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Challenges Evolving from ASHRAE 52.2 Test Method

Challenges Evolving from ASHRAE 52.2 Test Method. T.J. Ptak Presented at National Air Filtration Association, TECH 2013. Scope. Introduction Test methods ASHRAE 52.2 test method Current variability Potential causes of variability ASHRAE 52.2 – Conditioning method Conclusions.

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Challenges Evolving from ASHRAE 52.2 Test Method

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  1. Challenges Evolving from ASHRAE 52.2 Test Method T.J. Ptak Presented at National Air Filtration Association, TECH 2013

  2. Scope • Introduction • Test methods • ASHRAE 52.2 test method • Current variability • Potential causes of variability • ASHRAE 52.2 – Conditioning method • Conclusions

  3. Test Method • Definition (ASTM) “Definitive procedure for the identification, measurement, or evaluation of one or more qualities, characteristics, or properties of a material, product, or system” • General Requirements • Test method must measure characteristic or property that will predict usefulness of a product when it is put to its intended use • Test method is supposed to predict performance in later stage in the life of a material or product

  4. Test Method • Main Components and Steps • Test procedures • Test method tolerances • Reducing variability • Determine sources of unnecessary variability • Ruggedness test • Procedure for interlaboratory testing • It is not for detecting and eliminating sources of variability • Precision and bias

  5. ASHRAE 52.2 – Performance Characteristics • Test standard – ASHRAE 52.2 • Differential pressure • Fractional efficiency for particle size range 0.3 – 10 µm • Initial, intermediate and final • Dust holding capacity at specified terminal ΔP • Reporting • PSE curve after each step of dust loading • Develop a composite minimum efficiency curve • Report average E1 0.3 – 1.0 µm E2 1.0 – 3.0 µm E3 3.0 - 10 µm • MERV - Minimum Efficiency Reporting Value

  6. ASHRAE 52.2 –Check List • Differential pressure + • Efficiency • Initial + • Intermediate +/- • Final +/- • Filter life - • Tolerances - • Process to reduce variability - (+) • Precision and other statistics -

  7. ASHRAE 52.2 – Current Situation • Round Robin Test – report issued in 2005 • 1088-RP – Coordinate and Analyze Interlaboratory Testing of Filters under ASHRAE 52.2 • Differences between laboratories • Differences still exist • SSPC 52.2 activities

  8. ASHRAE 52.2 – Round Robin Test • Round Robin Test sponsored by ASHRAE* • Participating labs 8 • Selected filters 4 • Type 1 – 24 x 24 x 12” glass (MERV 10-11) • Type 2 – 24 x 24 x 4” electret (MERV 8-11) • Type 3 – 24 x 24 x 4” cotton/PET (MERV 5-7) • Type 4 – 24 x 24 x 12” electret (MERV 15-16) • Filters were pre-tested at independent lab • Statistical methodology • Repeatability – precision of the method within a given lab • Sr – repeatability standard deviation • Reproducibility - precision of the method when comparing labs • SR – reproducibility standard deviation NOTE: * from ASHRAE 1088-RP

  9. ASHRAE 52.2 – RRT Variability • Round Robin Test results • Precision statistics for pressure drop measurement • Repeatability CV 1.8 – 6.7% • Reproducibility CV 5.3 – 6.8% • Precision statistics for weight gain • Repeatability CV 7.5 – 26.5% • Reproducibility CV 8.1 – 26.5% • MERV summary • Type 1 (1st stage) MERV 11 (5); MERV 10 (1) • Type 2 MERV 8 (9); MERV 10 (1); MERV11 (2) • Type 3 MERV 5 (1); MERV 6 (10); MERV 7 (1) • Type 4 MERV 14 (4); MERV 15 (8)

  10. ASHRAE 52.2 - RRT Variability • Round Robin Test results • Precision statistics for Type 4 filters • Repeatability Sr E1 – 1.71; E2 – 0.50; E3 – 0.0 Reproducibility SR E1 – 2.63; E2 – 0.93; E3 – 0.41 • Precision statistics for Type 3 filters • Repeatability Sr E1 – 1.91; E2 – 2.42; E3 – 3.94 Reproducibility SR E1 – 2.61; E2 – 3.88; E3 – 4.98 • Precision statistics for Type 2 filters • Repeatability Sr E1 – 2.86; E2 – 4.99; E3 – 2.45 Reproducibility SRE1 – 5.00; E2 – 6.05; E3 – 3.04 • Calculated 95% confidence interval for individual results • “2 Sr “ = 1.96 Sr • “2 SR ” = 1.96 SR

