EN 16211:2024

SLOVENSKI STANDARD
01-januar-2025
Nadomešča:
SIST EN 16211:2015
Prezračevanje stavb - Meritve pretoka zraka v sistemu prezračevanja - Metode
Ventilation for buildings - Measurement of air flow rates on site - Methods
Lüftung von Gebäuden - Luftvolumenstrommessung vor Ort - Verfahren
Ventilation des bâtiments - Mesurages des débits d'air sur site - Méthodes
Ta slovenski standard je istoveten z: EN 16211:2024
ICS:
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 16211
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2024
EUROPÄISCHE NORM
ICS 17.120.10; 91.140.30 Supersedes EN 16211:2015
English Version
Ventilation for buildings - Measurement of air flow rates
on site - Methods
Ventilation des bâtiments - Mesurages des débits d'air Lüftung von Gebäuden - Luftvolumenstrommessung in
sur site - Méthodes Lüftungssystemen - Verfahren
This European Standard was approved by CEN on 30 September 2024.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 16211:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols and abbreviated terms . 7
5 Expression of air flow rate and parameters of influence . 10
5.1 Hydraulic diameter . 10
5.2 Flow disturbances . 11
5.3 Stability of the air flow rate . 11
5.4 Air density . 11
5.5 Conversion of dynamic pressure into air velocity . 11
5.6 Correction and conversion of measured air flow rate . 12
5.6.1 General . 12
5.6.2 Correction of the air flow rate . 12
5.6.3 Conversion of the air flow rate . 13
6 Measuring instruments requirements . 14
6.1 General . 14
6.2 Air flow rate measuring instruments . 14
6.3 Differential pressure measuring instruments (manometers) . 14
6.4 Air velocity measuring instruments . 14
6.4.1 General . 14
6.4.2 Anemometers . 14
6.4.3 Pitot static tubes . 14
6.5 Temperature measuring instruments (thermometers) . 15
6.6 Atmospheric pressure measuring instruments (barometers) . 15
7 Methods for measurement of air flow rates . 16
7.1 Overview of described methods . 16
7.2 Multi‐point measurement in the duct cross‐section – with measurement plane
criteria (ID1) . 17
7.2.1 Principle . 17
7.2.2 Apparatus . 17
7.2.3 Measurement procedure . 18
7.2.4 Expression of results . 23
7.3 Multipoint measurement in the duct cross‐section – without measurement plane
criteria (ID2) . 25
7.3.1 Principle . 25
7.3.2 Apparatus . 25
7.3.3 Measurement procedure . 26
7.3.4 Expression of results . 32
7.4 Fixed devices for air flow rate measurement (ID3, ST1 and ET1) . 37
7.4.1 Principle . 37
7.4.2 Apparatus . 38
7.4.3 Measurement procedure . 38
7.4.4 Expression of results . 38
7.5 Air flow rate measurement with tight bag at supply ATDs (ST2) . 39
7.5.1 Principle . 39
7.5.2 Apparatus . 40
7.5.3 Measurement procedure . 40
7.5.4 Expression of results . 40
7.6 Air flow rate measurement with flow hood (ST3 and ET2) . 40
7.6.1 Principle . 40
7.6.2 Apparatus . 41
7.6.3 Measurement procedure . 43
7.6.4 Expression of results . 44
Annex A (informative) Additional methods . 45
A.1 Tracer gas measurement (ID4) . 45
A.1.1 Principle . 45
A.1.2 Apparatus . 45
A.1.3 Measurement procedure – Conditions for homogeneous mixing of tracer gas . 46
A.1.4 Expression of result – Calculation of air flow rate . 47
A.2 Measurement using anemometer at air intake (IN1) or air exhaust (EX1) . 48
A.2.1 Principle . 48
A.2.2 Apparatus . 48
A.2.3 Measurement procedure . 48
A.2.4 Expression of results . 49
A.3 Point measurements using thermal anemometers on rectangular intake (IN2) and
extract (ET3) grilles on walls . 49
A.3.1 Principle . 49
A.3.2 Measurement instruments/Apparatus . 50
A.3.3 Measurement procedure . 50
A.3.4 Standard measurement uncertainty . 52
Annex B (informative) Measurement uncertainty . 53
B.1 Uncertainty of the result of a measurement . 53
B.2 Type B evaluation of standard uncertainty . 53
B.3 Combined standard uncertainty . 55
B.4 Expanded uncertainty . 55
B.5 Examples . 56
Bibliography . 61

