Why do airplanes need filters anyhow? What does HEPA stand for? We’ll answer those and other frequently asked questions for you.
Why do airplanes need cabin air filters?
Modern commercial jets typically use a 50/50 mix of outside air and recirculated cabin air to generate greater fuel efficiency. Air circulation is continuous. All of the air inside the cabin is replaced by a mixture of outside air and filtered air over a two to three-minute interval, resulting in 20 to 30 air changes per hour. This replenishment assures that the recirculated portion of the air does not endlessly recirculate but is diluted and replaced with outside air. Using recirculated air also results in a more comfortable humidity level inside the cabin, as 100% outside air is extremely dry. Cabin air filters maintain optimal quality of the recirculated air by trapping dust, lint and other airborne particles.
What is the right filter to use in an aircraft recirculation system?
Passengers, airline employees, aircraft manufacturers and special interest groups all have an opinion on the right amount of filtration needed in aircraft recirculation systems. You’ll find conflicting reports on cabin air quality. Donaldson Company’s position is to provide airlines a choice of air recirculation filters using today’s best available technologies. Donaldson offers particulate, high efficiency, HEPA and BIOAdvantage filters for reducing bacteria, viruses, dust, lint, pollen and other contaminants from cabin air.
What is a HEPA filter and why is it important?
High Efficiency Particulate Air (HEPA) filters are used in hospital cleanrooms, nuclear ventilation systems, biological safety benches, and other critical indoor environments. HEPA filters are rated on their ability to capture and retain particles of 0.3 microns in diameter.
The 0.3 micron particle size was selected to test critical filters because it approximates the most difficult size for a filter to capture and retain. Particles that are smaller and larger than 0.3 microns are captured by three primary filtration mechanisms: diffusion, direct interception, and inertial impaction. Particles smaller than 0.3 microns are easily captured due to the Brownian motion of the particle (diffusion). Particles larger than 0.3 microns are also easily captured because of direct interception and inertial impaction. Direct interception occurs when the particle encounters a fiber near the airstream. Inertial impaction is when particles directly impact on the fiber surface, because the particles’ inertia causes them to deviate from the airstream around the fiber.
What are the sizes of typical contaminants in the cabin air and will these filters capture them?
The sizes of typical contaminates for critical filters to capture are:
Pollens 10µ to 100µ
Household Dust 0.3µ to 5µ
Human Skin Cell 3 µ to 15 µ
Atmospheric Dust 0.001µ to 15µ
Tobacco Smoke 0.01µ to 1µ
Bacteria 0.05µ to 50µ
Virus 0.005µ to 0.1µ
Source: Dr. Liu, University of Minnesota
What are the efficiencies of Donaldson’s various cabin filter product line?
BIOAdvantage and HEPA Filters are 99.97% efficient on 0.3 micron particles
High efficiency pleated media filters are 99.9% efficient on 0.3 micron particles
1-Piece Filters and 2-Piece Filters are 95% efficient on 0.3 micron particles
These efficiency results are measured at the operating airflow for each aircraft. All three classes of filters are nearly 100% efficient as the particle size approach 0.01 and 1.0 microns. The difference in the efficiency performance between these filters occurs at particle sizes between 0.01 and 1 microns. In this range of particle sizes, BIOAdvantage and HEPA filters collect a greater percentage of particles.
Which airplanes can use Donaldson cabin filters to protect the passengers, crew, and electronic equipment?
Contact Donaldson for the most recent applications and filter availability.
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