  11. ASHRAE 52.2 – RRT Variability • What does it mean for filter users? • Pressure drop • Filter Type 2 Type 3 Type 4 • Average ΔP, [in. H2O] 0.34 0.28 0.76 • 95% Confidence, 2 SR ±0.05 ±0.03 ±0.11 • 95% Confidence range 0.29 – 0.39 0.25 – 0.31 0.65 – 0.87 • Dust holding capacity • Filter Type 2 Type 3 Type 4 • Average DHC, [gram] 197 248 138 • 95% Confidence, 2 SR ±32 ±44 ±72 • 95% Confidence range 165 – 229 204 – 292 66 – 210

  12. ASHRAE 52.2 – RRT Variability • What does it mean for filter users? • Filter Average efficiency • Type 2 E1=19 E2=57 E3=82 • 95% Confidence, 2 SR 10 12 6 • 95% Confidence range 2 – 29 45 – 69 77– 88 • MERV 10 >50 >85 • MERV 11 >65 >85 • Is the current situation acceptable? • Statistical evaluation can not be applied to MERV • Report was published in 2005 • ASHRAE SSPC 52.2 activities • Significant variability still exist

  13. ASHRAE 52.2 - Potential Sources of Variability • General requirements: • Test duct configuration • Specified dimensions, locations of measuring points, transitions • Straight test duct, U - shaped • Particle counters • Optical particle counter, (OPC) • Aerodynamic particle counter, (APC) • Other test instruments • Pressure gauges manometer • Flow meter ASTM nozzle • Aerosol generation atomizing nozzle • Dust feeder

  14. ASHRAE 52.2 - Potential Sources of Variability • General requirements: • Recommended range of flow rate • 472 – 2990 cfm • Air velocity 118 – 748 fpm • Air velocity 492 fpm if not specified (for residential 295 fpm) • Recommended range for temperature and relative humidity • T = 50 – 100oF • RH = 20 – 65% • Challenge aerosol • KCl • Loading dust • ASHRAE dust (75% - SAE J726 dust; 23% powdered carbon; 5% milled cotton linters)

  15. ASHRAE 52.2 – Residential Filtration • Test method is not applicable to: • Electrostatic precipitators • Hybrid filters with external electrostatic field • Selection of the air velocity – historical approach • 1 inch deep filters tested at 295 fpm • 4 inch deep filters tested at 492 fpm • Confusion with claims and test results • Claims for 1 inch filters based on V = 295 fpm • Claims for 4 inch filters based on V = 492 fpm

  16. ASHRAE 52.2 - Performance of Selected Filters Filter dimensions 20 x 25 x 4 and 20 x 25 x 1in. Filter pressure drop Q=1024 cfm Q=1708 cfm

  17. ASHRAE 52.2 - Performance of Selected Filters Filter dimensions 20 x 25 x 4 and 20 x 25 x 1in. Filter efficiency at 1200 cfm

  18. ASHRAE 52.2 - Performance of Selected Filters Filter dimensions 20 x 25 x 4 and 20 x 25 x 1in. Filter efficiency at 2000 cfm

  19. Sources of Variability – Filter Pressure Drop • Pressure drop data from RRT • Filter Type 2 Type 3 Type 4 • Average ΔP, [in. H2O] 0.34 0.28 0.76 • 95% Confidence, 2 SR ±0.05 ±0.03 ±0.11 • 95% Confidence range 0.29 – 0.39 0.25 – 0.31 0.65 – 0.87 • Temperature and relative humidity range • Potential sources of variability • Pressure drop across empty section ΔP<0.03” wg. • Pressure drop gauge accuracy ±2.5% (?) • Differential pressure transducers are used for convenience • Generally it is ±0.25% of full scale • For gauge 0 -10” wg. range ±0.025” wg.

  20. Sources of Variability – Filter Pressure Drop • Measurement of flow rate • ASME long-radius nozzle • Uncertainty of ±2% for nozzles with beta = 0.2-0.8 • Surface finish 16 RMS (16 micro inches) • Calibrated nozzle can have accuracy as low as ±0.25% • Required input – temperature, air density, pressure • Laminar flow elements are used flow measurements • Better accuracy, generally 0.8% of reading • LFE with accuracy =1% and flow rate Q=2000 cfm • Flow measurement accuracy is ± 20 cfm → ΔP > 0.01” wg • Pressure drop measurement across ASME nozzle • No information on filter pressure drop at high elevation, correction for temperature, humidity

  21. Sources of Variability – Filter Efficiency • Temperature and relative humidity range • Impact of relative humidity on particle size • Particle counters • Optical particle counter • Flow rate 0.1 cfm; ±2% • < 10% coincidence error at 300,000 particles/min • Aerodynamic particle counter • No requirements • Aerosol neutralization • Radioactive (beta or gamma) with activity >5 mCi • Corona discharge with 3 µA current • Annual measurement of activity is recommended