European foreword
This document (EN 16211:2024) has been prepared by Technical Committee CEN/TC 156 “Ventilation
for buildings”, the secretariat of which is held by BSI.
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 May 2025, and conflicting national standards shall be
withdrawn at the latest by May 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 16211:2015.
In addition to a number of editorial revisions, the main changes compared with EN 16211:2015 are as
follows:
— the whole document has been rearranged;
— the method described previously in EN 12599:2012 to measure air (volume) flow rate in ductwork
has been included;
— the tracer gas method has been moved in Annex A (informative);
— two new methods to measure air flow rate at exhaust and intake grille have been added in Annex A
(informative);
— parts dealing with uncertainty have been replaced by Annex B (informative);
— requirements on measuring devices are now expressed in MPME (maximum permissible
measurement error).
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Introduction
Measurement of the air (volume) flow rate in a ventilation system is of general interest that is not related
to a specific operation or stage (e.g. installation, inspection, commissioning or handover). It was therefore
agreed to take advantage of the simultaneous revision of EN 16211:2015 and EN 12599:2012 to address
this subject in a single document (EN 16211:2024) rather than scattering or repeating it in various
documents.
In this document, all types of measurements are air (volume) flow rate. For the sake of readability, the
term "air (volume) flow rate" is replaced in the text by the contracted term "air flow rate".
1 Scope
This document specifies methods for the measurement of air flow rates on site. It provides a description
of the air flow rate measurement methods and how measurements are performed within the margins of
stipulated method uncertainties. It gives the necessary measurement conditions (e.g. length of straight
duct, uniform velocity profile) to achieve the stipulated measurement uncertainties.
The methods for measuring the air flow rate inside ducts do not apply to:
— ducts that are not circular or rectangular (e.g. oblong ducts);
— flexible ducts.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
EN 12792, Ventilation for buildings — Symbols, terminology and graphical symbols
EN 14277, Ventilation for buildings — Air terminal devices — Method for airflow measurement by
calibrated sensors in or close to ATD/plenum boxes
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12792 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp/
3.1
measuring interval
set of values of quantities of the same kind that can be measured by a given measuring instrument or
measuring system with specified instrumental measurement uncertainty, under defined conditions
Note 1 to entry: In some fields, the term is “measuring range” or “measurement range”.
[SOURCE: JCGM 200:2012, 4.7, modified – Note 2 has not been reproduced.]
3.2
maximum permissible measurement error
extreme value of measurement error, with respect to a known reference quantity value, permitted by
specifications or regulations for a given measurement, measuring instrument or measuring system
Note 1 to entry: More information on the calculation of the measurement uncertainty based on the maximum
permissible measurement error is given in Annex B.
[SOURCE: JCGM 200:2012, 4.26, modified – The accepted terms “maximum permissible error” and “limit
of error” have been removed, NOTE 1 and NOTE 2 have been removed, a Note 1 to entry has been added.]
3.3
standard uncertainty
measurement uncertainty expressed as a standard deviation
Note 1 to entry: More information on the use of standard uncertainty in measurement uncertainty is given in
Annex B.
[SOURCE: JCGM 200:2012, 2.30, modified – The preferred term and the first accepted term have been
removed and a Note 1 to entry has been added.]
3.4
calibration
operation that, under specified conditions, in a first step, establishes a relation between the quantity
values with measurement uncertainties provided by measurement standards and corresponding
indications with associated measurement uncertainties and, in a second step, uses this information to
establish a relation for obtaining a measurement result from an indication
