In the pharmaceutical industry, clean rooms are critical environments where air quality control is essential to avoid product contamination. Within the multiple parameters that govern the design and operation of these spaces, the air renewal rate or renewals per hour (ren/h) plays an essential role in the elimination of suspended particles and microorganisms.
This white paper explains what air changes per hour are, their importance in pollution prevention, the regulatory requirements depending on the type of room, how they are carried out and the available control strategies. Finally, it discusses the transition from traditional control to adaptive control, a more efficient and flexible approach to HVAC system management.
What are Air Renewals per Hour?
Air turnover rate is defined as the number of times the total volume of air in a clean room is replaced by filtered air in one hour.
This parameter is key in the pharmaceutical industry, since an adequate number of renewals ensures that the environment remains within the established levels of cleanliness, minimizing the presence of particles and microorganisms.
Air renewals per hour depend on the balance between:
- air supply filtered by HEPA or ULPA filters,
- extraction of contaminated air or its recirculation after filtration,
- maintenance of pressure gradients between zones.
Importance in Pollution Control
Air quality control in clean rooms depends directly on the number of air renewals per hour. Among its main effects:
- Dilution and removal of particles generated by personnel, equipment and processes.
- Microbiological control, reducing the proliferation of microorganisms in suspension.
- Recovery time: a higher number of renewals accelerates the return to clean conditions after a disturbance (door opening, personnel entry, occasional ventilation failure).
These factors work in conjunction with HEPA filtration, airflow directionality and pressure control.
Air Renewal Requirements according to Clean Room Classification
GMPs classify cleanrooms as Grade A, B, C and D. Although GMPs do not set normative values for renewals per hour, they do require the HVAC system to ensure a recovery time of less than 20 minutes (according to Annex 1, rev. 2022).
Typical values of renewals per hour in the pharmaceutical industry (non-normative):
- Grade A (critical areas): the main criterion is the unidirectional flow velocity (0.36 – 0.54 m/s), not the ren/h.
- Grade B: 40-60 ren/h (depending on the process, some designs exceed 70).
- Grade C: 20-40 ren/h (usually ≥ 25-35 according to modern validation).
- Grade D: 10-20 ren/h.
These values depend on the type of process, expected particulate load, occupancy and HVAC design risk analysis. Other requirements (such as product protection, thermal loads or microbiological control) can significantly raise the applied ren/h.
In addition, performance evaluation follows ISO 14644-3 criteria for tests such as recovery, filter integrity and flow patterns.
How are Clean Room Air Renewals Performed?
The air renewal process is performed by an HVAC system specifically designed for controlled environments.
Key phases include:
- Air supply filtered through HEPA/ULPA filters.
- Extraction or return of contaminated air for expulsion or recirculation.
- Air directionality, depending on the type of room:
- unidirectional (laminar) flow in Grade A and part of B,
- turbulent flow in less critical areas.
- Control of environmental conditions such as temperature, humidity and differential pressure.
Air Renewal Control Methods
Traditional Control: Fixed Flow
The traditional method maintains a constant flow rate and a fixed rate of renewals, regardless of occupancy or level of particulate generation.
- Constant flow fans.
- Manual or automatic adjustments to compensate for filter clogging.
- Guarantee of stable conditions, but without flexibility and with high energy consumption.
Adaptive Control: Dynamic Optimization
The adaptive control adjusts the airflow according to the actual environmental conditions, using:
- real-time sensors (non-viable particles, pressure, temperature and humidity),
- BMS systems,
- intelligent control algorithms,
- fans with variable speed drives (VSD).
Advantages of adaptive control
- significant reduction in energy consumption,
- better response to actual occupation and activity,
- continuous optimization of air quality,
- compliance while maintaining efficiency.
Considerations
- greater control complexity,
- higher initial investment,
- feasible monitoring cannot be integrated into control loops, although it does complement the overall system evaluation.
Conclusions
Air renewals per hour are a key parameter in cleanroom design and operation, contributing to particle control, microbiological quality and recovery time.
Traditional control ensures stability, but at the cost of low energy efficiency. Adaptive control represents a necessary evolution, making it possible to adjust ventilation to actual demand and optimize resources without compromising regulatory compliance.
The combination of proper HVAC design, robust risk analysis and advanced control technologies makes it possible to ensure air quality with significantly lower energy and operational impact. 🚀
