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

2. Learning Objectives
Explain the differences in laboratory air filter testing between ASHRAE and ISO
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
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.

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

4. 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

5. 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.

6. 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; is number based.
PM values are for specific size ranges based on sampling hardware.

7. Ambient distribution

8. 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.

9. 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

10. Compare Efficiency Test Aerosol
ASHRAE 52.2 requires KCl solid particles
ISO 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.

11. 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

12. 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

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

14. 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.

15. 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.

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

17. 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.

19. 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.

20. 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.

21. 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

22. ISO 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.

23. 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

24. 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

25. 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.

26. Calculate ePM values from 52.2 data
Examples only. NOT actual 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

28. Efficiency curves of example filters

33. MERV to ISO Group
The values used to determine the ISO 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 groups compare to MERV?

35. 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!

36. 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 is useful and already being written into ASHRAE standards.
So MERV’s days are numbered.

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

38. Bibliography
ISO FDIS , 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 , Air filters for general ventilation — Part 4: Conditioning method to determine the minimum fractional test efficiency
EPA PM Criteria Document (EPA, 1996), Chapter 6

39. Bibliography
ISO : 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, pp

40. Questions?
Bruce McDonald

41. 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 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 The table 4 used in this presentation is directly from the FDIS version of
Need oil aerosol, need conditioned efficiency

43. Note offset

46. 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.