Particulate air filters for general ventilation — Determination of the filtration performance

ISO 21220:2008 refers to particulate air filters for general ventilation. It describes testing methods and the test rig for measuring filter performance. The test rig is designed for an air flow rate 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 21220:2008 applies to air filters having an initial efficiency of less than 99 % with respect to 0,4 µm particles. Filters in the higher end and above 99 % initial efficiency are tested and classified according to other standards. Two test methods are combined in ISO 21220:2008: a “fine method” for air filters in the higher efficiency range and a “coarse method” for lower efficiency filters. In either case, a flat sheet media sample or media pack sample from an identical filter shall be 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 one step until its final test-pressure drop is reached. Information on the loaded performance of the filter is then obtained. The performance results obtained in accordance with ISO 21220:2008 cannot, by themselves, be quantitatively applied to predict performance in service with regard to efficiency and lifetime. It is necessary to take into account other factors influencing performance.

Filtres à air de ventilation générale pour l'élimination des particules — Détermination des performances de filtration

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FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 21220
ISO/TC 142
Particulate air filters for general
Secretariat: UNI
ventilation — Determination of the
Voting begins on:
filtration performance
2008-07-15
Voting terminates on:
Filtres à air de ventilation générale pour l'élimination des particules —
2008-09-15
Détermination des performances de filtration
Please see the administrative notes on page iii
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPORT-
ING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 21220:2008(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2008
---------------------- Page: 1 ----------------------
ISO/FDIS 21220:2008(E)
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ii © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)

In accordance with the provisions of Council Resolution 15/1993, this document is circulated in the

English language only.
© ISO 2008 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 21220:2008(E)
Contents Page

Foreword............................................................................................................................................................ vi

Introduction ...................................................................................................................................................... vii

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

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

3 Terms and definitions........................................................................................................................... 1

4 Symbols and abbreviated terms.......................................................................................................... 4

5 Requirements ........................................................................................................................................ 6

6 Classification/Rating............................................................................................................................. 6

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

7.1 Test conditions...................................................................................................................................... 6

7.2 Test rig ................................................................................................................................................... 7

7.3 DEHS test aerosol generation.............................................................................................................. 9

7.4 KCl test aerosol generation ............................................................................................................... 10

7.5 Aerosol-sampling system .................................................................................................................. 12

7.6 Flow measurement.............................................................................................................................. 13

7.7 Particle counter ................................................................................................................................... 13

7.8 Differential pressure measuring equipment..................................................................................... 14

7.9 Dust feeder........................................................................................................................................... 14

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

8.1 General ................................................................................................................................................. 17

8.2 Air-velocity uniformity in the test duct ............................................................................................. 17

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

8.4 Particle-counter sizing accuracy....................................................................................................... 19

8.5 Particle-counter zero test................................................................................................................... 19

8.6 Particle-counter overload test ........................................................................................................... 20

8.7 100 % efficiency test ........................................................................................................................... 20

8.8 0 % efficiency test ............................................................................................................................... 20

8.9 Aerosol generator response time...................................................................................................... 20

8.10 Correlation ratio .................................................................................................................................. 21

8.11 Pressure-drop checking ..................................................................................................................... 21

8.12 Dust feeder air flow rate ..................................................................................................................... 22

8.13 Reference filter check......................................................................................................................... 23

8.14 Activity of the aerosol neutralizer ..................................................................................................... 24

8.15 Summary of qualification requirements ...........................................................................................24

8.16 Apparatus maintenance ..................................................................................................................... 25

9 Test materials ...................................................................................................................................... 25

9.1 Test air.................................................................................................................................................. 25

9.2 Test aerosol ......................................................................................................................................... 25

9.3 Loading dust........................................................................................................................................ 26

9.4 Final filter ............................................................................................................................................. 27

10 Test procedure .................................................................................................................................... 27

10.1 General ................................................................................................................................................. 27

10.2 Preparation of filter being tested....................................................................................................... 28

10.3 Initial pressure drop............................................................................................................................ 28

10.4 Efficiency measurement..................................................................................................................... 28

10.5 Conditioning test................................................................................................................................. 30

10.6 Dust loading......................................................................................................................................... 30

iv © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)

11 Uncertainty calculation of the test results ....................................................................................... 32

12 Reporting ............................................................................................................................................. 33

12.1 General................................................................................................................................................. 33

12.2 Interpretation of test reports ............................................................................................................. 33

12.3 Summary.............................................................................................................................................. 34

12.4 Efficiency ............................................................................................................................................. 36

12.5 Pressure drop and air flow rate......................................................................................................... 36

12.6 Marking ................................................................................................................................................ 36

Annex A (normative) Conditioning test procedure ..................................................................................... 43

Annex B (informative) Shedding from filters ............................................................................................... 47

Annex C (informative) Commentary ............................................................................................................ 49

Annex D (normative) Pressure-drop calculation ........................................................................................ 54

Bibliography ..................................................................................................................................................... 56

© ISO 2008 – All rights reserved v
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ISO/FDIS 21220:2008(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.

