SIST EN ISO 16911-1:2014

SLOVENSKI STANDARD
01-julij-2014
(PLVLMHQHSUHPLþQLKYLURY5RþQRLQDYWRPDWVNRGRORþHYDQMHKLWURVWLLQ
YROXPHQVNHJDSUHWRNDYRGYRGQLNLKGHO5RþQDUHIHUHQþQDPHWRGD,62

Stationary source emissions - Manual and automatic determination of velocity and
volume flow rate in ducts - Part 1: Manual reference method (ISO 16911-1:2013)
Emissionen aus stationären Quellen - Manuelle und automatische Bestimmung der
Geschwindigkeit und des Volumenstroms in Abgaskanälen - Teil 1: Manuelles
Referenzverfahren (ISO 16911-1:2013)
Émissions de sources fixes - Détermination manuelle et automatique de la vitesse et du
débit-volume d'écoulement dans les conduits - Partie 1: Méthode de référence manuelle
(ISO 16911-1:2013)
Ta slovenski standard je istoveten z: EN ISO 16911-1:2013
ICS:
13.040.40 (PLVLMHQHSUHPLþQLKYLURY Stationary source emissions
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 16911-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2013
ICS 13.040.40
English Version
Stationary source emissions - Manual and automatic
determination of velocity and volume flow rate in ducts - Part 1:
Manual reference method (ISO 16911-1:2013)
Émissions de sources fixes - Détermination manuelle et Emissionen aus stationären Quellen - Manuelle und
automatique de la vitesse et du débit-volume d'écoulement automatische Bestimmung der Geschwindigkeit und des
dans les conduits - Partie 1: Méthode de référence Volumenstroms in Abgaskanälen - Teil 1: Manuelles
manuelle (ISO 16911-1:2013) Referenzverfahren (ISO 16911-1:2013)
This European Standard was approved by CEN on 23 February 2013.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 16911-1:2013: E
worldwide for CEN national Members.

Contents Page
Foreword . 3

Foreword
This document (EN ISO 16911-1:2013) has been prepared by Technical Committee CEN/TC 264 “Air quality",
the secretariat of which is held by DIN, in collaboration with Technical Committee ISO/TC 146 "Air quality".
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by September 2013, and conflicting national standards shall be
withdrawn at the latest by September 2013.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
INTERNATIONAL ISO
STANDARD 16911-1
First edition
2013-03-01
Stationary source emissions — Manual
and automatic determination of velocity
and volume flow rate in ducts —
Part 1:
Manual reference method
Émissions de sources fixes — Détermination manuelle et automatique
de la vitesse et du débit-volume d’écoulement dans les conduits —
Partie 1: Méthode de référence manuelle
Reference number
ISO 16911-1:2013(E)
©
ISO 2013
ISO 16911-1:2013(E)
© ISO 2013
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
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Published in Switzerland
ii © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
4.1 Symbols . 3
4.2 Abbreviated terms . 7
5 Principle . 7
5.1 General . 7
5.2 Principle of flow velocity determination at a point in the duct . 8
5.3 Principle of measurement of volume flow rate . 8
6 Selection of monitoring approach .10
6.1 Monitoring objective .10
6.2 Choice of technique to determine point flow velocity .11
6.3 Choice of technique for volume flow rate and average flow determination .12
7 Measuring equipment .12
7.1 General .12
7.2 Measurement of duct area .13
8 Performance characteristics and requirements .13
9 Measurement procedure .14
9.1 Site survey before testing .14
9.2 Determination of sampling plane and number of measurement points .14
9.3 Checks before sampling .14
9.4 Quality control .16
9.5 Measurement of flow at locations within the measurement plane .16
9.6 Post-measurement quality control .17
10 Calculation of results .17
10.1 General .17
10.2 Measurement of velocity .17
10.3 Determination of the mean velocity .18
10.4 Correction of average velocity for wall effects .18
10.5 Calculation of the volume flow rate from the average velocity .18
10.6 Conversion of results to standard conditions.19
11 Establishment of the uncertainty of results .20
12 Evaluation of the method .20
Annex A (normative) Measurement of velocity using differential pressure based techniques .22
Annex B (normative) Vane anemometer .34
Annex C (normative) Tracer gas dilution method determination of volume flow rate and
average velocity .40
