SIST EN ISO 15112:2019
(Main)Natural gas - Energy determination (ISO 15112:2018)
Natural gas - Energy determination (ISO 15112:2018)
This document provides the means for energy determination of natural gas by measurement or by calculation, and describes the related techniques and measures that are necessary to take. The calculation of thermal energy is based on the separate measurement of the quantity, either by mass or by volume, of gas transferred and its measured or calculated calorific value. The general means of calculating uncertainties are also given.
Only systems currently in use are described.
NOTE Use of such systems in commercial or official trade can require the approval of national authorization agencies, and compliance with legal regulations is required.
This document applies to any gas-measuring station from domestic to very large high-pressure transmission.
New techniques are not excluded, provided their proven performance is equivalent to, or better than, that of those techniques referred to in this document.
Gas-measuring systems are not the subject of this document.
Erdgas - Bestimmung von Energiemengen (ISO 15112:2018)
Dieses Dokument sieht Maßnahmen vor zur Bestimmung von Energiemengen von Erdgas durch Messung oder Berechnung und beschreibt die dabei erforderlichen anzuwendenden Techniken und Maßnahmen. Die Berechnung von thermischer Energie beruht auf der gesonderten Messung der Gasmenge, entweder als Masse oder Volumen des (an Übergabestellen) übertragenen Gases und auf seinem gemessenen oder berechneten Brennwert. Allgemeine Maßnahmen zur Berechnung von Unsicherheiten sind ebenfalls angegeben.
Ausschließlich derzeit verwendete Systeme werden beschrieben.
ANMERKUNG Der Einsatz derartiger Systeme in kommerziellem oder offiziellem Handel erfordert möglicherweise die Zulassung durch nationale Zulassungsbehörden, und die Übereinstimmung mit gesetzlichen Vorschriften ist erforderlich.
Dieses Dokument gilt für alle Gasmessstationen, von Endkunden im privaten Bereich bis hin zu sehr großen Hochdrucktransportanlagen.
Neue Verfahren sind nicht ausgeschlossen, sofern ihre nachgewiesene Leistungsfähigkeit gleichwertig der oder besser als die jener Techniken ist, auf die in diesem Dokument Bezug genommen wird.
Gasmesssysteme sind nicht Gegenstand dieses Dokuments.
Gaz naturel - Détermination de l'énergie (ISO 15112:2018)
Le présent document fournit les moyens permettant de déterminer l'énergie du gaz naturel par mesurage ou par calcul, et décrit les techniques associées et les mesures nécessaires à prendre. Le calcul de l'énergie thermique est fondé sur le mesurage séparé de la quantité de gaz transféré, exprimée en masse ou en volume, et sur son pouvoir calorifique mesuré ou calculé. Il fournit également les moyens généraux permettant le calcul des incertitudes.
Seuls les systèmes actuellement utilisés sont décrits dans le document.
NOTE Qu'il s'agisse du secteur privé ou public, l'utilisation de tels systèmes dans le commerce peut requérir l'approbation d'organismes d'agrément nationaux et il est alors nécessaire qu'ils soient conformes aux dispositions de la loi.
Le présent document s'applique à tout poste de comptage de gaz, de la distribution intérieure au transport à très haute pression.
Le recours à de nouvelles techniques est admis sous réserve de performances éprouvées équivalentes ou supérieures aux techniques citées en référence dans le présent document.
Les systèmes de comptage de gaz ne sont pas abordés dans le présent document.
Zemeljski plin - Določevanje energijske vrednosti (ISO 15112:2018)
Ta dokument zagotavlja sredstva za določevanje energijske vrednosti zemeljskega plina z merjenjem ali izračunom ter opisuje s tem povezane tehnike in ukrepe, ki jih je potrebno sprejeti. Izračun toplotne energije temelji na ločenem merjenju količine (masa ali prostornina) prenesenega plina in njegove izmerjene ali izračunane kalorične vrednosti. Podana so tudi splošna sredstva za izračun negotovosti.
