Clean rooms demand air handling systems designed to create and maintain controlled conditions. Contamination control at levels far beyond normal building requirements needs specialised equipment and careful design.
What Makes Clean Rooms Different
Clean rooms control airborne particle concentrations to specified limits. The cleaner the room, the tighter the control:
| ISO Class | Max Particles ≥0.5μm per m³ |
|---|---|
| ISO 5 | 3,520 |
| ISO 6 | 35,200 |
| ISO 7 | 352,000 |
| ISO 8 | 3,520,000 |
For comparison, typical office air contains millions of particles per cubic metre. Clean rooms need air handling systems specifically designed for contamination control.
Air Handling Requirements
Filtration
The defining feature of clean room air handling. HEPA (High Efficiency Particulate Air) filters remove 99.97% of particles at 0.3μm. ULPA (Ultra Low Penetration Air) filters remove 99.999%.
Filter location matters. Terminal filters at the point of supply into the room provide the cleanest air. Pre-filtration protects expensive terminal filters and extends their life.
Air Change Rates
High air change rates dilute any particles generated within the room. Required rates depend on classification:
- ISO 5: 240-600 air changes per hour
- ISO 6: 90-180 air changes per hour
- ISO 7: 30-60 air changes per hour
- ISO 8: 10-25 air changes per hour
These rates are far higher than normal building ventilation, requiring substantial air handling capacity.
Airflow Patterns
Unidirectional (Laminar) Flow – Parallel streamlines moving uniformly across the room. Used for highest cleanliness classes. Air sweeps particles toward return grilles without turbulent mixing.
Non-Unidirectional (Turbulent) Flow – Mixed airflow pattern. Suitable for lower cleanliness classes. Less critical positioning of supply and return.
Pressurisation
Clean rooms maintain positive pressure relative to surrounding spaces. This ensures air leakage flows outward, preventing contamination entering through gaps and openings.
Pressure cascades from cleanest to least clean areas. Airlocks maintain pressure during personnel movement.
Temperature and Humidity Control
Many clean room applications require tight temperature and humidity control – for process requirements, product stability, or electrostatic discharge prevention.
Tolerances are often ±0.5°C or tighter, demanding precise control systems.
Design Considerations
Air Handling Unit Design
Clean room AHUs differ from standard units:
- Low-leakage construction minimises bypass
- Internal surfaces are smooth and cleanable
- Materials resist particle generation
- Access enables thorough cleaning
- Filters integrate properly without bypass
Ductwork
Clean room ductwork must not contribute contamination:
- Sealed construction prevents leakage
- Internal surfaces are smooth
- Materials resist particle shedding
- Cleaning access is provided
Terminal Devices
Supply terminals for clean rooms include:
- HEPA filter housings for terminal filtration
- Laminar flow diffusers for unidirectional applications
- Appropriate dampers for balancing
Controls
Clean room controls must maintain:
- Precise temperature and humidity
- Stable pressure relationships
- Alarm conditions when parameters drift
- Monitoring and recording for compliance
Testing and Certification
Clean rooms require testing to verify performance:
Installation Verification
- Filter integrity testing
- Air velocity measurements
- Pressure differential verification
Operational Verification
- Particle counting at operational conditions
- Recovery testing after contamination events
- Performance at various operational states
Ongoing Monitoring
- Continuous particle counting in critical applications
- Regular verification testing
- Trend analysis to detect degradation
Regulatory Considerations
Clean rooms in regulated industries must comply with relevant standards:
- GMP (Good Manufacturing Practice) for pharmaceuticals
- ISO 14644 for general clean room classification
- Industry-specific requirements (electronics, aerospace, medical devices)
Documentation demonstrating compliance is essential. Air handling systems must support required documentation.
Our Clean Room Capability
i-Flow manufactures air handling units for clean room applications. We design systems to meet specific classification requirements and support compliance documentation.
Contact us to discuss your clean room air handling needs.
