SIST EN ISO 21654:2021

SLOVENSKI STANDARD
01-oktober-2021
Nadomešča:
SIST EN 15400:2011
Trdna alternativna goriva - Določevanje kalorične vrednosti (ISO 21654:2021)
Solid recovered fuels - Determination of calorific value (ISO 21654:2021)
Feste Sekundärbrennstoffe - Bestimmung des Brennwertes (ISO 21654:2021)
Combustibles solides de récupération - Détermination du pouvoir calorifique (ISO
21654:2021)
Ta slovenski standard je istoveten z: EN ISO 21654:2021
ICS:
75.160.10 Trda goriva Solid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 21654
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2021
EUROPÄISCHE NORM
ICS 75.160.10 Supersedes EN 15400:2011
English Version
Solid recovered fuels - Determination of calorific value
(ISO 21654:2021)
Combustibles solides de récupération - Détermination Feste Sekundärbrennstoffe - Bestimmung des
du pouvoir calorifique (ISO 21654:2021) Brennwertes (ISO 21654:2021)
This European Standard was approved by CEN on 19 March 2021.

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, 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
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21654:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 21654:2021) has been prepared by Technical Committee ISO/TC 300 "Solid
recovered materials, including solid recovered fuels" in collaboration with Technical Committee
CEN/TC 343 “Solid Recovered Fuels” the secretariat of which is held by SFS.
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 January 2022, and conflicting national standards shall
be withdrawn at the latest by January 2022.
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 15400:2011.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN websites.
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, 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, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 21654:2021 has been approved by CEN as EN ISO 21654:2021 without any modification.

INTERNATIONAL ISO
STANDARD 21654
First edition
2021-06
Solid recovered fuels — Determination
of calorific value
Combustibles solides de récupération — Détermination du pouvoir
calorifique
Reference number
ISO 21654:2021(E)
©
ISO 2021
ISO 21654:2021(E)
© ISO 2021
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
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 21654:2021(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 Gross calorific value . 2
4.2 Net calorific value . 3
5 Reagents . 3
6 Laboratory conditions . 4
7 Apparatus . 5
7.1 General . 5
7.2 Auxiliary equipment . 7
7.3 Balances . 7
8 Preparation of test sample . 8
9 Calorimetric procedure . 8
9.1 General . 8
9.2 Preparing the combustion vessel for measurement . 9
9.2.1 General procedure . 9
9.2.2 Using combustion aids .10
9.3 Assembling the calorimeter .11
9.4 Combustion reaction and temperature measurements .11
9.5 Analysis of products of combustion .12
9.6 Corrected temperature rise θ .12
9.6.1 Observed temperature rise .12
9.6.2 Isoperibol and static-jacket calorimeters .12
9.6.3 Adiabatic calorimeters .14
9.6.4 Thermometer corrections .14
9.7 Reference temperature .14
10 Calibration .14
10.1 Principle .14
10.2 Calibration reference .15
10.2.1 Certification conditions.15
10.2.2 Calibration conditions .15
10.3 Valid working range of the effective heat capacity ε .15
10.4 Ancillary contributions .16
10.5 Calibration procedure .16
10.6 Calculation of effective heat capacity for the individual experiment .17
10.6.1 Constant mass-of-calorimeter-water basis .17
10.6.2 Constant total-calorimeter-mass basis .17
10.7 Precision of the mean value of the effective heat capacity ε .18
10.7.1 Constant value of ε . .18
10.7.2 ε as a function of the observed temperature rise.19
10.8 Repetition of the determination of effective heat capacity .19
11 Gross calorific value .19
11.1 General .19
11.2 Combustion .20
11.3 Calculation of gross calorific value .20
ISO 21654:2021(E)
11.3.1 General.20
11.3.2 Constant mass-of-calorimeter-water basis .20
11.3.3 Constant total-calorimeter-mass basis .22
11.3.4 ε as a function of the observed temperature rise.23
11.4 Expression of results .23
11.5 Calculation to other bases .23
12 Precision .24
12.1 Repeatability limit .24
12.2 Reproducibility limit .24
13 Calculation of net calorific value at constant pressure .24
13.1 General .24
13.2 Calculations .24
14 Test report .25
Annex A (normative) Adiabatic combustion vessel calorimeters .27
Annex B (normative) Isoperibol and static-jacket combustion vessel calorimeters .31