Annex D (normative) Transit time tracer gas method determination of average velocity .46
Annex E (normative) Calculation of flue gas volume flow rate from energy consumption .53
Annex F (informative) Example of uncertainty budget established for velocity and volume flow
rate measurements by Pitot tube .61
Annex G (informative) Description of validation studies .72
ISO 16911-1:2013(E)
Annex H (informative) Differential pressure measurement .79
Annex I (informative) The use of time of flight measurement instruments based on modulated
laser light .82
Annex J (informative) Relationship between this International Standard and the essential
requirements of EU Directives .83
Bibliography .84
iv © ISO 2013 – All rights reserved

ISO 16911-1:2013(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 16911-1 was prepared by the European Committee for Standardization (CEN) in collaboration with
ISO Technical Committee TC 146, Air quality, Subcommittee SC 1, Stationary source emissions.
ISO 16911 consists of the following parts, under the general title Stationary source emissions — Manual
and automatic determination of velocity and volume flow rate in ducts:
— Part 1: Manual reference method
— Part 2: Automated measuring systems
ISO 16911-1:2013(E)
Introduction
EN ISO 16911-1 describes a method for periodic determination of the axial velocity and volume flow rate
of gas within emissions ducts and stacks and for the calibration of automated flow monitoring systems
permanently installed on a stack.
EN ISO 16911-1 provides a method which uses point measurements of the flow velocity to determine
the flow profile and mean and volume flow rates. It also provides for alternative methods based on
tracer gas injection, which can also used to provide routine calibration for automated flow-monitoring
systems. A method based on calculation from energy consumption is also described. EN ISO 16911-1
provides guidance on when these alternative methods may be used.
vi © ISO 2013 – All rights reserved

INTERNATIONAL STANDARD ISO 16911-1:2013(E)
Stationary source emissions — Manual and automatic
determination of velocity and volume flow rate in ducts —
Part 1:
Manual reference method
1 Scope
EN ISO 16911-1 specifies a method for periodic determination of the axial velocity and volume flow rate
of gas within emissions ducts and stacks. It is applicable for use in circular or rectangular ducts with
measurement locations meeting the requirements of EN 15259. Minimum and maximum duct sizes are
driven by practical considerations of the measurement devices described within EN ISO 16911-1.
EN ISO 16911-1 requires all flow measurements to have demonstrable metrological traceability to
national or international primary standards.
To be used as a standard reference method, the user is required to demonstrate that the performance
characteristics of the method are equal to or better than the performance criteria defined in
EN ISO 16911-1 and that the overall uncertainty of the method, expressed with a level of confidence of
95 %, is determined and reported. The results for each method defined in EN ISO 16911-1 have different
uncertainties within a range of 1 % to 10 % at flow velocities of 20 m/s.
Methods further to these can be used provided that the user can demonstrate equivalence, based on the
[10]
principles of CEN/TS 14793.
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 20988, Air quality — Guidelines for estimating measurement uncertainty
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
EN 14789, Stationary source emissions — Determination of volume concentration of oxygen (O2) —
Reference method — Paramagnetism
EN 14790, Stationary source emissions — Determination of the water vapour in ducts
EN 15259:2007, Air quality — Measurement of stationary source emissions — Requirements for measurement
sections and sites and for the measurement objective, plan and report
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO 16911-1:2013(E)
3.1
Pitot tube
device to measure flow velocity at a point, operating on the principle of differential pressure measurement
Note 1 to entry: A number of designs of Pitot tube may be used, including standard L-type, S-type, 2D, and 3D Pitot
tubes. Annex A describes a number of Pitot designs currently in use in Europe.