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

vi © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)
Introduction

The procedures described in this International Standard have been developed from those given in EN 779 and

ANSI/ASHRAE 52.2 and includes testing of performance of air filters mainly used in general ventilation

applications.

Representative samples of particles upstream and downstream the filters are analysed by an optical particle

counter (OPC) to provide filter particle size efficiency data.

Classification or rating of air filters is determined by national bodies or other associations and is not a part of

this International Standard.
A brief principle description of the method is given in Annex C.

Initiatives to address certain filtration characteristics, such as the potential problems of particle re-entrainment,

shedding and the in-service charge neutralization characteristics of certain types of media, have been

included in Annexes A and B.

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 normative test procedure, described in

Annex A, provides techniques for identifying this type of behaviour. This procedure is used 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. The procedure is selected because it is well

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

is 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 a captured particle and dislodge it into the air stream. Fibres or particles

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

important to know this; see Annex B.
Annexes A and D form a normative part of this International Standard.
Annexes B and C are for information only.
© ISO 2008 – All rights reserved vii
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 21220:2008(E)
Particulate air filters for general ventilation — Determination
of the filtration performance
1 Scope

This International Standard refers to particulate air filters for general ventilation. It describes testing methods

and the test rig for measuring filter performance. The test rig is designed for an air flow rate between

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

This International Standard applies to air filters having an initial efficiency of less than 99 % with respect to

0,4 µm particles. Filters in the higher end and above 99 % initial efficiency are tested and classified according

to other standards.

Two test methods are combined in this International Standard: a “fine method” for air filters in the higher

efficiency range and a “coarse method” for lower efficiency filters. In either case, a flat sheet media sample or

media pack sample from an identical filter shall be 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 one step until its

final test-pressure drop is reached. Information on the loaded performance of the filter is then obtained.

The performance results obtained in accordance with this International Standard cannot, by themselves, be

quantitatively applied to predict performance in service with regard to efficiency and lifetime. It is necessary to

take into account other factors influencing performance, as described 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, Measurement of fluid flow by means of pressure differential devices inserted in circular

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

3 Terms and definitions
3.1
arrestance
weighted (mass) removal of loading dust
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 final test

pressure drop
© ISO 2008 – All rights reserved 1
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ISO/FDIS 21220:2008(E)
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
DES

liquid di(2-ethylhexyl)sebacate or bis(2-ethylhexyl)sebacate used for generating the DEHS test aerosol

See 9.2.1.
3.8
dust-holding capacity (deprecated)
See test dust capacity (3.35).
3.9
dust-loaded efficiency

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

3.10
effective filtering area
area of filter medium in the filter that collects dust
3.11
efficiency

See initial efficiency (3.17), conditioned efficiency (3.4) or dust-loaded efficiency (3.9).

3.12
filter-face area
frontal face area of the filter including the header frame
NOTE The nominal values are 0,61 m × 0,61 m (24 in × 24 in).
3.13
filter-face velocity
air flow rate divided by the filter-face area
3.14
final filter

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

3.15
final pressure drop, recommended

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

2 © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)
3.16
final test pressure drop
pressure drop of the filter up to which the filtration performance is measured
3.17
initial efficiency
efficiency of the clean, untreated filter operating at the test air flow rate
3.18
initial pressure drop
pressure drop of the clean filter operating at the test air flow rate
3.19
isokinetic sampling

sampling of the air within a duct under conditions such that the probe inlet air velocity is the same as the

velocity in the duct at the sampling point
3.20
KCl

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

3.21
loading dust
test dust specifically formulated for loading of the filter

NOTE Two types of loading dusts are used: ISO fine test dust is used for the loading of filters in accordance with the

fine-dust method and ASHRAE dust is used for the filters tested in accordance with the coarse method.

3.22
mean diameter
geometric mean of the upper- and lower-limit diameters in a size range
3.23
medium velocity
air flow rate divided by the effective filtering area

NOTE The medium velocity is expressed to an accuracy of three significant figures.

3.24
minimum efficiency
lowest efficiency among the initial, conditioned or dust-loaded efficiencies
3.25
neutralization

bringing the aerosol to a Boltzmann charge equilibrium distribution with bipolar ions

3.26
particle bounce
behaviour of particles that impinge on the filter without being retained
3.27
particle size
equivalent optical diameter of a particle
3.28
particle-number concentration
number of particles per unit volume of the test air
© ISO 2008 – All rights reserved 3
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ISO/FDIS 21220:2008(E)
3.29
penetration
ratio of the particle concentration downstream to that upstream of the filter
3.30
re-entrainment
releasing of particles previously collected on the filter into the air flow
3.31
shedding

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

or particulate matter from the filter or filtering material
3.32
synthetic test dust
See loading dust (3.21).
3.33
test air flow rate
volumetric rate of air flow through the filter under test
3.34
test aerosol
aerosol used for determining the efficiency of the filter
3.35
test dust capacity
TDC
amount of loading dust kept by the filter at final test pressure drop
4 Symbols and abbreviated terms

For the application of this International Standard, the following symbols and abbreviated terms apply.

