How to Select Filters: HEPA, ULPA, and Pre-Filters for HVAC



How to Select Filters: HEPA, ULPA, and Pre-Filters for HVAC

Published on 08/12/2025

How to Select Filters: HEPA, ULPA, and Pre-Filters for HVAC

Step 1: Understanding User Requirements Specification (URS) & Risk Assessment

The foundation of any validation lifecycle begins with a clear understanding of the User Requirements Specification (URS). This document outlines the specific needs and expectations that the HVAC system must meet. For filter selection, this includes criteria such as filtration efficiency, airflow requirements, and maintenance capabilities.

A comprehensive risk assessment should follow the URS creation, aligning with the principles outlined in ICH Q9. Identify risks associated with filter performance as it relates to product quality, contamination control, and regulatory compliance. Use tools such as Failure Mode and Effects Analysis (FMEA) to systematically evaluate potential failure points and their impact on product integrity.

  • Key Considerations: Identify critical parameters that affect the filtration method.
  • Documentation: Create a risk assessment report that details identified risks, mitigation strategies, and responsible individuals.
  • Regulatory Expectations: Ensure compliance with FDA Process Validation Guidance and EU GMP Annex 15.

Step 2: Protocol Design for Filter Selection Testing

The next step in the validation process

involves the creation of a detailed protocol that outlines the approach for filter evaluation. This includes determining the types of tests, acceptance criteria, and necessary documentation. Incorporate guidance from ICH Q8 regarding product and process design.

There are primarily three filter types to consider: HEPA (High Efficiency Particulate Air) filters, ULPA (Ultra-Low Penetration Air) filters, and pre-filters. Each filter type has specific applications, advantages, and limitations. Your protocol should define the testing methods required to assess the filtration efficiency and the operational limits of each filter type.

  • Sampling Plans: Establish a clear sampling plan that includes the number of samples, locations, and frequency of testing.
  • Statistical Criteria: Define the criteria for passing or failing the filters based on filtration efficiency and pressure drop data. Utilize control charts or process capability indices for validation.
  • Documentation: Include a version-controlled protocol that lists responsible personnel and outlines all procedures to ensure compliance with GxP.
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Step 3: Installation Qualification (IQ) for Filter Systems

Installation Qualification (IQ) is vital to verify that the HVAC system is installed correctly according to the specifications outlined in the URS and design protocol. The IQ phase should confirm that HEPA and ULPA filters are set up properly, utilizing qualified and calibrated instrumentation.

During the IQ, document the installation steps, including materials used, system configurations, and installation site details. Confirm that the filters adhere to the specified dimensions, and verify tightness against leakage as part of the installation process.

  • Key Activities: Check physical configuration and filter media integrity.
  • Documentation: Prepare an IQ report that summarizes the findings, configuration details, and any discrepancies noted during installation.
  • Regulatory Expectations: Align with Annex 15 for installation activities and system component verification.

Step 4: Operational Qualification (OQ) for Filter Performance Testing

Operational Qualification (OQ) focuses on verifying that the HVAC system operates within defined limits and performs according to the specifications under normal operating conditions. OQ is essential to demonstrate that filters, once installed, function as intended to maintain environmental control.

This step entails conducting performance tests on the filters, which should include airflow measurements, pressure drop evaluations, and particulate counts. It is recommended to conduct these tests under various operating conditions to simulate real-world usage.

  • Testing Procedures: Develop and execute protocols that specify the conditions and methods for measuring operational parameters.
  • Statistical Requirements: Use statistical methods to analyze data and affirm that filters maintain performance within the defined acceptance criteria.
  • Documentation: Generate and retain an OQ report that provides a detailed account of tests performed, results obtained, and conclusions drawn.
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Step 5: Performance Qualification (PQ) of HVAC Filters

Performance Qualification (PQ) serves to confirm the HVAC system, including selected filters, consistently maintains required operational parameters and product specifications over time. The PQ should occur after successful IQ and OQ completion and must account for the complete use cycle of the HVAC system.

During PQ, monitor the environment for a defined period under normal operating conditions post-filter installation. This phase should also include periodic challenges to the filters, such as increased particulate load simulations, to assess their long-term effectiveness and integrity.

  • Monitoring Approach: Establish a continuous or semi-continuous monitoring approach to assess filter performance in real time.
  • Documentation: Create a comprehensive PQ report summarizing the effectiveness of the filters over extended operation, including any failures or issues faced.
  • Regulatory Considerations: Ensure documentation aligns with requirements set forth by PIC/S and relevant local regulations.

Step 6: Continued Process Verification (CPV) Post-Qualification

Continued Process Verification (CPV) is an ongoing process that underpins the validation lifecycle’s sustainability post-qualification. The essential goal of CPV is to establish a procedure by which the filter performance is monitored continuously, and deviations are addressed promptly to ensure that quality is maintained.

CPV should include a program for routine monitoring of the HVAC system’s performance that is aligned with consistent data collection, trending, and statistical analysis. It should also encompass scheduled maintenance and service checks of filters, ensuring that records are maintained throughout the system’s life cycle.

  • Data Requirements: Define what data will be collected and how it will be used for trending and decision-making processes.
  • Documentation: Maintain records of all performance data and evaluations, which can be vital for demonstrating compliance during audits or inspections.
  • Regulatory Compliance: Ensure procedures are consistent with FDA and EMA standards by following the risk management principles from ICH Q9.

Step 7: Revalidation Strategy for HVAC Filters

Even after successful initial validation, revalidation of HVAC filters should be considered as part of the lifecycle management. Aging systems, changes in materials, or updates to regulatory requirements necessitate a revalidation strategy that reflects current practices and demands.

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The revalidation process should involve a thorough review of previous validations, assessment of any changes to installations, or filter replacements. It is critical to conduct periodic reviews and perform a complete validation cycle if significant changes are made.

  • Assessment Criteria: Identify triggers that may necessitate revalidation, such as equipment upgrades, modification in processes, or changes in regulatory requirements.
  • Documentation: Develop a revalidation plan that encompasses the activities to be performed, generating new documentation to reflect updated practices.
  • Regulatory Recommendations: Adhere to guidelines established by the relevant agencies and follow any specific mandates for ongoing validation practices.