3.2
measurement line
line across the stack, on a measurement plane, along which flow measurements are made to characterize
the flow velocity profile or to determine the average flow
3.3
measurement plane
plane normal to the centreline of the duct at the measurement location at which the measurement of
flow velocity or volume flow rate is required
3.4
measurement point
sampling point
position in the measurement plane at which the sample stream is extracted or the measurement data
are obtained directly
3.5
volume flow rate
volume flow of gas axially along a duct
Note 1 to entry: If not specifically stated, the term may be taken to mean the mean volume flow passing through
the measurement plane.
Note 2 to entry: Volume flow rate is expressed in cubic metres per second or cubic metres per hour.
3.6
point flow velocity
local gas velocity at a point in the duct
Note 1 to entry: Unless otherwise specified, the term may be taken to mean the axial velocity at the
measurement location.
Note 2 to entry: Point flow velocity is expressed in metres per second.
3.7
average flow velocity
<1> velocity which, when multiplied by the area of the measurement
plane of the duct, gives the volume flow rate in that duct
<2> quotient of the volume flow rate in the duct and the area of the measurement plane of the duct
3.8
standard conditions
reference value a pressure 101,325 kPa and a temperature 273,15 K
3.9
uncertainty (of measurement)
parameter, associated with the result of a measurement, that characterizes the dispersion of the values
that could reasonably be attributed to the measurand
2 © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
3.10
uncertainty budget
statement of a measurement uncertainty, of the components of that measurement uncertainty, and of
their calculation and combination
[5]
Note 1 to entry: For the purposes of EN ISO 16911-1, the sources of uncertainty are according to ISO 14956 or
ISO/IEC Guide 98-3.
3.11
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.12
expanded uncertainty
quantity defining an interval about the result of a measurement that may be expected to encompass a
large fraction of the distribution of values that could reasonably be attributed to the measurand
Note 1 to entry: In EN ISO 16911-1, the expanded uncertainty is calculated with a coverage factor of k = 2, and with
a level of confidence of 95 %.
3.13
overall uncertainty
expanded combined standard uncertainty attached to the measurement result
Note 1 to entry: The overall uncertainty is calculated according to ISO/IEC Guide 98-3.
3.14
swirl
cyclonic flow
tangential component of the flow vector providing a measure of the non-axial flow at the measurement plane
3.15
automated measuring system
AMS
measuring system permanently installed on site for continuous monitoring of flow
Note 1 to entry: See EN ISO 16911-2.
3.16
metrological traceability
property of a measurement result whereby the result can be related to a reference through a documented
unbroken chain of calibrations, each contributing to the measurement uncertainty
Note 1 to entry: The elements for confirming metrological traceability are an unbroken metrological traceability
chain to an international measurement standard or a national measurement standard, a documented measurement
uncertainty, documented measurement procedure, accredited technical competence, metrological traceability to
the SI, and calibration intervals
4 Symbols and abbreviated terms
4.1 Symbols
A area of the measurement plane m
A internal area of the measurement section m
I
A cross-sectional area of stack ft
s
B number of component B
ISO 16911-1:2013(E)
a , a angle between sensing holes °
1 2
c constant
d outer tube diameter mm
d stack diameter mm
s
e net specific energy (NSE) of the fuel as received MJ/kg
(N)
e absolute error of measurement
P
F force acting on the vane wheel N
F (i) pitch angle ratio at traverse point i 1
F (i) 3D probe velocity calibration coefficient at traverse point i 1
−1
f vane frequency s
f velocity factor
v
f wall adjustment factor
WA
i ith measurement point
K coefficient of the Pitot tube which includes the Pitot calibration factor and
constant values relating to the Pitot design
0.5
K conversion factor, 85.49 ft/s[(lb/lb-mol)(inHg)/(R)/(inH 0)]
p 2
non-linear calibration factor dependent on density, ρ , and viscosity, η
0 dyn
K ρ
)
( 0,η
dyn
k coverage factor
L length of the measuring section, i.e. the stack length between the two m
measurement levels
