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Optimum Air Filtration
This Is the Air We Breathe
Indoor airborne contaminants include, but are not limited to, pet dander, pet hair, dust mite droppings, mold, dust, bacteria (pathogens), allergens (pollen and the like), viruses, radioactive radon daughters, undesirable gasses (CH4, CO, H2S, etc.), solvent vapors and odors.
This Is How We Clean the Air We Breathe
There are essentially three methods of residential air filtration:
Capture Airborne Particles
First, I want to put my prejudice right out in the open: those 'consumer quality' disposable, and washable, cheap filters you buy from local stores do next to nothing for you except keep airborne material from damaging the inner workings of your air handling unit, coils and furnace.
"95% Efficiency" boasts the label of more costly particle filters. What does that mean, 95% efficiency? It's a holdover from the old days when manufacturers used the "dust arrestance" method. Basically, the manufacturer first records the weight of a clean test filter, then places it in a small wind tunnel with certain airspeed and progressively dumps three different grades of dirt into the air stream. After dumping the dirt, the manufacturer records the weight of the dirty filter and compares its weight to the known weight of the three grades of test dirt. If the filter can absolutely hold 100% of all the three samples of dirt, he rates the filter efficiency at 100%. It is helpful to note that no one ever calibrates household dirt. I consider this method worthless as a measure of how effective a filter serves the homeowner. In fact, the high efficiency rating actually translates to an energy penalty, due to excessive pressure drop across the filter that contributes to overall fan system inefficiency.
The ultimate disposable filter is the HEPA filter, originally designed to protect workers in atomic energy plants, is commonly used in hospitals. They are very effective and they are very expensive -- not really practical for a residence.
We still want to capture the big stuff to protect our equipment and duct work, but we want to do it as part of a larger strategy to maintain a healthy indoor environment.
Electronic Air Cleaners, my favorite, incorporate three mechanisms: a pre-filter to capture the really big stuff, an electronic filter to capture the very smallest stuff and a post filter to capture the small, but high mass, particles that make it passed the electronic section. Here, I quote Honeywell: "The Honeywell Electronic Air Cleaner is an advanced and easy-to-use, whole-house solution that traps and filters up to 98% of pollutants from the air passing through your heating and cooling system. This advanced air cleaner captures microscopic impurities like dust, smoke and smog particles in addition to larger particles like mold spores and cat dander. It works by placing an electric charge on airborne particles, and then collecting the charged pollutants like a magnet. Plus, you can say goodbye to monthly filter replacements by simply washing the air cleaner cells in your dishwasher or sink."
Flexible air duct actually enhances the performance of electronic air cleaners because the designer selects flexible ducting for low velocity to overcome high resistance relative to metal ducting. Consequently, return air encounters the electronic air cleaner at a low face velocity.
My favorite electronic air cleaner: the Honeywell F300 series. I use it for my residence:
Remove Gaseous Pollutants
Activated charcoal filters do an excellent job of absorbing volatile organic compounds (VOC). This material is excellent for odor control, but it is wholly ineffective for the removal of deadly carbon monoxide (CO) produced by automotive engines, gas-burning appliances, grandma's old kerosene lamps and wood-burning fireplaces. Note -- CO is an insidious threat only detectable by either an electronic monitor or a pathologist.
Destruction of Pathogens
Ultraviolet air treatment equipment destroys pathogens with high-intensity ultraviolet. The product pictured destroys "up to 87% of certain airborne bacteria". The only maintenance is the annual lamp replacement.
No single method is perfect and effectiveness can be diminished if equjipment is improperly installed.