EPA/600/A-95/1 02
AIR CLEANING FOR ACCEPTABLE INDOOR AIR QUALITY
D. S. ENS OR1, J. T. HANLEY1, D. W. VANOSDELL1, K. K. FOARDE1, M. K. OWEN1
L. E. SPARKS2
Center for Environmental Technology, Research Triangle Institute
P.O. Box 12194, Research Triangle Park, N.C. 27709 U.S.A.
2Air and Energy Engineering Research Laboratory, Mail Drop 54
U.S. Environmental Protection Agency, Research Triangle Park, N.C. 27711 U.S.A.
ABSTRACT
Air cleaning has performed an important role in heating, ventilation, and air conditioning systems for
many years. Traditionally, general ventilation-air filtration equipment has been used to protect cooling
coils and fans. Air cleaning is suggested as a means to reduce the need for fresh air to meet
ventilation requirements. Outdoor contaminants (such as pollen and pollutants) may need to be
removed before air is introduced into occupied spaces. High-efficiency filters could also reduce the
need to clean ducts by preventing the deposition of particulate matter.
Critical to the understanding and application of air cleaners are scientifically valid ways of testing
performance. Experimental techniques to evaluate in-duct air cleaners for both particles and organic
compounds have been developed. Laboratory performance data of a number of air cleaners will be
presented. Building simulation models including laboratory performance data have been used to
estimate the importance of air cleaners from a building system standpoint.
KEYWORDS
air cleaning; building simulation model: chamber tests; filter test system; gaseous absorbers; particle
size dependent efficiency; ventilation.
INTRODUCTION
Indoor air quality depends on ventilation, source control, and air cleaning. Ventilation is critical to
the health and comfort of a building's occupants, providing fresh air at controlled temperature and
humidity as well as diluting and transporting bio-effluents and other contaminants from the occupied
space. The flow rate of fresh air introduced into the building greatly affects energy costs from heating
and cooling. ASHRAE Standard 62 (1989) prescribes the air flow rate per occupant or floor area-
Figure 1 shows the location of air cleaners in a ventilation system. Source control involves selecting
furnishings and equipment with low emissions.
Although source control, ventilation, and air cleaning are all methods of improving indoor air quality,
this paper focuses on the role of air cleaners. Specifically, it addresses the evaluation of new test
methods for particle size dependent efficiency and for gaseous absorbers.

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Other
Air Cleaner
Location
Exhaust
Outdoor
Air
(Makeup
Air)
Energy
Recovery
Unit
Air Cleaner
Location
Air Conditioning
Unit
Infiit ration
Alternate
Paths for .
Recirculated
Air
General,
Exhaust
1

Ventilating
Air
Other
Air Cleaner
Locations
Ik
Other
Air Cleaner
Location
J Locatn
r> Supply Air
Breathing
Zone
i
i
_ r ¦
-~V!
J
Local
Makeup
Air
Local
Exhaust
In-Room Air
Cleaning
Return Air
Occupied
Space
- Local
Ventilation
Exfiltration
Fig, 1. Location of air cleaners in a ventilation system (after ASHRAE, 1989).
AIR CLEANER EVALUATION
Particle Removal
Particle size collection efficiency for air cleaners usually has a minimum in the 0.1- to 1.0-pm range.
The overall efficiency is a function of the filter design and air flow rate (Ensor et al., 1994).
Particulate biological materials can be removed by filters depending on their physical size. Also,
viable material may be associated with dust. The capability of filters to remove biological materials
was reviewed recently by Foarde et al. (1994).
General ventilation filters are usually tested in the United States following ASHRAE 52.1-1992 (1992).
The method has two major parts: the arrestance test and the atmospheric dust spot test The
arrestance test, which was designed primarily to test the filter's ability to protect ventilation equipment,
is conducted with a mixture of dust, carbon powder, and lint The dust spot efficiency test is
conducted with outdoor air and is a measure of the reduction of soiling by the filter.
The requirements for test data more appropriate for indoor air quality specifications have prompted
the development of new test methods with particle counting instrumentation to obtain particle size
dependent efficiencies (Ensor et al., 1994). In a project conducted for the U.S. EPA, Hanley et al.
(1994) measured the particle size dependent efficiency for a wide range of air cleaners. These data
provided background for a research program conducted for ASHRAE (Hanley et al., 1993) to resolve
technical problems and develop a quality assurance framework required for a new standard test
method. The test duct is shown in Figure 2. Water containing potassium chloride is either atomized
or sprayed to form solution droplets that evaporate to form solid particles. Particle size is controlled
by the solution salt concentration and droplet size. An optical particle counter is used to obtain the
concentration as a function of particle diameter (0.3-10 pm) up- and downstream of the air filter.
Electrical mobility separators and condensation nuclei counters have been used to measure removal
efficiencies of particles to 0.014-pm diameter. Arrestance dust from ASHRAE 52.1 without the
carbon can be injected into the system to artificially load the filter to simulate use. Figure 3 shows
an example of the test results. The test system can be used to test a wide range of filters, from simple
furnace filters to high-efficiency filters used for cleanrooms.