Annex C (normative) Automated combustion vessel calorimeters .36
Annex D (normative) Removed ash contributors .39
Annex E (informative) Checklists for the design and procedures of combustion experiments .42
Annex F (informative) Examples to illustrate the main calculations used in this document if
an automated (adiabatic) combustion vessel calorimeter is used for determinations .47
Annex G (informative) List of symbols used in this document .50
Annex H (informative) Flow chart for a routine calorific value determination .53
Annex I (informative) Interlaboratory test results .54
Annex J (informative) Additional terms for the basis of results expression .57
Annex K (informative) Environmental aspects .58
Bibliography .60
iv © ISO 2021 – All rights reserved

ISO 21654:2021(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 of 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 www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 300, Solid recovered fuels, in collaboration
with the European Committee for Standardization (CEN) Technical Committee CEN/TC 343, Solid
Recovered Fuels, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
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 21654:2021(E)
Introduction
[1]
This document is based on EN 15400 .
The result obtained is the gross calorific value of the sample analysed at constant volume with all the
water of the combustion products as liquid water. In practice, solid recovered fuels are burned at a
constant (atmospheric) pressure and the water is either not condensed (removed as vapour with the
flue gases) or condensed. Under both conditions, the operative heat of combustion to be used is the net
calorific value of the fuel at constant pressure. The net calorific value at constant volume can also be
used; Formulas are given for calculating both values.
General principles and procedures for the calibrations and the solid recovered fuels experiments are
presented in the main part of this document, whereas those pertaining to the use of a particular type of
calorimetric instrument are specified in Annexes A to C. Annex D contains the formulae to calculate the
removed ash contributors. Annex E contains checklists for performing calibration and fuel experiments
using specified types of calorimeters. Annex F gives examples to illustrate some of the calculations.
vi © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 21654:2021(E)
Solid recovered fuels — Determination of calorific value
WARNING — Strict adherence to all of the provisions specified in this document should ensure
against explosive rupture of the combustion vessel, or a blow-out, provided that the vessel is of
standard design and construction and in good mechanical condition.
1 Scope
This document specifies a method for the determination of gross calorific value of solid recovered
fuels at constant volume and at the reference temperature 25 °C in a combustion vessel calorimeter
calibrated by combustion of certified benzoic acid.
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 10304-1, Water quality — Determination of dissolved anions by liquid chromatography of ions —
Part 1: Determination of bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate
ISO 16993, Solid biofuels — Conversion of analytical results from one basis to another
ISO 21637, Solid recovered fuels — Vocabulary
ISO 21644, Solid recovered fuels — Methods for the determination of biomass content
1)
ISO 21646, Solid recovered fuels — Sample preparation
ISO 21660-3, Solid recovered fuels — Determination of moisture content using the oven dry method —
Part 3: Moisture in general analysis sample
EN 15358, Solid recovered fuels — Quality management systems — Particular requirements for their
application to the production of solid recovered fuels
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21637 and the following 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 http:// www .electropedia .org/
3.1
gross calorific value at constant volume
absolute value of the specific energy of combustion, in Joules, for unit mass of a solid recovered fuel
burned in oxygen in a calorimetric combustion vessel under the conditions specified
Note 1 to entry: The products of combustion are assumed to consist of gaseous oxygen, nitrogen, carbon dioxide
and sulfur dioxide, of liquid water (in equilibrium with its vapour) saturated with carbon dioxide under the
conditions of the combustion vessel reaction, and of solid ash, all at the reference temperature (3.4).
1) Under preparation. Stage at the time of publication: ISO/DIS 21646:2021.
