Particulate air filters for general ventilation — Determination of filtration performance

ISO/TS 21220:2009 presents test methods and specifies a test rig for measuring the filter performance of particulate air filters used for general ventilation. The test rig is designed for an air flow rate of between 0,25 m3/s [900 m3/h (530 ft3/min)] and 1,5 m3/s [5 400 m3/h (3 178 ft3/min)]. ISO/TS 21220:2009 is applicable to air filters having an initial efficiency of less than 99 % with respect to 0,4 µm particles. Filters in the higher end and those with an above 99 % initial efficiency are tested and classified according to other standards. It combines two test methods: a “fine” method for air filters in the higher efficiency range and a “coarse” method for filters of lower efficiency. In either case, a flat‑sheet media sample or media pack sample from an identical filter is conditioned (discharged) to provide information about the intensity of the electrostatic removal mechanism. After determination of its initial efficiency, the untreated filter is loaded with synthetic dust in a single step until its final test pressure drop is reached. Information on the loaded performance of the filter is then obtained. The performance results thus obtained cannot alone be quantitatively applied to predict in‑service performance with regard to efficiency and lifetime, so other factors influencing performance are also presented.

Filtres à air particulaires pour ventilation générale — Détermination des performances de filtration

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Status
Withdrawn
Publication Date
21-Sep-2009
Withdrawal Date
21-Sep-2009
Current Stage
9599 - Withdrawal of International Standard
Start Date
28-Nov-2016
Completion Date
28-Nov-2016
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TECHNICAL ISO/TS
SPECIFICATION 21220
First edition
2009-10-01
Particulate air filters for general
ventilation — Determination of filtration
performance
Filtres à air particulaires pour ventilation générale — Détermination
des performances de filtration
Reference number
ISO/TS 21220:2009(E)
ISO 2009
---------------------- Page: 1 ----------------------
ISO/TS 21220:2009(E)
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ii © ISO 2009 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 21220:2009(E)
Contents Page

Foreword............................................................................................................................................................. v

Introduction ....................................................................................................................................................... vi

1 Scope ..................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms, definitions, symbols and abbreviated terms......................................................................... 2

4 Filter ....................................................................................................................................................... 6

5 Classification/rating.............................................................................................................................. 6

6 Test rig and equipment ........................................................................................................................ 6

6.1 Test conditions ..................................................................................................................................... 6

6.2 Test rig ................................................................................................................................................... 6

6.3 DEHS test aerosol generation ............................................................................................................. 7

6.4 KCl test aerosol generation ............................................................................................................... 10

6.5 Aerosol sampling system .................................................................................................................. 12

6.6 Flow measurement ............................................................................................................................. 13

6.7 Particle counter................................................................................................................................... 13

6.8 Differential pressure-measuring equipment .................................................................................... 13

6.9 Dust feeder .......................................................................................................................................... 13

7 Qualification of test rig and apparatus............................................................................................. 17

7.1 General................................................................................................................................................. 17

7.2 Air velocity uniformity in the test duct ............................................................................................. 17

7.3 Aerosol uniformity in the test duct ................................................................................................... 18

7.4 Particle counter sizing accuracy....................................................................................................... 18

7.5 Particle counter zero test................................................................................................................... 19

7.6 Particle counter overload test ........................................................................................................... 19

7.7 100 % efficiency test........................................................................................................................... 19

7.8 Zero % efficiency test......................................................................................................................... 19

7.9 Aerosol generator response time ..................................................................................................... 20

7.10 Correlation ratio .................................................................................................................................. 20

7.11 Pressure drop checking..................................................................................................................... 20

7.12 Dust feeder air flow rate..................................................................................................................... 21

7.13 Reference filter check......................................................................................................................... 22

7.14 Activity of the aerosol neutralizer ..................................................................................................... 23

7.15 Summary of qualification requirements...........................................................................................23

7.16 Apparatus maintenance ..................................................................................................................... 24

8 Test materials...................................................................................................................................... 24

8.1 Test air ................................................................................................................................................. 24

8.2 Test aerosol......................................................................................................................................... 24

8.3 Loading dust ....................................................................................................................................... 25

8.4 Final filter............................................................................................................................................. 26

9 Test procedure .................................................................................................................................... 26

9.1 General................................................................................................................................................. 26

9.2 Preparation of filter to be tested ....................................................................................................... 27

9.3 Initial pressure drop ........................................................................................................................... 27

9.4 Initial efficiency measurement .......................................................................................................... 27

9.5 Conditioning test ................................................................................................................................ 29

9.6 Dust loading ........................................................................................................................................ 29

10 Uncertainty calculation of the test results ....................................................................................... 31

© ISO 2009 – All rights reserved iii
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ISO/TS 21220:2009(E)

11 Test report............................................................................................................................................ 32

11.1 General ................................................................................................................................................. 32