L probe length
p
M molar mass of wet gas effluent kg/mol
M molar mass of component B kg/mol
B
M molar mass of gas, dry basis lb-lb/mol
d
M molar mass of gas, wet basis lb-lb/mol
s
n number of measurement points
P energy production MW
p flue gas pressure kPa
p . p pressures at points P . P
1 5 1 5
p stagnation point pressure Pa
p static pressure Pa
4 © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
(p − p ) velocity differential pressure at traverse point i inH O
1 2 i 2
(p − p ) pitch differential pressure at traverse point i inH O
4 5 i 2
p atmospheric pressure inHg
atm
p absolute pressure in the duct, in the measurement section Pa
c
p dynamic pressure on the vane wheel Pa
dyn
p static pressure inH O
g 2
p stack absolute pressure inHg
s
p standard absolute pressure 29.92 inHg
std
average static pressure in the measurement section Pa
p
stat
q tracer mass flow rate kg/s
m,t
q volume flow rate m /s
V
q dry volume flow rate, under standard conditions of temperature and pres- m /s
V,0d
sure
dry volume flow rate, under standard conditions of temperature and pres- m /s
q
V,0d,O
sure and on actual oxygen concentration
dry volume flow rate, under standard conditions of temperature and pres- m /s
q
V,,0dO ,ref
sure, and reference oxygen concentration
q stack gas flow rate at sample O content and moisture under standard m /s
V,0,O
conditions
q average dry-basis stack gas volume flow rate corrected to standard condi- dscf/h
V, sd
tions
q average wet-basis stack gas volume flow rate corrected to standard condi- wscf/h
V, sw
tions
q volume flow rate under the conditions of temperature and pressure of the m /s
V,w
duct, on wet gas
R gas constant 8,314 J/(K mol)
r geometry of the vane wheel
Sp
T flue gas temperature K
T temperature of gas in the measurement section K
c
T average absolute stack gas temperature across stack R
s(avg)
T °F stack gas temperature at traverse point i °F
s(i)
T R absolute stack gas temperature at traverse point i R
s(i)
T standard absolute temperature 528 R
std
t transit time of the tracer pulse between the two measurement points s
ISO 16911-1:2013(E)
u(v) uncertainty of measurement of the flow velocity m/s
v start-up velocity m/s
v velocity corrected for flow direction m/s
c
ν local velocity at measurement point i m/s
i
v measured velocity m/s
meas
v peripheral velocity, v = ϖr
t t Sp
v axial approach velocity m/s
∞
v
mean velocity m/s
v
mean axial velocity m/s
v
v corrected mean velocity m/s
c
v average of the point velocity measurements m/s
p
w ash yield mass fraction of solid fuel as received
ash
w carbon mass fraction in fuel as received
C
w fuel mass fraction in fuel as received
f
w hydrogen mass fraction in fuel as received
H
w
moisture mass fraction in solid fuel as received
HO
w nitrogen mass fraction in fuel as received
N
w oxygen mass fraction in fuel as received
O
w sulfur mass fraction in fuel as received
S
α pitch of blade
Δp differential pressure Pa
average dynamic pressure measured at the point i of the measurement sec- Pa
Δp
i
tion
η thermal efficiency
η dynamic viscosity Pa s
dyn
θ measured angle °
meas
ρ density of the gas effluent under ambient conditions of temperature and kg/m
pressure of wet gas
σ standard deviation of the m dynamic pressure measurements in the point i
Δp
i
Φ process heat release MW
(N)F
6 © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
φ volume fraction of component B volume fraction
B
ϕ
concentration of CO in the gas stream in wet gas % volume
CO ,w
fraction
ϕ flue gas water content, wet % volume
HO
fraction
ϕ flue gas oxygen content, dry % volume
O
fraction
ϕ oxygen concentration measured in the duct during the exploration of the % volume
O,d
duct on dry gas fraction
ϕ reference oxygen concentration % volume
O,ref
fraction
ϕ
concentration of O in the gas stream in wet gas % volume
Ow,
fraction
−1
ω angular frequency s
−1
ϖ pulsatance s
4.2 Abbreviated terms
AMS automated measuring system
NSE net specific energy
SRM standard reference method
QA quality assurance
WAF wall adjustment factor
5 Principle
5.1 General
EN ISO 16911-1 provides a method for the determination of gas velocity and volume flow rate within
an emissions duct. It describes a method to determine the velocity profile of the gas flow across a
measurement plane in the duct, and a method to determine the total volume flow rate at a measurement
plane in the duct based on a grid of point velocity measurements made across the measurement plane.
