ISO/TS 21220:2009

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 2009
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ii © ISO 2009 – All rights reserved

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
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

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.
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

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
1)
JIS Z 8901:1995, Test powders and test particles

1) Japanese Industrial Standard.
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
A
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
A
m
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

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
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, %
m
CL Concentration limits of particle counter
C Coefficient of variation
V
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
i
d Lower border diameter in a size range, µm
l
d Upper border diameter in a size range, µm
u
E Average efficiency in size range i
i
m Mass passing filter, g
m Mass of dust downstream of the test filter, g
d
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

m Mass of final filter after dust increment, g
N Number of points
N Number of particles downstream of the filter
d
N Number of particles in size range i downstream of the filter
d,i
N Average number of particles downstream of the filter
d
N Number of particles upstream of the filter
u
N Number of particles in size range i upstream of the filter
u,i
N Average number of particles upstream of the filter
u
n Exponent
OPC Optical particle counter
2)
p Pressure, Pa (in WG)
p Absolute air pressure upstream of filter, kPa (in WG)
a
p Air flow meter static pressure, kPa (lb/in )
sf
q Mass flow rate at air flow meter, kg/s (lb/s)
m
3 3
q Air flow rate at filter, m /s (ft /min)
V
R Correlation ratio
R Correlation ratio for size range i
i
T Temperature upstream of filter, °C (°F)
T Temperature at air flow meter, °C (°F)
f
TDC Test dust capacity, g [formerly dust holding capacity (DHC)]
Distribution variable
t
α
1−
( )
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
ff
∆p Filter pressure drop, Pa (in WG)

∆p Air flow meter differential pressure, Pa (in WG)
f
∆p Filter pressure drop at air density 1,20 kg/m , Pa (in WG)
1,20
2) Water inch gauge (non-SI unit).
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

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 test aerosol and loading dust could leak
into the laboratory, while at negative pressure particles could leak into the test system and affect the number
of measured particles. These possible air leaks shall be located and sealed prior to filter testing.
The dimensions of the test rig and the position of the pressure taps are shown in Figure 2. Additional duct
details are shown in Figure 3.
The pressure drop of the tested filter shall be measured using static pressure taps located as shown in
Figure 3. Pressure taps shall be provided at four points over the periphery of the duct and connected together
by a ring line.
The entry plenum and the relative location of high-efficiency filters and aerosol injections are discretionary and
a bend in the duct is optional, thereby allowing both straight duct and U-shaped duct configurations. Except for
the bend itself, all dimensions and components are the same for straight and U-shaped configurations. A
downstream mixing baffle shall be included in the duct after the bend, whose purpose is to straighten out the
flow and mix any aerosol that is downstream of the bend.
6.3 DEHS test aerosol generation
The test aerosol shall consist of untreated and undiluted DEHS, or other aerosols in accordance with 8.2. A
test aerosol of DEHS (DiEthylHexylSebacate) produced by a Laskin nozzle aerosol generator is widely used
in the performance testing of high-efficiency filters.
Figure 4 gives an example of a system for generating the aerosol. It consists of a small container with DEHS
liquid and a Laskin nozzle. The aerosol is generated by feeding compressed particle-free air through the
Laskin nozzle. The atomized droplets are then directly introduced into the test rig. The pressure and air flow to
the nozzle are varied according to the test flow and the required aerosol concentration. For a test flow of
3 3 2
0,944 m /s (2 000 ft /min), the pressure is about 17 kPa (2,5 lb/in ), corresponding to an air flow of about
3 3 3
0,39 dm /s [1,4 m /h (0,82 ft /min)] through the nozzle.
Any other generator capable of producing droplets in sufficient concentrations in the size range of 0,3 µm to
1,0 µm may be used.
Before testing, regulate the upstream concentration so as to reach steady state and obtain a concentration
below the coincidence level of the particle counter.

Key
1 inlet point for DEHS particles
2 high-efficiency filter (at least 99,97 % on 0,3 µm particles)
3 mixing orifice
4 upstream sampling head
5 downstream sampling head
6 duct section of the test rig
7 duct section of the test rig
8 duct section including the filter to be tested
9 filter to be tested
10 duct section of the test rig
11 perforated plate
12 dust injection nozzle
13 duct section of the test rig (entry plenum)
Figure 1 — Test rig — Schematic diagram
Dimensions in millimetres
Figure 2 — Test rig dimensions
8 © ISO 2009 – All rights reserved

