Ventilation Filters

Classification of air filters used in ventilation systems

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

Overall length about 20 m
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

a) Flat Panel type - disposable Filters

Air velocity 0.1 - 1.0 m/s
Resistance 25 - 250 N/m²
Efficiency 20-35%

b) Continuous roll - self cleaning Filters

Air velocity 2.5 m/s
Resistance 30 - 175 N/m²
Efficiency 25%

c) Bag Filters

Efficiency 40-90%

d) HEPA (High Efficiency Particulate Air) Filters

Efficiency 99.97% for 0.3 micron particles and larger

d) ULPA (Ultra Low Penetrating Air) Filters

Efficiency 99.9997 for 0.12 micron particles or larger

Viscous Filters

a) 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

b) 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
		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, theatres, hospital rooms, data rooms
		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.
		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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