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TOP VIEW
ROOM
AIR
EXHAUST
TO ROOM
OUTLET
FILTER
BANK
OPTICAL
PARTICLE
COUNTER
ASME
NOZZLE
DOWNSTREAM
MIXER
\
BLOWER
FLOW CONTROL
VALVE
t j
X TEST BACKUP
I
\ SECTION FILTER
INLET FILTER
\ HOLDER
BANK
N.

^ UPSTREAM MIXER
AEROSOL INJECTION
SPRAY NOZZLE
SIDE VIEW
AIR
SALT SOLUTION ESSS"8*"
CHARGE
NEUTRALIZER
«¦ DRYING AIR
TEST
SECTION
BACKUP
FILTER
HOLDER
BLOWER
INLET FILTER
BANK
UPSTREAM MIXER
FLOW CONTROL
VALVE
AEROSOL INJECTION
Fig 2. Schematic illustration of new filter test system.
Gas Removal
Removal of gases is highly dependent on the chemical and physical properties of specific compounds.
The absorption of a gas is not a steady-state process. Gases can be absorbed and desorbed as changes
in concentration cause shifts from equilibrium. Standard tests are not now available to evaluate air
cleaners for gaseous compounds to obtain efficiency and long-term life data required for indoor air
quality applications. Two laboratory tests are under development: media samples and full-scale air
cleaners. The test conditions were developed by examining two application scenarios: filtering
outdoor air and filtering indoor recirculated air (VanOsdell, 1992). Because activated charcoal is very
sensitive to relative humidity above 50%, relative humidity and temperature must be carefully
controlled (Liu, 1993).
Chamber Tests
The evaluation of in-room air cleaners has generally been conducted in test chambers. One standard
method was published by AHAM (1987) for particle challenges of tobacco smoke, Arizona road dust,
and pollen. The clean air delivery rate (CADR), a product of initial efficiency and air flow, is
computed from the concentration decay in the chamber. The CADR is used to compare air cleaners
in a voluntary program by the manufacturers. 3

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100
-e- 25 Pa: Pressure Drop Clean
-A- 125 Pa: Pressure Drop Loading 1
-©- 250 Pa: Pressure Drop Loading 2
»+—
LU
c
q
ra
1—
•4—*
U- 20
0.01
0.1
1
10
Particle Diameter (jim)
Figure 3. Fractional filtration efficiency of 25-30% ASHRAE efficiency pleated panel
filter at 1.30 mfs for clean and dust-loaded condition.
AIR CLEANER APPLICATION
As air cleaners become better characterized as individual units, the next step will be understanding the
effectiveness of the devices. A number of factors-affect application of air cleaners in buildings: the
location of air cleaners in the ventilation system may be critical because of environmental conditions
such as humidity and transport of contaminants to the filters; in-duct laboratory tests are conducted
at constant volume while in heating, ventilation, and air conditioning (HVAC) systems the air flow
may diminish as the filter pressure increases with loading; infiltration and exfiltration in the building
may have a significant effect on the indoor air concentrations; contaminants in the building may be
complex mixtures affecting efficiency; and maintenance, ease of use, and costs may be significant
considerations in selection.
Computer simulations to estimate the changes in contaminant concentrations in a building have been
conducted with various air cleaning scenarios (Owen et ah, 1990,1992). A building model consisting
of rooms connected by the ventilation systems and by doors and corridors was used to evaluate air
cleaner efficiencies, location, and sources of contaminants on concentration in the rooms as a function
of time. There is a need for field studies to confirm these computer predictions based on laboratory
air cleaner efficiency data. An important challenge will be understanding the integration of air
cleaning in the building system.
CONCLUSIONS
Air cleaning has a very significant role in the indoor environment by protecting the HVAC system and
the occupants from contaminants. Recent research in the development of new test methods for both
particulate and gas air cleaners will greatly facilitate selection of appropriate systems. However, much
research needs to be done before we understand the interaction of air cleaning and the occupied space.