[SOURCE: JCGM 200:2012, 2.39, modified — NOTE 1 and NOTE 2 have been removed.]
3.5
correction
compensation for an estimated systematic effect
[SOURCE: JCGM 200:2012, 2.53, modified — NOTE 1 and NOTE 2 have been removed.]
3.6
hypothetical
obtained by making hypothesis on the existing conditions
3.7
dynamic pressure
velocity pressure
pressure equivalent of the kinetic energy of the fluid at a point
3.8
static pressure
pressure exerted, in a moving fluid, on an element moving at the same velocity as the fluid
3.9
total pressure
sum of static pressure (3.8) and dynamic pressure (3.7) at any point of a fluid
4 Symbols and abbreviated terms
For the purposes of this document, the symbols given in Table 1 and the abbreviated terms given in
Table 2 apply.
Table 1 — Symbols
Symbol Description Unit
a, b, c, d, e, f Dimensions of length mm
a/D Relative distance —
h
2 2
A Cross-section area m , mm
2 2
A Effective cross-section area of the probe m , mm
g
3 3
C Initial tracer gas concentration cm /m
i
3 3
C Tracer gas concentration in the sampling cross-section cm /m
s
D Diameter mm
D Hydraulic diameter mm
h
D Diameter of the centroidal ring of the annulus mm
i
D Probe diameter mm
so
e Device’s flow exponent given by the manufacturer (usually 0,5) —
H Height of the duct mm
i Ordinal number —
I Irregularity of the velocity profile %
k Characteristic of the fixed device depending on its setting —
(k-factor)
K Coverage factor —
K Correction factor (for method IN2 and EX2) —
k Correction factor for density —
k Correction factor for duct shape —
L Length of head of the pitot static tube mm
L Mixing length for the tracer gas mm
L Smaller dimension of a rectangular duct cross section mm
L Larger dimension of a rectangular duct cross section mm
n Number —
n Number of measuring points along the smaller dimension —
L1
n Number of measuring points along the larger dimension —
L2
p Atmospheric pressure Pa
atm
p Atmospheric pressure in actual conditions Pa
atm,act
p Atmospheric pressure in device hypothetical condition Pa
atm,hyp
p Atmospheric pressure in standardized conditions (101 325 Pa) Pa
atm,std
p Dynamic pressure Pa
d
p Static pressure Pa
s
Symbol Description Unit
p Total pressure Pa
t
P Perimeter of the cross-section m, mm
3 3
q Air flow rate m /s, m /h, l/s
3 3
q Tracer gas flow rate m /s, m /h, l/s
s
3 3
q Tracer gas flow rate at duct temperature m /s, m /h, l/s
sϑduct
3 3
q Tracer gas flow rate at rotameter temperature m /s, m /h, l/s
sϑtracer
3 3
qv,act Actual air flow rate (in actual conditions) m /s, m /h, l/s
3 3
q Hypothetical air flow rate assuming device default conditions m /s, m /h, l/s
v,hyp
3 3
q Measured air flow rate m /s, m /h, l/s
v,m
3 3
q Standardized air flow rate (in standard conditions) m /s, m /h, l/s
v,std
t Time s
T Air temperature in actual conditions K
act
T Air temperature in device default condition K
hyp
T Air temperature in standardized conditions (293,15 K) K
std
u Standard uncertainty —
u Combined standard uncertainty —
c
U Expanded uncertainty —
v Air velocity m/s
v Actual air velocity m/s
act
v Air velocity reading m/s
g
v Air velocity for measuring point k m/s
k
v Average air velocity m/s
m
v Maximum of the arithmetic mean of velocities in a quarter of the m/s
max
cross-section or at a radius
v Minimum of the arithmetic mean of velocities in a quarter of the m/s
min
cross-section or at a radius
v Air velocity for a given quarter m/s
q
v Air velocity for a given radius m/s
r
V Volume of the measuring bag m
W Width of the duct mm
x Distance from the duct wall mm
i
y Distance from the duct wall mm
i
Δl Tolerance for the probe location mm
Δp Measured pressure difference Pa
θ Air temperature in actual conditions (= T − 273,15) °C
act act
Symbol Description Unit
ρ Air density kg/m
ρ Air density in actual conditions kg/m
act
ρ Air density in device default condition kg/m
hyp
ρ Air density in standardized conditions kg/m
std
ρ Air density at the temperature inside the duct kg/m
ϑduct
ρ Air density at the temperature of tracer gas kg/m
ϑtracer
ϑ Temperature of air °C
ϑ Temperature inside the duct °C
duct
ϑ Temperature of tracer gas °C
tracer
Table 2 — Abbreviated terms
Abreviated terms Description
ATD Air terminal devices
MPME Maximum permissible measurement error
RH Relative humidity of the air

