I. What Parameters Should Be Confirmed When Selecting an FFU?
| Parameter | Role in Selection |
|---|---|
| Rated airflow | Determines the air supply capacity and the required number of FFUs |
| External static pressure | Determines whether the unit can overcome the resistance of the filter and air system |
| Air velocity | Affects cleanroom airflow distribution |
| HEPA filter class | Determines the particle filtration efficiency |
| Noise level | Affects the working environment and project acceptance |
| Overall dimensions | Must match the ceiling grid and available installation space |
| Motor type | Affects energy consumption, speed control and maintenance |
| Control method | Determines whether individual, group or centralized control can be achieved |
Parameters must be compared under the same test conditions. For example, the maximum airflow, rated airflow and actual airflow after filter installation stated by a supplier are not the same.
II. How Are the Rated Airflow and Number of FFUs Determined?
The number of FFUs should be calculated according to the room volume, target air changes per hour or designed average air velocity.
When using air changes per hour:
Required Airflow = Room Volume × Air Changes per Hour
The quantity should then be calculated according to the effective airflow of each FFU under the actual system resistance, with an appropriate allowance for system balancing and the performance reduction caused by filter dust loading.
For unidirectional airflow clean areas, the total airflow should be determined according to the effective air supply area and target cross-sectional air velocity. More FFUs are not always better. Excessive installation increases investment, noise and energy consumption and may also cause uneven airflow distribution.
III. Why Should Static Pressure Not Be Ignored?
Static pressure represents the FFU’s ability to overcome airflow resistance. System resistance usually comes from:
Pre-filter + HEPA Filter + Ceiling Plenum + Return Air Path
The resistance of a HEPA filter gradually increases as dust accumulates during operation. If the fan does not have sufficient static-pressure reserve, the supply airflow may decrease after a period of operation, resulting in insufficient air changes and abnormal cleanroom pressure.
Purchasers should ask the supplier to provide an airflow–static pressure curve instead of only a “maximum static pressure” value. The selected operating point should fall within the stable and efficient operating range of the fan, while the airflow change at the final filter resistance should also be considered.
IV. Should an H13 or H14 HEPA Filter Be Selected?
H13 and H14 filters are commonly used for terminal filtration in cleanrooms, but a higher class does not mean that every project must use H14. Higher filtration efficiency usually also increases resistance and purchasing costs.
For electronics manufacturing and general clean areas, H13 or H14 may be selected according to the cleanliness class and process requirements. For pharmaceutical aseptic areas, critical hospital areas and high-risk environments, the selection should be based on project standards, validation requirements and risk assessment.
Purchasers are advised to confirm:
HEPA filter class and applicable standard;
MPPS efficiency test results;
Initial pressure drop at rated airflow;
Filter scan leak test report;
Sealing method and on-site PAO leak test requirements.
V. How Should the Dimensions and Installation Method Be Matched?
Common FFU specifications should match ceiling modules of approximately 600 mm or 1,200 mm. However, actual unit dimensions may vary depending on the ceiling grid system, such as approximately 575 × 575 mm, 1,175 × 575 mm or 1,175 × 1,175 mm.
Orders should not be placed based only on descriptions such as “600 × 600” or “1,200 × 600.” The ceiling opening, internal grid dimensions, unit height, maintenance direction and power connection should be provided. Insufficient installation space may affect fan heat dissipation, filter replacement and future maintenance.
VI. How Should Noise and Energy Consumption Be Evaluated?
FFU noise is affected by airflow, fan speed, static pressure, unit structure and test distance. Purchasers should confirm the operating setting, test distance and background noise conditions corresponding to the stated noise data. Values measured under different conditions should not be compared directly.
EC motors may be preferred for projects requiring continuous operation. Compared with conventional AC motors, EC motors generally provide a wider speed-control range, higher efficiency under partial load and easier centralized control. However, the input power per unit, efficiency at the design operating point and annual operating hours should still be compared.
VII. How Should FFUs Be Selected for Different Applications?
Electronics and semiconductor cleanrooms: Airflow uniformity, low energy consumption and centralized control are important. A large-area FFU layout may be used.
Pharmaceutical cleanrooms: HEPA filter class, sealing method, integrity testing and validation documents should be given priority.
Hospitals and laboratories: In addition to airflow and cleanliness, noise, room pressure and the relationship between supply and exhaust air should be considered.
Local clean-air equipment: Clean booths, laminar flow units and similar applications should be selected according to the effective working area and local air velocity. Whole-room air-change calculations should not be applied directly.
VIII. Frequently Asked Purchasing Questions
Is a higher FFU airflow always better?
No. The airflow should match the cleanroom class and airflow distribution requirements. Excessive airflow increases noise, energy consumption and the difficulty of balancing room pressure.
Is it sufficient to consider only the HEPA filter class?
No. The initial pressure drop, actual airflow, leak test report and sealing structure must also be confirmed.
What should be done when filter resistance increases?
Dust loading should be evaluated by monitoring the pressure difference and airflow. The filter should be replaced when it reaches the final resistance specified by the project, when the airflow becomes insufficient or when it fails the leak test.
IX. Jiangsu Yueboyang FFU Filtration Solution
Jiangsu Yueboyang can provide FFUs and matching H13/H14 HEPA filtration solutions according to the cleanroom class, room dimensions, target airflow, ceiling module and noise requirements. The company can also assist with airflow matching, resistance evaluation, dimensional customization and filter testing.
Proper FFU selection should simultaneously meet the following requirements:
Airflow + Static Pressure + Noise + HEPA Efficiency + Installation Size
Only by considering fan performance, filter resistance, ceiling structure and the control system together can stable cleanliness, reasonable energy consumption and lower long-term operating costs be achieved.