In addition, alternative methods are described for the determination of volume flow rate based on the
measurement of tracer dilution, tracer transit time, and by calculation from energy consumption.
Techniques for determining gas velocity at a point include a calibrated differential pressure device
(Pitot) and a calibrated vane anemometer. Selection criteria for the use of different types of Pitot and
the vane anemometer are given in Clause 6. However, it is up to the user to ensure the method selected
for a given application meets the performance criteria defined by EN ISO 16911-1. The volume flow
rate within a duct is determined by measuring the duct axial gas velocity at a series of points along
measurement lines across the duct on a single measurement plane. The number of measurement lines
and measurement points required depends on the duct shape and size. The spacing of the measurement
points is based on the principle of equal areas as defined in EN 15259. The volume flow rate is calculated
from the average axial velocity and the duct area at the measurement plane. If required a correction is
applied to account for wall effects (see 10.4).
ISO 16911-1:2013(E)
Three alternative methods are also described to determine volume flow rate and average flow velocity.
— Annex C describes a method based on tracer dilution measurements. In this method, the volume
flow rate is determined from the dilution of a known concentration of injected tracer.
— Annex D describes a method based on a tracer transit time measurement technique. The volume flow rate
is determined from the time for a pulse of tracer gas to traverse between two measurement locations.
— Annex E describes a method to determine the volume flow rate using a calculation-based approach
to derive the flow from the energy consumption of a combustion process.
EN ISO 16911-1 provides quality control checks for the verification of the conditions for accurate
measurements.
The volume flow rate may be reported at stack conditions or may be expressed at standard conditions
(273,15 K and 101,325kPa) on either the wet or dry basis.
5.2 Principle of flow velocity determination at a point in the duct
The axial flow velocity at a point in the duct is determined using one of two techniques described in
EN ISO 16911-1: differential pressure based measurement using Pitot tubes and vane anemometry. The
annexes describe the techniques in detail, Annex A provides for the use of differential pressure based
techniques, Annex B describes the vane anemometer.
The flow velocity is determined as the duct axial velocity at each point determined according to EN 15259.
The differential pressure based techniques are based on the principle of the Pitot tube as defined in
[3]
ISO 3966. A probe with one or more pressure taps is inserted into the flow. The basic principle is that
one pressure tap is impacted by the flowing gas, and one or more other pressure taps are exposed to the
static pressure in the duct. The probe assembly allows the resultant pressure difference between these
to be measured by an external differential pressure measuring device.
Different implementations of the differential pressure approach are available. These include standard
L-type, S-type, and multi-axis Pitot tubes (3D and 2D Pitot tubes). Each has their own specific advantages
and disadvantages, and these are described in EN ISO 16911-1. The methods used are based on those
[4] [3] [14]
defined in ISO 10780, ISO 3966, and US EPA Method 2. Performance requirements and quality
assurance procedures are applied to achieve the uncertainties defined in EN ISO 16911-1.
[16]
If 2D Pitot tubes are to be used, then they should be subject to QA/QC as defined in US EPA Method 2G.