Opisani so samo sistemi, ki se trenutno uporabljajo.
OPOMBA: Za uporabo takšnih sistemov v komercialnem ali uradnem trgovanju je morda potrebna odobritev nacionalnih agencij za izdajo dovoljenj in skladnost z zakonskimi predpisi.
Ta dokument se uporablja za vse merilne postaje za plin od gospodinjskih do velikih postaj z visokotlačnim
prenosom.
Nove tehnike niso izključene, če je dokazano, da delujejo enako dobro ali bolje kot tiste, opisane v tem dokumentu.
Sistemi za merjenje plinov niso predmet tega dokumenta.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-marec-2019
1DGRPHãþD
SIST EN ISO 15112:2014
=HPHOMVNLSOLQ'RORþHYDQMHHQHUJLMVNHYUHGQRVWL ,62
Natural gas - Energy determination (ISO 15112:2018)
Gaz naturel - Détermination de l'énergie (ISO 15112:2018)
Ta slovenski standard je istoveten z: EN ISO 15112:2018
ICS:
75.060 Zemeljski plin Natural gas
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 15112
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2018
EUROPÄISCHE NORM
ICS 75.060 Supersedes EN ISO 15112:2014
English Version
Natural gas - Energy determination (ISO 15112:2018)
Gaz naturel - Détermination de l'énergie (ISO
15112:2018)
This European Standard was approved by CEN on 27 October 2018.
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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15112:2018 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 15112:2018) has been prepared by Technical Committee ISO/TC 193 "Natural
gas" in collaboration with Technical Committee CEN/TC 238 “Test gases, test pressures, appliance
categories and gas appliance types” the secretariat of which is held by AFNOR.
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 June 2019, and conflicting national standards shall be
withdrawn at the latest by June 2019.
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 ISO 15112:2014.
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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 15112:2018 has been approved by CEN as EN ISO 15112:2018 without any modification.
INTERNATIONAL ISO
STANDARD 15112
Third edition
2018-11
Natural gas — Energy determination
Gaz naturel — Détermination de l'énergie
Reference number
ISO 15112:2018(E)
©
ISO 2018
ISO 15112:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
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Published in Switzerland
ii © ISO 2018 – All rights reserved
ISO 15112:2018(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 6
5 General Principles. 7
6 Gas measurement . 8
6.1 General . 8
6.2 Volume measurement . 9
6.3 Calorific value measurement . 9
6.3.1 Measurement techniques and sampling . 9
6.3.2 Direct measurement — Calorimetry .10
6.3.3 Inferential measurement .10
6.3.4 Correlation techniques .10
6.3.5 Pressure and temperature .10
6.3.6 Gas quality tracking .10
6.4 Volume conversion .10
6.4.1 General.10
6.4.2 Density .11
6.4.3 Compression factor .11
6.5 Calibration .11
6.6 Data storage and transmission .11
7 Energy determination .12
7.1 Interfaces .12
7.2 Methods of energy determination .14
7.2.1 Direct determination of energy .14
7.2.2 Indirect determination of energy .14
8 Strategy and procedures .16
8.1 General .16
8.2 Strategies for energy determination .17
8.2.1 Strategies for single interfaces .18
8.3 Plausibility checks .22
9 Assignment methods .23
9.1 Fixed assignment .23
9.1.1 Fixed assignment of a measured calorific value .23
9.1.2 Fixed assignment of a declared calorific value .24
9.2 Variable assignment .25
9.2.1 Input at two or more different stations with zero floating point .25
9.2.2 Input at two or more different stations with comingled gas flows .26
9.3 Determination of the representative calorific value .27
9.3.1 Arithmetically averaged calorific value .27
9.3.2 Quantity-weighted average calorific value .27
9.3.3 Gas quality tracking .27
10 Calculation of energy quantities .30
10.1 General formulae for energy .30
10.2 Calculation of averaged values — Calculation from average calorific values and
cumulative volumes .31
10.2.1 Arithmetic average of the calorific value .31
10.2.2 Quantity-weighted average of the calorific value .32
ISO 15112:2018(E)
10.3 Volume and volume-to-mass conversions .32
10.4 Energy determination on the basis of declared calorific values .32
11 Accuracy on calculated energy .32
11.1 Accuracy .32
11.2 Calculation of uncertainty .33
11.3 Bias .34
12 Quality control and quality assurance .35
12.1 General .35
12.2 Check of the course of the measuring data .35
12.3 Traceability .36
