Do Air Cleaners Really Work

1
Do Air Cleaners Really Work?

• Professor Shelly Miller
• Mechanical Engineering
• University of Colorado at Boulder

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Motivation and Background
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• Adverse health effects due to exposure to
  airborne particulate matter could be more
  significant than effects due to exposure to many
  other airborne pollutants (Vedal, 1997)

4

• Airborne particles come in many different sizes
  and composition.

fine
mechanicallygenerated
coarse
Lung depositionefficiency curve
DV/DlogDp (mm3/cm3)
ultrafine
Fraction particles deposited
2.5
10
0.01
0.1
diameter Dp, mm

• An idealized particle size distribution, showing
  coarse, fine, and ultrafine particles. Also
  shown are major formation and growth mechanisms,
  example compositions, and lung deposition
  efficiency upon inhalation.

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OK, so how bad are the health effects?

• London Fog
• Donora, PA
• Chimney sweeps
• And now, we are looking into fine particles
  (a.k.a. PM2.5)

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Across the board, fine particles are associated
with increased risk
A 10 mg/m3 increment is associated with an
increase in overall mortality risk of 1.06,
cardiopulmonary mortality of 1.09, and lung
cancer of 1.14. For a US city these increased
risks are roughly equivalent to the risk
associated with being moderately obese.
NOTE The increase in overall mortality
associated with being a smoker is 2.58,
cardiopulmonary mortality is 2.89, and lung
cancer is 14.80.
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People spend gt85 of their time inside and 3/4 of
that time is at home.
Long et al., 2001
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Indoor Particle Dynamics
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Factors governing indoor particle concentrations
include
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Factors governing indoor particle concentrations
include
Emissions fromindoor sources
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Factors governing indoor particle concentrations
include
ventilation supply from outdoor air
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Factors governing indoor particle concentrations
include
Operating portable air cleaners
13
Factors governing indoor particle concentrations
include
deposition onto indoor surfaces
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Factors governing indoor particle concentrations
include
Removal by ventilation
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Air Cleaning

• In-duct air cleaners, designed to be integrated
  with a forced-air heating/cooling system
• Air follows a single pass through particle
  removal technology
• Unducted air cleaners which are portable and
  designed primarily for cleaning in one room
• Air is multi-pass, recirculated through particle
  removal technology
• Consumers bought 3.4 million portable air
  cleaners in 2001, 70 more than in 2000

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Do you have forced-air?

• If so, then get best results from in-duct air
  cleaning, since so much air is circulated through
  the heating/cooling system
• Furnace filters are not adequate, need a filter
  with a higher efficiency (usually rated with a
  Min Effic Reporting Value or MERV)

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Portable Air Cleaners
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Filters
Electrostatic precipitators

• Fan draws particle-laden air through a fibrous
  filter media

• Fan draws particle-laden air through an
  electrical field

• Charged particles are deposited on oppositely
  charged collector plates

NOTE some ESPs have no fan (for example, Sharper
Image)
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Remember the particle size distribution?
Filter efficiency curve
Fraction particles deposited
diffusion
Impaction and interception
2.5
10
0.01
0.1
diameter Dp, mm

• An idealized particle removal efficiency as a
  function of particle size for a typical fibrous
  filter.

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Air cleaner standards

• Currently there are no standards for
  testing/rating portable air cleaners
• Many air cleaners certified by the Association of
  Home Appliance manufacturers in a widely accepted
  voluntary program (www.cadr.org)

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Quantifying air cleaner performance
1. Effectiveness
2. CADR
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Effectiveness, E

• Quantifies improvement in indoor air quality that
  is associated with the technologys use

E can range between 0 and 1E 1 represents
ideal performanceE 0 indicates complete lack
of improvement
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Determining Effectiveness

• Measure particle concentrations both with and
  without air cleaner operating and compare

No air cleaner
Particle / m3
air cleaner
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Fire study
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Experimental Design
Locate wildfire producing smoke that will impact
local residents
Install air cleaners in one of the 2
homes Instruct residents to keep windows closed
Monitor indoor and outdoor PM2.5 concentrations
at both homes during fire
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Air Cleaner
Friedrich C-90a Electrostatic Precipitator

• PRE-FILTER catches larger particles
• IONIZING CELL electrically charges particles when
  they pass through an electric field
• COLLECTOR PLATES immediately attract "charged"
  particles
• ACTIVATED CARBON FILTER removes most common odors
  and fumes

• 3 tests performed on the air cleaners in a test
  chamber to measure Clean Air Delivery Rate (CADR)
• We measured an average CADR of 420 m3/ h
• Agrees with CADR of 325-370 m3/ h that is
  published by Association of Home Appliance
  Manufacturers

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Air cleaners effective at reducing particle
concentrations inside from fire smoke outside
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Keeping windows and doors closed not very
effective at reducing particle concentrations
inside from fire smoke outside
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Clean air delivery rate

• single-pass efficiency of the device (fractional
  removal of pollutants from the air stream as it
  passes through the device) multiplied by the
  airflow rate through the device (Nazaroff, 2000)
• airflow rate that represents the effective amount
  of particle-clean air produced by the air cleaner
  (Offermann et al., 1985)

• The Association of Home Appliance Manufacturers
  (AHAM) has published method ANSI/AHAM AC-1-2002,
  which determines the CADR for three types of
  particulate matterdust, tobacco smoke, and
  pollen (AHAM, 2002).

