Ventilation Filters
Classification of air filters used in ventilation systems
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Ventilation filters may be classified and characterized after
- Separation efficiency - ability to retain synthetic standard dust. Weight and % statement.
- Blacking efficiency - capability to retain atmospheric dust. Optical measured and % statement.
- Particle separation efficiency - capability to retain particles at fixed sizes. Particle concentration measured and % statement.
- Dust accumulation capacity - capability to keep standard dust before the pressure drop extend a certain value.
- Airflow resistance and static pressure drop of the filters.
Dust Concentration
Common dust concentrations exposed to filters in ventilation and air-condition systems
- Rural and suburban districts - 0.45 to 1.0 mg/m3 air
- Metropolitan districts - 1.0 to 1.8 mg/m3 air
- Industrial districts - 1.8 to 3.5 mg/m3 air
Types of Filters
Washers
- Large
- Air velocity through washer 2.5 m/s
- Water pressure required for spray nozzles 140 - 170 kN/m2
- Water pressure required for flooding nozzles 30 - 70 kN/m2
Dry Filters
Felt, cloth, cellulose, glass, silk etc. without adhesive liquid
Flat Panel type - disposable Filters
- Air velocity 0.1 - 1.0 m/s
- Resistance 25 - 250 N/m2
- Efficiency 20-35%
Continuous roll - self cleaning Filters
- Air velocity 2.5 m/s
- Resistance 30 - 175 N/m2
- Efficiency 25%
Bag Filters
- Efficiency 40-90%
HEPA (High Efficiency Particulate Air) Filters
- Efficiency 99.97% for 0.3 micron particles and larger
ULPA (Ultra Low Penetrating Air) Filters
- Efficiency 99.9997 for 0.12 micron particles or larger
Viscous Filters
Panel type - cloth with viscous fluid coating - washable or disposable
- Plates about 500 mm x 500 mm
- Air velocity 1.5 - 2.5 m/s
- Resistance 20 - 150 N/m2
Continuous roll - continuously moving, self cleaning
- Air velocity 2.5 m/s
- Resistance 30 - 175 N/m2
Electrostatic Precipitators
- Cleaned automatically
- Air velocity 1.5 - 2.5 m/s
- Resistance negligible
- Efficiency 30-40%
Absolute
- Dry panel with special coating - disposable or self cleaning
- Air velocity 2.5 m/s
- Resistance 250 - 625 N/m2
Standard European Filter Classification
| Filter | General properties | Class | Effect | Applications |
| Basis filters | In general: - produced in synthetic fibers - efficient for particles > 4-5 mm - air speed < 2.5 m/s - start pressure drop approximately 50 Pa - final pressure drop approximately 150 Pa |
EU1 | Protects against insects and fibers. Limited effect against larger pollen (<70%) Ineffective against smoke and blacking particles |
Window units Heat exchangers Air heaters Fiber filters in textile industry |
| EU2 | Effective against larger pollen (>85%) and larger atmospheric dust. Limited effect against dust and blacking particles |
Heating and cooling units in electrical transformers garages industrial halls offices in industry |
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| EU3 | Effective against larger pollen (>85%) and larger atmospheric dust. Limited effect against dust and blacking particles |
Heating and cooling units in electrical transformers garages industrial halls offices in industry |
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| EU4 | Limited effect against dust and blacking particles | In addition to EU3 kitchens and spray paint work shops | ||
| Fine filters | In general: - produced in glass fibers - efficient for particles > 0.1 mm - air speed < 2- 3 m/s - start pressure drop approximately 50-100 Pa - final pressure drop approximately 200 -250 Pa |
EU5 | Effective against pollen and finer atmospheric dust Considerable effect against smoke. No effect against tobacco smoke |
Churches, sport halls, department stores, schools, hotels Food stores |
| EU6 | As EU5 | As EU5 | ||
| EU7 | Effective against pollen and blacking dust | As EU6 and food industry, laboratories, theatres, hospital rooms, data rooms |
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| EU8 | Very effective against particles and blacking. Very effective against microbes. Effective against tobacco smoke. |
Operating theatres, production rooms for fine optics and electronics. Hospital examination rooms. |
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| EU9 | As EU8 | As EU8 | ||
| Micro filters | In general: - produced in glass fibers in combination with separators of paper, plastic or aluminum - efficient for particles > 0.01 mm - air speed < 0.5 - 1.0 m/s - start pressure drop approximately 250 Pa - final pressure drop according life span and economy |
EU10 | ||
| EU11 | ||||
| EU12 | ||||
| EU13 | ||||
| EU14 |
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