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How do filters change throughout their lives?
Kathleen Owen RTI International Research Triangle Park, NC 27709 NAFA Conference Savannah, GA September 2013
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Background Filters change over time in:
Efficiency Pressure drop What is on or in them Filters can capture particles or gases Real exposure and lab testing Much of the current data is confidential
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Outline of Presentation
ASHRAE RP-1360 investigated particle filters Filter performance Dust properties Gas-Phase project investigated sorbent air cleaners (filters)
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Project Design for RP-1360 RP-1360: “How do Pressure Drop, Efficiency, Weight Gain, and Loaded Dust Composition Change throughout Filter Lifetime” Task 1: 4-City Study - filter performance: real world exposure and lab testing Task 2: Multi-City Study - dust properties
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Task 1: 4-City Study – Approach
Purpose: Determine changes in filter performance Compare to ASHRAE 52.2 testing Three filters chosen to cover range of MERV and charged/not charged: Pleated residential, MERV 7, uncharged Pleated residential, MERV 11, charged Mini-pleated V-Cell, MERV 15, uncharged Four “Cities”: Durham, NC; Minneapolis, MN; Atlanta, GA; and San Francisco, CA
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Task 1. Efficiency Testing
Full ASHRAE 52.2 tests Full ASHRAE 52.2 tests with Appendix J conditioning Efficiency testing after in-situ use: Residential filters: half- and full-life Commercial filters: 4-, 8-, and 12-months
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Atlanta Filter Installations
Commercial Residential
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2” Residential “MERV 7” Filter
ASHRAE 52.2 Test
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Pictures of Used Residential Filters
GA: 5 months NC: 2 month
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Efficiency Comparisons for 2” Residential Filters
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1” Residential, Charged, MERV 11, Filter
ASHRAE 52.2 with App. J Test
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Pictures of Used Residential Filters
GA: 1.5 months MN: 3.5 months
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Efficiency Comparisons
1” Residential Filters
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12” Commercial, MERV 15, Filter
ASHRAE 52.2 Test
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Used Commercial Filters
CA filters: 5-month and 11-month
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Commercial Filters Efficiency Comparison
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Relationship of Pressure Drop to Weight Gain
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MERV 15 Filter: Actual vs. Lab Test
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Task 1: 4-City Study Summary
Low efficiency, uncharged, filters can significantly increase in efficiency as dust is captured, especially for large particles. However, filters are usually changed before sufficient dust is collected. The electret filters all showed decreases in efficiency. For the high-efficiency, uncharged, filter, the efficiency either remained steady or increased with use. The weight gains of the filters with use, in general, did not predict pressure drop. Overall, ASHRAE 52.2 dust loading did not correlate well with the pressure drop changes due to in-situ dust.
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Task 2: Multi-City Analysis of Dust Properties
Collect and analyze dust on filters used in houses and commercial buildings in 15 cities Collect 30 used filters Find out how they were used - Survey form includes likely dust sources, HVAC usage, time of year, location Analyze the dust on filters Visual examination: color, fibers, animal hair, degree of loading SEM, XRF (Metals), Organic and Elemental Carbon (OC/EC) Relate the dust to the data from the Survey forms
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Filter Locations
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Used Filters – DUST
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Used Filters – DUST
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SEM Analysis Atlanta, GA commercial filter has particles from ~3-100 µm. Typical particles are µm. They are irregular and amorphous and fairly cohesive. Many are agglomerations of smaller particles. Some are spherical; others include fibers, insect parts, and feathers. Primarily aluminosilicates (earth crustal particles).
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SEM Analysis Cary, NC residential filter has particles from ~3-100 µm.
Typical particles are µm. They are irregular and amorphous with an abundance of flattened particles (dander). Over 90 percent of the material is organic, with a minority of µm aluminosilicate particles.
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SEM Analysis Atlanta, GA commercial: primarily earth crustal particles
Cary, NC residential: over 90% organic (dander)
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Champaign, IL commercial: agglomerates of 2-10 µm particles
SEM Analysis Champaign, IL commercial: agglomerates of µm particles Champaign, IL residential: dander, spores, hair, feathers, cellulosic fibers
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XRF Results
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Organic Carbon Concentrations
Commercial Residential
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Multi-City Summary Collected dust had a wide range of colors, textures, loading levels, and odors. There was no strong correlation between geographic location and any of these characteristics. Type of building showed a strong correspondence with the dust collected. Commercial: mostly aluminosilicates. Residential: strong predominance of dander. Dust composition did not match ASHRAE dust.
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Particle Filter Highlights
Efficiency over time does not match the ASHRAE 52.2 dust loading steps. Appendix J conditioning was needed to predict the efficiency of the used electret filters. Filters did not reach final efficiency levels as high as the ASHRAE 52.2 test maximum. Weight gain did not predict pressure drop. Typically quoted service lives were too short; filters did not reach the pressure drop recommendations. Dust was distinct between commercial and residential sites. The SEM size analysis showed the dust particles to be in a wide size range from about 3–200 µm with dander ~20–100 µm and aluminosilicates ~5-20 µm. Dust on HVAC filters does not match ASHRAE dust for chemical composition.