ISO 21654:2021(E)
3.2
net calorific value at constant volume
absolute value of the specific energy of combustion, in Joules, for unit mass of a solid recovered fuel
burned in oxygen under conditions of constant volume and such that all the water of the reaction
products remains as water vapour (in a hypothetical state at 0,1 MPa), the other products being, as for
the gross calorific value, all at the reference temperature (3.4)
3.3
net calorific value at constant pressure
absolute value of the specific heat (enthalpy) of combustion, in Joules, for unit mass of a solid recovered
fuel burned in oxygen at constant pressure under such conditions that all the water of the reaction
products remains as water vapour (at 0,1 MPa), the other products being as for the gross calorific value,
all at the reference temperature (3.4)
3.4
reference temperature
international reference temperature for thermo-chemistry of 25 °C is adopted as the reference
temperature for calorific values (see 9.7)
Note 1 to entry: The temperature dependence of the calorific value of solid recovered fuels is small [less than 1 J/
(g ⋅ K)].
3.5
effective heat capacity of the calorimeter
amount of energy required to cause unit change in temperature of the calorimeter
3.6
corrected temperature rise
change in calorimeter temperature caused solely by the processes taking place within the combustion
vessel calorimeter
Note 1 to entry: It is the total observed temperature rise corrected for heat exchange, stirring power etc. (see 9.6).
Note 2 to entry: The change in temperature can be expressed in terms of other units: resistance of a platinum or
thermistor thermometer, frequency of a quartz crystal resonator etc., provided that a functional relationship is
established between this quantity and a change in temperature. The effective heat capacity of the calorimeter (3.5)
can be expressed in units of energy per such an arbitrary unit. Criteria for the required linearity and closeness in
conditions between calibrations and fuel experiments are given in 9.3.
Note 3 to entry: A list of the symbols used and their definitions is given in Annex G.
Note 4 to entry: Annex J explains additional relevant terms that could be of interest, more specifically in
association to Annex D. The terms can provide some clarification in certain cases.
3.7
removed ash contributors
rac
coarse inert material (i.e. metals, glass, stones, tiles, etc.) removed from the sample before preparation,
in order to avoid damage to the preparation equipment
Note 1 to entry: The removed ash contributors (rac), after sample pre-drying, are taken into account for the
calculation of the ash, carbon, hydrogen, nitrogen and sulfur content in the analysed sample.
Note 2 to entry: See Annex D for further information.
4 Principle
4.1 Gross calorific value
A weighed portion of the analysis sample of a solid recovered fuel is burned in high-pressure oxygen
in a combustion vessel calorimeter under specified conditions. The effective heat capacity of the
2 © ISO 2021 – All rights reserved

ISO 21654:2021(E)
calorimeter is determined in calibration experiments by the combustion of certified benzoic acid under
similar conditions, accounted for in the certificate. The corrected temperature rise is established from
observations of temperature before, during and after the combustion reaction takes place. The duration
and frequency of the temperature observations depend on the type of calorimeter used. Water is added
to the vessel initially to give a saturated vapour phase prior to combustion (see 9.2.1 and 10.2.2),
thereby allowing all the water formed, from the hydrogen and moisture in the sample, to be regarded
as liquid water.
The gross calorific value is calculated from the corrected temperature rise and the effective heat
capacity of the calorimeter, with allowances made for contributions from ignition energy, combustion of
the fuse(s) and for thermal effects from side reactions such as the formation of nitric acid. Furthermore,
a correction is applied to account for the difference in energy between the aqueous sulfuric acid formed
in the combustion vessel reaction and gaseous sulfur dioxide, i.e. the required reaction product of sulfur
in the solid recovered fuel. The corresponding energy effect between aqueous and gaseous hydrochloric
acid can be negligible for solid recovered fuels of mainly biomass origin.
The corresponding energy effect between aqueous and gaseous hydrochloric acid depends on the
sample characteristics, e.g. the content of inorganic and organic chlorine, mineral composition and the
actual pH-value in combustion vessel liquid. At the present time no values are available for this chlorine
correction. Attention should be paid to the extremely high chlorine content in the test sample because
e.g. PVC fractions can affect the calorific value significantly.