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REFERENCES
AHAM (1987). Standard Method for Measuring Performance of Portable Household Electric Cord-
Connected Room Air Cleaners. Association of Home Appliance Manufacturers, Chicago, IL.
ASHRAE (1989). ASHRAE 62-1989. Ventilation for Acceptable Indoor Air Quality. American
Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.
ASHRAE (1992). ASHRAE Standard 52.1-1992. Method of Testing Air-Cleaning Devices Used in
General Ventilation for Removing Particulate Matter. American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.
Ensor, D.S., B.C. Krafthefer and T.C. Ottney (1994). Changing requirements for air filtration test
standards, ASHRAE Journal, 36, 52-60.
Foarde K.K., D.W. VanOsdell and J.J. Fischer (1994). Investigate and Identify Indoor Allergens and
Biological Toxins that Can Be Removed by Filtration. ASHRAE RP-760 American Society of
Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA.
Hanley, J.T., D.D. Smith and D.S. Ensor (1993). Define a Fractional Efficiency Test Method that Is
Compatible with Particulate Removal Air Cleaners Used in General Ventilation. Final Report,
ASHRAE 671. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.,
Atlanta, GA.
Hanley, J.T., D.D. Smith and D.S. Ensor (1994). An Evaluation of the Fractional Filtration Efficiency
of Air Cleaners. Air and Energy Engineering Research Laboratory, U.S. Environmental
Protection Agency, Research Triangle Park, NC.
Liu, R. (1993). Model Simulation of the Performance of Activated Carbon Absorbers for the
Control of Indoor VOC. In: Indoor'93, Helsinki, Finland, July 4-8, pp. 423-428.
Owen, M.K., P.A. Lawless, D.S. Ensor and L.E. Sparks (1990). A Comparison of Local and Central
Controls for Indoor Air Quality. In: The 5 th International Conference on Indoor Air Quality and
Climate, Toronto, Canada, July 29-August 3, Vol. 3, pp. 193-198.
Owen, M.K., P.A. Lawless, D.D. Smith, D.S. Ensor and L.E. Sparks (1992). Predicting Indoor Air
Quality with IAQPC. In: Proceedings of the Indoor Air Quality, Ventilation, and Energy
Conservation 5th International Jacques Carder Conferences, Oct 7-9, Montreal, Canada, pp. 101-
108.
VanOsdell, D.W. (1992). Evaluation of Test Methods for Determining the Effectiveness and Capacity
of Gas Phase Air Filtration Equipment for Indoor Air Applications. Phase I: Literature Review.
ASHRAE 674 RP. American Society of Heating, Refrigerating and Air-Conditioning Engineers,
Inc., Atlanta, GA.

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„.p TECHNICAL REPORT DATA
ii -tii JLxt U~ Jr ~ lZ^O (Please read Iniayctions on the reverse before completing,
1. REPORT NO. 2.
EPA/600/A-95/102
3. re.
4. TITLE AND SUBTITLE
Air Cleaning for Acceptable Indoor Air Quality
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) a s. Ensor, J. T. Hanley, D. W. VanOsdell, K. K.
Poarde (RTI); L. E. Sparks (EPA/AEERL)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P. O. Box 12184
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR817083
12. SPONSORING AGENCY NAME AND ADORESS
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; 11/93-9/64
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notes AEERL project officer is Leslie E. Sparks, Mail Drop 54, 919/
541-2458. Presented at International Workshop: Indoor Air—An Integrated
Approach, Gold Coast, Australia, 11/27-12/1/94.
is. abstractTIm paper discusses air cleaning for acceptable indoor air quality. Air
cleaning-has performed an important role in heating, ventilation, and air-condition-
ing systems for many years. Traditionally, general ventilation air-filtration equip-
ment has been used to protect cooling coils and fans. Air cleaning is suggested as a
means to reduce the need for fresh air to meet ventilation requirements. Outdoor
contaminants (such as pollen and pollutants) may need to be removed before air is
introduced into occupied spaces. High-efficiency filters could also reduce the need
to clean ducts by preventing the deposition of particulate matter. Critical to the
understanding and application of air cleaners are scientifically valid ways of testing
performance. Experimental techniques have been developed to evaluate in-duct air
cleaners for both particles and organic compounds. Laboratory performance data of !
a number of air cleaners will be presented. Building simulation models including
laboratory performance data have been used to estimate the importance of air clean-
ers from a building system standpoint.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Simulation
Air Cleaners Test Chambers
Ventilation Air Filters
Particles
Organic Compounds
Mathematical Models
Pollution Control
Stationary Sources
Indoor Air
Particulate
13 B
13 A, 131 14 B
13K
14G
07C
12 A
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)

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