  22. Sources of Variability – Filter Efficiency • Dust migration after dust loading • Airflow for 20 minutes • Duration less than 20 minutes is allowed if release rate <5% • Potential duct contamination due to dust loading • Dust loading is sometimes performed in a different test duct • Potential particle settling at low air velocity • Issues with statistical evaluation • Ruggedness Tests could find variables that strongly influence measurements

  23. Sources of Variability – Dust Holding Capacity • Filter Type 2 Type 3 Type 4 • Average DHC, [gram] 197 248 138 • 95% Confidence, 2 SR ±32 ±44 ±72 • 95% Confidence range 165 – 229 204 – 292 66 – 210 • Temperature and relative humidity range • Test dust and filter components are to some degree hygroscopic – increase weight when exposed to high RH • Size distribution of ASHRAE dust • Potential difference between filter and dust loaded in two different test rigs

  24. ASHRAE 52.2 - Conditioning • Initial conditioning with a dust loading of 30 grams or increase pressure drop by ΔP=0.04” wg. • Real life test data for filter efficiency made of some electrostatically enhanced media is lower • Research has been initiated to simulate this behavior • ASHRAE 1190-RP – Develop a New Loading Dust • Other conditioning methods: • Exposure to diesel soot • Exposure to cigarette smoke • Exposure to ultrafine particles • Exposure to alcohol (spray, dip, vapor) Conditioning = removal of electrostatic enhancement? Conditioning = simulation of real life performance?

  25. ASHRAE 52.2 - Conditioning • Impact of the initial loading on efficiency

  26. NIOSH - Conditioning • How do other organizations test filters? • National Institute for Occupational Safety and Health (NIOSH) • Procedure for testing particulate respirators – 42 CFR 84 regulation • 3 types of class of filters: Class Agent Load Particle size N-Series NaCl 200 g 0.3 µ R-Series DOP oil 200 g 0.3 µ P-Series DOP oil stabilized 0.3 µ

  27. NIOSH - Conditioning • Loading with NaCl particles using TSI 8130 After alcohol P=50% After alcohol P= 30%

  28. ASHRAE 52.2 - Conditioning • MERV 15 filter tested at 492 fpm • Electrostatically enhanced material • Field test data Different conditioning process

  29. ASHRAE 52.2 - Conditioning High Efficiency Electrets • Performance after loading with cigarette smoke, combustion particles and real life • Initial Efficiency at 0.3 µm particles, E >99.99% TreatmentEfficiency, [%] 12 months real life 99.98 300 cigarettes >99.97 Diesel soot (60 min)at 450 µg/m3 >99.97 What would be efficiency of this filter after alcohol ?

  30. ASHRAE 52.2 – Conditioning • Exposure to alcohol • Limitations: • Does not simulate real life • Can not be applied to filters with external electric field • Can not be applied to gas phase filters, PCO, UV • Can affect filters with surface tackifiers • Can affect high efficiency electrets • Conditioning with UFP particles (ASHRAE 52.2 J) • Eliminates all the above concerns • Test method requires some improvements to reduce variability

  31. ASHRAE 52.2 – Conditioning App. J • ASHRAE 52.2 Appendix J (1190-RP) • Size distribution of challenge aerosol - number

  32. ASHRAE 52.2 – Conditioning App. J • Ambient aerosol – size distribution

  33. ASHRAE 52.2 - Conditioning App. J and Field Test • Can mechanical media be affected by conditioning • Field test and conditioning – high efficiency mechanical Field test Conditioning

  34. ASHRAE 52.2 - Conditioning App. J and Field Test • Can mechanical media be affected by conditioning • Field test and conditioning – high efficiency electret Field test Conditioning

  35. ASHRAE 52.2 - Conditioning App. J and Field Test • Can mechanical media be affected by conditioning • Field test and conditioning – MERV 8 mechanical Field test Conditioning

  36. ASHRAE 52.2 – Conditioning Summary • Conditioning method according to the ASHRAE 52.2 Appendix J should be used in filter testing • Simulates better real life performance • Requires some improvements • Flat sheet test of filter media according to this test method is an inexpensive and not time consuming • Alcohol treatment should be used only to determine if filter material poses an electrostatic charge • Severely overestimate performance degradation

  37. Conclusions • Variability of the ASHRAE 52.2 test method is not acceptable • Results from Round Robin Test and other Research Projects (PR) were never implemented • Reproducibility • Some variability sources could be quickly evaluated by conducting Ruggedness Tests • Conditioning test method according to the Appendix J should be improved and adopted as a test method

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