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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

FilterGeneral propertiesClassEffectApplications
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
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
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, theaters, hospital rooms, data rooms
EU8 Very effective against particles and blacking.
Very effective against microbes.
Effective against tobacco smoke.
Operating theaters, production rooms for fine optics and electronics.
Hospital examination rooms.
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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