Automatic equipment may be used if the method is validated by parallel measurements. This automatic
equipment shall fulfil all the requirements regarding sample size, heating procedure, temperature,
atmosphere, and weighing accuracy. Deviations from this paragraph shall be reported and justified.
NOTE Annex H shows a flow chart for a routine determination of calorific value.
4.2 Net calorific value
The net calorific value at constant volume and the net calorific value at constant pressure of the solid
recovered fuel are obtained by calculation from the gross calorific value at constant volume determined
on the analysis sample. The calculation of the net calorific value at constant volume requires information
about the moisture and hydrogen contents of the analysis sample. In principle, the calculation of the net
calorific value at constant pressure also requires information about the oxygen and nitrogen contents
of the sample.
NOTE Annex H shows a flow chart for a routine determination of calorific value.
5 Reagents
5.1 Oxygen, at a pressure high enough to fill the combustion vessel to 3 MPa, pure with an assay of at
least 99,5 % volume fraction, and free from combustible matter.
NOTE Oxygen made by the electrolytic process can contain up to 4 % volume fraction of hydrogen.
5.2 Fuse
5.2.1 Ignition wire, of nickel-chromium 0,16 mm to 0,20 mm in diameter, platinum 0,05 mm to
0,10 mm in diameter, or another suitable conducting wire with well-characterized thermal behaviour
during combustion.
5.2.2 Cotton fuse, of white cellulose cotton, or equivalent, if required (see NOTE 1 of 9.2.1).
5.3 Combustion aids, of known gross calorific value, composition and purity, e.g. benzoic acid,
n-dodecane, paraffin oil, combustion bags or capsules.
ISO 21654:2021(E)
5.4 Standard volumetric solutions and indicators, only for use if analysis of final combustion vessel
solutions is required.
5.4.1 Barium hydroxide solution, c[Ba(OH) ] = 0,05 mol/l.
5.4.2 Sodium carbonate solution, c(Na C0 ) = 0,05 mol/l.
2 3
5.4.3 Sodium hydroxide solution, c(NaOH) = 0,1 mol/l.
5.4.4 Hydrochloric acid solution, c(HCI) = 0,1 mol/l.
5.4.5 Screened methyl orange indicator, 1 g/l solution: dissolve 0,25 g of methyl orange and 0,15 g
of xylene cyanole FF in 50 ml of ethanol with a volume fraction of 95 % and dilute to 250 ml with water.
5.4.6 Phenolphthalein, 10 g/l solution: dissolve 2,5 g of phenolphthalein in 250 ml ethanol with a
volume fraction of 95 %.
5.5 Benzoic acid, of calorimetric-standard quality, certified by (or with certification unambiguously
traceable to) a recognized standardizing authority.
NOTE 1 Benzoic acid is the sole substance recommended for calibration of an oxygen-combustion vessel
calorimeter. For the purpose of checking the overall reliability of the calorimetric measurements, test substances,
e.g. n-dodecane, are used. Test substances are mainly used to prove that certain characteristics of a sample, e.g.
burning rate or chemical composition, do not introduce bias in the results.
NOTE 2 Annex K shows an environmental checklist (see Table K.1) that indicates possible environmental
aspects according to the analysis of solid recovered fuels to take into account.
NOTE 3 The benzoic acid is burned in the form of pellets. It is usually used without drying or any treatment
other than pelletizing; the sample certificate provides information. It does not absorb moisture from the
atmosphere at relative humidities below 90 %.
The benzoic acid shall be used as close to certification conditions as is feasible; significant departures
from these conditions shall be accounted for in accordance with the directions in the certificate. The
energy of combustion of the benzoic acid, as defined by the certificate for the conditions utilised, shall
be adopted in calculating the effective heat capacity of the calorimeter (see 10.2).
6 Laboratory conditions
The laboratory for the determination of calorific value shall meet the following conditions.
a) A laboratory for the determination of calorific value should not carry out other test items
simultaneously in the same room.
b) The room temperature should remain relatively stable, the change of room temperature should not
exceed 1 °C per measurement, and the room temperature should be in the range of (15-30) °C.
c) There should be no strong air convection in the room, so there should be no strong heat source, cold
source and fan, etc.
d) The experiment should avoid sunlight, otherwise the calorimeter should be placed in a place free
from direct sunlight.
