Handbook of air conditioning and refrigeration / Shan K

15.15 ELECTRONIC AIR CLEANERS
AIR SYSTEMS: COMPONENTS—FANS, COILS, FILTERS, AND HUMIDIFIERS 15.69
An electronic air cleaner uses the attraction between particles of opposite charges. Dust particles
charged within the cleaner attract and agglomerate to greater sizes at the collecting plates. They are
therefore easily removed from the airstream.
A typical electronic air cleaner is shown in Fig. 15.39. A high dc potential of 1200 V is supplied
to the ionizing field. The positive ions generated from the ionizer wire charge the dust particles.
Right after the ionizing section, the dust particles come to a collecting section, which consists of
several plates that are alternately grounded and insulated. A strong electric field is produced by supplying
a dc potential of 6000 V to these plates. The positively charged dust particles are attracted by
the grounded plates of opposite charge, and attach themselves to the plates.
Because of the numerous points of contact, the bond between particles held together by intermolecular
forces is greater than that between the particles and plates. Therefore, the dust particles
agglomerate and grow to such sizes that they are blown off and carried away by the airstream. The
agglomerates are then collected by a medium-efficiency air filter located downstream from the collecting
section.
Kemp et al. (1995) showed that electronic air cleaners are efficient for removing small particles
of 0.5 to about 8 �m. When dust particle sizes were approached and exceeded 10 �m, the filter’s
efficiency dropped from its highest peak. In a year-long test with the outdoor ambient air, no microbial
growth was observed on any of the filters.
The pressure drop across the ionizer section and collecting section is low and ranges from 0.15
to 0.25 in. WC (37 to 62 Pa) against an air velocity of 300 to 500 fpm (1.5 to 2.5 m/s). Safety
FIGURE 15.39 An electronic air cleaner.