How to choose FFU wind speed?

Why is FFU wind speed a key parameter in clean room design?

The core function of the FFU (fan filter unit) is to filter the air through a high-efficiency filter and send it out at a uniform wind speed to maintain the cleanliness of the clean room. Wind speed is one of the most important performance parameters of FFU。

The size of the wind speed directly determines the three core indicators of the clean room:

• Whether the cleanliness can meet the standard : the wind speed is too low, the air flow thrust is insufficient, and the pollutants cannot be effectively taken away; the wind speed is too high, turbulence may be generated and particles will be stirred up

• Level of energy consumption : every time the wind speed increases by 0.1m/s, the fan power consumption increases by about 15%-20%

• Operating noise level : the higher the wind speed, the greater the noise

Therefore, a reasonable selection of FFU wind speed is the key to finding a balance between cleanliness standards and energy saving and noise reduction.

1. Core standards of FFU wind speed

The industry-recognized FFU standard surface wind speed is 0.45m/s。

The filtered clean air 0.45m/s±20% . is evenly sent out on the entire air outlet surface at a wind speed of In other words, the allowable fluctuation range of wind speed on the FFU outlet is 0.36-0.54m/s。

The typical wind speed configuration of FFU five-speed speed adjustment is: 0.3-0.35-0.4-0.45-0.5m/s. 0.45m/s is the 'base value' of FFU wind speed, and is used as a starting point for most clean room designs.

2. How to choose wind speed for different cleanliness levels?

Different cleanliness levels have different requirements for FFU wind speed. The following are the wind speed reference ranges for each ISO level:

Selection logic :

• ISO Class 5 (Class 100) clean room : It is a unidirectional flow clean room that relies on continuous laminar airflow to take away pollutants. The wind speed is usually 0.45m/s as the design value. If the wind speed is too low, the airflow cannot push the pollutants, but if the wind speed is too high, turbulence will be generated and particles will be stirred up.

• ISO Class 6-8 (Class 1,000/Class 10,000/Class 100,000) clean room : It is a non-unidirectional flow (turbulent flow) clean room and relies on dilution ventilation to maintain cleanliness. The wind speed range can be relaxed to 0.30-0.45m/s . If the wind speed is too low (<0.30m/s), it will affect the number of air changes and cleanliness, and if it is too high, it will increase energy consumption.

3. Conversion method of wind speed and air volume

The air volume of FFU (m³/h) is determined by the air outlet area and face wind speed:

Air volume (m³/h) = Air outlet area (m²) × Surface wind speed (m/s) × 3600

Air volume reference for common specifications :

Taking the 1175×575mm FFU as an example, at a surface wind speed of 0.45m/s, the air volume of a single unit is approximately 0.65×0.45×3600≈1053m³/h.

4. Wind speed uniformity: more important than wind speed

An often overlooked but extremely important indicator in FFU selection is wind speed uniformity.。

Even if the average wind speed reaches the standard, if the wind speed difference at each point on the air outlet surface is too large, local vortices will be generated, affecting cleanliness.

Test standards :

• Select evenly on the FFU air outlet surface 6-12 points to test the surface wind speed.

• The average value between the maximum value and the minimum value shall not exceed ±20%

• The relative standard deviation of wind speed at each point is not greater than 15%

Selection tip : Ask the supplier to provide actual measured data on wind speed uniformity, rather than just looking at the average wind speed.

5. Five considerations for wind speed selection

1. Cleanliness level requirements

The higher the cleanliness level, the greater the dependence on wind speed. ISO level 5 (level 100) relies on unidirectional flow and must ensure sufficient face wind speed; ISO level 7-8 ensures cleanliness through the number of air changes, and the wind speed can be appropriately reduced.

2. Filter resistance

As dust accumulates on the high-efficiency filter, the resistance gradually increases and the air volume decreases. When selecting, it is necessary to confirm that the FFU can still maintain the target wind speed under the final resistance state of the filter.

3. Installation height and space

The higher the FFU installation height, the greater the indoor disturbance when the airflow reaches the work surface. Cleanrooms with higher floor heights may require higher initial air speeds to compensate for attenuation along the way.

4. Process sensitivity

Processes that are sensitive to air flow disturbance, such as photolithography and coating, require stable and uniform wind speed, and fluctuations should be controlled within a small range.

5. Energy consumption and noise restrictions

Every time the wind speed increases by 0.1m/s, the power consumption increases by 15%-20%, and the noise also increases. On the premise of meeting the requirements of cleanliness, the wind speed should be selected as low as possible to reduce operating costs.

6. Common misunderstandings in FFU wind speed selection

Myth 1: The higher the wind speed, the cleaner it is. Too high wind speed will create turbulence, which will stir up particles on the ground and equipment surfaces. Cleanliness depends on the rationality of air flow organization, not simply high wind speed.

Misunderstanding 2: All clean rooms use 0.45m/s. 0.45m/s is a typical value for a unidirectional flow clean room (Class 100). Class 1,000 and Class 10,000 clean rooms have non-unidirectional flow and rely on the number of air changes to ensure cleanliness. The wind speed can be as low as 0.30m/s.

Misunderstanding 3: Only look at average wind speed and ignore uniformity. Even if the average wind speed reaches the standard, if the wind speed deviation at each point exceeds ±20%, local eddy currents will still be generated and affect the cleanliness.

Misunderstanding 4: Only talk about wind speed without looking at static pressure. There is a matching relationship between the air volume of FFU and the static pressure outside the machine. If the supplier only reports wind speed but not static pressure, the wind speed may be seriously insufficient after actual installation.

Summary: FFU Wind Speed ​​Selection Cheat Sheet

The core principle of selection : on the premise of meeting the cleanliness level and process requirements, choose the lowest possible wind speed - which can not only ensure cleanliness, but also reduce energy consumption and noise.

Aili Industry—Full industry chain FFU manufacturer

Aili Industrial has been deeply involved in the field of clean room equipment for nearly two decades. From fan winding, box processing to control system development, the entire industry chain independently manufactures FFU fan filter units. The product supports stepless adjustment of wind speed from 0-0.6m/s, with five speed adjustment options of 0.3-0.5m/s. The wind speed uniformity is better than industry standard requirements (relative standard deviation ≤15%), and the external static pressure can reach more than 100Pa when the surface wind speed is 0.45m/s. Aili Industrial can provide customized FFU wind speed solutions based on your cleanliness level, process requirements and energy consumption goals, adapting to the different cleaning needs of 13 major industries including semiconductors, panel displays, pharmaceuticals, food, and data centers.

If you need FFU wind speed selection suggestions or customized solutions, please contact the professional technical team of Aili Industry.