Environmental Engineering Reference
In-Depth Information
a
b
Figure 12.10
Residential in-duct and free-standing electronic air cleaners. (Courtesy
of Honeywell, Inc., Minneapolis.)
3.
Charged-media nonionizing cleaners
These cleaners include characteristics of electrostatic and dry-filter particle
collection. They consist of a dielectric filter mat made of glass fiber, cellulose,
or other fibrous materials supported on or in a gridwork of alternately
charged (12,000 V) or grounded members. Consequently, a strong electro-
static field develops in the filter medium. Particles approaching the filter
medium are polarized and drawn to it, where deposition takes place. Because
of increased resistance to air flow associated with soiling, such filters need
to be replaced periodically.
C. Performance measurement
Air cleaners vary in their collection efficiency (as well as overall particle
removal) for particles of different aerodynamic diameters, resistance to air
flow, service life, and particle-holding capacity. As a consequence, there is a
need for uniform evaluation and rating of filter performance. Test procedures
prescribed under ASHRAE (American Society of Heating, Refrigerating and
Air-Conditioning Engineers) Standards 52.1-76 provide performance char-
acteristics of most commercially available filters and filtration systems. Two
different ASHRAE test methodologies were used to evaluate filter and fil-
tration system performance. In the Spring of 2000, ASHRAE published a
new standard, 52.2-1999, which is likely to serve as the primary filter test
methodology in the future. These methodologies, plus an additional meth-
odology for HEPA filters, are described below.
 
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