Selection and placement of air filters 

Ⅱ.Application areas and filtration range of air filters:

1. Coarse filters are mainly used as pre-filters at the fresh air inlet of air conditioning systems to retain large particles from the atmosphere. They are designed to capture suspended particles larger than 5 microns, settling particles larger than 10 microns, as well as various foreign objects, preventing them from entering the system. Rubberized wool, polyester non-woven material and polypropylene fibers are usually used as filter materials. Filtration efficiency is determined by trapping particles ≥5 µm in size.

2.Medium efficiency air filters, since large particles are already retained by the preceding pre-filter, can be used as final filters in conventional air conditioning systems, as well as pre-filters for medium and high efficiency filters in air purification systems. Polyester non-woven fabric, polypropylene fibers and glass fiber are commonly used as filter media.

Primarily used to capture suspended particles 1-10 µm in size, efficiency is determined by filtering particles ≥1 µm in size.

3. Medium and high efficiency filters can be used as final filters in systems with a general purification level, as well as intermediate filters before high-efficiency filters; Polyester non-woven fabric, polypropylene fibers and glass fiber are commonly used as filter media. Primarily used to capture particles 1–5 µm in size, efficiency is determined by filtering particles ≥1 µm in size.

4.Semi-high efficiency filters are mainly used as final filters in clean rooms, and also as pre-filters for high efficiency filters and final filters in supply air systems to improve the quality of supply air. Polypropylene fibers and glass fiber are commonly used as filter media. Primarily used to capture particles smaller than 1 µm, efficiency is determined by filtering particles ≥0.5 µm in size.

5.High efficiency filters (ultra high efficiency filters) are mainly used as final filters in cleanrooms to ensure the required level of cleanliness.

Their effectiveness is determined by filtering particles ≥0.5 microns in size. Ultra-thin glass fiber is usually used as a filter material.

Ⅲ.Various ways to indicate the efficiency of air filters: If the concentration of dust in the filtered gas is expressed as mass concentration, then the efficiency is called mass efficiency; if it is expressed as a quantitative concentration, then the effectiveness is called quantitative efficiency; if it is expressed as a relative value for other physical quantities, then it is colorimetric efficiency or turbidity efficiency, etc.

The most common designation is quantified efficiency, expressed as the concentration of dust particles in the air flow at the filter inlet and outlet.

1.At rated air flow, in accordance with the provisions of national standards GB/T14295-93 "Air Filters" and GB13554-92 "High Efficiency Air Filters", the efficiency range of different filters is as follows:

Coarse filters: for particles ≥5 µm in size, filtration efficiency 80 > E ≥ 20, initial resistance ≤ 50 Pa

Medium efficiency filters: for particles ≥1 µm, filtration efficiency 70 > E ≥ 20, initial resistance ≤ 80 Pa

High efficiency filters: for particles ≥1 µm, filtration efficiency 99 > E ≥ 70, initial resistance ≤ 100 Pa

Semi-high efficiency filters: for particles ≥0.5 µm, filtration efficiency E ≥ 95, initial resistance ≤ 120 Pa

High efficiency filters: for particles ≥0.5 µm, filtration efficiency E ≥ 99.99, initial resistance ≤ 220 Pa

Ultra-high efficiency filters: for particles ≥0.1 µm, filtration efficiency E ≥ 99.999, initial resistance ≤ 280 Pa

2. Since many enterprises currently use imported filters, and their efficiency designation system differs from the domestic one, for ease of comparison we present a table of the relationships between them:

According to European standards, coarse filters are divided into four classes (G1–G4):

G1: particle efficiency ≥5.0μm, filtration efficiency E ≥20% (meets American standard C1)

G2: Efficiency for particles ≥5.0 µm, filtration efficiency 50 > E ≥ 20% (meets American standard C2–C4)

G3: Efficiency for particles ≥5.0 µm, filtration efficiency 70 > E ≥ 50% (meets American standard L5)

G4: Efficiency for particles ≥5.0μm, filtration efficiency 90 > E ≥ 70% (meets American standard L6)

Average efficiency filters are divided into two classes (F5~~F6):

F5 Efficiency: for particles ≥1.0μm in size, filtration efficiency 50 > E ≥ 30% (meets American standard M9, M10)

F6 efficiency for particles ≥1.0μm: filtration efficiency 80 > E ≥ 50% (meets American standard M11, M12)

Medium and high efficiency filters are divided into three levels (F7~~F9):

F7 efficiency for particles ≥1.0 µm: filtration efficiency 99 > E ≥ 70% (meets US standard H13)

F8 Efficiency: for particles ≥0.5μm in size, filtration efficiency 90% > E ≥ 75% (meets American standard H14)

F9 Efficiency: for particles ≥0.5μm in size, filtration efficiency 99% > E ≥ 90% (meets American standard H15)

Semi-high efficiency filters are divided into two classes (H10, H11):

H10: Efficiency for particles ≥0.5μm, filtration efficiency 99% > E ≥ 95% (meets American standard H15)

H11: Efficiency for particles ≥0.5μm, filtration efficiency 99.9% > E ≥ 99% (meets American standard H16)

High efficiency filters are divided into two classes (H12, H13):

H12: Particle filtration efficiency ≥0.5μm, E filtration efficiency ≥99.9% (meets American standard H16)

H13: Particle filtration efficiency ≥0.5μm, E filtration efficiency ≥99.99% (meets American standard H17)