EPA/600/A^93/183
A19
Removal Efficiencies in Terms of Particle Size
and Concentration in a Suburban Home of Console
Air Cleaners
Raymond S. Steiber
and
Leslie E. Sparks
Air and Energy Engineering Research Laboratory
United States Environmental Protection Agency
Research Triangle Park, North Carolina 27711
ABSTRACT
Data are presented on the removal efficiencies of two
commercially available console air cleaners, one equipped with a
high efficiency filter, the other with an electrostatic
precipitator (ESP). Room air particle size distribution is
examined in detail both before and during use, and time-slice data
are given on the effect on overall concentration of the operation
of the units. The data show that both the filter-equipped unit and
the ESP unit are highly efficient at removing particles with
diameters of 1.0 micrometer and larger, the size range of pollens
and spores, but less efficient at removing submicrometer
particles. The paper concludes with a brief discussion of the
cost/benefits of each unit.
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INTRODUCTION
In response to public concerns about environmental tobacco
smoke, allergens, and other sources of indoor air pollution, a host
of air cleaners, ozonators, and negative ion generators have come
on the market. The manufacturers of these products frequently make
broad claims about their efficacy, substantiating them with
testimonials and little else. The purpose of this paper is to
present data on two console-size air cleaners, one equipped with a
high efficiency filter and the other with an electrostatic
precipitator (ESP). Both units are produced by the same
manufacturer and are marketed under their own name and also under
the house name of one of the nation's larger retail chains. Our
aim in this work was both to compare the two types of air cleaners
and to define their operating parameters in a typical setting in
which they might be used.
EXPERIMENTAL
The Association of Home Appliance Manufacturers (AHAM) has
developed test methods for evaluating air cleaners based on their
ability to clear a test chamber containing a known concentration of
particles. While this method can provide useful information, it
does not really test in-room air cleaners under the conditions in
which they are likely to be used. Therefore, we decided to design
an experiment that more closely reflected the homeowner's actual
experience.
The experiment was set up in the master bedroom of a typical
suburban house. The room was approximately 168 square feet in
area, and the tests were run with the doors and windows shut so
that the room would constitute a single site. The measuring device
was an Amherst (API) Mach II Aerosizer. This instrument uses time-
of-flight (drag coefficient) between two laser beams to determine
particle size and also provides count rates and count totals for
each size it measures. Using air flow rates at the intake and the
known density of the material being sampled, one can also use
instrument data to calculate total mass. The calibration of the
instrument was checked using monodisperse polystyrene latex spheres
(PSL). Counting efficiency was checked by comparing its response
to a PSL aerosol against that of a LASE-X particle counter. The
results showed that Aerosizer counting efficiency dropped rapidly
for PSL particles smaller than about 0.7 micrometer in diameter.
Shakedown runs had indicated that background particulate
levels varied too widely to allow for an adequate determination of
removal efficiencies. Therefore, we decided to use a particle
generator in order to maintain room air concentrations. The
generator consisted of an ultrasonic cool mist humidifier whose
reservoir had been filled with a 5 gram/liter solution of potassium
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A19
chloride (KC1) in deionized water. Preliminary tests had shown
that humidifier moisture output, and hence KC1 output, was
reproducible at the same setting within + 15%, and this was deemed
adequate for the work to be done. It should be noted at this point
that a low humidifier setting was used, and that the moisture added
to room air was minimal.
Figure 1 shows the relative positions of the detector, the air
cleaner, and the particle generator within the room. Except for a
stand to elevate the particle generator to a height of
approximately 1.5 meters and a table to support the detector, the
room contained no furniture. The floor was covered with wall-to-
wall carpeting.
The tests were conducted as follows: First a background run
was made with the humidifier off in order to determine room levels
of particulate. Then the humidifier was turned on and allowed to
run continuously throughout the test. In some tests the air
cleaner was switched on as soon as room levels of particulate had
reached an adequate concentration (10,000-12,000 counts/second on
the detector). In other cases the humidifier was allowed to run as
long as 2 or 3 hours before the air cleaner was activated. In the
latter tests it was noted that at the setting used (25-30
milliliters/hour) particulate levels reached a plateau of 12,000-
15,000 counts/second after a period of 80 minutes and no further
increases were seen. Similar tests were run with both the unit
containing the high efficiency filter and the one equipped with an
ESP.
RESULTS
Both the unit equipped with the high efficiency filter and the
one with the ESP behaved in a similar manner. As soon as either
was switched on, there was an immediate decrease in room
particulate concentrations. By the time 20 or 30 minutes had
passed, concentrations had fallen to a level near the lowest
detection limit of the instrument (10-008 milligrams/cubic meter) .
This means that not only was the humidifier-generated particulate
being removed, but a substantial portion of the background as well.
Figure 2 shows variations in particle concentrations over the
course of a 360 minute run. The unit being tested was the one
equipped with an ESP. At time zero (A) , the particle generator was
turned on and allowed to run throughout the test. After 120
minutes (B), the air cleaner was activated, and there was a steady
decrease in concentration over the next 20-30 minutes. After 300
minutes the air cleaner was switched off again (C), and particulate
concentrations immediately increased. In addition to the ESP, this
unit also contains a metal foil prefilter and an activated carbon
backup filter. In order to determine the effect of these filters,
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A19
the ESP was removed and the unit activated with the switch in the
fan-only position (D). No statistically appreciable decrease in
particulate concentrations occurred, indicating that the prefilter
and the backup filter were playing a minimal role in the removal
process. Figure 3 presents similar data from one of the tests with
the unit equipped with a high efficiency filter. As can be seen,
the results were roughly the same.
