Hybrid Filters

Hybrid
filters are a type of air filter, which incorporate two or more filter
control technologies. They may combine the mechanical filters with an
electronic filters in an integrated system or single self-contained device.
Like mechanical filters, they contain a type of filter media as well as like
the electronic filters they have the ability to charge the particles in the
air and collect them in charged collection plates.
The filters inside the hybrid filters can be replaced just like a
mechanical filtering system. Their efficiency is very good as they are able
to handle a lot of airflow. They are capable of removing different types of
unwanted and harmful particles from indoor air.
Types of Hybrid Filters
- Electret Media Filter: Electret media filter is a type of
hybrid filter. It uses a permanently charged media, which is fabricated
into either flat panel filters or extended media filters. The media
filter, made from synthetic fibers, is inherently charged in the
manufacturing process and it retains the charge which attracts airborne
particles that are snared and retained within the fibers in the formal
methods of impingement and diffusion of other dry-type filters. As the
filter becomes more soiled, the resistance to airflow increases
gradually. Therefore the filter must be replaced periodically.
The main advantages of an 'electret' filter are their relatively low
energy cost and high efficiency when clean. However the disadvantages
are high maintenance costs as they are frequently needed to be replaced
and their efficiency that drops with use.
- Ionizing Charged-Media Filters: Another category of hybrid
filters is ionizing charged-media type filters. This type of filter
works differently as dust in the air is initially charged and then it is
collected on a charged-media filter.
Their mode of operation is very simple. They charge the particles in
the air with negative or alternating negative and positive charges.
Charging of the particles enhances their deposition in conventional
extended-media high-efficiency filters. The advantages of such systems
are that they decrease the particulate counts in the occupied space,
enhance the performance of the particulate filters, and diminish the
housekeeping costs of particle soiling in the space. The main
disadvantage is that its initial equipment cost is high and far above
the cost of conventional high-efficiency filters.
- Electrostatically Enhanced Filters: Electrostatically
enhanced filters are another category of hybrid filters. In this type of
filter, an electric field is superimposed on the fibrous, media-based
air filters. The principle behind this technology is electrostatic
precipitation superimposed on other capture mechanisms, like
sedimentation, diffusion, impaction. However, they aren't largely
popular as they aren't commercially available. But under experimental
conditions, this technology has proved to increased filtration
efficiency, compared to media-based filters alone.