When I started the project of overseeing the updating to the NAFA Guide to Air Filtration, I was overwhelmed with not knowing where or how to start on this monumental task. After reviewing what had been done in the past, I had a better idea of what was needed. Lots of help from others!
I would be remiss if I didn’t call out all the NAFA members who helped to contribute to the 2021 update. From Past Presidents, whom I nominated to take chapters to review, to past contributors, industry consultants and experts and in general, anyone who I could convince to lend their knowledge and expertise. To each of you who contributed, on behalf of NAFA and our members, I thank and salute you.
The 2021 update contains many new materials, charts, graphs, pictures and tables, updates on material that is still relevant, corrections to old materials and just about anything that we found that needed freshening up. With that said, just like any document that you produce, I’m sure some intrepid reader of the Guide will find an error or omission. In advance, if you do, please make a note of it and let NAFA Staff know, so that when we do the next update, we can include your wisdom.
In reading the updated guide, you’ll find that we’ve included new standards, such as the ISO 16890 section, which was important enough that we’ve created a new addendum just on that topic. We’ve also included a table in Chapter 7: HVAC Filter Testing, that compares ASHRAE 52.2-2017, EN779 and the new ISO 16890 test criteria. Also included are discussion and tables covering the new ISO 29463 standard which replaced EN 1822:2009 for HEPA/ULPA filter testing. There’s new information in Chapter 9: Controlled Environments which covers new standards and updated language relative to the various industries covered. Chapter 12: Indoor Air Quality contains new terminology and a updates of 62.1 – 2019, which covers Classes 1-4. One of the most significant updates has come in Chapter 14: Ultraviolet Germicidal Irradiation, Photocatalytic Oxidation. This is a subject that has become extremely important since our last update and the chapter now contains substantially more information and charts/graphs/tables explaining how this technology is being implemented in the industry. Be sure to review this information to increase your knowledge of the subject.
ISO 16890 addendum
On the following pages, you will find an excerpt from the new Guide, Addendum 7.2 A Brief Description of ISO 16890, which, “…establishes an efficiency classification system of air filters for general ventilation based upon particulate matter (PM). It also provides an overview of the test procedures, and specifies general requirements for assessing and marking the filters, as well as for documenting the test results. It is intended for use in conjunction with ISO 16890?2, ISO 16890?3 and ISO 16890?4.”1
If you’re like me, you probably have a copy of the Third, Fourth, or maybe even the Fifth Edition of the NAFA Guide to Air Filtration sitting on your shelf as a reference. With all the changes in technology and updates to standards, in order to be fully knowledgeable and best positioned to assist your customers, you’ll want to order the new Sixth Edition as soon as possible so that you can read and review everything that I’ve mentioned and much more that I’ve not even touched upon. Be sure to call or email NAFA HQ and place your order for the new edition as soon as it’s available in print. You won’t be sorry.
Lastly, again I want to thank all the NAFA members, industry experts and NAFA staff who so graciously gave of their time and expertise to provide information that has been included in this Sixth Edition. Without their efforts, I would still be working on this update.
Jay Reese, CAFS
A Brief Description of ISO 16890
Excerpted from the NAFA Guide to Air Filtration, 6th edition
ISO 168901-4 determines the ability of an air cleaner (air filter) to remove particles of a specific size from an air stream. This test method is very similar, but not identical, to ANSI/ASHRAE Standard 52.2. ISO 16890 tests filter efficiency for clean and conditioned efficiency, pressure drop and test dust capacity. For smaller particle sizes, the aerosol is DEHS, an oil. For larger sizes the aerosol is the same KCl aerosol, a dry salt, as for 52.2.
An air filter’s performance is determined by measuring the particle counts upstream and downstream and comparing them. Particle counts are measured over the range of particle sizes from 0.3 – 10 um in 12 size channels beginning with a clean filter and, then, after an IPA (isopropyl alcohol) conditioning test.
A laboratory aerosol generator is used to create a challenge aerosol covering the required particle sizes. The challenge aerosol is injected into the test duct and particle counts are taken for each of the size ranges. Particle counts are measured in particle size ranges defined by the test. The recommended, but not required ranges are the same as those of ASHRAE 52.2 (See Figure 7.2.1).
Since the IPA conditioning step is expected to overpredict the loss in efficiency in real use for charged filters, the average of the two values in each size range is then calculated as representative of the filter’s efficiency in use.
In ISO 16890 the amount of particulate matter a filter will be exposed to in situ is represented by two different particle size distributions (psd) called rural and urban. The rural psd is used for calculating the mass removal efficiency for the ePM10 rated filters while the urban psd is used for the ePM2.5 and ePM1 rated filters. To calculate the mass removal efficiency for each particle size, the efficiency of the filter at that size is weighted by the amount of mass of that size in the psd. In practice, this means that a larger particle’s removal counts for more mass removal in the PM efficiency than a smaller, less massive, particle.
To determine the PM removal efficiency for particles smaller than 10 µm, the entire data set of weighted mass removal values from 0.3-10 µm (channels 1-12) are summed up to give the ePM10 value. The ePM2.5 value covers the sizes from 0.3-3 µm, and the ePM1 value covers the sizes from 0.3-1.0 µm. Dust holding data does not enter the PM efficiency calculations nor is that part of the test required.
ISO Coarse are rated based only on the initial gravimetric arrestance, so the particle size dependent efficiency test data is not used.