11.2 Interpretation of test reports.............................................................................................................. 32

11.3 Summary.............................................................................................................................................. 33

11.4 Efficiency ............................................................................................................................................. 35

11.5 Pressure drop and air flow rate ......................................................................................................... 35

11.6 Marking................................................................................................................................................. 35

Annex A (normative) Conditioning test.......................................................................................................... 42

Annex B (informative) Shedding from filters ................................................................................................. 45

Annex C (informative) Commentary................................................................................................................ 47

Annex D (normative) Pressure drop calculation........................................................................................... 51

Bibliography ..................................................................................................................................................... 53

iv © ISO 2009 – All rights reserved
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ISO/TS 21220:2009(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

In other circumstances, particularly when there is an urgent market requirement for such documents, a

technical committee may decide to publish other types of document:

⎯ an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in

an ISO working group and is accepted for publication if it is approved by more than 50 % of the members

of the parent committee casting a vote;

⎯ an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical

committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting

a vote.

An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a

further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is

confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an

International Standard or be withdrawn.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO/TS 21220 was prepared by Technical Committee ISO/TC 142, Cleaning equipment for air and other

gases.
© ISO 2009 – All rights reserved v
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ISO/TS 21220:2009(E)
Introduction
[5] [1]

This Technical Specification is based on EN 779 and ANSI/ASHRAE 52.2 , and covers the testing of the

performance of air filters mainly used in general ventilation applications. During its preparation, it was

perceived that the document was not sufficiently mature for publication as an International Standard, and so

its publication as a Technical Specification was decided as an intermediate step. Moreover, with such a

document covering the needs of the air filtration industry and of the end users, it is envisaged that a future

revision in the form of an International Standard could also include a classification system.

The classification or rating of air filters is determined by national bodies or other associations and is not within

the scope of this Technical Specification

In the method set out in this Technical Specification, representative samples of particles upstream and

downstream of the filters are analysed by an optical particle counter (OPC) to provide filter particle size

efficiency data.

Initiatives to address the potential problems of particle re-entrainment, shedding and the in-service charge

neutralization characteristics of certain types of media are presented.

Certain types of filter media rely on electrostatic effects to achieve high efficiencies at low resistance to air

flow. Exposure to some types of challenge, such as combustion particles or other fine particles, can inhibit

such charges, with the result that filter performance suffers. The conditioning test procedure given in Annex A

provides techniques for identifying this type of behaviour and can be used both to determine whether the filter

efficiency is dependent on the electrostatic removal mechanism and to provide quantitative information about

the importance of the electrostatic removal. This procedure was selected because it is well established,

reproducible, simple to perform and relatively quick and ultimately because an acceptable alternative

procedure was not available.

In an ideal filtration process, each particle would be permanently arrested at the first contact with a filter fibre,

but incoming particles can impact on a captured particle and dislodge it into the air stream. Fibres or particles

from the filter itself could also be released, due to mechanical forces. From the user’s point of view it might be

important to know this, and a description is given in Annex B.
A brief overview of the test method and its principles is given in Annex C.
A means for calculating pressure drop is set out in Annex D.
vi © ISO 2009 – All rights reserved
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TECHNICAL SPECIFICATION ISO/TS 21220:2009(E)
Particulate air filters for general ventilation — Determination
of filtration performance
1 Scope

This Technical Specification presents test methods and specifies a test rig for measuring the filter

performance of particulate air filters used for general ventilation. The test rig is designed for an air flow rate of

3 3 3 3 3 3

between 0,25 m /s [900 m /h (530 ft /min)] and 1,5 m /s [5 400 m /h (3 178 ft /min)].

This Technical Specification is applicable to air filters having an initial efficiency of less than 99 % with respect

to 0,4 µm particles. Filters in the higher end and those with an above 99 % initial efficiency are tested and

classified according to other standards.

It combines two test methods: a “fine” method for air filters in the higher efficiency range and a “coarse”

method for filters of lower efficiency. In either case, a flat-sheet media sample or media pack sample from an

identical filter is conditioned (discharged) to provide information about the intensity of the electrostatic removal

mechanism. After determination of its initial efficiency, the untreated filter is loaded with synthetic dust in a

single step until its final test pressure drop is reached. Information on the loaded performance of the filter is

then obtained.

The performance results thus obtained cannot alone be quantitatively applied to predict in-service

performance with regard to efficiency and lifetime, so other factors influencing performance are presented in

Annexes A and B.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 2854, Statistical interpretation of data — Techniques of estimation and tests relating to means and

variances

ISO 5167-1:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular

cross-section conduits running full — Part 1: General principles and requirements

ISO 12103-1:1997, Road vehicles — Test dust for filter evaluation — Part 1: Arizona test dust

ISO 21501-1, Determination of particle size distribution — Single particle light interaction methods — Part 1:

Light scattering aerosol spectrometer

ISO 21501-4, Determination of particle size distribution — Single particle light interaction methods — Part 4:

Light scattering airborne particle counter for clean spaces
JIS Z 8901:1995, Test powders and test particles
1) Japanese Industrial Standard.
© ISO 2009 – All rights reserved 1
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ISO/TS 21220:2009(E)
3 Terms, definitions, symbols and abbreviated terms

For the purposes of this document, the following terms, definitions, symbols and abbreviated terms apply.

