By Ryan Rennie, from the Spada-Rennie Group

Air Handling Units (AHUs) are the backbone of pharmaceutical HVAC systems, playing a critical role in maintaining precise temperature, humidity, room pressure and cleanliness levels.

Ryan Rennie, from the SpadaRennie Group.

Ryan Rennie, from the Spada Rennie Group. Supplied by Ryan Rennie

The pharmaceutical industry has stringent regulatory requirements, including Good Manufacturing Practices (GMP), ISO 14644, and other regional guidelines, making the design and manufacturing of AHUs more complex than in other industries. This article outlines best practices for designing, manufacturing, and installing pharma-grade AHUs to ensure compliance, efficiency, and long-term reliability.

Design considerations for pharma AHUs

  1. Material selection and construction

Pharmaceutical AHUs must be built from materials that resist corrosion, microbial growth and contamination. The most commonly used materials include:

  • Stainless steel (SS 304/316L) – Ideal for internal surfaces in high-contamination areas
  • Chromadek – Lightweight and resistant to chemical exposure
  • Double-skinned panels with insulation – Provides thermal efficiency and minimises condensation risk

AHUs should be designed with smooth internal surfaces to prevent dust accumulation and microbial growth. Welded joints and minimal fasteners inside the unit help maintain a contamination-free environment.

 

  1. Filtration strategy

Air filtration is a critical component of pharma-grade AHUs. A multi-stage filtration approach is required to meet cleanroom standards:

  • Primary filters (G4/MERV 8) – Captures larger particulates to extend the life of fine filters
  • Secondary filters (F7-MERV 13/F9-MERV 15) – Removes smaller particles before air enters critical areas
  • HEPA filters (H13/H14) – Essential for cleanrooms, removing 99.97% of particles ≥0.3 microns

The filter selection depends on the cleanroom classification and risk assessment of the pharmaceutical process.

 

  1. Airflow control and pressurisation

Maintaining the correct air balance and pressure differentials is crucial to preventing cross-contamination. AHUs should be designed to:

  • Ensure positive pressurisation in clean areas
  • Maintain unidirectional airflow in sterile environments
  • Use Variable Air Volume (VAV) controls to optimise energy use

 

  1. Energy efficiency measures

Pharma facilities operate 24/7, making energy efficiency a key factor in AHU design. Best practices include:

  • Heat recovery wheels and run-around coils – Reduce heating and cooling loads by reclaiming energy
  • EC fans with Variable Frequency Drives (VFDs) – Improve efficiency by adjusting fan speed to real-time demand
  • Intelligent control systems – Optimise airflow and temperature based on occupancy and environmental conditions

Manufacturing best practices

  1. Precision fabrication and assembly

AHUs must be manufactured with high precision to ensure compliance with pharmaceutical regulations. Best practices include:

  • Automated welding and bending to minimise human error
  • Modular construction for ease of assembly and maintenance
  • Rigorous surface finishing to eliminate microbial growth risks

 

  1. Factory Acceptance Testing (FAT)

Before an AHU leaves the manufacturing facility, it must undergo rigorous testing to verify performance and compliance:

Leakage testing – Ensures casing integrity and filter efficiency

Airflow and pressure testing – Confirms design parameters

Noise and vibration testing – Evaluates operational stability

HEPA filter integrity testing – Validates filter performance

Installation best practices

 

  1. Site preparation and handling

Pharmaceutical AHUs are large and delicate systems that require careful handling during installation. Best practices include:

  • Ensuring site readiness with proper access, supports and vibration isolation
  • Using dedicated lifting and transport equipment to prevent structural damage
  • Installing units in compliance with cGMP guidelines to avoid contamination risks

 

  1. Ductwork and piping connections

Ductwork and piping must be installed with precision to maintain system performance:

  • Sealed, insulated ducts – Prevent leakage and condensation
  • Stainless steel ducting for high-cleanliness areas – Reduces particulate contamination
  • Flexible connections for vibration isolation – Protects against structural stress

 

  1. Commissioning and validation

Once installed, the AHU must undergo thorough commissioning and validation:

  • IQ/OQ/PQ protocols – Installation Qualification, Operational Qualification, and Performance Qualification ensure compliance with GMP standards
  • Airflow and balancing tests – Adjust and verify pressure differentials
  • Microbial and particulate testing – Confirms cleanliness levels meet cleanroom classifications

Designing, manufacturing, and installing pharma-grade AHUs requires a meticulous approach to meet stringent regulatory requirements. By implementing best practices in material selection, filtration strategies, energy efficiency, and quality control, HVAC professionals can ensure reliable, compliant and cost-effective AHU solutions for pharmaceutical manufacturing facilities. The ongoing evolution of smart monitoring and AI-driven BMS integration will further enhance the performance and compliance of pharma HVAC systems in the coming years.

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