Other filtration systems

HEPA/ULPA Filtration

If the electrostatic precipitator technology has its claim to fame as being used in US nuclear submarines, HEPA filtration has its claim to fame as being designed in the highest level of Top Secret government projects. During the Manhattan Project, there was a need to filter very fine radioactive particulate contaminates.

The HEPA filter, or High Efficiency Particulate Air cleaner is a mechanical filter which is required to filter out 99.97% of contaminants 0.3 microns in size. ULPA (ultra low penetration air) filters catch more than 99.9995% of contaminants as fine as 0.15 microns. A mechanical filter is trivial to understand as it is simply a very fine grill that traps the physical compartments.

There are a number of reasons why this may be less than ideal. First, mechanical filters need very high air pressures to continually force air through the HEPA filter itself. Remember, cleaning 99.9999% of pollutants in the air is useless, if only a small volume of air is filtered. The actual HEPA filter itself has a very high resistance and so the fan needs more power than electrostatic precipitation systems, which have minimal air resistance.

As the HEPA filter clogs up, the filter rapidly becomes less and less efficient while simultaneously adding strain to the fan mechanisms. Finally, the filters are disposable and can be costly to replace.

It's important to keep your perspective. HEPA filters are great if you need absolute filtration – in terms of absolute performance, they're probably among the best. Austin Air HEPA filters have been used to protect US citizens living near chemical stockpile destruction facilities. However, chances are that you've got a working immune system and it's OK if there's some bacteria or viruses floating in the air. It's OK if the compounds that give your freshly laundered clothes a pleasant fragrance are in the air. It's dust that'll hurt your PC.

The main disadvantage of the system is the cost of replacement filters ($100 is not uncommon; some designs last 5 years, some only 1 year). In addition, HEPA filters tend to be bulky and noisy and are often overkill. Some HEPA filter manufacturers have taken on the razor model – they'll sell the unit at a bargain price, but then make huge profits on the replacement filters.