1. How do filters change throughout their lives?
Kathleen Owen
RTI International
Research Triangle Park, NC 27709
NAFA Conference
Savannah, GA
September 2013

2. 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

3. Outline of Presentation
ASHRAE RP-1360 investigated particle filters
Filter performance
Dust properties
Gas-Phase project investigated sorbent air cleaners (filters)

4. 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

5. 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

6. 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

7. Atlanta Filter Installations
Commercial
Residential

8. 2” Residential “MERV 7” Filter
ASHRAE 52.2 Test

9. Pictures of Used Residential Filters
GA: 5 months
NC: 2 month

10. Efficiency Comparisons for 2” Residential Filters

11. 1” Residential, Charged, MERV 11, Filter
ASHRAE 52.2 with App. J Test

12. Pictures of Used Residential Filters
GA: 1.5 months
MN: 3.5 months

13. Efficiency Comparisons
1” Residential Filters

14. 12” Commercial, MERV 15, Filter
ASHRAE 52.2 Test

15. Used Commercial Filters
CA filters: 5-month and 11-month

16. Commercial Filters Efficiency Comparison

17. Relationship of Pressure Drop to Weight Gain

18. MERV 15 Filter: Actual vs. Lab Test

19. 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.

20. 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

22. Filter Locations

23. Used Filters – DUST

24. Used Filters – DUST

25. 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).

26. 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.

27. SEM Analysis Atlanta, GA commercial: primarily earth crustal particles
Cary, NC residential: over 90% organic (dander)

28. 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

29. XRF Results

30. Organic Carbon Concentrations
Commercial
Residential

31. 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.

32. 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.

33. 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

34. 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

35. 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

36. 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

37. Gas-Phase Pressure Drop Curves

38. 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

39. Initial Efficiency Test, Average Efficiency (%)

40. Lowest Efficiency of Capacity Test (%)

41. Capacity Test – SO2 Efficiency

42. Capacity Test – Ozone Efficiency

43. Capacity Test – Toluene Efficiency

44. 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

45. 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.

46. 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

47. 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

48. 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

49. 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

50. GA 2” Residential Filters

51. 2” Residential Used Filters
Below clean filter efficiency

52. 1” Residential Filters Efficiencies

53. 1” Residential Filter Efficiencies

54. NC Commercial Filters Efficiency Comparison

55. GA Commercial Filters Efficiency Comparison

56. Used Commercial Filters
GA filters: 5-month and 8-month

57. 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

58. 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