4 © ISO 2021 – All rights reserved

ISO 21654:2021(E)
7 Apparatus
7.1 General
7.1.1 Calorimeter (see Figure 1), consists of the assembled combustion vessel (7.1.2), the calorimeter
can (7.1.3 ) (with or without a lid), the calorimeter stirrer (7.1.4), water, temperature sensor, and
leads with connectors inside the calorimeter can required for ignition of the sample or as part of
temperature measurement or control circuits. During measurements the calorimeter is enclosed in a
thermostat (7.1.5). The manner in which the thermostat temperature is controlled defines the working
principle of the instrument and hence the strategy for evaluation of the corrected temperature rise.
Key
1 stirrer (7.1.4) 5 calorimeter can (7.1.3)
2 thermostat lid 6 thermostat (7.1.5)
3 ignition leads 7 combustion vessel
4 thermometer
Figure 1 — Classical-type combustion vessel calorimeter with thermostat
In aneroid systems (systems without a fluid) the calorimeter can, stirrer and water are replaced by a
metal block. The combustion vessel itself constitutes the calorimeter in some aneroid systems.
In combustion vessel calorimetric instruments with a high degree of automation, especially in
the evaluation of the results, the calorimeter is in a few cases not as well-defined as the traditional,
classical-type calorimeter. Using such an automated calorimeter is, however, within the scope of
this document as long as the basic requirements are met with respect to calibration conditions,
comparability between calibration and fuel experiments, ratio of sample mass to combustion vessel
volume, oxygen pressure, vessel liquid, reference temperature of the measurements and repeatability
of the results. A print-out of some specified parameters from the individual measurements is essential.
Details are given in Annex C.
As the room conditions (temperature fluctuation, ventilation etc.) can have an influence on the precision
of the determination, the manufacturer's instructions for the placing of the instrument shall always be
followed.
Equipment, adequate for determinations of calorific value in accordance with this document, is
specified in 7.2 to 7.4.
ISO 21654:2021(E)
7.1.2 Combustion vessel, capable of withstanding safely the pressures developed during combustion.
The design shall permit complete recovery of all liquid products. The material of construction shall resist
corrosion by the acids produced in the combustion of solid recovered fuels. A suitable internal volume of
the combustion vessel would be from 250 ml to 350 ml.
WARNING — Combustion vessel parts shall be inspected regularly for wear and corrosion;
particular attention shall be paid to the condition of the threads of the main closure.
Manufacturers' instructions regarding the safe handling and use of the vessel shall be observed.
Take into account any local regulations regarding the safe handling and use of the vessel. If more
than one combustion vessel of the same design is used, it is imperative to use each vessel as a
complete unit. Swapping of parts can lead to a serious accident.
7.1.3 Calorimeter can, made of metal, highly polished on the outside and capable of holding an
amount of water sufficient to completely cover the flat upper surface of the combustion vessel while
the water is being stirred. A lid generally helps reduce evaporation of calorimeter water, but unless it
is in good thermal contact with the can it lags behind in temperature during combustion, giving rise to
undefined heat exchange with the thermostat and a prolonged main period.
7.1.4 Stirrer, working at constant speed. The stirrer shaft should have a low-heat-conduction and/or
a low-mass section below the cover of the surrounding thermostat (7.1.5) to minimise transmission of
heat to or from the system; this is of particular importance if the stirrer shaft is in direct contact with the
stirrer motor. If a lid is used for the calorimeter can (7.1.3), this section of the shaft should be above the
lid.
NOTE The rate of stirring for a stirred-water type calorimeter is determined large enough to make sure that
hot spots do not develop during the rapid part of the change in temperature of the calorimeter. A rate of stirring
such that the length of the main period can be limited to 10 min or less is usually adequate (see Annexes A and B).