Filters are placed into Groups based on their efficiencies. Each group consists of the acronym ISO followed by the type of class reporting value. Thus, the groups are ISO Coarse, ISO ePM10, ISO ePM2.5, and ISO ePM1. The group is determined through the rules shown in Figure 7.2.1. ISO Coarse filters are rated using only the initial gravimetric arrestance. The other groups are rated based on the efficiency testing without including the dust-loading data. Filters should only be compared using values in the same group.
There is strong emphasis on the standardization and calibration of components. The apparatus must undergo qualification tests very similar to those of 52.2 before filter testing begins. Theoretically, a filter tested by ISO 16890 in one laboratory should have the same performance values when tested in any other correctly-operating laboratory.
Components of the ISO 16890 test duct are shown in Figure 7.2.2. More complete details of all the components will be found in the ISO 16890 Standard Documents.
After a filter is tested for clean filter efficiency, it is placed in a special chamber and exposed to isopropyl alcohol vapor (IPA) for 24 hours. This exposure is designed to completely remove the electrostatic charge on filters to show how the filter would perform with only its mechanical filtration. This charging increases the removal efficiency of filters above that provided by mechanical means. In real use, as small particles are captured, the charge is partially masked, and filters often have reduced efficiency. Conditioning with IPA, then taking the average of the clean and conditioned efficiencies, is intended to give a useful approximation of actual filter performance. IPA conditioning, rather than a particle/dust exposure, is used as the exposure is straightforward and simple to perform.
Particle Size Distributions
Two psd were selected by the ISO committee based on published atmospheric aerosol distributions from around the world for use in the calculations of mass removal efficiency. The rural distribution has more of the mass located in larger size particles; whereas, the urban distribution has more of the mass in the smaller particles. These distributions are not intended to represent a specific location or to match anyone’s actual use but are used as the standard distributions to allow for test to test (filter to filter) comparisons.
Arrestance And Test Dust Capacity
Dust loading is optional except for ISO Coarse filters. If done, it is run after the clean and conditioned efficiency tests. The dust loading is done in increments with ISO 15957 L2 dust (i.e., ISO Fine). The filter arrestance is determined by comparing fed and captured dust weights. The test dust capacity is the amount of dust captured by the filter.
This capacity is intended for comparison across filters and not to determine the lifetime of a filter in a specific location.
The test procedure (after the system has met all qualification requirements) consists of the following steps:
- Determine the pressure drop of the filter under test at 50%, 75%, 100% and 125% of the test airflow rate.
- Determine particle size efficiency (PSE) of the filter at the required airflow rate. At least 5 runs are made for each PSE curve, more may be required to achieve statistical accuracy. The particle size ranges of 52.2 are the standard ones for ISO 16890 although others are acceptable.
- The particle counts upstream and downstream of the filter are recorded for each test point of each size group. Filter efficiency at each point is calculated using the formula:
Eff. = (1 - Cd/ Cu) x 100 Where: Cu = Upstream particle count Cd = Downstream particle count
- The testing procedure is as follows:
- Determine the PSE of the exposed filter
- “Condition” the filter by exposure to IPA vapor for 24 hours.
- Determine the PSE of the exposed filter at 50% airflow
- If indicated, repeat the IPA 24-h exposure
- Average the clean and exposed PSE values
- Calculate the ePM values by weighting the efficiencies by the psd.
- Determine the ePM group and efficiency from these values. Round the efficiency values down to the nearest 5% for reporting.
- If desired or if the ePM10 is <50%, perform the dust loading procedure
- Calculate the gravimetric efficiency
Filter Test Report Form
ISO 16890 does not require any specific report format. The efficiency tests and optional dust loading tests may be reported separately or together. Overall the whole 4-part test procedure requires the following information:
- Name, location of, and contact information for the test laboratory
- Date of the test
- Test operator’s name(s)
- Brand, model number, and coincidence value of the particle counting and sizing device(s)
- Method of airflow measurement
- Identification of part of ISO 16890
- Unique test report identification
- Air cleaner manufacturer’s name (or name of the marketing organization, if different from the manufacturer)
- How the sample was obtained
- Description of the test air cleaner, including:
- Brand and model number
- Physical description of construction (e.g. extended surface – number of pockets or number of pleats; pleated panel number and depth of pleats)
- Device condition (clean, conditioned, dust-loaded)
- Face dimensions and depth
- For fiber media air cleaners:
- Type and color of media
- Effective media area
- Type and amount of additives, if known
- Electrostatic charge, if known
- Any other pertinent descriptive attributes
- Device data as stated by the manufacturer
- Test device initial resistance to airflow at the test airflow rate;
- Rated final resistance
- Initial particle removal efficiency
- Other literature data available or furnished operating data
- Test conditions
- Test airflow rate
- Test air temperature and relative humidity
- Test aerosol used
- Test data
- Resistance to airflow, table and graph
- Fractional efficiency in each measured particle size range, table and graph
- Total upstream counts by size range
- Resistance to air flow vs test dust load, if test is run, table and graph
- Arrestance values vs test dust load, if test is run, table and graph
- ISO 16890-1:2016. Air filters for general ventilation — Part 1: Technical specifications, requirements and classification system based upon particulate matter efficiency (ePM), International Organization for Standardization (ISO).
- ISO 16890-2, Air filter for general ventilation — Part 2: Measurement of fractional efficiency and air flow resistance, International Organization for Standardization (ISO).
- ISO 16890-3, Air filter for general ventilation — Part 3: Determination of the gravimetric efficiency and the air flow resistance versus the mass of test dust captured, International Organization for Standardization (ISO).
- ISO 16890-4, Air filter for general ventilation — Part 4: Conditioning method to determine the minimum fractional test efficiency, International Organization for Standardization (ISO).