Workshop 1 (Intermediate) Are rumors of MERV’s Death Exaggerated? Bruce McDonald Retired Filter Geek brucesfilterteststandards@live.com Workshop 1 (Intermediate) Are rumors of MERV’s Death Exaggerated? How Do ISO 16890 and ASHRAE 52.2 Compare?

Learning Objectives Explain the differences in laboratory air filter testing between ASHRAE 52.2 and ISO 16890. Describe ambient aerosol: multi-modal, universal modes determined aerosol physics. Demonstrate how lab measured filter efficiency can be used to estimate filter efficiency on ambient aerosol. Demonstrate with multiple examples how filter efficiency measurement using current methods relate to estimated filter efficiency on ambient aerosol. Describe how ASHRAE standards and guidelines will be affected by ISO 16890. ASHRAE is a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to ASHRAE Records for AIA members. Certificates of Completion for non-AIA members are available on request. This program is registered with the AIA/ASHRAE for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

Acknowledgments Don Thornburg – Camfil Don provided the data used in this presentation.

Outline Background Compare ASHRAE 52.2 and ISO 16890: Equipment Procedures, Data reduction/presentation Review sample data. MERV vs. ePM Restricted to mechanical filters Conclusion

Background ISO TC 142/WG 3 has developed international standard test methods for HVAC filters Their first effort, TS 21220, has issues. Consensus developed around measurement/classification based on filter efficiency in the size ranges represented by PM10, PM2.5 and PM1 measurements of ambient aerosol. Be very careful to say efficiency based on PM size ranges. DO NOT confuse filter efficiency with actual PMx measurements.

Why filter efficiency based on PMX? PMX values are ambient aerosol mass concentrations based on specific sampling equipment and methods. PMX concentrations used by environmental scientists to quantify ambient aerosol and by governments to regulate pollution. PM10 aerosol mass less than ~10 µm PM2.5 aerosol mass less than ~2.5 µm PM1 aerosol mass less than ~1 µm PM is Mass based; 52.2 is number based. PM values are for specific size ranges based on sampling hardware.

Ambient distribution

Logic: Filter efficiency values based on PMX size ranges and atmospheric mode shapes are understandable and useful. For example, ASHRAE 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, is already using filter efficiencies for PM2.5 Shape of modes in ambient aerosols is relatively consistent, set by physics.

Equipment Comparison: Test duct ASHRAE 52.2 ISO FDIS 16890 Positive pressure Straight or U shaped Mostly prescribed Qualification tests required Must meet qualification requirements Allows use of either ASHREAE 52.2 duct or EN 779 duct Positive or negative pressure Less prescriptive Qualification tests required Must meet qualification requirements 52.2 has strict qualifications requirements. Virtually all have been included in 16890.

Compare Efficiency Test Aerosol ASHRAE 52.2 requires KCl solid particles ISO 16890 requires: DEHS (liquid) and KCl (solid) Reference aerosol for the given size ranges: DEHS for 0.3 to 1.0 µm KCl for 1 to 10 µm Liquid is OK for 1 to 10 µm only if Vmedia < 20 cm/s Method to determine if the reference aerosol can be used outside the above ranges and criteria for match are given. So if a lab can show equivalence, it may be possible to run the entire size range with KCl.

Compare Aerosol Sizing and Counting ASHRAE 52.2 requires OPC with prescribed size channels: range 0.3 to 10 µm 16890 requires OPC with partially prescribed size channels Requires channel boundaries at: 0.3, 1, 3, 10 µm Minimum range required 0.3 to 3 µm

Updating test facilities ASHRAE 52.2 to ISO 16890 Add oil aerosol generator Add IPA vapor conditioning chamber EN 779 to ISO 16890 To test low efficiency filters and to report ePM10 Add KCl aerosol generator Add aerosol neutralization May need new OPC Add downstream mixing baffle

Compare Loading Test Dust ASHRAE 52.2 Loading test dust: ISO 12103-1 A2 fine + carbon black + cotton linters ISO 16890 Loading Test Dust: ISO 15957:2015 L2 aka: ISO 12103-1 A2 Fine (AC fine) Optional except for coarse filters Anticipate improved repeatability and reproducibility using A2 fine instead of ASHRAE dust.

Compare Procedures ISO FDIS 16890 ASHRAE 52.2 One procedure, complete test required including loading Conditioning optional using ultrafine solid aerosol. Appendix J, Conditioned results reported separately as MERV-A Allows use of partial test: small oil aerosol Loading test optional except for coarse filters Fractional efficiency optional for coarse filters Conditioning required using IPA vapor 16890 – if test high efficiency filters, can test with oil and don’t need KCl.

Data processing ASHRAE 52.2 ISO FDIS 16890 Calculate fractional efficiency for 12 size bins for initial and after each loading step (6 total) Develop composite minimum efficiency curve Calculate E1, E2, E3 Find MERV from table Calculate fractional efficiency for: as received, conditioned and the average. Calculate ePM1, ePM2.5, ePM10 from average Calculate , ePM1min, ePM2.5min from minimum efficiency. Find filter class from table.

Example 16890 data Use minimum efficiency to calculate ePM2.5,min Use average efficiency to calculate ePM2.5

How to get the ePM values? Measure fractional efficiency. As received and as condition. Calculate average Assume an upstream size distribution as sampled by PMX method. A “virtual test aerosol”. Use urban size distribution for ePM1, ePM2.5. Use rural size distribution for ePM10 The assumed size distributions are “typical” but the real world varies a lot.

