Comment Log Display

I support the proposed regulation but it appears ambiguous to me in
its coverage.  Specifically, does it apply to in-duct air cleaners?
(These are air cleaners, either electronic or mechanical, generally
 costing $1000 or so, that are installed in the ductwork of
forced-air HVAC systems in private homes.)

If so, then the proposed test method is not suitable for such air
cleaners, and needs to be modified to test these air cleaners
under the conditions they will be used.

The reason for this is that ozone created by an in-duct air
cleaner may be largely removed by reaction with particles in the
duct, particles collected on the duct lining, or the duct material
itself before emerging into the conditioned space. 

This is an important consideration for a class of air cleaners
known as electrostatic precipitators (ESPs).  These air cleaners
use an electric potential to force particles to settle out on a
series of metal vanes.  Some ozone is created by this method, but
as stated above, it is possible that the ozone concentration will
be reduced during passage through the ductwork to minimal levels
by the time the filtered air emerges into the breathing space. 

I have tested both in-duct ESPs and in-duct high-quality
mechanical filters under normal living conditions in a home over 
more than one year. (Wallace, L.A. and Howard-Reed, C.H. 
Continuous Monitoring of Ultrafine, Fine, and Coarse Particles in
a Residence for 18 Months in 1999-2000.  J Air Waste Manage.
Assoc. 52(7):828-844. 2002.) The efficiency of the two air
cleaners was determined for 6 particle size categories (0.3-0.5
microns, 0.5-1, 1-2.5, 2.5-5, 5-10, 10-20 microns).  The ESP was
able to remove all sizes with better than 90% efficiency (when
properly cleaned).  But the mechanical filter was unable to remove
the fine particles smaller than 2.5 microns. Since these fine
particles are regulated by the US EPA as potentially harmful, it
is important to have a method to remove them; the mechanical
filter tested failed at this. In addition, although the efficiency
for ultrafine particles was not tested in this study, it is likely
that they too can be effectively removed by ESPs as well as HEPA
filters. Ultrafines have not been fully characterized with respect
to health effects, but it is possible that they will be found to be
harmful at some concentrations.

Since in-duct ESPs may have an important health advantage for
users, it is important to test them under the conditions of use
(that is, installed in a duct).  Therefore, if in-duct air
cleaners are in fact covered under this regulation, then the test
method should be augmented by a method employing ductwork in the
test room to emulate the conditions under which they will be
used.