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And. . .Gas-Phase Air Cleaners
Gas-phase air cleaners may remove VOCs, ozone, SO2, and many others Efficiency changes over time Capacities (amount captured) vary widely ASHRAE laboratory test method
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ASHRAE Test Method “Laboratory Test Method for Assessing the Performance of Gas-Phase Air-Cleaning Systems: Air-Cleaning Devices” For HVAC air cleaners using sorbent media Performed in ASHRAE 52.2-type rig Additional air cleanup, temperature and humidity (RH) control Pressure drop curves Gas challenges: Low concentration “Initial Efficiency” High concentration “Capacity” Contaminant-off desorption check
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Recent Project Using ASHRAE 145.2, we tested a small number of representative gas-phase air cleaners Residential and commercial types Four gas challenges: SO2, ozone, toluene, and hexane The data show: how these air cleaners can work how they differ what the test can show a user, a manufacturer
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Air Cleaner Descriptions
Air cleaner ID A B C D E Size (in.) 20 x 25 x <1 20 x 25 x 1 24 x 24 x 4 24 x 24 x 12 Application Residential Commercial Airflow (cfm) 1024 2000 Type flat panel pleated panel v-cell deep pleat Number of pleats or Vs NA 23 pleats 20 pleats 6 Vs 36 pleats Media color green/black gray/black gray black/purple Media type activated carbon Granular activated carbon, ~250 g/m2 impregnated activated carbon & permanganate-impregnated alumina activated carbon & potassium permanganate, 48 lb/filter activated carbon, small granule, ~12.8 lbs/filter
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Gas-Phase Pressure Drop Curves
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ASHRAE 145.2 Required Concentrations
Category Chemical Low Concentration (ppb) High (ppm) Required Chemical Acid Gases Sulfur Dioxide 50 35 Oxidizing Gases Ozone 75 0.5 VOCs Toluene 400 Hexane 25
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Initial Efficiency Test, Average Efficiency (%)
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Lowest Efficiency of Capacity Test (%)
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Capacity Test – SO2 Efficiency
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Capacity Test – Ozone Efficiency
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Capacity Test – Toluene Efficiency
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Gas-Phase Data Summary
Challenge Gas Filter A B C D E Initial weight, g 266 463 2043 27,264 17,234 Pressure Drop, in. H2O 0.18 0.27 0.48 0.39 0.35 SO2 Initial Efficiency, % 9 31 79 72 99 Capacity Test, Lowest Efficiency, % 8 21 36 Capacity, g 3.1 1.7 109.9 276.0 480.6 Ozone 26 47 68 97 29 57 87 1.2 5.9 11 16.2 Toluene 30 35 61 91 4 3 37 24 4.4 47.3 56 773.8 417.2 Hexane 6 27 34 70 95 2 15 2.1 17.0 13.3 285.6 406.7
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Gas-Phase Conclusions
The ASHRAE test method yields a wealth of useful information. The ASHRAE test results show that gas-phase air cleaners can vary tremendously with efficiencies from 0 to 99%. Air cleaners have different efficiency levels for different compounds and at different times during their exposure to contaminants. The best air cleaner for a specific use depends on the contaminants and the HVAC system; ASHRAE testing can help the user make this decision.
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So, How Do Filters Change with Use?
Pressure Drop Increases for particle filters May not increase for gases Appearance Dust can be barely visible or extremely heavy Gas-phase air cleaners may look the same Weight increase due to dust or gas adsorption Efficiency Increases or decreases for particle filters Decreases for gas-phase
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Summary Filters change significantly with use
Test methods are useful for predicting these changes, but the data must be used for guidance not for specific predictions Filters should be chosen carefully for your use Changes in efficiency and pressure drop should be considered when: you choose your filter and when you set your change-out schedule
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Acknowledgements ASHRAE for funding RP-1360
All the people who sent in and/or sited filters The RP-1360 Project Committee for their insight: KJ Choi, Don Thornburg, Peter Shipp, Shane Tincher, and Bob Whitt RTI for internally funding the gas-phase testing The RTI Speciation Lab for the dust analysis: Owen Crankshaw (SEM), Andrea McWilliams (XRF), and Mel Richards (EC/OC) Roger Pope and Clint Clayton for running the ASHRAE 52.2 and tests
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Still Curious? ASHRAE RP-1360 full test report (419 pages) is available from ASHRAE at Transactions paper on RP-1360 will be published in ASHRAE Transactions in ~January 2014 Gas-phase paper will be available in January at the ASHRAE meeting as part of the Conference Proceedings and through ASHRAE
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GA 2” Residential Filters
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2” Residential Used Filters
Below clean filter efficiency
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1” Residential Filters Efficiencies
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1” Residential Filter Efficiencies
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NC Commercial Filters Efficiency Comparison
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GA Commercial Filters Efficiency Comparison
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Used Commercial Filters
GA filters: 5-month and 8-month
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Pressure Drop and Weight Gain
MERV 7 2-in. pleat Cities/ Areas Exposure Time, months Weight Gain, g Pressure Drop, in. H2O Lab new NA 0.11 MN 1 0.0 0.14 2 NC 18.2 0.23 31.3 0.37 GA 5 3.3 0.12 12 4.8 CA 4.0 0.10 36.1 0.60 29.2
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Pressure Drop and Weight Gain
MERV 11 1” pleat Cities/Areas Exposure Time, months Weight Gain, g Pressure Drop, in. H2O Lab new NA 0.22 MN 2 5.1 0.35 4 12.9 0.27 NC 1.5 11.4 0.39 3.5 3.9 0.26 GA 0.7 0.23 5 4.9 0.25 76.8 1.0 81.8
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