ASHRAE Journal - February 2014 - S15

Feature
of the ﬁlter class as speciﬁed in EN 1822.
As seen in the data, replacing U 15, H 14, H13 or H12 ﬁlters
with one of a lower class results in a higher or equal CADR. That
is, these four classes can be replaced without affecting the quality
of air delivered. Since H13 and higher classes are often used in
regulated industries, it may be more acceptable to eliminate H12
and replace it with H11 for general ventilation and similarly replace
U15 with H14 for non cleanroom applications. One could simply
use H 11 and H14 for most applications outside of cleanrooms
without loss of clean air delivered.

Summary
The classiﬁcation of general ventilation ﬁlters has expanded
from a few about twenty ﬁve years ago to 16 in the US Standard
and 10 in the European Norms. Since many of these classes
overlap in performance or are within the potential variability in
measurements, an example of reduced number of classes-6 for
ASHRAE and 4 for the European Norms-has been presented.
Analyses of CADR delivered by commercial ﬁlters of adjacent
ﬁlter classes shows that replacing ﬁlters with ﬁlters of an adjacent
ﬁlter class does not seriously affect the CADR. In several of the
cases examined, one obtained a higher CADR when a lower ﬁlter
class was used to replace a higher class ﬁlter, thus offering a
potential for cleaner air delivery at lower pressure drops. Similar

analyses of the CADR of HEPA and ULPA ﬁlters most often used
in non regulated industries or non critical applications, showed
that the four ﬁlter classes between H11 - U15 (EN 1822) can be
replaced with just two without adversely affecting the cleanliness
of the delivered air. As a practical recommendation, perhaps
specifying just H11 and H14 ﬁlter classes will be adequate for most
non regulated industries or non critical applications that currently
specify H11 - U 15 ﬁlters.

Future Work
Analyses of data from additional commercial ﬁlter types and
classes, as well as experimental measurements will be required to
make a stronger case for reducing the number of ﬁlter classes and
returning to the simplicity of a few ﬁlter classes of the years past.

References
ASHRAE 52.2 - 2007: Method of Testing Ventilation Air-Cleaning
Devices for Removal Efﬁciency by Particle Size, ASHRAE, USA
ANSI/AHAM AC-1: Method for Measuring the Performance of
Portable Household Electric Room Air Cleaners, AHAM, USA
EN 779 - 2002: Particulate Air Filters for General Ventilation:
Determination of the Filtration Performance
EN 1822- 2009: High Efﬁciency Air Filters (HEPA and ULPA),
Part 1 - 5

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February 2014

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ASHRAE Journal - February 2014

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