12.4 Substitute values .36
Annex A (informative) Main instruments and energy-determination techniques .38
Annex B (informative) Different possible patterns in the change of the calorific value.42
Annex C (informative) Volume conversion and volume-to-mass conversion .45
Annex D (informative) Incremental energy determination .46
Annex E (informative) Practical examples for volume conversion and energy quantity
calculation .48
Annex F (informative) Practical examples for averaging the calorific value due to different
delivery situations .52
Annex G (informative) Ways of determining substitute values .57
Annex H (informative) Plausibility check graphical example .59
Annex I (informative) Uncorrected data, bias correction and final result graphical example.60
Annex J (informative) Single-reservoir calorific value determination .62
Annex K (informative) .64
Bibliography .70
iv © ISO 2018 – All rights reserved
ISO 15112:2018(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 193, Natural gas.
This third edition cancels and replaces the second edition (ISO 15112:2011), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Figures 7 and 8 have been redrafted;
— Clause 9 has been updated;
— Annex K has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
ISO 15112:2018(E)
Introduction
Since the early 1 800s, it has been general practice for manufactured gas and, subsequently, natural
gas to be bought and sold on a volumetric basis. Much time and effort has therefore been devoted to
developing the means of flow measurement.
Because of the increasing value of energy and variations in gas quality, billing on the basis of thermal
energy has now become essential between contracting partners and the need to determine calorific
value by measurement or calculation has led to a number of techniques. However, the manner in which
calorific value data are applied to flow volume data to produce the energy content of a given volume of
natural gas has been far from a standardized procedure.
Energy determination is frequently a necessary factor wherever and whenever natural gas is metered,
from production and processing operations through to end-user consumption. This document has been
developed to cover aspects related to production/transmission and distribution/end user. It provides
guidance to users of how energy units for billing purposes are derived, based on either measurement or
calculation or both, to increase confidence in results for contracting partners.
Other standards relating to natural gas, flow measurement, calorific value measurement, calculation
procedures and data handling with regard to gas production, transmission and distribution involving
purchase, sales or commodity transfer of natural gas can be relevant to this document.
This document contains eleven informative annexes.
vi © ISO 2018 – All rights reserved
INTERNATIONAL STANDARD ISO 15112:2018(E)
Natural gas — Energy determination
1 Scope
This document provides the means for energy determination of natural gas by measurement or
by calculation, and describes the related techniques and measures that are necessary to take. The
calculation of thermal energy is based on the separate measurement of the quantity, either by mass
or by volume, of gas transferred and its measured or calculated calorific value. The general means of
calculating uncertainties are also given.
Only systems currently in use are described.
NOTE Use of such systems in commercial or official trade can require the approval of national authorization
agencies, and compliance with legal regulations is required.
This document applies to any gas-measuring station from domestic to very large high-pressure
transmission.
New techniques are not excluded, provided their proven performance is equivalent to, or better than,
that of those techniques referred to in this document.
Gas-measuring systems are not the subject of this document.
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.
ISO 6976, Natural gas — Calculation of calorific values, density, relative density and Wobbe index from
composition
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at https: //www .electropedia .org/
3.1
accuracy of measurement
closeness of the agreement between the result of a measurement and a true value of the measurand
[SOURCE: ISO/Guide 98-3:2008, definition B.2.14]
3.2
adjustment
of bringing a measuring instrument into a state of performance suitable
for its use
Note 1 to entry: Adjustment may be automatic, semi-automatic or manual.
