Is excessive FFU air volume good for cleanliness?

When many sites encounter high particles, the first reaction is to increase the FFU speed, thinking that the greater the air volume, the better the cleanliness. In fact, increasing air volume does not necessarily improve cleanliness. Proper air supply can help dilute or remove particles, but excessive air volume may cause backflow, turbulence, increased noise and energy consumption, and even draw background contamination near the product.

Whether the air volume is appropriate depends on the process objectives, protection paths, filter resistance and air flow organization. It cannot just look at the total air volume. Let’s start with several practical aspects.

Air volume and protection path need to be looked at together

Whether the air reaches the product first and then leaves the contaminated area is more important than a single total air volume. When the air supply is too strong and the outlet is restricted, background pollution may be discharged along nearby gaps or entrained, causing an airflow short circuit.

If the key workstation is at the edge of the air supply, blindly increasing the rotation speed may cause the wind speed in the central area to be higher, and the edge area will become unstable due to backflow. To judge the protection effect, the wind speed and air flow direction at the workpiece location should be measured instead of just looking at the wind surface reading. Related methods can be found in How to convert face wind speed and air volume? and How should we look at the effective air outlet area of ​​FFU?。

Excessive air volume may cause backflow and disturbance

In a closed or semi-closed space, when the air supply volume is too large and the return air or exhaust air is insufficient, the air flow will look for other outlets and form a backflow or vortex. The recirculation zone may cause particles to pass repeatedly through the product rather than being efficiently carried away.

Open workstations are particularly susceptible. When lateral airflow meets excessively strong air supply, it may form entrainment at the edge of the workstation, bringing background air into the protected area. Specific performance can be referred to How does supply air vortex affect open workstations? and Why is it easy for contamination to accumulate in the return flow area?。

Disturbance to product and process

Some products are sensitive to drafts. For light and thin materials, powder materials, precision measurement stations or optical fiber parts, high wind speed may cause vibration, displacement or measurement drift. At this time, even if the particle concentration is qualified, the process itself may not be stable.

When selecting the operating speed, the disturbance to the product should also be considered. If the product is blown under vertical air supply, you can adjust the air supply direction, increase damping, or change the workstation layout instead of continuing to increase the wind speed. When it comes to detection platforms, please refer to How does a wafer inspection platform balance cleanliness and low vibration?。

Noise and energy consumption increase with speed

FFU air volume is related to rotational speed, and an increase in rotational speed is usually accompanied by an increase in noise and input power. For a cleanroom that operates throughout the day, the difference in energy consumption can add up to significant operating costs.

When comparing operating costs, the input power of the complete machine under the same load should be used, and calculated separately based on actual work and duty hours. Rated power cannot be used directly to calculate annual expenses. For details, please refer to What is the difference between FFU rated power and actual power consumption?。

If multiple FFUs need to adjust speed according to regions and time periods, they can be combined The FFU group control system is managed in a unified manner to avoid regional imbalance caused by manual adjustment.

Filter resistance and working point changes

When the air volume is too large, the wind speed facing the filter will increase, and the resistance and power consumption will also increase. Long-term high wind speed operation may accelerate the aging of the filter material or increase the risk of damage. The impact of excessive wind speed on the face of the filter can be referred to What will be the impact if the wind speed facing the filter is too high?。

After adjusting the rotation speed, the working point with filter should be rechecked. If you only look at the maximum air volume or maximum pressure, you may not be able to judge the actual air supply capacity under the target conditions. For the complete performance curve and the judgment method of external static pressure, please refer to Why should we look at the complete performance curve when selecting FFU? and What does FFU external static pressure mean?。

How to determine the appropriate air volume

To determine the appropriate air volume, usually in the following order:

• Clarify the protection object and air flow form: whether it is one-way protection, dilution and exclusion, or compensated exhaust;

• Determine the target wind speed or air exchange demand: calculated according to process and standard requirements;

• Check the filter resistance and system operating point: check the static pressure and power under actual air volume;

• Measure wind speed and airflow direction at key workstations: confirm that air passes through the product first;

• Verification under dynamic conditions: covering human actions, door openings and mechanism movements;

• Adjust according to area and time period: avoid local excessive strength or weakness caused by uniform high speed.

If there are abnormal particles on site, you should first check the source of pollution and the air flow path instead of directly increasing the speed. For more troubleshooting methods, please refer to What are the on-site manifestations of insufficient FFU quantity? and What particle problems can airflow short circuits cause?。

Equipment selection and speed adjustment methods

When selecting equipment, please refer to the background air supply of the room. FFU clean air supply products , please refer to the local protection of the equipment side. EFU equipment side fan filter unit . The logic of division of labor between the two lies in The division of labor between device-side EFU and room FFU is explained in detail.

Filter selection should correspond to target particle size and actual resistance.The HEPA and ULPA filter pages have parameters for different levels of products. When selecting, check the efficiency of the specific model at the target air volume. If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency?。

Project judgment example

The particles at an open station were occasionally high, so the FFU speed was adjusted to the highest value on site. As a result, the edge of the workstation appeared to be rolled back, the particles at the product position were not reduced, and the noise and energy consumption increased significantly. The investigation found that the return air channel was partially blocked, and the airflow was short-circuited from a nearby gap after the rotation speed was increased. Adjustment method: clean the return air channel, reduce the rotation speed, and add lateral baffles. After adjustment, the airflow at the workstation returned to stability.

In another project, after the wind speed was increased at a precision measurement station, the measurement data drifted. The reason is that airflow disturbance affects the measurement stability. Adjustment method: reduce wind speed, optimize air supply direction, and increase local damping. Particle and measurement stability are simultaneously improved.

These two situations illustrate that excessive FFU air volume is not necessarily conducive to cleanliness. A comprehensive judgment needs to be made based on the air flow path, process disturbance and system resistance.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Aili Industry covers motor manufacturing, independent research and development and production of fans, control system development, sheet metal processing, air filter manufacturing and complete machine assembly. For FFU air volume and air flow optimization projects, FFU, EFU, HEPA/ULPA filters, group control systems, air volume static pressure and installation interfaces can be uniformly checked to connect equipment configuration with on-site evaluation boundaries and reduce the disconnect between component parameters and complete machine operating conditions.

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