The role of HEPA Filters in clean rooms
Today, clean rooms have been widely used in electronics, aerospace, machinery, chemicals, pharmaceuticals, food, medical care, bioengineering...all walks of life. With the rapid development of the national economy and scientific research, the application of air showers and clean rooms will become more and more extensive and more and more important.
Clean rooms can be classified according to airflow patterns, usage purposes and main objects of control: vertical unidirectional flow is an airflow pattern in which the airflow flows from the ceiling to the floor at a certain speed (0.25m/s~0.5m/s). This airflow can create a clean level of 100, 10, 1 or higher. However, its initial investment and operating costs are very high. In the project, its area is compressed to the minimum as much as possible and used only in the necessary parts. Horizontal unidirectional flow is an airflow pattern in which the airflow flows from one wall to the opposite wall at a certain speed (0.3m/s~0.5m/s). This airflow can create a purification level of 100. Its initial investment and operating costs are lower than those of the vertical unidirectional flow pattern. The four major technical elements of a clean room are: three-stage filtration of coarse, medium and high efficiency, sufficient purified air supply, establishment and maintenance of positive pressure in the room, and the setting of terminal high efficiency or ultra-high efficiency filters.
To achieve the required cleanliness, filtering, intercepting and adsorbing particles are essential, and high efficiency air filters are also necessary in clean room applications.
High-efficiency air filter HEPA (high efficiency particulate air filter), underrated air volume, the capture efficiency of particles with a particle size greater than or equal to 0.3μm is more than 99.9% and the air flow resistance is less than 250Pa. Ultra HEPA air filter ULPA (ultra low penetration air filter), underrated air volume, the capture efficiency of particles with a particle size of 0.1-0.2μm is more than 99.999% and the air flow resistance is less than 280Pa.
Cleanroom HEPA filter application guide
For ISO5 unidirectional flow, ISO40 H-class HEPA filters (99.99% minimum particle retention rate for penetrating particle size) should be used.
For non-unidirectional flow below ISO5, ISO35 H-class HEPA filters (99.95% minimum particle retention rate for penetrating particle size) should be used.
Materials used for HEPA Filters and pre-filters
The HEPA Filters at the end of the air-conditioning system (including the partitions of the partition filters) should not use hydrophilic materials, and materials that are easy to breed microorganisms should not be selected.
The filter material of the HEPA Filter is generally glass fiber, but it should not contain glass fiber with high sodium and potassium content that is easy to degrade.
A pre-filter should be installed in the air supply system, and the retention efficiency of the pre-filter should not be less than 90%.
The pre-filter section should have a simple and practical resistance monitoring device to accurately and intuitively provide filter replacement information.
