The purification air conditioning system of the clean room is equipped with various air filters – coarse efficiency, medium efficiency, sub-high efficiency, and HEPA, ULPA, and chemical filters, etc., according to the dust concentration in the atmosphere, the concentration of various pollutants in the atmosphere and the characteristics and requirements of the production process.
Principle 1: According to the cleanliness level of the cleanroom and the requirements of the product production process
The configuration and selection of air filters in specific purification air conditioning systems should be reasonably configured and selected according to the air cleanliness level of the clean room and the special requirements of the production process (when there are no special requirements for the process, it is generally configured according to the air cleanliness level).
ISO 6 or Lower cleanrooms
For ISO 6 (class 1000) cleanrooms and those with a cleanliness level lower than ISO 6, three-stage air filtration is usually used, namely, coarse-efficiency, medium-efficiency, and HEPA filters.
Coarse and medium-effect (or medium-efficiency) filters are usually installed in the air handling unit (AHU), and medium-efficiency or medium-high-efficiency filters are installed in the positive pressure section.
HEPA or sub-high efficiency filters are generally installed at the end of the clean room purification air conditioning system.
There are also cases where HEPA filters are concentrated in centralized air handling units (AHUs), but at this time, strict cleaning requirements should be put forward for the air supply ducts to avoid contamination of the purified air.
ISO 5 or stricter cleanrooms
For the configuration of air filters in the purification and air conditioning system of ISO 5 (Class 100) and stricter clean rooms, various types of filters should be configured according to the overall design of the clean room and the requirements of the purification and air conditioning system adopted.
For example, some integrated circuit production uses ISO 4 (0.1μm) and higher clean rooms with centralized fresh air treatment.
In order to strictly remove particles and various pollutants in the atmosphere, coarse-effect, medium-effect (medium-high-efficiency), sub-high-efficiency, or even HEPA filters and chemical filters or water spray devices are usually installed in the fresh air treatment device; the circulating air system in the clean room is also equipped with HEPA, ULPA, and chemical filters.
Some clean rooms used for integrated circuit production also have micro-environment devices in certain production areas, production processes, or process equipment during the production process to ensure the air cleanliness requirements required for production.
Principle 2: Understand the process requirements of the product and the local air quality
In recent years, due to the decline in air quality, especially the increase in some chemical pollutants or microorganisms other than atmospheric dust, and the more stringent requirements for the production environment of some industrial products, in many cases, the concept of air purification treatment using only “three-stage filters” can no longer meet the needs.
Therefore, when designing a clean room’s purification and air conditioning system, one should carefully understand the product production process requirements and the local air quality conditions and realistically configure the air filters.
Principle 3: Less than or equal to the rated airflow
The rated air volume of an air filter is the air volume when the filter efficiency and resistance are reasonably selected at a certain filtration speed; therefore, when determining the model and specifications of the air filter, it should generally be selected based on a volume less than or equal to the rated air volume.
Sometimes, in specific engineering designs, after technical and economic comparisons and actual possibilities, filters are selected for less than the rated air volume to reduce resistance and the operating energy consumption of the purification air conditioning system.
According to my experience, if the filter is made by molding, the filter resistance can be further reduced, which is beneficial to reducing the energy consumption of the purification air conditioning system.
Principle 4: Install the cleanroom air filters in the appropriate locations
Medium-efficiency filters should be concentrated in the positive pressure section of the system. This is because if they are installed in the negative pressure section, air with more pollutants that have not passed through the medium-efficiency air filters will easily leak into the system, increasing the load on subsequent HEPA filters and shortening the service life of HEPA filters.
When the HEPA filter in the purification air conditioning system is used as the terminal filter, it should be installed at the end of the purification air conditioning system, generally on the ceiling of the clean room.
For clean rooms that may produce harmful gases or harmful microorganisms, the cleanroom HEPA filter should be installed as close to the clean room as possible to prevent these harmful pollutants from contaminating the pipeline or the unfiltered dirty air from polluting the production environment due to pipeline leakage.
ULPA filters must be installed at the end of the purification air conditioning system to ensure the required air cleanliness level in the cleanroom.
To facilitate airflow distribution and the adjustment of the airflow velocity field within the cleanroom, cleanroom HEPA filters with similar resistance and efficiency are generally installed in the same cleanroom or clean zone. This makes it easier to balance the system resistance.
Principle 5: Understand the standards of various countries
When selecting air filters, clean room designers are most concerned about the main performance parameters of the filter, such as efficiency and resistance at rated air volume.
These performance parameters have their own standards and corresponding testing methods in various countries and regions. Each filter manufacturer also formulates its own product standards based on the above standards and provides them to users. The standards and test methods of filter efficiency are different.
In the 1970s, Europe introduced the EU series of air filter standards, with 14 grades from EU1 to EU14; in the 1990s, the G-F-H-U grouping standard was introduced, with a total of 17 grades. In 1996, the United States also introduced filter efficiency classification standards with C1~C4, L5~L7, M9~M12, H13~H16, and UH17~UH20; in 1999, the European Committee for Standardization (CEN) issued the test method and classification standard for MPPS (most penetrating particle size) in EN1822-1.
To date, some of the most notable standards in the world include EN1822, ISO16890, and MERV.
Conclusion
This concludes this article. In summary, there are many factors to consider when configuring cleanroom air filters. We hope this article was helpful to you. If you have further questions, please feel free to contact us.
