1. ANSI/ASHRAE 52.2
A destructive test to measure minimum efficiency reporting value (MERV)
Efficiency test aerosol is Potassium Chloride (KCl) particles, 0.3 to 10 micrometers
Dust loading aerosol is ASHRAE Standard Test Dust:
Size classified Arizona Road Dust
Cotton linters
Carbon black
Because the 52.1 test did not measure the size of the particle – just the amount – an ASHRAE Committee was formed and a research project was done to develop a method to show removal by a filter based on particle size. A new challenge aerosol had to be found because outdoor air does not have consistent particle size distribution nor quantity. Potassium chloride was found to be the best and easiest aerosol for this purpose. Also, the Committee wanted to know the minimum efficiency of the filter, rather than average efficiency as reported by ASHRAE The minimum efficiency of the filter is typically in its clean configuration, since it would only become more efficient from this number. And this number, called a Minimum Efficiency Reporting Value (MERV) would be more like the European one-number system.
Copyright-National Air Filtration Association V6 2010

2. ANSI/ASHRAE 52.2 Initial Resistance
Pressure required to move air through filter at a certain air flow written in inches water, Pascal or millimeters water
Final Resistance
Pressure at which the filter would be considered fully loaded
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3. ANSI/ASHRAE 52.2 Test Duct Configuration
Outlet
Filters
ASME
Nozzle
Downstream Mixer
Exhaust
Room Air
OPC
Inlet
Filters
Aerosol
Generator
Even a new style of test device was developed to help shorten the distance for the particle counter lines. The 52.2 test duct begins by taking laboratory room air that is conditioned to ASHRAE Standard 55 (temp & relative humidity parameters) and using a HEPA filter, removes all particles. Potassium chloride is then injected upstream of the first optical particle counter (OPC) sample point and upstream of the filter under test. The particle counter determines the number and size of particles in the challenge stream. This aerosol then passes through the filter under test and, if not captured, pass around to the second particle counter sample point downstream. The air is then HEPA filtered to remove all remaining particles and recirculated to the laboratory. By this method, we know exactly how many of what size particles are captured by the filter under test. The dust loading is done exactly as in 52.1 and an efficiency test is run between each loading. The final efficiency numbers are used to determine the MERV value.
Upstream
Mixer
Device
Section
Blower
Flow
Control
Valve
Backup Filter
Holder (Used
When Dust loading)
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4. Typical 52.2 Complete Loading Test Data Report
Size Range
(micrometers)
Fractional Efficiency (%) at Resistance (in H20)
Composite
Minimum
Average
0.28
0.32
0.46
0.64
0.82
1.00
0.3 to 0.4
2.7
6.7
17.2
29.4
37.1
37.9
E1 = 9.8
0.4 to 0.55
7.8
15.9
27.7
43.3
53.2
54.6
0.55 to 0.7
11.2
30.2
46.0
60.7
70.5
71.6
0.7 to 1.0
17.6
42.6
59.3
73.7
81.3
81.8
1.0 to 1.3
20.4
51.6
70.3
80.8
83.7
85.2
E2 = 27.2
1.3 to 1.6
23.9
58.2
76.5
84.7
86.1
87.2
1.6 to 2.2
28.3
69.6
84.1
89.1
90.2
91.0
2.2 to 3.0
36.3
83.9
91.9
94.2
94.4
93.2
3.0 to 4.0
39.4
89.4
93.7
95.8
96.4
94.9
E3 = 44.8
4.0 to 5.5
42.8
90.6
95.3
96.5
97.9
95.6
5.5 to 7.0
46.5
92.3
97.1
98.0
98.4
7.0 to 10.0
50.4
94.8
97.5
98.3
100
99.2
After all of the testing and dust loading to final resistance, this is the data produced. Here you see the composite minimum of a MERV 6 filter.
Minimum Efficiency Reporting Value is 6 at 492 fpm
Copyright-National Air Filtration Association V6 2010

