Design Considerations for Fan Filter Units in Life Science and Healthcare Spaces

The integration of fan filter units (FFUs) in life science and healthcare environments is a proven strategy when strict particle control is required within existing facilities. FFUs can be highly effective, provided that the current air handling system supports essential temperature, humidity, and pressurization parameters. These modular, ceiling-mounted systems combine a fan, motor, and a HEPA filter to deliver consistent, localized, and filtered airflow, serving crucial roles in cleanrooms, operating suites, pharmaceutical laboratories, and other contamination-sensitive areas. To maximize performance outcomes, engineers should thoroughly assess client requirements and select both configurations and accessories that align closely with the needs of the project.

Case Study: FFU Implementation in GMP Manufacturing Space

JB&B has partnered with clients aiming to develop classified GMP manufacturing areas within non-classified laboratory environments. Although dedicated air handling units are often preferred, practical constraints—such as first-floor placement within multi-story facilities and the significant expense of stand-alone systems—can render this approach impractical. After confirming the existing air handling unit’s ability to provide necessary cooling, heating, and pressurization, though noting its inability to meet required air changes per hour (ACH), JB&B recommended the use of FFUs to supply filtered air. During design and construction, ambiguity arose regarding available FFU options and their functionalities. This article addresses common commercial FFU offerings and provides guidance for selecting appropriate solutions for specific project demands.

FFU Motors and Fan Selection

FFU motors are primarily available as electronically commutated motors (ECM) or permanent split capacitor (PSC) motors. ECM motors are favored due to their enhanced energy efficiency and simplified balancing, whereas PSC motors offer lower upfront costs. Accordingly, JB&B generally advocates for ECM motors, given their long-term benefits.

Fan blade designs for FFUs include backward-curved and forward-curved types. Backward-curved blades, oriented opposite rotation, excel at moving high air volumes efficiently. Conversely, forward-curved blades follow airflow and are suited to lower volumes. When paired with ECM motors, backward-curved fans operate in “constant torque” mode, maintaining speed but gradually reducing airflow as filters load. Forward-curved fans with ECM motors facilitate “constant volume” operation, automatically increasing fan speed to sustain consistent airflow via calibrated algorithms. Preferences for these modes differ. Some clients accept gradual airflow reduction, especially with pre-filters, while others prioritize consistent airflow. Where skepticism exists regarding preset algorithms, JB&B has installed real-time airflow monitoring. According to the ISPE Baseline Guide for Sterile Product Manufacturing, new or renovated facilities should include airflow monitors to signal and alert any reduction in airflow. JB&B recommends monitoring room airflow through algorithms or airflow monitors, depending on budget and space limitations. Monitoring airflow can provide energy-efficiency savings by allowing for room airflow reductions during unoccupied hours.

Choosing the FFU at 90 FPM keeps noise, pressure drop, and turbulence low in the cleanroom.

FFU Filter and Maintenance Access Options

Filter replacement methods for FFUs include room-side replaceable and benchtop replaceable configurations. Room-side replaceable filters allow maintenance from within the cleanroom without dismounting the unit, advantageous in spaces without walkable mezzanine ceilings. However, they may reduce overall efficiency due to decreased free area for airflow. Benchtop replaceable filters necessitate removing the unit for changes, which presents challenges where overhead access is limited but can improve airflow efficiency. A recent project initially involved benchtop FFUs, selected for their lower initial cost, since fewer units were needed compared to room-side models. Ultimately, due to the absence of a walkable mezzanine and restricted overhead access, room-side replaceable FFUs were chosen to streamline maintenance.

JB&B advises using a pressure transducer with your FFU to monitor the HEPA filter’s pressure drop. Typically, filters are replaced when their pressure drop reaches twice the initial value. An alarm can be set to notify cleanroom facility staff when it’s time to replace the HEPA filter.

Images courtesy of 2025 Price Industries.

 

FFU Filter Material Options

Materials for plenums and grilles include stainless steel, aluminum, and powder-coated steel, selected based on chemical resistance, cleaning protocols, and aesthetic considerations. In cleanrooms exposed to aggressive cleaning agents such as Spor-Klenz or vaporized hydrogen peroxide, 304 SS or 316L SS are commonly specified. It’s imperative to review cleaning procedures and environmental exposures with the client to ensure material suitability for FFUs.

Benefits and Drawbacks of Fan Filter Units (FFUs)

Benefits

• Scalability: FFUs offer scalability, allowing for the addition or removal of units as needed to achieve the desired cleanroom classification.
• Energy Efficiency: These systems are generally more energy-efficient, especially when high air change rates are required, compared to a central air handling unit system.
• Simplified Installation: Recirculating FFUs requires less ductwork and coordination during installation than central air handling units.
• Cost Savings: The overall cost is reduced when FFUs are utilized instead of installing a new central air handling system designed to meet the full air change requirements of the space. Costs are even lower if the existing base building air handling unit can be leveraged.

Drawbacks

• Increased Maintenance: Each FFU contains motor and control components that require servicing over their operational lifespan, resulting in more maintenance compared to a dedicated air handling unit.
• Noise Generation: FFUs produce sound from their individual motors, which typically results in a higher noise level within the space than ducted HEPA filtration supplied by a central air handling unit.

Conclusion

Fan filter units are vital for ensuring controlled air purity, pressure, and flow within cleanroom and healthcare settings. Proper selection of fan type, motor, materials, and maintenance access is fundamental to optimizing system performance, energy utilization, and ongoing maintainability. Engineers must fully comprehend client needs to make informed decisions that balance initial costs against long-term operational requirements.