3.1
arrestance
weighted (mass) removal of loading dust by a filter

NOTE It is expressed as the percentage of the dust captured by the filter in terms of the mass of the total dust fed

into it.
3.2
average arrestance

ratio of the total amount of loading dust retained by the filter to the total amount of dust fed up to the final test

pressure drop
3.3
charged filter
filter in which the filter media is electrostatically charged or polarized
3.4
conditioned efficiency

efficiency of the conditioned filter media operating at an average media velocity corresponding to the test air

flow rate in the filter
3.5
counting rate
number of counting events per unit of time
3.6
correlation ratio

ratio of downstream to upstream particle counts without the test filter in the test duct

3.7
DEHS
DiEthylHexylSebacate
liquid used for generating the DEHS test aerosol
3.8
dust loaded efficiency

efficiency of the filter operating at test flow rate and after dust loadings up to the final test pressure drops

3.9
effective filtering area
area of filter medium in the filter which collects dust
3.10
filter face area
frontal face area of the filter including the header frame
NOTE Nominal values: 0,61 m × 0,61 m (24 in × 24 in).
3.11
filter face velocity
air flow rate divided by the filter face area
2 © ISO 2009 – All rights reserved
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ISO/TS 21220:2009(E)
3.12
final filter

air filter used to collect the loading dust passing through or shedding from the filter under test

3.13
final test pressure drop
pressure drop of the filter up to which the filtration performance is measured
3.14
initial efficiency
efficiency of the clean untreated filter operating at the test air flow rate
3.15
initial pressure drop
pressure drop of the clean filter operating at the test air flow rate
3.16
isokinetic sampling

sampling of the air within a duct such that the probe inlet air velocity is the same as the velocity in the duct at

the sampling point
3.17
KCl

solid potassium chloride (KCl) particles generated from an aqueous solution and used as a test aerosol

3.18
loading dust
synthetic test dust
test dust specifically formulated for loading of the filter

NOTE Two types of loading dusts are used: ISO 12103-A fine test dust is used for the loading of filters according to

the fine dust method and ASHRAE dust is used for the filters tested according to the coarse method.

3.19
mean diameter
geometric mean of the upper and lower border diameters in a size range
3.20
media velocity
air flow rate divided by the effective filtering area
NOTE It is expressed to an accuracy of three significant figures.
3.21
minimum efficiency
lowest efficiency of initial, conditioned or dust loaded efficiencies
3.22
neutralization

process by which the aerosol is brought to a Boltzmannn charge equilibrium distribution with bipolar ions

3.23
particle bounce
behaviour of particles that impinge on the filter without being retained
3.24
particle size
equivalent optical diameter of a particle
© ISO 2009 – All rights reserved 3
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ISO/TS 21220:2009(E)
3.25
particle number concentration
number of particles per unit volume of the test air
3.26
penetration
ratio of the particle concentration downstream to upstream of the filter
3.27
recommended final pressure drop

maximum operating pressure drop of the filter as recommended by the manufacturer at rated air flow

3.28
re-entrainment
release to the air flow of particles previously collected on the filter
3.29
shedding

release to the air flow of particles due to particle bounce and re-entrainment as well as the release of fibres or