5 Expression of air flow rate and parameters of influence
5.1 Hydraulic diameter
The hydraulic diameter, D , is the diameter of a circular duct which causes the same pressure drop, at
h
equal air velocity and equal roughness factor, than the considered duct and is defined by Formula (1).
A
D 4⋅ (1)
h
P
where
A is the area of the cross-section, in mm ;
P is the perimeter of the cross-section, in mm.
For a rectangular duct, Formula (1) becomes Formula (2).
LL⋅
D 2⋅ (2)
h
LL+
( )
where
L is the smaller dimension of the rectangular duct, in mm;
L is the larger dimension of the rectangular duct, in mm.
=
=
For a circular duct, Formula (1) becomes Formula (3).
D = D (3)
h
5.2 Flow disturbances
Within an air flow, disturbances result in irregular velocity profiles. Irregular velocity profile can induce
additional measurement errors and complicate the measurement. Away from any disturbance the
velocity profile gets more and more regular. For some methods, requirements are set regarding the
position of the measurement device from flow disturbances.
NOTE Flow seldom has a symmetrical appearance except after long straight sections. The symmetry is often
disturbed by varying resistance, for example after a bend, an area decrease or an area increase. The velocity profile
also becomes disturbed by singularities such as damper and branch as well as before and after a fan.
5.3 Stability of the air flow rate
Measurement methods described in this document are based on the assumption that the air flow rate
does not change during the measurement time.
NOTE Variation of the air flow rate increases the measurement uncertainty.
5.4 Air density
The density of dry air, ρ, varies with atmospheric pressure and temperature in accordance with
Formula (4).
p
273,15
atm
ρ=1,293⋅⋅
(4)
101 325 273,15+ϑ
where
p is the atmospheric pressure, in Pa;
atm
ϑ is the temperature of the air, in °C.
The relative humidity of the air (RH) has very little influence on the density of air at room temperature.
The density of air at 20 °C and 101 325 Pa which is saturated with water vapour is only approximately
1 % less than equivalent dry air.
If the static pressure of the ventilation system is above about 2 000 Pa, the influence of the static pressure
on air density should be considered and the calculation is then performed using Formula (5).
pp+
273,15
atm s
ρ=1,293⋅⋅ (5)
101 325 273,15+ϑ
where
p is the static pressure in the ductwork, in Pa.
s
5.5 Conversion of dynamic pressure into air velocity
Dynamic pressure within an air flow can be measured with a Pitot static tube connected to a manometer
(see Figure 1 in 6.4.3).
Air velocity can be calculated from dynamic pressure using Formula (6).
2p
d
v = (6)
act
ρ
act
where
v is the actual air velocity (in prevailing conditions);
act
p is the dynamic pressure;
d
ρ is the air density (in prevailing conditions).
act
5.6 Correction and conversion of measured air flow rate
5.6.1 General
By nature, air flow rate measurements on site are done in actual conditions (i.e. conditions existing in a
particular place and at a particular time).
The actual conditions refer to the place where measurements are made. For measurements in ducts,
atmospheric pressure may be measured outside the duct for practical reasons. In this case, the static
pressure in the duct should be added to the atmospheric pressure for calculation purpose. When the static
pressure in the duct is below 2 000 Pa in absolute value it may be neglected.
However, depending on their settings, some measuring systems may:
— give uncorrected air flow rate, q , by making the hypothesis that the air is at the device default
v,hyp
condition (e.g. 1,204 kg/m corresponding to 293,15 K and 101 325 Pa). This hypothetical air flow
rate is neither the actual air flow rate nor the standardized air flow rate and corrections given in 5.6.2
shall be done;
— automatically calculate or convert quantity values into different than actual conditions (e.g. standard
conditions). In this case, conversion to actual conditions, as given in 5.6.3, shall be done.
In any case, the technical data sheet should be consulted to find out to which conditions (actual, standard,
etc.) the indicated quantity values correspond and how to correct or convert them into actual conditions.
5.6.2 Correction of the air flow rate
The formula to convert hypothetical air flow rate into actual air flow rate (air flow rate occurring in actual
conditions) depends on the measuring device used.
To obtain the actual air flow rate, the user shall refer to manufacturer specifications to determine
whether:
— the correction is done automatically, in this case no further corrections shall be done, the read value
is equal to the actual value; or
— the correction shall be done by the user.
If formulae to perform the correction are available in the manufacturer specifications they should be
used.
If the correction is not done automatically and no correction’s formula is available on manufacturer
specifications the following corrections should be used:
— When the air flow rate varies with the inverse of the square root of the air density (e.g. for Pitot static
tubes or fixed measuring device with exponent (reference of the measurement method ID3X)),
Formula (7) shall be used.
     