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Clean air delivery rate
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Determining CADR experimentally

• Generate particles continuously until
  concentration in room reached suitable level for
  detection. Stop generation, turn on air cleaner.
  Concentration within the room will decrease over
  time. Sample during decay. Mixing fans should
  be on to ensure well-mixed conditions. Experiment
  repeated with air cleaner off.

No air cleaner
Particle / m3
air cleaner
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Determining CADR analytically

• Apply mass-balance indoor air quality model,
  which assumes indoor environment represented as a
  single, well-mixed zone.

QIndoor conc C
Ventilation QOutdoor conc Co
CADR
Deposition rate k
Emissions E
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Indoor air quality model
The indoor particle concentration as a function
of time is given by (Miller and Macher, 2000)
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Using model to interpret experimental data
Concentration of particles measured sequentially
during the decay period are statistically fit to
the log form of model equation using linear
regression
With air cleaner
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Using model to interpret experimental data
Slope of fit gives sum of rates for experiment
with and without air cleaner and subtractions
gives rate of particle removal due to air cleaner
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Air Cleaner CADR study
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Objectives

• To quantify the CADR of two currently portable
  air cleaners, which contain UV-C lamps
• Air cleaners challenged with pure cultures of
  airborne microorganisms
• UV-C lamp performance was evaluated by estimating
  the percentage of captured bacteria and fungi
  that were inactivated on the filter surface

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Aerosolized Mycobacteria and Fungi

• Aspergillus versicolor, fungus, diameter ranges
  5-7 mm, spores can be used as subpathogenic
  surrogates

• Mycobacteriumparafortuitum, bacterium, diameter
  around 1 mm, has a structure and environmental
  sensitivity similar to the bacteria that causes
  tuberculosis

Aspergillus versicolor
Mycobacterium parafortuitum
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Determining UV Lamp Performance

• Load filter media with bioaerosol. Expose
  sections of media to UV irradiation for varying
  lengths of time. Extract exposed organisms and
  assay using culturing
• UV-C lamp performance defined as fraction of
  culturable bacteria, normalized to total number
  of bacteria, that survive with UV-C lamp turned
  on compared to without UV-C lamp operating

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Ionic Breeze (Sharper Image)manufacturer
specified flow rate 46 m3 h-1, 500
Jaguar (Shaklee)manufacturer specified flow
rate 425 m3 h-1, prototype
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Ionic Breeze and Jaguar averaged clean-air
delivery rates for mycobacteria and fungi
The CADRm for A. versicolor was statistically the
same as CADRm for M. parafortuitum provided by
both Jaguar and Ionic Breeze. This finding
suggests that when these units are operated in
multi-pass fashion, in which indoor air laden
with biological particles passes through the air
cleaner multiple times, the difference in
particle size is not a larger factor in
performance. A. versicolor aerosol contains
larger particles (gt5 ?m) compared to the M.
parafortuitum aerosol (on the order of 1 ?m).
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Jaguar UV-C Lamp performance for inactivating
captured M. parafortuitum and A. versicolor
expressed as percentage inactivated
Inactivation due to UV ()
FUNGI
BACTERIA
UV-C lamp inactivated captured organisms within
60-120 minutes
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How big of a room can the air cleaner clean?

• Another way of looking at data is to predict
  volume of space that can be adequately cleaned --
  defined as reducing concentration by 80 -- by
  the air cleaner
• The Jaguar can clean a 30 m3 room and the Ionic
  Breeze can clean a 4 m3 room

30 m3
4 m3
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SO, Do Air Cleaners Really Work?
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Yes, they DO!

• If you have respiratory problems, or are
  concerned with episodic elevated exposures
  (i.e.fires), you will benefit from using an air
  cleaner
• If its an option, use forced-air system, with
  efficient filters
• If not, choose an air cleaner thats AHAM
  certified and designed to cover an area somewhat
  larger than the one you need to treat
• Example of air cleaners that work Friedrich
  C-90A, (see Consumer Reports, 2003)

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Acknowledgements

• US EPA Region 8
• Firefighters and families
• Shaklee and Jay Julos
• Elmira Kujundzic
• Fatimah Matalkah
• Cody Howard
• David Henderson
• Mark Hernandez