5.3 Principle of measurement of volume flow rate
5.3.1 General
Volume flow rate may be determined from a series of measurements of the point velocity in a duct made
across the measurement plane or by alternative techniques including tracer dilution, tracer transit time or
calculation from energy consumption. Annexes C, D and E provide details of these alternative approaches.
5.3.2 Principle of volume flow rate determination from point velocity measurements
Volume flow rate is determined from a number of point measurements of the axial flow velocity over a
measurement plane. Sufficient point measurements are made to characterize non-uniformities in the
flow profile. The measurement points across the measurement plane are selected to be representative
of regions of equal area. The average velocity passing through the measurement plane is calculated
with good approximation as equal to the average of the point flow measurements. The procedures
in EN 15259 are used to determine the measurement points for circular or rectangular ducts. The
tangential methodology provided in EN 15259 is used for circular ducts as described in EN ISO 16911-1.
The reason that for circular ducts, the tangential methodology is preferred from the two schemes
for determining equal areas provided for in EN 15259, is that this scheme has points which provide
8 © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
measures of the average flow in each equal area. The central point in the general method does not provide
a measure of the average flow in the central area, but rather the maximum value. This may be useful for
reconstructing the flow profile, but is not recommended for determining the average flow in the duct.
The measurement plane is selected to be representative of the required duct volume flow rate, and also
to be in a region where it is uniform and stable. If non-axial flow (swirl or cyclonic flow) is expected at
the measurement plane due to geometry of the duct or other upstream conditions, then the degree of
swirl is determined using S-type, 3D or 2D Pitot tube measurements and if it is significant, as defined in
EN ISO 16911-1, then it is taken into account through the use of additional measurement procedures, or
a different measurement plane is selected.
If required, improved uncertainty in the results is achieved by taking wall effects into account,
[17] [13]
following a procedure based on the US EPA Method 2H for circular ducts, and US EPA CTM-041 for
rectangular ducts.
The volume flow rate, q , is determined by multiplying the average velocity by the area of the measurement
V
plane (i.e. the internal area of the duct at the measurement plane).
qv= A (1)
V p
where
is the average of the point velocity measurements;
v
p
A is the area of the measurement plane.
NOTE It is also possible to determine an array of volume flow rates, determined from the point measurements
at each equal area multiplied by the area represented by each sample point. Each sample point area is, by definition,
equal to the area of the measurement plane divided by the number of points. The volume flow rate is then
n
A
qv= (2)
Vi∑
n
i=1
where
v is ith point measurement;
i
A is the area of the measurement plane;
n is the number of measurement points.
which is equivalent to Formula (1).
5.3.3 Determination of volume flow rate using tracer dilution measurements
Trace gas injection is used to measure the volume flow rate by determining the dilution of the injected
tracer by the stack gas flow. A known, traceable, flow rate of calibrated tracer gas is injected into the
stack. The concentration of this tracer gas is measured at a location downstream, representative of the
measurement plane, after complete mixing of the tracer with the stack gas has occurred. The dilution of
the tracer gas by the stack gas provides a measurement of the volume flow rate, provided that:
— the tracer gas is fully mixed in the stack gas;
— there is no tracer gas present in the stack gas prior to injection or the background concentration can
be measured and subtracted accurately.
ISO 16911-1:2013(E)
5.3.4 Determination of volume flow rate using transit time tracer measurements
A small amount of tracer material is injected rapidly into the stack gas flow, to produce a short pulse
of tracer. After the tracer pulse has mixed over the cross-section of the flow, its transit time between
two measurement points placed on a suitable straight duct section is measured. The volume flow rate
is calculated by dividing the duct volume between the measurement points by the transit time. The
flow determined using this technique is representative of a region of the duct defined by the pulse
measurement locations, and these are chosen to be representative of the required measurement plane.
5.3.5 Determination of volume flow rate from plant thermal input
For most combustion sources the volume flow rate may be calculated from the stoichiometric flue
gas volume, determined from the fuel composition and the thermal energy input rate. The possible
[7]
calculation methods are described in EN 12952-15, which includes both direct and indirect methods.