ISO 15112:2018(E)
3.3
assignment method
method to derive a calorific value to be applied to the gas passing specified
interfaces having only volume measurements
3.4
availability
probability, at any time, that the measuring system, or a measuring instrument forming part of the
measuring system, is functioning according to specifications
[SOURCE: EN 1776:1998]
3.5
bias
systematic difference between the true energy and the actual energy determined of the gas passing a
gas-measuring station
3.6
calibration
set of operations that establish, under specified conditions, the relationship between values of quantities
indicated by a measuring instrument or measuring system, or values represented by a material measure
or a reference material, and the corresponding values obtained using working standards
[SOURCE: ISO 14532:2014, definition 2.5.1.1, modified — Definition has been slightly changed and Notes
to entry have been removed.]
3.7
superior calorific value
energy released as heat by the complete combustion in air of a specified quantity of gas, in such a
way that the pressure, p , at which the reaction takes place remains constant, and all the products of
combustion are returned to the same specified temperature, T , as that of the reactants, all of these
products being in the gaseous state except for water formed by combustion, which is condensed to the
liquid state at T
[SOURCE: ISO 14532:2014, definition 2.6.4.1, modified — Definition has been slightly reworded and
Notes to entry have been removed.]
3.8
inferior calorific value
energy released as heat by the complete combustion in air of a specified quantity of gas, in such a
way that the pressure, p , at which the reaction takes place remains constant, and all the products of
combustion are returned to the same specified temperature, T , as that of the reactants, all of these
products being in the gaseous state
[SOURCE: ISO 14532:2014, definition 2.6.4.2, modified — Definition has been slightly reworded and
Notes to entry have been removed.]
3.9
calorific value station
installation comprising the equipment necessary for the determination of the calorific value of the
natural gas in the pipeline
3.10
adjusted calorific value
calorific value measured at a measuring station compensated for the time taken for the gas to travel to
the respective volume-measuring station
3.11
corrected calorific value
result of correcting a measurement to compensate for systematic error
2 © ISO 2018 – All rights reserved
ISO 15112:2018(E)
3.12
declared calorific value
calorific value that is notified in advance of its application to interfaces for the purpose of energy
determination
3.13
representative calorific value
calorific value which is accepted to sufficiently approximate the actual calorific value at an interface
3.14
charging area
set of interfaces where the same method of energy determination is used
3.15
conversion
determination of the volume under reference conditions from the volume under operating conditions
3.16
correction
value added algebraically to the uncorrected result of a measurement to compensate for systematic error
Note 1 to entry: The correction is equal to the negative of the estimated systematic error.
Note 2 to entry: Since the systematic error cannot be known perfectly, the correction cannot be complete, see
Annex I.
3.17
correction factor
numerical factor by which the uncorrected result of a measurement is multiplied to compensate for a
systematic-error object
Note 1 to entry: Since the systematic error cannot be known perfectly, the correction cannot be complete, see
Annex I.
3.18
determination
set of operations that are carried out on an object in order to provide qualitative or quantitative
information about this object
Note 1 to entry: In this document, the term “determination” is only used quantitatively.
3.19
direct measurement
measurement of a property from quantities which, in principle, define the property
Note 1 to entry: For example, the determination of the calorific value of a gas using the thermoelectric
measurement of the energy released in the form of heat during the combustion of a known amount of gas.
[SOURCE: ISO 14532:2014, definition 2.2.1.2, modified — The word “that” has been replaced by “which”
in the definition.]
3.20
energy
product of gas quantity (mass or volume) and calorific value under given conditions
Note 1 to entry: The energy may be called energy amount.
Note 2 to entry: Energy is usually expressed in units of megajoules.
