Electrostatic Air Filters
(Electrostatic Precipitator Air Cleaners)

What is an Electostatic Air Cleaner?

Electrostatic precipitators are commonly used to remove particles from airstreams having large steady flow rates. Typical applications include coal-burning plants and cement kilns. A typical two-stage electrostatic precipitator has a stage of corona wires and a stage of collecting plates. The corona wires are maintained at several thousand volts which produces a corona that releases electrons into the airstream. These electrons attach to dust particles and give them a net negative charge.

The collecting plates are grounded and attract the charged dust particles. The collecting plates are periodically rapped by mechanical rappers to dislodge the collected dust, which then drop into hoppers below. The air velocity between the plates needs to be sufficiently low to allow the dust to fall and not to be re-entrained into the airstream. It takes between 0.01 and 0.1 second for dust particles to acquire a charge in the corona region. Industrial systems are normally designed with more than 1 second residence time in the first stage to assure the charging of dust particles. Industrial systems are capable of removing particles in the size range 0.01 -- 10 microns and can achieve efficiencies in the neighborhood of 95%.

Small electrostatic precipitators designed for home or other non-industrial applications are known as electronic air cleaners. These do not have rappers, but must be taken apart and cleaned periodically. Also, these devices are often inserted into airstreams without regard to residence time or air velocities, and hence efficiencies can be much lower than those used in industrial applications.

A well-designed electronic air cleaner for home or office building applications would not only be relatively large and have a high energy demand, but it would also generate ozone at potentially hazardous levels. Even a well-sized, efficiently operating air cleaner cannot achieve the efficiency necessary to guarantee complete interception of airborne bacteria, let alone viruses. However, as a means of simply improving air quality and decreasing dust and airborne microbes, electronic air cleaners do indeed have some value in home and office building environments.

Source of the above information: Aerobiological Engineering, Pennsylvania State University

Furnace Problems

Electrostatic air filters are too dense for most furnaces. As a result, they can interfere with the airflow of the furnace, causing the air conditioner to freeze up in the summer. Electrostatic air filters can also cause the furnace to overheat in the winter.

Maintenance

Electrostatic air filters require frequent cleaning, usually more than once a month. They cannot just be installed and forgotten about. Unfortunately, they are usually neglected because most people simply do not remember to get inside the furnace at least once a month to clean the filter and re-install it. Even if you did, this routine is still a pain because electrostatic air filters usually have several layers you have to remove and clean individually.

Effectiveness

The problem with electrostatic and all other air filters is that they can only remove the larger airborne particulates. What they fail to mention is that most airborne pollutants are smaller than the 0.3 microns that they are capable of removing. Allergens, particulates and toxins from cigarette smoke, etc. still manage to slip through these screens and back into the air we breathe.

Black Wall Effect

Electrostatic air filters work by electrically charging particles so they are attracted to the metal plates in the machine. However, these charged particles are also attracted to all surfaces, resulting in black markings on walls, etc.

A Better Choice

A better alternative is the Air Oasis Probe Induct Air Purifier for HVAC installation. It eliminates all the negatives of an electrostatic filter, has no yearly maintenance, and is superior in its ability to purifier the air of a much broader range of air pollution, and does so throughout the entire house or building.

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