Rural distribution has sufficient coarse mode particles such that ePM10 values reflect the performance of the filter on the coarse mode and to separate the ePM10 performance from the ePM2.5 performance.

Calculations For each size channel use the fractional efficiency to calculate the fractional efficiency on the virtual test aerosol, Sum over the PMx size range to get overall efficiency on the virtual test aerosol Standard caveat: Laboratory tests do not predict field performance. But allow filter comparisons.

ePMx equations Where q is std particle size distribution d is particle size Δ ln d is width of size bin E is efficiency in i th size bin

ISO 16890 classifications Use to classify filters: initial arrestance, ePM1, ePM2.5, ePM10, ePM1 min, ePM2.5 min Use average of as received and conditioned efficiencies to report results. ePM values rounded down to nearest multiple of 5 for reporting. Values > 95% reported as >95% i.e. ePM2.5 85% or ePM1 > 95% Filter may fit more than one group. Only one group and one classification on label.

ISO 16890-1: Table 4 Filter groups To determine group To report efficiency Group designation Requirement Class reporting value ePM 1, min ePM 2.5, min ePM 10 ISO Coarse -- <50% Initial arrestance ISO ePM10 ≥50% ISO ePM2.5 ePM 2.5 ISO ePM1 ePM 1

Reported Values ISO FDIS 16890 ASHRAE 52.2 MERV # (flow rate) E1, E2, E3 Performance curves: 6 stages plus composite minimum Efficiency data table (Addendum f) If E3<20%, average arrestance Optional: MERV-A ISO filter class (group+eff) Efficiency vs. particle size as received, as conditioned and the average Average efficiency values ePM1, ePM2.5, ePM10 , including uncertainties. Minimum efficiencies ePM1min, ePM2.5min, including uncertainties If ePM10<50%, initial arrestance

Assumptions Fractional efficiency curves are based on number concentration and optical sizing. PMX values are mass based and use aerodynamic sizing. Ignore difference in size definitions, For ISO 16890; calculations start at 0.3 µm Use 1, 3, and 10 µm upper optical size boundaries Ignore particle density as function of size. The assumptions are serious from the point of view of aerosol physics. But unimportant from the point of view of the end user comparing filter A and filter B.

Calculate ePM values from 52.2 data Examples only. NOT actual 16890 test result. But real 52.2 test data on 51 filters. These examples do not include conditioning. Examples use 52.2 data NOT the average of as received and conditioned efficiencies Reasonable comparisons for mechanical filters. Results do not apply to charged media Does not include loading or arrestance

Efficiency curves of example filters

MERV to ISO 16890 Group The values used to determine the ISO 16890 group are: ePM1 min, ePM2.5 min , ePM10 For mechanical filters it is reasonable to use ePM1 in place of ePM1 min and ePM2.5, in place of ePM2.5 min Using that approximation, how to the 16890 groups compare to MERV?

Compare ISO 16890 groups to MERV Approximate MERV ISO Coarse MERV 1 – 7 ISO ePM10 > MERV 7 ISO ePM2.5 > MERV 11 ISO ePM1 > MERV 12 Rough guide only! Only applies to mechanical filters!

Conclusions Is MERV dead? Not yet. It is written in specs and standards that may be slow to change. ASHRAE 52.2 won’t be replaced by ISO16890 overnight. Reporting air filter efficiency based on the methods in ISO FDIS 16890 is useful and already being written into ASHRAE standards. So MERV’s days are numbered.

Bibliography ANSI/ASHRAE Standard 52.2-2012, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size, with 2015 Supplement. ISO FDIS 16890-1, Air filters for general ventilation — Part 1: Technical specifications, requirements and classification system based upon particulate matter efficiency (ePM) ISO FDIS 16890-2, Air filters for general ventilation — Part 2: Measurement of fractional efficiency and air flow resistance

Bibliography ISO FDIS 16890-3, Air filters for general ventilation — Part 3: Determination of the gravimetric efficiency and the airflow resistance versus the mass of test dust captured ISO FDIS 16890-4, Air filters for general ventilation — Part 4: Conditioning method to determine the minimum fractional test efficiency EPA PM Criteria Document (EPA, 1996), Chapter 6

Bibliography ISO 12103-1: 2016, Road vehicles -- Test contaminants for filter evaluation -- Part 1: Arizona test dust ISO 15957:2015, Test dusts for evaluating air cleaning equipment Tronville, Paolo and Rivers, Richard, “New Method for Testing Air Filter Performance” ASHRAE Journal, May 2016, pp14 - 25

Questions? Bruce McDonald brucesfilterteststandards@live.com

Extra info. Check out the excellent article by Tronville and Rivers in May 2016 ASHRAE Journal! (But Table 4 is wrong) Can 52.2 test results predict ISO 16890 group and efficiency? NO But for mechanical filters there are reasonable approximations. (next slides) The approximation for ePM1 is good (E1) The approximation for ePM2.5 is less good (avg(E1,E2)) The approximation for ePM10 is not so good (E3) The Table 4 in the Tronville and Rivers article is from a early draft of 16890. The table 4 used in this presentation is directly from the FDIS version of 16890-1. Need oil aerosol, need conditioned efficiency

Note offset

What caused the kink in the ePM1 and ePM 2.5 curves at MERV 8? That is one filter. It is a large fiber, low solidity, high velocity, tackified filter. So it performs a lot like an impactor i.e. low efficiency for small particles and a relatively rapid rise in efficiency for larger particles. I expect the kink to disappear if a representative sample of MERV 8 filters are included in the average.