Air Filtration Basics


The ideal air filtration system does not include only one type of air filter. An ideal air purifying system includes multiple filter technologies in order to capture the full range of pollutants in your air stream. The most common types of air filters are media filled filters/carbon filters, HEPA filters, particulate filters/pre-filters, air ionization, and UV.

Media Filled Filters are filters packed with highly absorbents for removing chemical fumes, gases, and other VOCs. The absorbents also referred to as “media” may either be activated carbon or altered media such as impregnated zeolite. These types of filters will capture the pollutants and will not release them until thermally or chemically altered. After all the active ingredient or unoccupied pores are taken up– the media must be replaced.

Read more about Hydrosil’s Air Filter Media.

HEPA filters will remove the smallest particle sizes, less than 0.3 microns in diameter, which is why they are commonly used in clean rooms and hospitals. All filters have a MERV (Minimum Efficiency Reporting Value) rating. A HEPA filter is rated in the highest group as shown below. The MERV rating is ANSI/ASHRAE Standard 52.2 with ratings between one (1) and twenty (20).

MERV Rating Particle Size Ranges Typical Filter Type
1-4 > 10.0 um Metal, Synthetic, Disposable Panel Fiberglass
5-8 3.0-10.0 um Media Panel Filters
9-12 1.0-3.0 um Rigid Cell, Cartridge V-Cells
13-16 0.30-1.0 um Rigid Cell, Cartridge V-Cells
17-20 < 0.30 HEPA & ULPA

HEPA filters  work well at targeting dust, pollen, pet dander, and other allergens. HEPA filters are commonly used in combination with media filled filters to remove both ultra-small particles and vapors and odors.

Air Ionization works by negatively charging particles and causing them to collect on a charged plate. This type of filtration has been known to produce trace amounts of ozone and is not effective at removing smoke and odors.

Ultraviolet (UV) is effective at removing viruses, bacteria, mold. This technology can be used in combination with media filled filters to remove odors, vapors, and chemicals which cannot be removed with UV.

Installing or Retrofitting Air Filtration System

If you are looking at changing an existing system or installing a new one there are a few things to consider:

  1. How many air changes per hour do you need?
  2. What is the design and actual air flow?
  3. What odors or vapors do you notice?
  4. Do you notice corrosion on capital equipment?

Air filters are essential in providing protection for capital equipment. All air handling units such as fans need protection from corrosive gases and particulate build-up.

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