Cleanroom FFU: How to calculate air flow according to room area

1. What is an FFU and its role in cleanrooms?

What is an FFU (Fan Filter Unit)?

An FFU (Fan Filter Unit) is a device that integrates a fan and a HEPA or ULPA filter into a single unit, typically installed on the ceiling of a cleanroom. The FFU draws air from above, filters out ultrafine dust particles, and then blows clean air downward in a laminar flow.

The key advantage of an FFU is that it operates independently, without relying on a central HVAC system. It is a modular air filtration solution that allows users to flexibly determine the number of units based on the room’s size and required cleanliness level.

FFU applications across ISO 5 to ISO 8 cleanroom levels

FFUs are widely used in cleanrooms ranging from ISO Class 5 to ISO Class 8, thanks to their ability to deliver high and stable airflow. Some common applications include:

With flexible modular installation, FFUs help designers achieve the required air changes per hour (ACH) without relying entirely on central HVAC systems.

Comparison: FFU vs. HEPA Box vs. AHU Systems

Conclusion: If you're designing a small cleanroom or upgrading to a higher ISO level, FFUs are a more flexible and efficient choice than HEPA Boxes or traditional AHUs.

See more: Latest price list of FFU Fan Filter Unit used in medical clean rooms

2. What is FFU airflow rate and why should it be calculated based on room size?

What is airflow rate? (CFM / m³/h)

Airflow rate refers to the volume of air that flows through a device in a specific period. Common units include:

• CFM (Cubic Feet per Minute)
• m³/h (Cubic meters per hour) - commonly used in Vietnam and Europe

For example: An FFU with a 1000 m³/h rating can deliver 1000 cubic meters of clean air per hour into the room.

Why is airflow rate important in cleanrooms?

Cleanrooms require strict control of airborne particles. To maintain cleanliness levels as per ISO standards, the air must be continuously refreshed to remove contaminants from personnel, equipment, and materials.

If airflow is too low:

• Dust is not removed promptly → ISO level may be violated
• Higher risk of cross-contamination, especially in pharma/cosmetics

If airflow is too high:

• Energy waste, increased operational costs
• May impact pressure balance and temperature stability

Thus, calculating airflow based on actual room size and application is essential during design or renovation.

ISO 14644 air changes per hour (ACH) requirements

ACH (Air Changes per Hour) indicates how many times the air in a room is replaced every hour.

For example, an ISO 7 room may require at least 60 ACH, meaning all air in the room must be replaced 60 times per hour to maintain particle concentration below ISO limits.

See more: Unveiling the Advantages of FFU Systems in Cleanrooms

3. Formula for calculating required airflow based on room area

Basic airflow calculation formula

To determine the total airflow required for a cleanroom, use the following formula:

Airflow (m³/h) = Room Area (m²) × Ceiling Height (m) × Air Changes per Hour (ACH)

Where:

• Room area = length × width
• Ceiling height = typically 2.4 - 3.0 meters
• ACH = based on required ISO level

Reference ACH by ISO cleanroom class

Note: These values are for reference. Actual ACH may vary depending on industry requirements and room design.

Practical example: 20m² room, 2.5m high, ISO 7 requirement

Assuming 80 ACH is required:

• Room area = 20 m²
• Ceiling height = 2.5 m
• ACH = 80

Airflow = 20 × 2.5 × 80 = 4,000 m³/h

Therefore, to maintain ISO 7 standards, this 20m² cleanroom must receive 4,000 m³/h of clean air per hour.

In the next section, we will calculate how many FFUs are needed to meet this airflow requirement.

4. How to determine the appropriate number of FFUs

Standard airflow of each FFU

Typically, each FFU can provide an airflow ranging from 800 to 1200 m³/h, depending on:

• Size (e.g., 600×600mm, 1200×600mm)
• Fan type (AC or EC)
• Filter resistance (HEPA or ULPA)

Note: For design purposes, it's recommended to use an average value of 1,000 m³/h per FFU unless exact specifications of the selected model are known.

How to calculate the required number of FFUs

Once you’ve calculated the total required airflow, you can use the following formula:

Number of FFUs = Total airflow (m³/h) ÷ Airflow per FFU

Example:

For a cleanroom of 20 m² with a ceiling height of 2.5 m, targeting ISO 7:

• Required airflow = 4,000 m³/h
• FFU airflow = 1,000 m³/h

➡ Number of FFUs = 4,000 ÷ 1,000 = 4 FFUs

Recommended FFU layout based on ceiling configuration

Depending on airflow objectives and room shape, the FFUs can be arranged in the following ways:

Note: Combine with air return grilles, differential pressure gauges, and cleanroom lights to optimize airflow performance and illumination.

See more: Laminar Airflow Cleanroom Control in FFUs

5. Factors affecting FFU airflow performance

Although FFUs have a rated airflow capacity, actual performance may vary due to multiple influencing factors. Understanding these factors ensures accurate calculations and stable cleanroom performance.

Cleanroom ceiling height

Higher ceilings mean larger room volumes, which require higher airflow to maintain the same ACH (air changes per hour).
Rooms with the same floor area but different heights (e.g., 2.4 m vs. 3.0 m) will need a different number of FFUs.

