Environmental Engineering Reference
In-Depth Information
W
Figure 12.11
Relationship between filter loading and collection efficiency. (From
ASHRAE
Equipment Handbook
, ASHRAE, Atlanta, 1983, chapter 10. With permission.)
Because HEPA filters have efficiencies near 100%, penetration rather than
efficiency is typically reported. Penetration can be converted to % efficiency
by using the following equation:
E = 100 - P
(12.3)
where E = efficiency (%)
5.
Filter soiling and efficiency
As a filter becomes soiled, the mat of collected particles serves as a collection
medium so that collection efficiency increases with increased service life.
This increase in both arrestance values and dust spot efficiency as a function
of dust exposure can be seen in Figure 12.11 . As a consequence, “dirty”
filters have an associated increase in cleaning efficiency. Notice, however,
the significant effect on air flow resistance with increasing filter dust loads
in Figure 12.12 .
D. Use considerations
Air cleaners designed to control airborne particles are used in a variety of
applications. In mechanically ventilated buildings, low-efficiency dust stop
filters and renewable-media filters are used to protect mechanical equipment.
Increasingly, a higher level of particle cleaning and performance is being
designed and specified for mechanically ventilated buildings to achieve and
maintain cleaner indoor spaces. Medium efficiency extended-surface filters,
or bag filters, are commonly specified by mechanical engineers and installed
by building owners/operators.
In most residential environments, air cleaning is limited to dust stop
filters used in heating and cooling systems to protect mechanical equipment.
In the 1980s, a significant air cleaner market targeted to average consumers
 
Search WWH ::




Custom Search