Types of Filters Used in HVAC System

In pharmaceutical HVAC systems, filters are crucial for maintaining clean air quality and ensuring compliance with Good Manufacturing Practices (GMP) and other regulations. The filters used in these systems can be categorized based on their efficiency and application in different cleanroom environments. Here’s a detailed breakdown of the common filter types, their integrity tests, and testing frequencies:

Types of Filters

a. Pre-Filters (G3/G4 or MERV 7-8)

• Purpose: Capture larger particles (dust, fibers, contaminants) to protect downstream filters.
• Material: Typically synthetic fibers.
• Efficiency: 80–90% for particles >10 μm.

b. Medium Filters/Bag Filters (M5-M6 or MERV 13-14)

• Purpose: Remove medium-sized particles (1–10 μm) to ensure better air quality and to protect HEPA filters.
• Material: Polyester or glass fiber.
• Efficiency: 60–95% for particles of 1–10 μm.

c. HEPA Filters (H13-H14)

• Purpose: Critical for filtering submicron particles, bacteria, and microorganisms.
• Material: Glass fiber.
• Efficiency: 99.97% at 0.3 μm for H13; 99.995% for H14.

d. ULPA Filters (U15-U17)

• Purpose: Used in ultra-clean areas (e.g., aseptic filling), capable of removing particles down to 0.1 μm.
• Material: Glass fiber.
• Efficiency: 99.9995% to 99.999995%.

e. Activated Carbon Filters

• Purpose: Remove chemical fumes, gases, and odors.
• Material: Activated carbon granules.
• Efficiency: Based on chemical adsorption.

Integrity Tests and Methods

a. Pre-Filters and Medium Filters

Tests:

• Visual Inspection: Check for physical damage or clogging.
• Pressure Drop Measurement: Ensures the filter is not overloaded.
• Frequency: Every 3-6 months, or based on differential pressure readings.

b. HEPA Filters

Tests:

• DOP/PAO Test: Validates filtration efficiency by challenging the filter with aerosol particles (Dispersed Oil Particulate or Poly Alpha Olefin).
• Airflow Velocity Test: Ensures uniform airflow distribution.
• Integrity Test: Checks for leaks using a particle counter or photometer.
• Frequency: Every 6-12 months, or after installation/maintenance.

c. ULPA Filters

• Tests: Similar to HEPA filters (DOP/PAO and airflow tests).
• Smoke Test: For visualizing leaks in critical cleanroom environments.
• Frequency: Every 6-12 months, or after any major disturbance.

d. Activated Carbon Filters

Tests:

• Adsorption Efficiency Test: Assesses the filter’s ability to adsorb target gases (e.g., by chemical sampling).
• Air Quality Analysis: Checks for the presence of residual volatile organic compounds (VOCs).
• Frequency: Annually or as per the manufacturer’s recommendation.

General Testing Frequency with References

Pre-Filters and Medium Filters:

• Frequency: Every 3 months and replaced when pressure drop exceeds set limits.

HEPA Filters:

• Frequency: Every 6-12 months (DOP/PAO test and airflow test).

Reference: ISO 14644-3.

These filter types, integrity tests, and their testing frequencies help ensure that pharmaceutical HVAC systems provide clean, safe environments essential for the manufacturing of pharmaceutical products. Regular testing and maintenance are key to preventing contamination and ensuring compliance with industry standards.

Read also: PQ Tests Used in HVAC Qualification for Pharmaceutical Facilities

Resource Person: Asad Ali