particulate matter from the filter or filtering material
3.30
test air flow rate
volumetric rate of air flow through the filter under test
3.31
test aerosol
aerosol used for determining the efficiency of the filter
3.32
test dust capacity
TDC
dust holding capacity (deprecated)
DHC (deprecated)
amount of loading dust kept by the filter at the final test pressure drop
A Arrestance, %
A Average arrestance during test to final test pressure drop, %
CL Concentration limits of particle counter
C Coefficient of variation
C Coefficient of variation in size range i
V,i
C Mean of measuring points value for size range i
mean,i
DEHS DiEthylHexylSebacate
d Geometric mean of size range i, µm
d Lower border diameter in a size range, µm
d Upper border diameter in a size range, µm
E Average efficiency in size range i
m Mass passing filter, g
m Mass of dust downstream of the test filter, g
m Cumulative mass of dust fed to filter, g
tot
m Mass of final filter before dust increment, g
4 © ISO 2009 – All rights reserved
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ISO/TS 21220:2009(E)
m Mass of final filter after dust increment, g
N Number of points
N Number of particles downstream of the filter
N Number of particles in size range i downstream of the filter
d,i
N Average number of particles downstream of the filter
N Number of particles upstream of the filter
N Number of particles in size range i upstream of the filter
u,i
N Average number of particles upstream of the filter
n Exponent
OPC Optical particle counter
p Pressure, Pa (in WG)
p Absolute air pressure upstream of filter, kPa (in WG)
p Air flow meter static pressure, kPa (lb/in )
q Mass flow rate at air flow meter, kg/s (lb/s)
3 3
q Air flow rate at filter, m /s (ft /min)
R Correlation ratio
R Correlation ratio for size range i
T Temperature upstream of filter, °C (°F)
T Temperature at air flow meter, °C (°F)
TDC Test dust capacity, g [formerly dust holding capacity (DHC)]
Distribution variable
( )
U Uncertainty, % units
v Mean value of velocity, m/s (ft/min)
mean
δ Standard deviation
ν Number of degrees of freedom
3 3
ρ Air density, kg/m (lb/ft )
ϕ Relative humidity upstream of filter, %
∆m Dust increment, g
∆m Mass gain of final filter, g
∆p Filter pressure drop, Pa (in WG)
∆p Air flow meter differential pressure, Pa (in WG)
∆p Filter pressure drop at air density 1,20 kg/m , Pa (in WG)
1,20
2) Water inch gauge (non-SI unit).
© ISO 2009 – All rights reserved 5
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ISO/TS 21220:2009(E)
4 Filter

The filter shall be designed or marked so as to prevent incorrect mounting. It shall be designed so that when

correctly mounted in the ventilation duct, no air/dust leaks occur around the exterior filter frame or duct sealing

surfaces.

The complete filter (filter and frame) shall be made of materials suitable for withstanding normal usage and

exposure to the range of temperature, humidity and corrosive environments likely to be encountered in service.

The complete filter shall be designed to withstand mechanical constraints that are likely to be encountered

during normal use. Dust or fibre released from the filter media by air flow through the filter shall not constitute

a hazard or nuisance for people or devices exposed to filtered air.
5 Classification/rating

Filters are not classified or rated by this Technical Specification. Many national bodies and associations use

3 3 3

0,944 m /s (2 000 ft /min or 3 400 m /h) as the nominal air flow for classification or rating of air filters that are

a nominal 0,61 m × 0,61 m (24 in × 24 in) in face area. It is therefore recommended that filters be tested at

0,944 m /s (if the manufacturer does not specify any other flow for another application). The air flow velocity

associated with the volumetric flow is 2,54 m/s (500 ft/min).
6 Test rig and equipment
6.1 Test conditions

Either room air or outdoor air may be used as the test air source. Relative humidity shall be less than 65 % for

the KCl efficiency measurement and less than 75 % in the other tests. The exhaust flow may be discharged

outdoors, indoors or recirculated.

NOTE Requirements on certain measuring equipment can impose limits on the temperature of the test air.

Filtration of the exhaust flow is recommended when test aerosol, loading dust or odours from the filter can be

present.
6.2 Test rig

The test rig (see Figure 1) shall consist of several square duct sections with 610 mm × 610 mm (24 in × 24 in)

nominal inner dimensions except for the section where the filter is installed. This section shall have nominal

inner dimensions between 616 mm (24,25 in) and 622 mm (24,50 in). The length of this duct section shall be

at least 1,1 times the length of the filter, with a minimum length of 1 m (39,4 in).

The duct material shall be electrically conductive and electrically grounded, and shall have a smooth interior

finish and be sufficiently rigid to maintain its shape at the operating pressure. Smaller parts of the test duct

could be made in glass or plastic in order to make the filter and equipment visible. Provision of windows to

allow monitoring of test progress is desirable.

High-efficiency filters shall be placed upstream of section 1, as indicated in Figure 1, in which the aerosol for

efficiency testing is dispersed and mixed to create a uniform concentration upstream of the filter.

Section 2 includes in the upstream section the mixing orifice (3) in the centre of which the dust feeder

discharge nozzle is located. Downstream of the dust feeder is a perforated plate (11) intended to achieve a

uniform dust distribution. In the last third of this duct section is the upstream aerosol sample head. For dust

loading tests, this sampling head shall be blanked off or removed.

To avoid turbulence, the mixing orifice and the perforated plate should be removed during the efficiency test.

To avoid systematic error, removal of these items during pressure drop measurements is recommended.

6 © ISO 2009 – All rights reserved
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ISO/TS 21220:2009(E)

Section 5 may be used for both efficiency and dust loading measurements and is fitted with a final filter for the

loading test and with the downstream sampling head for the efficiency test. Section 5 could also be duplicated,

allowing one part to be used for the loading test and the other for the efficiency test.

The test rig can be operated in either a negative or positive pressure air flow arrangement. In the case of

positive pressure operation (i.e. the fan upstream of the test rig), the t
...

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