ISO 15112:2018(E)
3.21
energy determination
quantitative determination of the amount of energy of a quantity of gas based either on measurement
or calculation using measured values
3.22
energy flow rate
energy of gas passing through a cross-section divided by time
Note 1 to entry: Energy flow rate is usually expressed in units of megajoules per second.
3.23
fixed assignment
application without modification of the calorific value measured at one specific calorific-value-
measuring station, or the calorific value declared in advance, to the gas passing one, or more, interfaces
3.24
gas transporter
company that conveys gas from one place to another through pipelines
3.25
gas quality tracking
determination of gas quality properties (e. g. the calorific value) at the exit points of a gas grid based on
flow calculation; the calculation requires topology data, gas quality data at entry points, volume data at
entry and exit points and grid pressures as input information
3.26
interface
place on a pipe used for the transportation or supply of gas at which there is a change of ownership or
physical custody of gas
Note 1 to entry: Generally, an interface has an associated measuring station.
3.27
local distribution company
LDC
company that delivers gas to industrial, commercial and/or residential customers
3.28
measuring station
installation comprising all the equipment, including the inlet and outlet pipework as far as the isolating
valves and structure within which the equipment is housed, used for gas measurement in custody
transfer
[SOURCE: EN 1776:1998]
3.29
measuring system
complete set of measuring instruments and auxiliary equipment assembled to carry out specified
measurements
[SOURCE: ISO/IEC Guide 99:2007, definition 3.2, modified — Definition has been slightly reworded.]
3.30
measuring instrument
device intended to be used for making measurements, alone or in conjunction with one or more
supplementary devices
[SOURCE: ISO/IEC Guide 99:2007, definition 3.1, modified — Definition has been slightly reworded.]
4 © ISO 2018 – All rights reserved
ISO 15112:2018(E)
3.31
plausibility
property of a value to be within reasonable limits
3.32
producer
company that extracts raw natural gas from reservoirs which, after processing and (fiscal)
measurement, is supplied as dry natural gas to the transportation system
3.33
regional distributor
company that conveys gas to local distribution companies and/or industrial, commercial or residential
customers
3.34
residential customer
person whose occupied premises are supplied with gas, wholly or in part, such gas not being used for
any business purpose, commercial or industrial
3.35
systematic error
mean that would result from an infinitive number of measurements of the same measurand carried out
under repeatability conditions minus a true value of the measurand
3.36
traceability
property of the result of a measurement or the value of a standard whereby it can be related to stated
references, usually national or International Standards, through an unbroken chain of comparisons all
having stated uncertainties
Note 1 to entry: This chain of comparisons is called a traceability chain.
3.37
uncertainty
parameter, associated with the result of a measurement, that characterizes the dispersion of the values
that could reasonably be attributed to the measurand
3.38
variable assignment
application of a calorific value for an assignment procedure based on measurement(s) at calorific value
station(s) to the gas passing one, or more, interfaces
Note 1 to entry: That applied calorific value may take into account the time taken for the gas to travel from
the calorific value station to the respective volume-measuring stations and other factors, to derive an average
calorific value for a network, a state reconstruction of the variation of calorific values through a network, etc.
3.39
zero floating point
position in a grid conveying gas where there is a boundary with different gas qualities on either side
3.40
non-plausible data
measurement data that are obviously wrong taking into account the measurement situation at a
measuring station and the gas flow situation
3.41
grid node
connection of two or more pipes in a gas grid, grid nodes typically exist at interfaces (entry/exit) or at
points where the pipe geometry changes
ISO 15112:2018(E)
3.42
standard load profile
SLP
standard load profile (SLP) is a model to predict the expected hourly or daily energy consumption of
customers where the reading is taken only periodically (e.g. once per year)
4 Symbols and units
Symbol Meaning SI unit Customer unit
E energy MJ kWh
e energy flow rate MJ/s kWh/h
3 3
H calorific value MJ/m ; MJ/kg kWh/m
NOTE 1 Where the calorific value is in megajoules per cubic metre and the gas volume is in cubic me-
tres, or where the calorific value is in megajoules per kilogram and the gas mass is in kilograms, then
the calculated energy is in megajoules.