ρ pp
T θ + 273,15
hyp atm,hyp atm,hyp
act act
     
q =q ⋅=q =q (7)
v,act v,hyp v,hyp v,hyp
     
ρ p T p T
act atm,act hyp atm,act hyp
     
— When the air flow rate varies with the inverse of the air density (e.g. for hot-wire anemometers)
Formula (8) shall be used.
     
ρ pp
T θ + 273,15
hyp atm,hyp atm,hyp
act act
     
q = q ⋅= q = q (8)
v,act v,hyp v,hyp v,hyp
     
ρ p T p T
act atm,act hyp atm,act hyp
     
where
q is the hypothetical air flow rate assuming device default conditions;
v,hyp
q is the actual air flow rate (in actual conditions);
v,act
ρ is the air density in device default condition;
hyp
ρact is the air density in actual conditions;
p is the atmospheric pressure in device default condition;
atm,hyp
p is the atmospheric pressure in actual conditions;
atm,act
T is the air temperature in device default condition, in K;
hyp
T is the air temperature in actual conditions, in K;
act
θ is the air temperature in actual conditions, in °C.
act
NOTE The multiplier of qv,hyp is sometimes termed “k1”.
— For vane anemometers no corrections are needed for temperature and atmospheric pressure (air
density). In this case, the hypothetical air flow rate is equal to the actual air flow rate.
5.6.3 Conversion of the air flow rate
Standardized air flow rate (air flow rate converted to standardized conditions) can be converted into
actual air flow rate (air flow rate occurring in actual conditions) using Formula (9).
   
pp  
ρθT + 273,15
atm,std atm,std
std act act
   
q = q ⋅ = q = q   (9)
v,act v,std v,std v,std
  
   
ρ p T p T
act atm,act std atm,act  std 
   
Conversely, actual air flow rate can be converted into standardized air flow rate using Formula (10).
   