5. Composite Minimum Curve
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6. MERV Parameters Table 7.2.1
Minimum Efficiency Reporting Value
Composite Average Particle Size Efficiency (%)
Average Arrestance by ASHRAE 52.1
Minimum Final Resistance
0.3 to 1.0 E1
1.0 to 3.0 E2
3.0 to 10 E3 Pa
In Water 1
n/a
E3 < 20
Aavg < 65 75
0.3 2
65 ≤ Aavg < 70 3
70 ≤ Aavg < 75 4
75 ≤ Aavg 5
20 ≤ E3 < 35
150
0.6 6
35 ≤ E3 < 50 7
50 ≤ E3 < 70 8
70 ≤ E3 < 85 9
E2 < 50
E3 ≥ 85
250
1.0 10
50 ≤ E2 < 65 11
65 ≤ E2 < 80 12
E2 ≥ 80
E3 ≥ 90 13
E1 < 75
E2 ≥ 90
350
1.4 14
75 ≤ E1 < 85 15
85 ≤ E1 < 95 16
E1 ≥ 95
This chart is used to determine the MERV number. By working backward from the 3.0 to 10 micrometer removal efficiency, one completes the numbers until there is no removal above the stated number in the next column to the left– then across to the MERV number.
Copyright-National Air Filtration Association V6 2010

7. MERV Parameters Table 7.2.1 E1 = 9.8% E2 = 27.2% E3 = 44.8% MERV 6
Minimum Efficiency Reporting Value
Composite Average Particle Size Efficiency (%)
Average Arrestance by ASHRAE 52.1
Minimum Final Resistance
0.3 to 1.0 E1
1.0 to 3.0 E2
3.0 to 10 E3 Pa
In Water 1
n/a
E3 < 20
Aavg < 65 75
0.3 2
65 ≤ Aavg < 70 3
70 ≤ Aavg < 75 4
75 ≤ Aavg 5
20 ≤ E3 < 35
150
0.6 6
35 ≤ E3 < 50 7
50 ≤ E3 < 70 8
70 ≤ E3 < 85 9
E2 < 50
E3 ≥ 85
250
1.0 10
50 ≤ E2 < 65 11
65 ≤ E2 < 80 12
E2 ≥ 80
E3 ≥ 90 13
E1 < 75
E2 ≥ 90
350
1.4 14
75 ≤ E1 < 85 15
85 ≤ E1 < 95 16
E1 ≥ 95
E1 = 9.8%
E2 = 27.2%
E3 = 44.8%
MERV 6
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8. Addendum B
Added for ability to test lower efficiency filters (MERV 1-4) with an arrestance and dust holding capacity percentage.
Two new items added to 52.2 within the last two meetings of the Standing Standards Project Committee. First, Addendum B was added to bring the testing of lower MERV number filters using the Arrestance test and dust holding capacity from ANSI/ASHRAE 52.1 method of test. This allowed the Committee to retire the 52.1 Standard.
Copyright-National Air Filtration Association V6 2010

9. Addendum B
Arrestance – ability of an air cleaning device with efficiencies less than 20% in the size range of 3.0 to 10.0 micrometers to remove loading dust from test air. Average Arrestance - Difference between the weight of the dust fed versus dust passing through the device to final filter calculated as dust captured by test device.
With lower efficiency filters, you will find the arrestance information (explain from slide) and the average arrestance (explain from slide
Copyright-National Air Filtration Association V6 2010

10. Addendum B
Dust Holding Capacity – total weight of the synthetic loading dust captured by the air cleaning device over all of the incremental dust loading steps tested to a final resistance of 1.4” wg or specified final resistance.
In addition, total dust in grams captured by the filter under test will be shown. This information can possibly be useful in determining the time in service of a filter.
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11. Informative Appendix J
Optional method of Conditioning a filter using fine KCl particles (0.04 to 0.08 micrometers) on electrically charged (electret) media
Minimum efficiency in some types of may be less than the initial efficiency
The second item added to ANSI/ASHRAE 52.2 is the Informative Appendix J also known as the Conditioning Step. Some electrically enhanced media have the fiber charge blinded by dust then loaded with smaller particles such as those found in the outdoor environment. The conditioning step is designed to provide critical filter applications with a method of determining how much the efficiency will drop in efficiency when loaded with these smaller particles.
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12. Informative Appendix J
This chart shows the initial efficiency using the 52.2 laboratory test and then the tested efficiency of a 2-inch electrostatically charged (electret) media pleated filter after 10 weeks of filtering 100% outdoor air in service. The conditioning step is designed to show how smaller particles captured and bound around the filter fiber blind the charge in some filters and reduce the efficiency from initial. As they continue to load, the mechanical efficiency does occur and increases the filter efficiency.
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13. Informative Appendix J
MERV –A - Added to determine the amount of the efficiency loss a filter may realize in field application
Depending on the critical nature of the application, owner may want to ask for optional Appendix J testing
End users of filters applied in critical applications may want to have their filters tested with the Conditioning Step. When Appendix J testing is done, it is noted by an “A” after the word MERV…for example a MERV 14 filter tested with the conditioning step would have a test report shown MERV A14
Copyright-National Air Filtration Association V6 2010