Where the calorific value is in kilowatt-hours per cubic metre and the gas volume is in cubic metres, or
where the calorific value is in kilowatt-hours per kilogram and the gas mass is in kilograms, then the
calculated energy is in kilowatt-hours.
To convert the number of megajoules to the number of kilowatt-hours, divide the number by 3,6.
M mass kg t
p pressure (absolute) Pa, kPa bar, mbar
3 3
Q quantity of gas m , kg ft
NOTE 2 When the quantity is given in cubic metres, it is necessary that it should be qualified by tem-
perature and pressure.
3 3
sq volume flow rate m /h, m /s
v
q mass flow rate kg/s, kg/h
m
T temperature (absolute) K
t time s, h, d s, h, d
V volume (gas) m
Z compression factor
ρ density kg/m
ϑ temperature °C °F
Subscripts
i inferior calorific value
j number of time intervals
6 © ISO 2018 – All rights reserved
ISO 15112:2018(E)
n normal reference conditions (273,15 K; 101,325 kPa)
r ISO-recommended standard reference conditions (288,15 K; 101,325 kPa)
s superior calorific value
5 General Principles
The quantity of energy, E, contained in a given quantity of gas, Q, is given by the multiplication of the
calorific value, H, by the respective quantity of gas.
Energy may be either measured directly (see Figure 1) or calculated from the quantity and the calorific
value of the gas (see Figure 2).
Figure 1 — Energy-measurement scheme
Figure 2 — Energy-determination scheme
Generally, the quantity of gas is expressed as a volume and the calorific value is on a volumetric basis.
In order to achieve accurate determinations of energy, it is necessary that both the gas volume and
calorific value be under the same reference conditions. The determination of energy is based either
on the accumulation over time of calculation results from consecutive sets of calorific values and
the concurrent flow rate values, or on the multiplication of the total volume and the representative
(assigned) calorific value for that period.
Especially in situations of varying calorific values and when flow rates are determined at a place
different from that of the (representative) calorific value, the effect on the accuracy caused by the
ISO 15112:2018(E)
difference in time between the determination of the flow rate and the calorific value shall be considered
(see Clause 11).
The gas volume may either be measured and reported as the volume under the ISO-recommended
standard reference conditions or be measured under some other conditions and converted to an
equivalent volume under the ISO-recommended standard reference conditions, using an appropriate
method of volume conversion. The method of volume conversion used at a specific gas-volume-
measuring station may require gas quality data determined at other places. For the purpose of this
document, the ISO-recommended standard reference conditions of 288,15 K and 101,325 kPa, as
defined in ISO 13443, should be used.
NOTE For the gas supply, other conditions can be used, corresponding to national standards or laws.
Methods for conversion between different conditions for dry natural gases are given in ISO 13443.
The calorific value may be measured at the gas-measuring station or at some other representative point
and assigned to the gas-measuring station. It is also possible for the quantity of gas and the calorific
value to be expressed on a mass basis.
This general principle of energy determination is extended in Clause 10 to those cases when the
quantity of gas is expressed on either a volumetric or a mass basis.
To achieve the calculation of the quantity of energy of the gas passing a gas-measuring station over a
period of time, the methods of energy determination in Clauses 7 to 10 are used. Such methods involve
an integration over the time period; that integration may be
— of the energy flow, or
— of the gas flow rate over time to obtain the quantity of gas, which is then multiplied by the
representative calorific value.
The method of integration may depend on contractual agreements or national legislation.
The general principles of energy determination in Clauses 7 to 10 are independent of the method with
which the integrations are carried out. The method of integration influences the uncertainty of the
determined energy; these effects are considered in Clause 11.
