How many FFUs are needed for a clean room?

Clean Booth is a control device for local clean space, which is widely used in industries with high cleanliness requirements such as Electronics, Semiconductors, and biomedicine. As one of the core components of clean booths, fan filter unit (FFU) directly determines the cleanliness level and Wind speed distribution of clean booths. This article will discuss in detail the relationship between FFU and volume, the impact of FFU on environmental cleanliness, and the calculation of the number of FFUs to help designers reasonably plan the number of FFUs in clean booths.

1. Relationship between FFU and clean booth volume

As the main air circulation and filtration device of clean booths, FFU inhales external air through a built-in fan and evenly delivers Clean air into the work area through a filter. When designing a clean booth, the number of FFUs is closely related to the volume of the clean booth, because the volume determines the number of air changes (ACH, Air Changes per Hour) and the wind speed requirements of the clean area.

In general, the larger the volume of the clean booth, the more FFUs are required to ensure sufficient air flow and cleanliness. For example, for a Class 100 clean booth, the conventional air change frequency is required to be around 600 times/h. Therefore, the designer needs to select the appropriate number of FFUs and the Air volume of a single FFU (usually between 800-1200 cubic meters/hour) according to the specific volume of the clean shed to ensure the adequacy of air circulation.

Calculation formula: Number of FFUs = Volume of the shed × Number of ventilation times / Air volume of a single FFU

Through this formula, the designer can reasonably plan the number of FFUs according to the volume of the clean shed to ensure that the air circulation in the space meets the standard.

2. The impact of FFU on environmental cleanliness

Another key role of FFU is to ensure the cleanliness of the environment in the clean shed. The Air Filtering capacity depends on the filter grade equipped with the FFU. Generally, the FFU is equipped with HEPA (high efficiency filter) or ULPA (ultra-high efficiency filter), which can remove more than 99.99% of 0.3 micron particles. For different cleanliness levels (such as ISO 5 or Class 100), the number of FFUs and the configuration of wind speed are also different.

The achievement of cleanliness standards depends not only on the number of FFUs, but also on factors such as the air flow pattern in the clean shed, the generation and emission of pollutants, etc. Too few FFUs will lead to uneven air flow, forming vortices or dead corners, thus affecting the overall cleanliness; too many FFUs will increase energy consumption and equipment costs. Therefore, in the design process, it is crucial to balance the number of FFUs with air flow rate and filtration capacity. Class 100 clean sheds have the highest cleanliness at present.

3. Calculation of the number of FFUs

When designing the number of FFUs in a clean shed, in addition to the requirements of volume and cleanliness, some other factors need to be considered, such as room height, personnel activities, equipment exhaust heat, etc. The design of the number of FFUs can generally be carried out through the following steps:

(1) Calculate the required air flow

The air flow determines the number of FFUs. First, calculate the total air flow based on the volume of the clean shed and the required number of ventilation times. The ventilation times required for conventional clean sheds are between 200-600 times/hour, and the specific value should be determined according to the cleanliness level. For example, for a Class 100 clean shed, the recommended ventilation times are about 600 times/hour.

(2) Select FFU air volume

The air volume of different FFU models varies. The common FFU air volume is usually between 800 and 1200 cubic meters per hour. When selecting the FFU model, it is necessary to ensure that the air volume of each FFU is sufficient to meet the air circulation requirements in the clean room while ensuring its operational stability and energy efficiency.

(3) Determine the number of FFUs

Based on the calculated air flow and the air volume of the selected FFU, calculate the required number of FFUs.

Number of FFU = Total air flow/FFU air volume

For example, assuming that the clean room volume is 100 cubic meters, the Ventilation frequency is required to be 600 times/hour, and the air volume of FFU is 1000 cubic meters/hour, then:

Total air flow = 100*600 = 60000 cubic meters/hour

Number of FFU = 60000/1000 = 60 units

In actual applications, designers usually add 10%-20% redundant FFU to cope with changes in equipment operation and potential sources of pollution. In addition, considering the height of the clean room, FFUs are usually evenly arranged at the top to ensure vertical air flow, thereby achieving the ideal clean effect.

As an important part of the clean room, the number design of FFU is directly related to the air circulation efficiency and cleanliness compliance. Through scientific volume measurement, cleanliness requirement analysis, and reasonable FFU number calculation, it can be ensured that the clean room reaches the expected cleanliness level. In actual design, designers also need to comprehensively consider factors such as the layout of the clean room, equipment energy consumption, operation and maintenance costs, and ultimately formulate the optimal FFU configuration plan.