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.