1. NAFA Guide To Air Filtration
Fifth Edition
Chapter 7
HVAC Filter Testing
presented by the
National Air Filtration Association

2. HVAC Filter Testing Why Test?
Determine efficiency of particle-size removal
Determine Amount of Contaminant Removed
Determine Pressure drop
The ANSI/ASHRAE filter test is designed to test one filter against another in the laboratory. There are three main things that end users should know about their filter. Testing provides answers in these categories. 1. Efficiency – especially efficiency on what size particle? 2. How much Test Dust will the filter hold until it reaches the manufacturer’s stated pressure drop? 3. What amount of pressure will the filter add to the system?

3. ANSI/ASHRAE 52.1 (retired)
Two Main Problems:
Used outdoor air as
challenge aerosol
Did not show
removal based on
particle size
Problems with older ASHARE it used outdoor air as the challenge aerosol – varied in particle size, temperature and humidity 2. Did not show the efficiency based on the size of challenge particle

4. ANSI/ASHRAE 52.2-2012 A design qualification test
A destructive test to measure the minimum efficiency and provide the minimum efficiency reporting value (MERV)
Efficiency test aerosol is Potassium Chloride (KCl) particles, 0.3 to 10 micron
Dust loading aerosol to final pressure drop is ASHRAE Standard Test Dust
Because the earlier ASHRAE tests 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.

5. ANSI/ASHRAE 52.2 - 2012 Test Duct Configuration
Outlet
Filters
ASME
Nozzle
Downstream Mixer
Exhaust
HEPA
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.
HEPA
Upstream
Mixer
Device
Section
Blower
Flow
Control
Valve
Backup Filter
Holder (Used
When Dust loading)
Copyright-National Air Filtration Association V8 2015

6. 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

7. Composite Minimum Curve
This chart is the graph of our sample filter’s minimum efficiency curve.

8. MERV Parameters This is a New Parameter Table as of Sept. 2014
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
20<E2
70 ≤ E3 9
35<E2
75 ≥ E3
250
1.0 10
50 ≤ E2 < 65
80 ≥ E3 11
20<E1
65 ≤ E2 < 80
85 ≥ E3 12
35<E1
80 ≥ E2
90 ≥ E3 13
50<E1
90 ≥ E2
350
1.4 14
75 ≤ E1 < 85
95 ≥ E3 15
85 ≤ E1 < 95 16
95<E1
E2 ≥ 90
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.

9. How Can Filters Capture Particles Smaller Than 0.3 Micrometers ?
It is crucial to consider the efficiency below 0.3 micrometers
Commonly believed that filters only capture “down to 0.3 micrometers”
Better particle counters show efficiencies below 0.3 micrometers

10. ASHRAE 52.2 Initial Resistance
-Pressure required to move air through filter at a certain air flow written in inches water, or Pascals
Final Resistance
-Pressure at which the filter would be considered fully loaded
Both initial and final resistance levels were set by the Committee, solving one weakness of the 52.1 Standard. Also, the information is written in both inches of water and Pascal to link it to European nomenclature.

11. 52.2 Test Report
(cover items on the test report – not too lengthy) End users should look at all pages of the report including the composite curve and loading results.

12. 52.2 Test Limitations Not “real world” – what is?
May not give accurate results for some electrostatically enhanced filter media.
Addendum J added –
Conditioning Step is
shown as MERV-A
Limitations of the 52.2 include the fact that it may or may not tell how a filter will perform in-situ (real world) although no one has been able to describe “real world.” Second, it may not accurately show the dip in efficiency experienced by some electret filters. As an electret filter loads with particles, the charge may be blinded until the loading of dust forms a layer to produce an increase in efficiency same as a mechanical filter. The ASHRAE Standing Standards Project Committee 52.2 has inserted an appendix to the test that allows for loading of electret filters to show this curve.

13. Filter Testing Summary: ASHRAE Standard 52.2-2012 is current Standard
Filters should be independently procured and tested
Manufacturer should have filters tested for MERV number to compare to other filters
Highlight bullets – Questions Here**************************

14. Compare and Contrast 52.1/52.2 and European EN-779
The Europeans have long had a filter test standard called EN: 779. This standard is similar to the ASHRAE Standard It uses the designation “G” for general filters less than 40% efficiency on 0.4 micrometer particles and “F” for Fine when higher than 40%. The International Organization for Standardization (ISO) is now working to develop a worldwide standard.

15. Association of Appliance Manufacturers (AHAM) AC-1 2006
Tests “cord-connected” room air cleaners of all descriptions
Has test chamber for challenge of units
Uses 3 types of challenge aerosols – cigarette smoke/air cleaner fine dust/pollen
Gives 3 number Clean Air Delivery Rate (CADR) for units tested
The AHAM test is called – Portable Household Electric Cord-Connected Room Air Cleaners test. The test has recently been misapplied to whole house units by HVAC manufacturers (not filter manufacturers). This distortion has made some whole-house residential units appear to have higher performance values than actual performance. AHAM has issued a denial of these filter CADR rates.

16. Underwriters Laboratory (UL)
UL tests filters for fire listing:
Used to be:
Class 1 filters “when clean do not contribute fuel when attacked by flame and emit only negligible amounts of smoke” Class 2 filters “when clean burn moderately when attacked by flame or emit moderate amounts of smoke, or both.”
Now all filters are just “UL Listed”…Only Applies “When clean” is qualifier

17. Chapter 7 Addendum ASNI/ASHRAE 52.2 Test Method
Be familiar with the test in its entirety

18. Sample Questions
ANSI/ASHRAE 52.2 averages particles sizes in how many broad composite categories?
Three – E1, E2 & E3
What are the ranges of these averages?
0.3 to 1.0 µm/1.0 to 3 µm/3 to 10 µm
What is the name of the current European Air Filter Standard?
EN779:2002

19. Thank you.
Other Questions?