectional airflow may be appropriate for critical work zones that require a more controlled particle-removal path. Mixed-flow systems can be suitable for other cleanroom applications. The correct approach depends on the cleanliness target, process requirements, equipment arrangement, and contamination risks.
2. Industry Solutions: How Can Semiconductor Cleanrooms Improve Airflow? For semiconductor facilities, a practical evaluation should cover four areas. Optimize HEPA filter placement: Distribute terminal filters according to the required cleanliness level and airflow design rather than simply maximizing filter quantity.

Coordinate supply and return air: Avoid placing large equipment or storage units where they obstruct designed airflow paths.

Verify pressure relationships: Maintain the specified pressure differentials between adjacent areas to help control contaminant migration.

Test actual performance: Use airflow volume and velocity measurements, airflow visualization, HEPA filter integrity testing, and airborne particle measurements as applicable.

Energy efficiency should also be considered. Increasing airflow indiscriminately can raise fan energy consumption without necessarily solving the underlying distribution problem.
The goal is to achieve the required cleanliness and process protection with a properly balanced, verifiable airflow system.

1. Practical Application: A Typical Semiconductor R&D Cleanroom Scenario Consider a hypothetical semiconductor R&D facility preparing a cleanroom for wafer inspection and process development. During initial operation, the room achieves its specified average air change rate. However, particle readings near a large inspection tool remain higher than expected. Rather than immediately increasing the total airflow, the engineering team investigates several possible causes: The equipment may be obstructing the intended airflow path. Return air grilles may be poorly positioned relative to the equipment. Airflow distribution beneath the ceiling HEPA filters may be uneven. A filter seal or installation issue may require inspection.

The team then reviews the equipment layout, measures airflow, performs visualization testing, and checks filter integrity where necessary. Adjustments are made based on the findings, followed by repeat performance testing.
This is an illustrative scenario, not a report of a specific completed project. It demonstrates why airflow diagnosis should come before simply increasing ACH.

1. Product Considerations: Selecting the Right HEPA Air Filter Once the airflow design and required filtration performance are established, selecting an appropriate HEPA filter becomes an important part of the solution. For semiconductor cleanroom applications, engineers should consider: Required filtration efficiency and particle-size test basis Rated airflow and initial pressure drop Filter dimensions and compatibility with the housing Sealing method and installation requirements Chemical compatibility and environmental conditions Filter integrity testing and maintenance access

A higher airflow rating is not automatically better. The selected filter must operate within its specified conditions while meeting the cleanroom's performance requirements.
For example, an H13 HEPA air filter rated at 1,750 m³/h may be considered for a compatible air-handling or cleanroom filtration application. Its suitability must be verified against the actual system design, required efficiency, pressure drop, and installation conditions.
Conclusion
Good cleanroom airflow performance is not defined by ACH alone. It depends on effective airflow distribution, appropriate HEPA filtration, pressure control, equipment layout, and verification under relevant operating conditions.
For semiconductor facilities, the best approach is to evaluate the complete airflow system, identify the actual source of performance issues, and make adjustments based on measured evidence.
Further reading: H13 HEPA Cleanroom Air Filter - 1,750 m³/h
https://www.prefabcleanroom.com/sale-13568780-anticorrosion-1750m3-h-h13-clean-room-hepa-air-filter.html
GCC Tech provides cleanroom equipment and filtration solutions for industrial and controlled-environment applications.