ASHRAE Journal - September 2019 - 21

TECHNICAL FEATURE

consumers can absorb, in part because portable units
are not covered by ASHRAE Standard 52.2, the standard
that establishes performance criteria for MERV ratings.
Consequently, for portable unit performance ratings,
the EPA guidance refers to the Association of Home
Appliance Manufacturers (AHAM), an organization that
offers performance ratings and certiﬁcation for particle
removal by portable air cleaners.
AHAM testing measures the "clean air delivery rate"
(CADR) of the device. The CADR is the amount of air
(in cfm) that has been cleaned of particles in three size
ranges. The ranges are described by names that consumers can relate to, namely: "smoke", "dust" and "pollen."
AHAM deﬁnes these as 0.09 to1.0 µm for smoke, 0.5 to
3 µm for dust, and 5 to 11 µm for pollen.
Further, the CADR also estimates the ﬁltration effectiveness of the device-the reduction in particle concentrations in the occupied space, based on the maximum
recommended ﬂoor area for the rated unit. Rated units
are expected to remove 80% of the airborne small particles (0.09 to 1.0 µm) over an hour, above and beyond

the number of particles that would naturally settle out.
Rated removal is also based on the assumptions that
the ceiling height is no higher than 8 ft (2.4 m) and that
the space exchanges less than one air change per hour
with other spaces. The EPA guidance to consumers notes
that units with larger CADR ratings are better, and that
if ceiling heights are greater than 8 ft (2.4 m) (such as
spaces with cathedral ceilings) a consumer might consider using a larger unit or multiple units to achieve 80%
reduction in particle concentration.
Note the most important but unstated assumption is
that the unit is running continuously when the space in question is occupied. Short runtimes limit the effectiveness
of portable air cleaners, just as they limit the ﬁltration
effectiveness of central systems. And with portable air
cleaners, operating noise can be an issue. The noise
levels at which a given unit's CADR was achieved are
not currently described on the AHAM-veriﬁed label. It
would be helpful if consumer packaging displayed the
sound levels at which the CADR rating was achieved, to
provide a basis for better-informed consumer choices.

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ASHRAE Journal - September 2019

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