A Arrestance, expressed in percent

A Average arrestance during test to final test pressure drop, expressed in percent

ANSI American National Standards Institute
ASHRAE American Society of Heating, Refrigerating and Air Conditioning Engineers
ASTM American Society for Testing and Materials
CL Concentration limits of particle counter
C Coefficient of variation
C Coefficient of variation in size range, i
V,i
c Subscript indicating that the sample is conditioned
c Mean of measuring points value for size range, i
mean,i
CAS Chemical Abstracts Service
CEN European Committee for Standardization
d Geometric mean of a size range, expressed in micrometres
d Lower-limit diameter in a size range, expressed in micrometres
d Upper-limit diameter in a size range, expressed in micrometres
DHC Dust holding capacity, replaced by test dust capacity, TDC
4 © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)
Average efficiency in a size range, i
Average efficiency of conditioned samples in size range, i
i,c
Efficiency of conditioned sample “s” in size range, i
is,c,
Average initial efficiency of untreated samples in size range, i
i,u
Initial efficiency of untreated sample “s” in size range, i
is,u,
EN European Standard

EUROVENT European Committee of Air Handling and Refrigeration Equipment Manufacturers

ISO International Organization for Standardization
IPA Isopropanol
i Subscript indicating the size range
m Mass passing filter, expressed in grams
m Mass of dust downstream of the test filter, expressed in grams
m Cumulative mass of dust fed to filter, expressed in grams
tot
m Mass of final filter before dust increment, expressed in grams
m Mass of final filter after dust increment, expressed in grams
N Number of particles upstream of the filter
N Number of particles in size range, i, upstream of the filter
u,i
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; see Annex D
OPC Optical particle counter
p Pressure, expressed in pascals [inches water, gauge (inWG)]

p Absolute air pressure upstream of filter, expressed in kilopascals [inches water, gauge (inWG)]

p Average pressure drop of conditioned samples
p Pressure drop of conditioned sample “s”
c,s

p Air flow meter static pressure, expressed in kilopascals (pounds per square inch)

p Average initial pressure drop of untreated samples
p Pressure drop of untreated sample “s”
u,s
PAO Polyalphaolefins

q Mass flow rate at air flow meter, expressed in kilograms per second (pounds per second)

q Air flow rate at filter, expressed in cubic metres per second (cubic feet per minute)

q Air flow rate at air flow meter, expressed in cubic metres per second (cubic feet per minute)

R Correlation ratio
R Correlation ratio for size range, i
s Subscript indicating sample number (1, 2, 3, ...)
© ISO 2008 – All rights reserved 5
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ISO/FDIS 21220:2008(E)

T Temperature upstream of filter, expressed in degrees Celsius (degrees Fahrenheit)

T Temperature at air flow meter, expressed in degrees Celsius (degrees Fahrenheit)

Distribution variable
TDC Test dust capacity, expressed in grams
U Uncertainty, expressed in percent
v Mean value of velocity, expressed in metres per second (feet per minute)
mean
δ Standard deviation
ν Number of degrees of freedom
ρ Air density, expressed in kilograms per cubic metre (pounds per cubic foot)
ϕ Relative humidity upstream of filter, expressed in percent
∆m Dust increment, expressed in grams
∆m Mass gain of final filter, expressed in grams
∆p Filter pressure drop, expressed in pascals [inches water, gauge (inWG)]

∆p Air flow meter differential pressure, expressed in pascals [inches water, gauge (inWG)]

∆p Filter pressure drop at air density 1,20 kg/m , expressed in pascals [inches water, gauge (inWG)]

1,20
5 Requirements

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

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

duct sealing surfaces.

The complete filter (filter and frame) shall be made of material suitable to withstand 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 so that it can 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 the people (or devices) exposed to filtered air.

6 Classification/Rating
Filters are not classified or rated in this International Standard.
3 3 3

Many national and association bodies use 0,944 m /s (2 000 ft /min or 3 400 m /h) as nominal air flow for

classification or rating of air filters that have a nominal face area of 0,61 m × 0,61 m (24 in × 24 in). It is,

therefore, recommended to test filters 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).

7 Test rig and equipment
7.1 Test conditions

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 other tests. The exhaust flow may be discharged outdoors,

indoors or recirculated. Requirements of certain measuring equipment can impose limits on the temperature of

the test air.
6 © ISO 2008 – All rights reserved
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ISO/FDIS 21220:2008(E)

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

present.
7.2 Test rig

The test rig (see Figure 1) consists 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 has 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, shall have a smooth interior finish

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

may be
...

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