How To Choose A High-efficiency Filter for A Clean Room

High-temperature high-efficiency filters are significant devices that work under high-temperature conditions. Sealants are applied in the bonding and sealing process during their manufacturing process. Conventional sealants have a challenge of sustaining their physical qualities in elevated-temperature conditions, and thus lose their sealing and heat resistance qualities after relatively short periods of utilization, which influences the service life and effectiveness of the filter in use.

A Cleanroom is a well-sealed space where parameters such as air cleanliness, temperature, humidity, pressure, and noise are controlled according to specific requirements.

In order to reach the necessary level of cleanliness, a Clean Room has to take thorough measures, which cover process layout, building plan, building structure, building decoration, personnel and material purification, air cleanliness measures, maintenance and management, etc. Among them, air cleanliness measures constitute the basic ensuring of the achievement of the necessary level of cleanliness. Specific measures that are mostly applied in terms of air cleanliness are as follows:

1. The supply air for cleanrooms must be of very high cleanliness. Therefore, high-efficiency or sub-high-efficiency filters (for lower cleanliness levels) must be selected as terminal filters to perform the final stage of filtration on the air entering the cleanroom. To protect the terminal filters and extend their service life, the air must first be filtered through medium-efficiency filters.

2. Based on the cleanroom grade, the airflow distribution pattern should be selected appropriately. Vortex zones should be avoided in the work area, clean air with high cleanliness should be directed directly to the work area as much as possible. The airflow should facilitate the removal of particles from the cleanroom through the return air vents.

3. Sufficient airflow is required to both dilute the dust concentration in the air and ensure a stable airflow pattern.

4. A certain positive pressure value should be maintained between cleanrooms of different grades, between cleanrooms and non-cleanrooms, or between cleanrooms and the outdoors.

Cleanroom purification systems typically use high-efficiency filters or sub-high-efficiency filters. The efficiency ratings of high-efficiency filters are divided into four categories: Class A >99.9%, Class B >99.9%, Class C >99.999%, and Class D >99.999%. Sub-high-efficiency filters have an efficiency rating of 95–99.9% (for particles larger than 0.5 μm).

The more efficient a filter is rated, the higher the cost. When specifying filters, therefore, it is necessary to reconcile the need to ensure air cleanliness with economic viability. When cleanliness needs are taken into consideration, the main decision to be made is between low-efficiency air filters and high-efficiency air filters. As a rule, in a Class 1 million cleanroom, medium-efficiency filters may be ordered, and in cleanrooms worse than Class 10000, sub-high-efficiency or Class A high-efficiency filters may be selected.

For grades 10000 to 100, B-class filters are selected, and C-class filters are used for grades 100 to 1. Here, each cleanliness level has two types of filters to choose from, high-efficiency and low-efficiency, depending on the specific situation:

When environmental pollution is severe, or the indoor exhaust airflow ratio is high, or air filtration is particularly critical, a higher SAF. TY coefficient is required. In such cases, a high-efficiency filter should be selected. Conversely, a lower-efficiency filter can be chosen. For air filters requiring control of particles as small as 0.1 microns, a D-class filter should be selected, regardless of the concentration of controlled particles.

As mentioned above, from the perspective of filters alone, in fact, to select a good filter, we must fully consider the characteristics of air filters, air cleaners, and purification systems.