pp  
ρ T T
atm,act atm,act
act std std
   
qq= ⋅ = q = q   (10)
v,std v,act v,act v,act
  
   
ρθpT p + 273,15
std atm,std act atm,std  act 
   
where
q is the standardized air flow rate (in standard conditions);
v,std
q is the actual air flow rate (in actual conditions);
v,act
ρ is the air density in standardized conditions;
std
ρ is the air density in actual conditions;
act
p is the atmospheric pressure in standardized conditions (101 325 Pa), in Pa;
atm,std
p is the atmospheric pressure in actual conditions, in Pa;
atm,act
T is the air temperature in standardized conditions (293,15 K), in K;
std
T is the air temperature in actual conditions, in K;
act
θ is the air temperature in actual conditions, in °C.
act
6 Measuring instruments requirements
6.1 General
The present clause provides good practices values for maximum permissible measurement error (MPME)
of measuring instruments. For estimating the overall uncertainty of the measurement see Annex B and
be consistent with the purpose of the test.
In order to reduce measuring uncertainty, instruments with a mean value calculation function (e.g.
according to EN 13182) should be used.
EXAMPLE Instruments can calculate the mean value from 15 readings with 0,1 s apart.
6.2 Air flow rate measuring instruments
The MPME of an air flow rate measuring instrument, that provides air flow rate directly (such as flow
hood), should be lower or equal to 3,6 m /h + 5 % of the measured value for the measuring interval that
includes the measured quantity value.
6.3 Differential pressure measuring instruments (manometers)
The MPME of manometers should be lower or equal to 0,4 Pa + 3 % of the measured value, for the
measuring interval that includes the measured quantity value.
Manometers should be zeroed before each sequence of measurement according to manufacturer
instructions.
6.4 Air velocity measuring instruments
6.4.1 General
Air velocity is usually measured by anemometers or by Pitot static tubes.
The MPME of air velocity measuring instrument shall be lower or equal to 0,1 m/s + 5 % of the measured
value, for the measuring interval that includes the measured quantity value.
For in duct measurements, the projected area of the device obstructing the duct passage area should not
exceed 1/10th of the duct cross-section area.
Directional probes shall be oriented into the direction of the flow.
6.4.2 Anemometers
Anemometers, e.g. hot-wire anemometers or vane anemometers, provide a direct measurement of air
velocity values.
The MPME of the instrument shall be consistent with the MPME given in 6.4.1.
Hot wire anemometers usually show a better accuracy at low velocities, vane anemometers are less
temperature dependent and show a better accuracy at higher velocities. The velocity where there is a
transition between the two types of instruments is usually within range 1 m/s to 3 m/s, this information
is given in the manufacturer instructions.
6.4.3 Pitot static tubes
Pitot static tubes are described in EN ISO 16911-1 and ISO 3966. The principle of measurement with a
Pitot static tube is given in Figure 1.
Pitot static tubes are used with a manometer complying with 6.3 to measure the dynamic or the static
pressure within the duct. From the dynamic pressure measurement, air velocity can be calculated as
described in 5.5.
The derived MPME of the air velocity shall be consistent with the MPME of the air velocity measurement
devices given in 6.4.1 and this shall be checked using Formula (11).
MPME p ≤ 0,,1⋅⋅ρρv+ 0 05⋅⋅ v (11)
( )
d
where
MPME(p ) is the maximum permissible measurement error at the measured dynamic pressure.
d
In general, Pitot static tubes are best to measure velocity from 2 m/s and above if the MPME of the
manometer is consistent with 6.3.

