Understanding Cleanroom Filtration: From Pre-Filters to HEPA and ULPA Solutions
Cleanroom filter requirements vary depending on the cleanliness level, and a three-stage filtration system—pre-filter, medium filter, and HEPA/ULPA filter—is essential. For the electronics industry, H13 and H14 HEPA filters are commonly used; pharmaceutical settings require antimicrobial HEPA filters; and surgical rooms must include leak detection ports. Pre-filters are replaced every 1–3 months, while high-efficiency filters are tested every 1–3 years. PAO testing is used to ensure sealing integrity, and TÜV-certified brands are recommended for better cost control.
1. Define the Cleanroom Classification Requirements
- Cleanroom standards such as ISO 14644-1 or industry-specific regulations like GMP in pharmaceuticals help determine the required cleanliness class (e.g., ISO Class 5, Class 7).
- The higher the cleanliness class, the stricter the filtration efficiency requirements. Higher-grade filters must be combined for optimal air purity.
2. Selecting the Right Three-Stage Filtration System
Pre-Filter (Initial Efficiency Filter)
- Function: Captures large particles (≥5μm) and protects subsequent filters.
- Recommendation: Choose G3/G4 (EN779) or MERV 5–8 (ASHRAE) rated filters made from polyester or nonwoven fabric.
- Application: Typically installed at the air intake of HVAC or fresh air systems.
Medium Efficiency Filter
- Function: Filters medium-sized particles (1–5μm) such as dust and pollen.
- Recommendation: Select filters rated F5–F9 (EN779) or MERV 9–16, commonly made of fiberglass or synthetic fibers.
- Application: Placed after pre-filters and before HEPA filters to extend HEPA filter life.
HEPA/ULPA Filter (High-Efficiency Filters)
- Function: Captures fine particles (≥0.3μm) such as bacteria, viruses, and submicron particulates.
- Recommendation:
- HEPA: Use H13 (≥99.97% @ 0.3μm) or H14 (≥99.995%) for ISO Class 5–7 cleanrooms.
- ULPA: Use U15–U17 (≥99.9995% @ 0.12μm) for ISO Class 3–5 environments.
- Materials: Made from ultra-fine fiberglass media; proper sealing is critical (gel seal or knife-edge design is recommended).
3. Key Selection Criteria
- Filtration Efficiency and Certification: Ensure compliance with EN 1822 and IEST RP-CC001.5.
- Airflow and Pressure Drop: Match filter airflow with cleanroom needs, avoiding excessive pressure drop.
- Material and Construction: HEPA filters must be heat- and moisture-resistant; pre-/medium filters should be durable and easy to replace.
- Antibacterial and Chemical Resistance: Required for biomedical and chemical applications.
4. Application-Specific Recommendations
- Electronics: Use H13/H14 HEPA filters with pre-/medium stages.
- Pharmaceutical/Biotech: Choose antimicrobial HEPA filters with regular leak testing.
- Food Processing: Use moisture- and mold-resistant filters with stainless steel frames.
- Hospital Operating Rooms: Use medical-grade filters with leak test ports.
5. Maintenance and Cost Optimization
- Replacement Cycle:
- Pre-filter: 1–3 months
- Medium filter: 6–12 months
- HEPA filter: 1–3 years
- Cost Management: Use cost-effective pre-/medium filters to extend HEPA filter lifespan.
6. Installation and Testing
- Sealing: Use PAO/DOP testing to verify HEPA filter sealing.
- Pressure Monitoring: Install gauges to track filter blockage.
- Certified Brands: Choose TÜV, UL, or ISO-certified brands such as Camfil, AAF, or Freudenberg.
Summary: Typical Filter Configurations by Cleanroom Class
- ISO Class 7: G4 + F8 + H13
- ISO Class 5: G4 + F9 + H14 or ULPA U15
- ISO Class 3: ULPA U17 with FFU
By following these best practices and tailoring filter choices to specific cleanroom requirements, organizations can ensure long-term performance while optimizing operational costs.