Tip: Always determine the ceiling height early in the design phase to avoid underestimating FFU quantity.

Resistance of HEPA/ULPA filters

HEPA filters typically start with low resistance but increase over time due to particle buildup.

• Increased resistance → Reduced airflow → Inadequate air exchange → Cleanroom standard violations

Solutions:

• Use EC fan FFUs that automatically adjust pressure
• Monitor pressure drop using a differential pressure gauge
• Schedule filter replacements based on manufacturer guidelines

Airflow design: unidirectional, recirculated, or hybrid

• Unidirectional flow (laminar): Requires high airflow and dense FFU layout
• Recirculated via AHU or return fans: Reduces FFU supply airflow demand
• Hybrid systems: Offer flexibility but may lead to uneven airflow if poorly designed

If FFUs are used in a recirculated setup, account for return airflow to avoid turbulent zones that trap particles.

Application-specific requirements

Each industry has unique operating standards, directly affecting airflow demand:

Note: Select FFUs specialized for your industry and consider additional requirements such as pressure control, ESD protection, and noise levels.

6. Considerations When Choosing FFUs for Different Industries

Selecting an FFU is not solely based on airflow; it must also consider the operational characteristics and technical standards specific to each industry. Below are key considerations to help you choose the right unit that meets standards and ensures long-term performance.

FFUs for the Pharmaceutical Industry (GMP, EU-GMP, WHO-GMP)

Special requirements:

• Strict control of airborne particles and microorganisms
• Many zones require positive pressure and stable airflow
• Cross-contamination is likely if airflow patterns are incorrect

Recommended FFU specifications:

• EC fans capable of maintaining consistent airflow over time
• Low noise level: suitable for packaging and filling rooms
• HEPA filters rated H14 or higher, with individual test certification (scan test)
• Integrated pressure gauges or pressure test ports

Best used in: weighing rooms, aseptic filling areas, airlocks

FFUs for the Food Industry

Special requirements:

• Environments with odors, humidity, and vapors
• Rapid air exchange needed to prevent microbial growth
• Some production areas contain oil, grease, or light dust

Recommended FFU specifications:

• High airflow (above 1000 m³/h) for fast air changes
• Option to integrate odor removal filters (carbon filter) before the HEPA
• Easy-to-clean casing (powder-coated or stainless steel)
• Sealed motor to resist moisture

Best used in: dry food packaging, seasoning production, pre-processing zones

FFUs for Electronics, Semiconductors, SMT

Special requirements:

• Sub-micron particle control
• Electrostatic discharge (ESD) is a major risk for components
• Requires uniform, turbulence-free airflow

Recommended FFU specifications:

• EC fans with smooth operation and precise speed control
• Anti-static casing, DC motor fans that don’t generate sparks
• Optional built-in ionizers to neutralize static charge
• Minimal airflow fluctuation (±5%)

Best used in: SMT cleanrooms, PCB testing labs, chip printing rooms

See more: FFU Control Modes in Industrial Cleanrooms

7. Frequently Asked Questions about FFUs and Cleanroom Airflow

1. How much air can one FFU deliver per hour?

Typically, an FFU can deliver between 800 and 1200 m³/h depending on its model, size, and fan type (AC or EC). A standard value of 1,000 m³/h is often used for design calculations.

2. How many FFUs are needed for a 30 m² cleanroom with a 2.5 m ceiling, ISO 7?

Using the formula:
Airflow = Area × Height × ACH
= 30 × 2.5 × 80 = 6,000 m³/h

If each FFU provides 1,000 m³/h → 6 FFUs are required.

3. Are FFUs mandatory in all cleanrooms?

No. FFUs are not mandatory in every cleanroom. However, they are an ideal solution for small cleanrooms, ISO level upgrades, or areas requiring independent and stable airflow without the need for complex HVAC systems. For large spaces, AHUs combined with HEPA Boxes may be more cost-effective.

4. How can I tell if an FFU is underperforming?

Common signs include:

• Weak airflow despite fan operation
• Unusual increase in HEPA filter pressure drop
• Elevated particle counts during ISO tests

Installing a differential pressure gauge and conducting periodic inspections are recommended based on manufacturer guidelines.

5. Are FFUs noisy?

High-quality FFUs using EC fans typically produce low noise levels (~45-50 dB). However, using cheaper models, AC fans, or incorrect installation may result in noise that affects the working environment.

8. Need Help Calculating the Number of FFUs for Your Cleanroom?

Choosing and positioning FFUs isn’t just about “buying the right quantity.” Each industry, cleanroom, and ISO level has unique requirements for airflow, pressure, flow direction, and energy efficiency.

Avoid costly design mistakes and compliance issues with GMP or ISO standards.

Contact the VCR technical team for:

• Free consultation on FFU sizing tailored to your industry
• Supply of certified, genuine FFUs
• Support in designing the most effective FFU layout for your space

Hotline: 090.123.9008

Email: [email protected]

Website: https://ffu.com.vn/

Diep VCR