6 Gas measurement
6.1 General
The types of measuring devices and methods used in real measuring stations depend among other
things on
— the respective national requirements,
— the flow rate,
— the commercial value of the gas,
— the gas quality variations,
— the need for redundancy, and
— the instrument specification.
Only proven methods and measuring devices/products used at the respective interfaces should be
used. An overview of the techniques and procedures currently used in different countries is shown in
Annex A.
8 © ISO 2018 – All rights reserved
ISO 15112:2018(E)
Methods used for flow and calorific value measurement shall be in accordance with standards,
contractual agreements and/or national legislation, as appropriate. If no national legislation exists, the
OIML recommendation R140 should be applied.
Action should be taken to identify and reconcile systematic effects. For example, use of different
national standards, regulations and/or operating procedures can introduce systematic differences;
contract partners should determine the appropriate means to overcome these differences.
The quality of the measurement results, in general, depends on the following factors:
— operating conditions;
— maintenance frequency and quality;
— calibration standards;
— sampling and clean-up;
— changes in gas composition;
— ageing of measurement devices.
A high accuracy can be achieved if the requirements fixed by the manufacturers and by officials are met
and all operating procedures for operating, calibration and maintenance are strictly observed.
6.2 Volume measurement
The volume flow-metering system of a natural-gas-measuring station consists of one or more meter
runs. Generally, the meters measure the gas volume flow under actual operating conditions. Standards
for orifice meters (ISO 5167-1) and turbine meters (ISO 9951) exist.
The selection of a flow-metering system for a specific application depends, as a minimum, on the
following:
— conditions of flow;
— flow-measuring range;
— operating conditions, especially operating pressure;
— acceptable pressure loss;
— required accuracy.
For natural-gas volume flow measurement, the instruments mostly used at the interfaces 1 to 6 (see
7.1) are shown in Annex A.
6.3 Calorific value measurement
6.3.1 Measurement techniques and sampling
A calorific-value measuring system consists of a sampling system and a measurement device taken
from one of the following groups:
a) direct measurement (e.g. by combustion calorimeters);
b) inferential measurement [e.g. by a gas chromatograph (GC)];
c) correlation techniques;
d) gas quality tracking using measured entities.
ISO 15112:2018(E)
To achieve a high accuracy of calorific value measurement, representative sampling is required.
Guidelines are given in ISO 10715.
Depending on the measuring system, the operating procedures, the fluctuation of composition of the
gas, and/or the quantity of gas delivered, one of the following sampling techniques can be used:
— continuous direct sampling;
— periodical spot sampling;
— incremental sampling.
Samples are taken for either online analysis or offline analysis.
6.3.2 Direct measurement — Calorimetry
With direct measurement, natural gas at a constant flow rate is burned in an excess of air and the
energy released is transferred to a heat-exchange medium resulting in an increase in its temperature.
The calorific value of the gas is directly related to the temperature increase.
Calorimetry is used for interfaces 1 to 3 and 5. ISO 15971 gives details of the measurement of combustion
properties.
6.3.3 Inferential measurement
With inferential measurement, the calorific value shall be calculated from the gas composition in
accordance with ISO 6976.
The most widely used analytical technique is gas chromatography. Procedures for the determination of
the composition with defined uncertainty by gas chromatography are given in ISO 6974 (all parts). GC
measurement is used at interfaces 1 to 3 and 5.
6.3.4 Correlation techniques
Correlation techniques make use of the relationships between one or more physical properties and the
calorific value of the gas. Also, the principle of stoichiometric combustion can be used.
6.3.5 Pressure and temperature
Pressure and temperature measurements can be necessary for the conversion of the gas volume under
operating conditions to a volume under standard reference or normal conditions. Details are given in
ISO 15970.
6.3.6 Gas quality tracking
On the basis of input data (grid topology, gas quality, gas quantity, pressures), flow conditions
throughout the grid shall be determined using a flow mechanics calculation. On t
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