Figure 4 presents data from the ESP runs in terms of particle
size removal efficiency. The upper curve represents a profile of
the particle size distribution in the room with only the particle
generator, in operation. The lower curve shows how that size
distribution is altered by activating the ESP. As can be seen,
particle removal by the ESP was 100% for particles 1.05 micrometers
in diameter and larger. Removal rates for particles smaller than
1.05 micrometers were somewhat less impressive, but still
encompassed several orders of magnitude. To put this in
perspective, most fungal spore diameters lie in the range of 1-2
micrometers, while pollens are usually 30 micrometers in diameter
and larger.
Figure 5 shows particle size removal efficiencies for the
filter-equipped unit in terms of penetration. Penetration is a
term which for mathematical purposes assumes that all the particles
in a given area are passing through a media and that some are being
collected while others are "penetrating." Once again removal
efficiencies for particles above 1.05 micrometers were 100%.
However, the dropoff in filter collection below that size was
somewhat steeper than for the ESP. In examining these data and
also the data presented in Figure 4, consideration should be given
to the limits of the detection device. That is to say, particles
smaller than 0.7 micrometer are simply not being counted
effectively, and there is an absolute cutoff around 0.5 micrometer.
This means that room concentrations of submicrometer level
particles were probably much greater both before and during these
runs than is shown by the data.
In regard to the physical operation of the units, it appeared
that short-circuiting did not occur. This is the phenomenon in
which exhaust from the rear of the unit circles around and is taken
in the front again, thereby limiting the amount of room air that is
cleaned. In the units examined, the fan is mounted in a position
horizontal to both the intake and the exhaust grills. This causes
the intake air and the exhaust air to enter and leave at separate
angles, and that and the size of the fan are the probable reasons
why short circuiting is not a problem.
CONCLUSION
In summary, both the air cleaner equipped with the high
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A19
efficiency filter and the one with the ESP were high effective at
removing particles 1.0 micrometer and larger and also had
reasonable removal rates (several orders of magnitude) for smaller
particles. Since pollens and fungal spores, two of the most common
causes for allergenic responses in indoor environments, both lie in
diameter sizes 1.0 micrometer and larger, these types of units
would be useful as amelioratives in single-room settings. The
manufacturer recommends that under conditions of continuous use the
filter be changed frequently. The ESP, on the other hand,
requires only periodic cleaning with detergent and water, which
means that it would be less costly to maintain. However, it should
be noted that, even when equipped with activated carbon filters,
ESPs can emit ozone. At the face of the unit that was tested,
ozone levels of 14 parts per billion were measured with the fan at
its highest setting. This is well below the Occupational Safety
and Health Administration's limit for continuous exposure, but
could be annoying just the same.
In terms of whole house air cleaning, the best choice would be
an ESP directly installed in the HVAC system. These units are
relatively inexpensive, have a good track record, and are easy to
maintain. However, there are locations--offices, shops, rental
property—where an in-duct ESP may not be an option. In those
cases console units such as the ones examined in this paper offer
a useful alternative.
DISCLAIMER
Mention of commercially available equipment is for information
purposes only and does not constitute an endorsement by the United
States Environmental Protection Agency.
5.
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Figure 1. Test layout. Room not drawn to scale.
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Figure 2. Particulate removal test with ESP-equipped air cleaner.
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Figure 3. Particulate removal test with air cleaner
equipped with high-efficiency filter.
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Figure 4. Particle size distribution in room before and during
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Figure 5. Particle size distribution in room in terms of penetration
during a test with air cleaner equipped with a high-efficiency filter.
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AEBRL-P-1030
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before comple
1. REPORT NO.
EPA/600/A-93/183
3,
4. TITLE AND SUBTITLE
Removal Efficiencies in Terms of Particle Size and
Concentration in a Suburban Home of Console Air
Cleaners
5, REPORT DATE
G. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Raymond S. Steiber and Leslie E. Sparks
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
1O. PROGRAM ELEMENT NO.
See Block 12
11. CONTRACWGRANT NO.
NA (Inhouse)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 2~9^92
14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES AEERL project officer is Raymond S. Steiber, Mail Drop 54,
919/541-2288. AWMA National Conference, Denver, CO, 6/14-18/93.
16. ABSTRACT
The paper presents data on the removal efficiencies of two commercially
available console air cleaners, one equipped with a high efficiency filter, the other
with an electrostatic precipitator (ESP). Room air particle size distribution is exa-
mined in detail, both before and during use, and time-slice data are given on the
effect on overall concentration of the operation of the units. The data show that both
the filter-equipped unit and the ESP unit are highly efficiency in removing particles
with diameters of 1.0 micrometer and larger, the size range of pollens and spores,
but less efficient at removing smaller particles. The paper concludes with a brief
discussion of the cost/benefits of each unit. -
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Filters
Air Cleaners
Particle Size
Removal
Efficiency
Electrostatic Precipitators
Pollution Control
Stationary Sources
Particulate
Particle Concentration
13B
13A, 131
14G
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS {This Report)'
Unclassified
21. NO. OF PAGES
11
20. SECURITY CLASS (This page}
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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