Dimensions in millimetres
Key
1 mixing orifice
2 perforated plate with ∅ (152 ± 2) mm and 40 % open area
3 pressure tap
4 transition duct — test filter smaller than duct
5 transition duct — test filter larger than duct
L length
W width
Figure 3 — Test duct component details
Dimensions in millimetres
Key
1 Laskin nozzle
2 test aerosol (for instance DEHS)
3 hole, four of ∅ 1,0 mm, 90° apart, vis a vis hole top edge and just touching the bottom of the collar
4 hole, four of ∅ 2,0 mm next to tube, in line with radial holes
a 2
Particle-free air [pressure aprox. 17 kPa (2,5 lb/in )].
b
Aerosol to test rig.
Figure 4 — DEHS particle generation system
6.4 KCl test aerosol generation
The test aerosol shall comprise solid-phase dry potassium chloride (KCl) in particulate form, generated from
an aqueous solution.
The aerosol is generated by nebulizing an aqueous KCl solution with an external mixing air atomizing nozzle,
as shown in Figure 5. Operate the spray nozzle at a relatively low air pressure to keep the particle
concentrations in the duct below the coincidence error concentration limit of the particle counter.
Position the nozzle at the top of a 305 mm (12 in) diameter, 1 300 mm (51 in) high transparent acrylic spray
tower. This high tower serves two purposes: it allows the salt droplets to dry by providing an approximately
40 s mean residence time and larger-sized particles to fall out of the aerosol.
Use an aerosol neutralizer to reduce the charge level on the aerosol until the level is equivalent to a
Boltzmann charge distribution, the average charge found in ambient air. Electrostatic charging is an
unavoidable consequence of most aerosol generation methods.
Inject the aerosol in the entry plenum counter to the air flow in order to improve the mixing of the aerosol with
the airstream.
10 © ISO 2009 – All rights reserved

Prepare the KCl solution by combining 300 g of KCl with 1 kg of distilled water. Feed the solution to the
atomizing nozzle at 1,2 ml/min by a metering pump. Varying the operating air pressure of the generator allows
control of the challenge aerosol concentration.

Key
1 air control panel (rotometers with needle valve and outlet pressure gauge)
2 99,97 % efficiency filters (0,3 µm)
3 3
3 atomizing air — 0,000 5 m /s (1 ft /min) nominal (adjusted speed)
4 air atomizing nozzle
5 spray tower — 305 mm (12 in) diameter, 1 300 mm (51 in) height
6 metering pump 1,2 ml/min, 30 % mass fraction KCl in water (solution)
7 aerosol charger neutralizer
8 disk — 152 mm (6 in) outer diameter — to create turbulence in airstream and mix aerosol
3 3
9 drying air — 0,001 9 m /s (4 ft /min)
10 tube — 38 mm (1,5 in) inner diameter — with outlet towards airstream
a
Clean, dry compressed air source.
Figure 5 — KCl particle generator system — Schematic diagram
6.5 Aerosol sampling system
In the aerosol sampling system, two sample lines of equal length and equivalent geometry (bends and straight
lengths) shall connect the upstream and downstream sampling heads to the particle counter. The sample
tubes shall be electrically conducting or have a high dielectric constant. The tubing shall have a smooth inside
surface (steel, tygon, etc.).
Tapered sampling probes shall be placed in the centre of the upstream and downstream measuring sections.
The sampling heads shall be centrally located with the inlet tip facing the inlet of the rig parallel to the air flow.
3 3
The sampling shall be isokinetic within 10 % at a test flow rate of 0,944 m /s (2 000 ft /min).
Three one-way valves shall be used to make it possible to sample the aerosol upstream or downstream of the
filter under test, or to have a “blank” suction through a high-efficiency filter. These valves shall be of a
straight-through design. Due to possible particle losses from the sampling system, the first measurement after
a valve is switched should be ignored.
The flow rate can be maintained by the pump in the counter in the case of a particle counter with a high flow
-3 3 3
rate [e.g. 0,47 × 10 m /s (1 ft /min)] or by an auxiliary pump in the case of a counter with smaller sample
flow rates. The exhaust line (to the pump) shall then be fitted with an isokinetic sampling nozzle directly
connected to the particle counter to achieve isokinetic conditions within a tolerance of ± 10 %.
Particle losses will occur in the test duct, aerosol transport lines and particle counter. Minimization of particle
losses is desirable because a smaller number of counted particles will mean larger statistical errors and thus
less accurate results. The influence of particle losses on the result is minimized if the upstream and
downstream sampling losses are made as nearly equal as possible.
Figure 6 shows an example of an aerosol sampling system.

Key
1 filter
2 high-efficiency filter (clean air)
3 valve, upstream
4 valve, clean air
5 valve, downstream
6 computer
7 particle counter
8 pump
Figure 6 — Aerosol sampling system — Schematic diagram
12 © ISO 2009 – All rights reserved