Key
1 connection for static pressure p total pressure
t
2 connection for total pressure p dynamic pressure
d
l length of head ps static pressure
D diameter of tube
Figure 1 — Measurement principle of Pitot static tube
Some measuring instruments display directly velocity or air flow rate while they are measuring dynamic
pressure.
6.5 Temperature measuring instruments (thermometers)
Thermometers shall have a MPME of ±1 °C for the measuring interval that includes the measured quantity
value.
The duration of measurement should be consistent with the response time of the thermometer.
6.6 Atmospheric pressure measuring instruments (barometers)
Barometers shall have a MPME of ±500 Pa for the measuring interval that includes the measured quantity
value.
7 Methods for measurement of air flow rates
7.1 Overview of described methods
The methods described in this document are summarized in Table 3.
The following abbreviations are used in Table 3 and also in the document:
— ID: In duct;
— ST: Supply terminal;
— ET: Extract terminal;
— EX: Exhaust;
— IN: Intake.
Table 3 — Summary of the methods described in this document
Measurement location designation Clause(s)/
Measurement In duct At At At fan At At intake subclause(s)
method supply extract exhaust vent of this
vent document
Multi-point ID1XX      7.2
measurement in the
duct cross-section –
with measurement
plane criteria
Multipoint ID2XX      7.3
measurement in the
duct cross-section –
without measurement
plane criteria
Fixed devices for air ID3X ST1X ET1X ID31   7.4
flow rate
measurement
Measurement with  ST2     7.5
tight bag
Measurement with  ST3X ET2X    7.6
flow hood
Measurement with ID4      Annex A
tracer gas (informative)
Measurement at     EX1 IN1 Annex A
intake vents or (informative)
exhaust vents
Point measurements   ET3   IN2 Annex A
using hot wire (informative)
anemometer at
rectangular grilles
To determine the measurement conditions of the ventilation system the air temperature and atmospheric
pressure should be measured. For in duct measurement, the static pressure in the duct (at measurement
plane) should be measured.
Additional information, such as wind speed and outdoor temperature, might also be of interest for
uncertainty evaluation.
7.2 Multi‐point measurement in the duct cross‐section – with measurement plane
criteria (ID1)
7.2.1 Principle
Method ID1 involves the air flow rate being calculated from a series of air velocities determined by
measurements in the duct cross-section. The determination of velocity is carried out using a Pitot static
tube or an anemometer.
The air flow rate is then calculated by multiplying the average air velocity with the duct area and
correction factors (given in 5.6).
Table 4 gives method numbers according to the kind of ductwork and the kind of measurement device,
together with the standard method uncertainty.
Table 4 — Methods ID1 for measurement of air flow rates
Method/measurement device/kind of Method Standard method
a
ductwork number uncertainty
Multi-point measurement in the duct cross- ID1
section – with measurement plane criteria
Pressure measurements using a Pitot static tube ID11
a) Circular cross-section ID111 4 % (case A)
6 % (case B)
b) Rectangular cross-section ID112 4 %
Velocity measurement using a hot-wire ID12
anemometer or a mechanical anemometer
a) Circular cross-section ID121 4 % (case A)
6 % (case B)
b) Rectangular cross-section ID122 4 %
a
See Annex B for more information on standard uncertainty.
Random method uncertainties can arise, e.g. as a result of oblique velocity profile in the measurement
cross-section and oblique setting of the probe. The standard method uncertainty with a coverage
probability of approximately 68 % is given in Table 4.
7.2.2 Apparatus
For all methods, the equipment that shall be used is:
— a thermometer;
— a barometer;
and for:
— ID11 a manometer with Pitot static tube;
— ID12 an anemometer.
In both cases, the Pitot static tube or the anemometer shall include an indication of:
— insertion length;
— the orientation of the probe (to be aligned with the flow direction).
7.2.3 Measurement procedure
7.2.3.1 Preparations to be made at the site of measurement
7.2.3.1.1 Selection of the plane of measurement
The flow profile has a distorted appearance after certain disturbances to the flow, e.g. section change,
bends or dampers. If measurement takes place directly after a flow disturbance, there is a risk of low
accuracy.
The plane of measurement is accepted if it meets the following criteria:
— duct sections are free from disturbances for a distance, both before and after the plane of
measurement: see Table 5 for values;
— the highest dynamic pressure (ID11) in the measurement plane:
— is located more than 0,1 D from all duct walls;
h
— is less than twice the dynamic pressure in the centre;
— the highest velocity (ID12) in the measurement plane:
— is located more than 0,1 D from all duct walls;
h
— is less than 1,4 times the velocity in the centre;
— the likeliness of backflow in the cross-section is small.
If these three criteria are not met, a new plane of measurement shall be selected and tested.
To determine if there is a risk of backflow in the cross-section, insert the anemometer in the duct in the
measuring plane and sweep slowly to determine maximum value location. If negative or close to zero
values are noticed, there is a high possibility of backflow.
For rectangular ductwork, the “centre” is the intersection of diagonals.
NOTE A Pitot static tube can normally not detect velocities below approximatively 0,5 m/s and a hot-wire
anemometer is not able to detect the direction of the flow.
Table 5 — Necessary length of straight sections before and after the plane of measurement
Location of the straight section Length of the duct straight section
Circular Rectangular
Before plane of measurement a ≥ 5 ⋅ D a ≥ 6 ⋅ D
h
After plane of measurement a ≥ 2 ⋅ D a ≥ 2 ⋅ D
h
150 mm minimum from duct 50 mm minimum from duct
connections connections
7.2.3.1.2 Preparation
a) Select the location of the plane of measurement according to 7.2.3.1.1, taking into consideration the
required straight sections.
b) Remove the external insulation at the point of measurement.
c) Drill holes in the duct so that measurements can be made along lines in a cross-section:
1) the cross-section shall be perpendicular to the axis of the duct;
2) for circular ducts, the two lines shall be perpendicular to each other:
i) case A (preferred one, lower uncertainty): one of the lines of points is placed in the same
plane as the axis of the duct and the centre of the bent upstream the duct;
ii) case B (higher uncertainty): two perpendicular lines in the cross-section other than those of
case A are used (e.g. in case of access restriction).
The uncertainty is higher in case B. The reasons for the increase of uncertainty in case B are that the flow
profil
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