7.1.5 Thermostat (water jacket), completely surrounding the calorimeter, with an air gap of
approximately 10 mm separating calorimeter and thermostat.
The mass of water of a thermostat intended for isothermal operation shall be sufficiently large to
outbalance thermal disturbances from the outside. The temperature should be controlled to within
± 0,1 K or better throughout the experiment. A passive constant temperature (“static”) thermostat
shall have a heat capacity large enough to restrict the change in temperature of its water. Criteria for
satisfactory behaviour of this type of water jacket are given in Annex B.
NOTE 1 For an insulated metal static jacket, satisfactory properties are usually ensured by making a wide
annular jacket with a capacity for water of at least 12,5 I.
NOTE 2 Calorimeters surrounded by insulating material, creating a thermal barrier, are regarded as
static-jacket calorimeters.
If the thermostat (water jacket) is required to follow closely the temperature of the calorimeter, it should
be of low mass and preferably have immersion heaters. Energy shall be supplied at a rate sufficient to
maintain the temperature of the water in the thermostat to within 0,1 K of that of the calorimeter water
after the charge has been fired. If in a steady state at 25 °C, the calculated mean drift in temperature of
the calorimeter shall not exceed 0,000 5 K/min (see A.3.2).
7.1.6 Temperature measuring instrument, capable of indicating temperature with a resolution of at
least 0,001 K so that temperature intervals of 2 K to 3 K can be determined with a resolution of 0,002 K
or better. The absolute temperature shall be known to the nearest 0,1 K at the reference temperature of
the calorimetric measurements. The temperature measuring device should be linear, or linearized, in its
response to changes in temperature over the interval it is used.
As alternatives to the traditional mercury-in-glass thermometers, suitable temperature sensors are
platinum resistance thermometers, thermistors, quartz crystal resonators etc. which together with
a suitable resistance bridge, null detector, frequency counter or other electronic equipment provide
the required resolution. Because of environmental aspects mercury (thermometers) should be the last
6 © ISO 2021 – All rights reserved

ISO 21654:2021(E)
option due to disposal concerns according the Minamata treaty. The short-term repeatability of this
type of device shall be 0,001 K or better. Long-term drift shall not exceed the equivalent of 0,05 K for a
period of six months. For sensors with linear response (in terms of temperature), drift is less likely to
cause bias in the calorimetric measurements than are non-linear sensors.
[2] [3] [4] [5]
Mercury-in-glass thermometers which conform to ISO 651 , ISO 652 , ISO 1770 or ISO 1771 satisfy
the requirements, but only to be used if no other options are available. A viewer with magnification
about 5× is needed for reading the temperature with the resolution required.
A mechanical vibrator to tap the thermometer is suitable for preventing the mercury column from
sticking (see 9.4). If this is not available, the thermometer shall be tapped manually before reading the
temperature.
7.2 Auxiliary equipment
7.2.1 Crucible, of silica, nickel-chromium, platinum or similar unreactive material.
The crucible should be 15 mm to 25 mm in diameter, flat based and about 20 mm deep. Silica crucibles
should be about 1,5 mm thick and metal crucibles about 0,5 mm thick.
If smears of unburned carbon occur, a small low-mass platinum or nickel-chromium crucible, for
example 0,25 mm thick, 15 mm in diameter and 7 mm deep, may be used.
7.2.2 Ancillary pressure equipment
7.2.2.1 Pressure regulator, to control the filling of the combustion vessel with oxygen.
7.2.2.2 Pressure gauge (e.g. 0 MPa to 5 MPa), to indicate the pressure in the combustion vessel with a
resolution of 0,05 MPa.
7.2.2.3 Relief valve or bursting disk, operating at 3,5 MPa, and installed in the filling line, to prevent
overfilling the combustion vessel.
CAUTION — Equipment for high-pressure oxygen shall be kept free from oil and grease (high
vacuum grease recommended by the manufacturer may be used according to the operating
manual of the instrument). Do not test or calibrate the pressure gauge with hydrocarbon fluid.
7.2.3 Ignition cir
...