6.6 Flow measurement
Flow measurement shall be made using standardized flow measuring devices in accordance with ISO 5167-1.
EXAMPLE Orifice plates, nozzles, Venturi tubes.
The uncertainty of measurement shall not exceed 5 % of the measured value at 95 % confidence level.
6.7 Particle counter
This method requires the use of an optical particle counter (OPC) having a particle size range of at least
0,3 µm to 5,5 µm or two counters covering the size range 0,3 µm to 1,2 µm and 1 µm to 5,5 µm. The counting
efficiency shall be (50 ± 20) % for calibration particles with a size close to the minimum detectable size and
(100 ± 10) % for calibration particles 1,5 to 2 times larger than the minimum detectable particle size. Each size
range shall be divided into at least five size classes, the boundaries of which should be approximately
equidistant on a logarithmic scale. If a single counter is used to cover the entire size range, a minimum of
eight size classes are required.
The number of particle size measurements will enable the user to generate a curve of efficiency vs. particle
size data covering at least the 0,3 µm to 5,5 µm particle size range. The efficiency can then be calculated (by
interpolation) for any given geometric particle size, for example 0,4 µm, 1 µm, 1,5 µm, 2,5 µm and 5 µm.
The efficiency measurements may be made with one particle counter sampling sequentially upstream and
downstream or performed with two particle counters sampling simultaneously. If two particle counters are
used, they shall be closely matched in design and sampling flow rate.
Clause 7 contains further information and details about the calibration and operation of an OPC used for this
test.
An example of how a single or dual particle counter system might be configured is given by Table 1.
6.8 Differential pressure-measuring equipment
Measurements of pressure drop shall be taken between measuring points located in the duct wall as shown in
Figure 2. Each measuring point shall comprise four interconnected static taps equally distributed around the
periphery of the duct cross-section.
The pressure-measuring equipment used shall be capable of measuring pressure differences with an
accuracy of ± 2 Pa (± 0,01 in WG) in the range 0 Pa to 70 Pa (0,28 in WG). Above 70 Pa (0,28 in WG), the
accuracy shall be ± 3 % of the measured value.
6.9 Dust feeder
The purpose of the dust feeder is to supply the synthetic dust to the filter under test at a constant rate over the
test period. The general design of the dust feeder and its critical dimensions are as shown and given in
Figures 7 and 8. Any dust feeder may be chosen as long as it gives the same test result as the described dust
feeder.
The angle between the dust pickup tube and dust feed tray is 90° as shown in Figure 7 but could be less in
real application. A certain mass of dust previously weighed is loaded into the mobile dust feeder tray. The tray
moves at a uniform speed and the dust is taken up by a paddle wheel and carried to the slot of the dust pickup
tube of the ejector.
The ejector disperses the dust with compressed air and directs it into the test rig through the dust feed tube.
The dust injection nozzle shall be positioned at the entrance of duct section 2 (see Figure 1) and be collinear
with the duct centre line.
Backflow of air through the pickup tube from the positive duct pressure shall be prevented when the feeder is
not in use.
Table 1 — Dual/single particle counter system configuration — Examples
Dual counter example
Channel Geometric mean
boundaries diameter of range
Class
µm µm
Counter 1, fine range
Class 1 0,3–0,4 0,35
Class 2 0,4–0,52 0,46
Class 3 0,52–0,7 0,6
Class 4 0,7–0,9 0,8
Class 5 0,9–1,2 1,0
Counter 2, coarse range
Class 1 1,0–1,4 1,2
Class 2 1,4–2,0 1,7
Class 3 2,0–2,8 2,4
Class 4 2,8–4,0 3,4
Class 5 4,0–5,5 4,7
Single counter example
Channel Geometric mean
boundaries diameter of range
Class
µm µm
Complete range
Class 1 0,3–0,45 0,4
Class 2 0,45–0,65 0,5
Class 3 0,65–1,0 0,8
Class 4 1,0–1,5 1,2
Class 5 1,5–2,2 1,8
Class 6 2,2–3,0 2,6
Class 7 3,0–4,0 3,5
Class 8 4,0–5,5 4,7
The degree of dust dispersion by the feeder is dependent on the characteristics of the compressed air, the
geometry of the aspirator assembly and the rate of air flow through the aspirator. The aspirator Venturi is
subject to wear from the aspirated dust and will become enlarged with use. Its dimension shall be monitored
periodically to ensure that the tolerances shown in Figure 8 are met.
The gauge pressure on the air line to the Venturi, corresponding to an air flow of the dust-feeder pipe of
–3 3 –3 3 3 3
6,8 × 10 m /s ± 0,24 × 10 m /s (14,5 ft /min ± 0,5 ft /min), shall be measured periodically for different
static pressures in the duct. See 7.12 for qualification requirements of the dust feeder.
14 © ISO 2009 – All rights reserved

Dimensions in millimetres
Key
1 thin-wall galvanised conduit
2 Venturi ejector
3 ejector
4 dry compressed air feed
5 dust pickup tube (0,25 mm from dust feed tray)
6 dust paddle wheel — ∅ 88,9 mm (outer dimension), 114,3 mm long with 60 teeth 5 mm deep
7 teeth in paddle wheel (60 teeth)
8 dust feed tray
9 150 W infrared-reflector lamp
a
Dust feed tube to inlet of test duct.
Figure 7 — Dust feeder assembly — Critical dimensions
Dimensions in millimetres
a) Dust pickup tube b) Ejector

c) Venturi ejector
Tolerances: for integers ± 0,8 mm
for decimals ± 0,03 mm
Figure 8 — Ejector, Venturi ejector and pickup details for the dust feeder
16 © ISO 2009 – All rights reserved

7 Qualification of test rig and apparatus
7.1 General
A summary of the qualification requirements and frequency of maintenance is given in 7.15 and 7.16.
7.2 Air velocity uniformity in the test duct
The uniformity of the air velocity in the test duct shall be determined by measuring the velocity at nine points,
located as in Figure 9, immediately
...