Air Filters: Kinds, Principles, Materials

air filters

There are many types of air filters or air purifiers that are part of the process of keeping indoor air clean. These devices help remove particulate matter from the air and reduce the volatile organic compounds (VOCs) that are slowly emitted from synthetic fabric, rugs, paint, and disinfectants. 

Getting rid of airborne particles like moldy dust and spores, pet dander, and dust mite skeletons can be very important for people suffering from allergies.

There are many types of air cleaner devices.

Air filtration devices:

  • Air filter devices that push air through a fine mesh, like a strainer but much finer, to keep particles from going through them. 
  • Air filter devices that use various forces like static electricity to draw particles out of the airstream.

Ozone and negative ion devices:

  • There are also devices that convert a portion of oxygen in the air into ozone. These work by activating the oxygen in the air which makes the oxygen atoms cling together, converting to ozone (O3 instead of normal O2 molecules). Ozone is thought by many to have health-improving qualities, but conventional medicine considers ozone in quantity to be dangerous.
  • Devices that add an electron to the oxygen in the air enriches the air with negative ions, which are presumed to improve health and mood. Negative ions to the air are presumed to counteract the effect of an overload of positive ions (one fewer electron in the oxygen) which are generated by overexposure to computers and home electronics. Some companies add negative ion devices to air filter devices, others sell devices like magnetic bracelets that are presumed to do that.

Types of Air Filters.

Filters and filtration devices are designed to remove particles of impurities from the air.

  • The basic design of an air filter is based on a screen, a strainer, or coffee infuser, but much finer. Filters vary in the paths air is forced through in order to block particulate matter of different sizes.
  • Charged media filters pass a charge through an electrically conductive filter material attracting oppositely charged particles to the filter material. These devices also generate ozone and the filters have to be periodically changed.
  • One alternative to a filter is an "electrostatic precipitator" which electrically charges particles of air so they are attracted to a plate which is oppositely charged. The plates can be washed regularly. These devices produce some ozone.
  • Antibacterial and germicidal filters can be a supplementary clean air device. These expose the air to ultraviolet rays which kill organisms in the air. They are usually installed as part of a filtration cleaner.

Gradations of Air Filters.

Air filters are designed to catch and retain small particles that are suspended in the air, generally small and light enough that they can float around in air indefinitely.

Particle sizes:

The sizes of common particles can be as small as 1 micron (1 thousandth of a millimeter). Where typical raindrops are close to a millimeter in size (1,000 microns), particles of carbon black range between .001 microns and .12 microns in size. Smoke from tobacco, resins, coal and atmospheric dust ranges generally between .02 microns to 2 microns in size.

Bacteria range in size between .08 microns and 25 microns in size. Pollens are between .75 microns and 500 microns in size. [Particle Size Chart .pdf from].  The smallest thing visible by an acute naked eye is .1 millimeters or about 100 microns.

Filters and particle size:

High Efficiency Particulate Arresting (HEPA) filters are made of thin fiberglass filaments and contain an activated charcoal material. They can capture particles as small as .3 microns or medium-sized bacteria, dust mite debris, most household dust, plant spores, medium-sized tobacco smoke particles and most pollen, nearly all plant spores.

Activated Charcoal Filters are made of particles of charcoal treated with oxygen. The oxygen creates millions of tiny pores between the atoms of carbon. Chemicals passing through the pores tend to bond to the activated charcoal.

These filters are more like chemical sponges than strainers or screens. They are more effective at absorbing chemicals than trapping particles. They remove VOCs from the air but do not remove the particles that are caught by HEPA filters.

The thickness of the filter mesh and the shape configuration makes a difference in terms of the power of the filter. The mesh creates a maze of material through which particles have to travel.

The more material between entrance and exit, the more likely particles will get caught. Of course, the compromise has to do with the air pressure necessary to push the air through the filter. A careful design calls for a balance between thickness and air flow efficiency.

Dust Goblin filters are ten times thicker and hold five times more dust than standard filters. They are the perfect storm of design and function, by inhibiting microbial growth while reducing the overall strain on your HVAC system! To learn more please contact us.