In a direct method the fuel flow is measured and the thermal input is calculated from the specific energy
(“calorific value”) of the fuel and the fuel flow. Use of an indirect method includes measurement of the
energy produced and the thermal efficiency of the plant. Especially for heat generation, or combined heat
and power plants, with a high net thermal efficiency of typically 90 %, the uncertainty of the indirect
method to calculate the thermal input is very low.
To later determine the actual flue gas flow rate, the oxygen concentration at the measurement plane
in many cases shall be used to take account of the excess air. The oxygen concentration is determined
using EN 14789. However, the calculation method can also provide results at reference oxygen values
without requiring the determination of the oxygen composition in the duct. The calculation approach
determines the volume flow rate on a dry gas basis. It also may be used to determine the wet flue gas
flow but the uncertainty in such cases increases.
6 Selection of monitoring approach
6.1 Monitoring objective
EN ISO 16911-1 provides methods that can be used for a number of different objectives. The user of this
method shall understand the objective of the measurement task before undertaking the measurements
as required by EN 15259, as the selection of the method to use can depend on the measurement objective.
Measurement objectives include:
a) velocity measurement at a point in the duct — this may be required as a part of another measurement
method, e.g. for ensuring isokinetic sampling of particulates;
b) flow profile measurement across a plane in the duct;
c) determination of swirl;
d) calibration of a flow AMS — this calibration may be by volume flow rate or velocity;
e) periodic determination of volume flow rate passing through a measurement plane.
Table 1 outlines the techniques which can be used to achieve measurement objectives a) to e).
10 © ISO 2013 – All rights reserved

ISO 16911-1:2013(E)
Table 1 — Selection of measurement technique
Aim of measurement Suitable techniques to realize measurement
Velocity measurement at a point Point measurement:
— differential pressure devices;
— vane anemometer
Determination of swirl at the measurement plane Differential pressure device able to determine flow
direction:
— S-type Pitot tube;
— 3D or 2D Pitot tube
Periodic measurement of average velocity in duct Grid of point velocity measurements
Tracer dilution technique
Tracer transit time technique
Calculation approach based on energy consumption
Calibration of AMS for average velocity or volume Grid of point velocity measurements
Tracer dilution technique
Tracer transit time technique
The point velocity measurement methods described in EN ISO 16911-1 may be used to fulfil any of the
above objectives, subject to the performance requirements of this method being met.
The alternative methods described in EN ISO 16911-1 may be used to determine volume flow rate and
for the calibration of flow automated measuring systems (AMSs), provided specific requirements under
which they may be used are met. These are detailed in 6.3.
The objective of the flow measurement should be clearly defined before selecting the monitoring
approach. In particular, the required basis of the measurements, stack gas conditions or reference
conditions, on a wet or dry basis should be understood, as the selection of the measurement technique
may be influenced by this.
EXAMPLE If the flow measurements are to be used to calibrate an AMS which measures flow under stack
conditions, then the flow should be determined under these conditions to avoid additional uncertainties being
introduced when converting between different conditions. Similarly, if mass emission rates are to be calculated
using concentration data obtained in a dry basis, then flow values determined directly under dry conditions
would be preferred. It is not always possible to achieve this, and so EN ISO 16911-1 provides procedures to convert
the data to different reference conditions.
6.2 Choice of technique to determine point flow velocity
In order to fulfil objectives 6.1 a) to c), a technique able to determine point velocity shall be employed.
These techniques may also be employed to meet all other measurement objectives. EN ISO 16911-1
allows the use of differential pressure devices or vane anemometer to determine point flow velocity.
The following provides some general advice on the selection of the point monitoring technique. However,
expert judgement and specific conditions inform the choice of technique on a case-by-case basis.
There are a number of different designs of Pitot tube which may be used to carry out this method. Annex A
describes the use of these techniques. These include the L-type, S-type and 2D and 3D Pitot tubes. Pitot
tubes of different designs may be used provided t
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