ASTM E3137/E3137M-18

Standard Specification for Heat Meter Instrumentation

ABSTRACT
This specification applies to heat meters used to measure heat in heat exchange circuits in which energy is absorbed (cooling) or given up (heating) by a flowing liquid. For this specification, the necessary elements of a heat meter consist of a sensor to measure flow of the heat-conveying liquid, a pair of temperature sensors that measure the temperature differential across the heat exchange circuit, and a device that receives input from the flow and temperature sensors and calculates energy. This specification does not cover electrical safety or mechanical safety (including pressure safety).
This specification defines heat meters as complete or combined instruments. A complete instrument refers to a heat meter that does not have separable subassemblies, while a combined meter is a heat meter that has separable subassemblies. It specifies the allowable flow rate maximum permissible error (MPE) by accuracy class and turndown; the combined allowable error percentages for the temperature sensor pair and the heat calculator for measured difference temperatures in –17°C [2°F] increments; maximum lead cross section and length requirements; types of instruments; metrological characteristics of flow sensors of heat meters and complete instruments; data exchange and communications protocols; heat meter testing methods; operating conditions during testing; type approval tests and measurements; surge transients for signal and dc lines; surge transients for ac power lines; carrier frequencies; field strength; initial verification tests; test temperature ranges; product marking and inscriptions; and installation and operation instructions.
SCOPE
1.1 This specification defines general specifications for heat meters. Heat meters are instruments that measure heat in heat exchange circuits in which energy is absorbed (cooling) or given up (heating) by a flowing liquid.  
1.2 For this specification, the necessary elements of a heat meter consist of a sensor to measure flow of the heat-conveying liquid, a pair of temperature sensors that measure the temperature differential across the heat exchange circuit, and a device that receives input from the flow and temperature sensors and calculates energy.  
1.3 Electrical safety is not a part of this specification.  
1.4 Mechanical safety (including pressure safety) is not a part of this specification.  
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2018
• ICS: 17.200.10 - Heat. Calorimetry
• Technical Committee: E44 - Solar, Geothermal and Other Alternative Energy Sources
• Drafting Committee: E44.25 - Heat Metering

Relations

• Replaces: ASTM E3137/E3137M-17 - Standard Specification for Heat Meter Instrumentation
• Effective Date: 01-Apr-2018

Overview

ASTM E3137/E3137M-18: Standard Specification for Heat Meter Instrumentation defines the general requirements for heat meters used for measuring heat in heat exchange circuits where energy is either absorbed (cooling) or released (heating) by a flowing liquid. These meters are essential for accurately monitoring, controlling, and billing the energy used in heating and cooling applications. The standard ensures that manufacturers and users have a consistent set of criteria relating to performance, accuracy, construction, installation, and operability.

ASTM E3137/E3137M-18 establishes the elements required for a heat meter, including:

• A sensor to measure the flow of the heat-conveying liquid
• A pair of temperature sensors to determine temperature differential across the circuit
• A device that receives input from the flow and temperature sensors and calculates the transferred energy

The specification addresses allowable flow rates, maximum permissible error (MPE) by accuracy class, environmental considerations, and important installation and verification procedures, but does not cover electrical or mechanical safety aspects.

Key Topics

1. Types of Heat Meters

• Complete heat meters: Devices with inseparable subassemblies.
• Combined heat meters: Meters with separable subassemblies (flow sensor, temperature sensor pair, heat calculator).
• Hybrid and subassembly considerations for combined meters.

2. Accuracy and Performance

• Accuracy Classes: Class 1 (highest), Class 2, and Class 3 - based on flow sensor precision.
• Temperature difference measurement: Must specify both lower and upper limits for reliable operation.
• Maximum Permissible Error (MPE): Defined for flow sensors, temperature sensors, and heat calculators.

3. Construction and Installation Criteria

• Sensors: Construction requirements for flow sensors and temperature sensor pairs, including materials, minimum immersion or insertion depths, and compatibility with thermowells.
• Process Connections: Must comply with recognized standards such as NPT, ANSI, or AWWA.
• Protection: Requirements to prevent fraud or unauthorized tampering, such as security seals and enclosure ratings (e.g., NEMA 3R, IP54).

4. Environmental Classification

• Environmental Classes (A, B, C, D): Define the suitability of heat meters for different installation environments (e.g., domestic indoor, outdoor, industrial), including specified temperature ranges and required levels of protection against dust, moisture, and electromagnetic interference.

5. Data Exchange and Testing

• Communication protocols: Reference to IEC and NEMA standards for data exchange and telecontrol.
• Testing: Requirements for type approval, initial verification, and ongoing metrological control.

Applications

Heat meters conforming to ASTM E3137/E3137M-18 are crucial for:

• District heating and cooling systems: For accurate submetering and energy allocation
• Building management: To optimize HVAC system performance and support fair billing practices in residential, commercial, and industrial facilities
• Industrial process monitoring: Ensuring process efficiency in applications where precise heat measurement is necessary
• Compliance and certification: Helping manufacturers and end users demonstrate conformance to standardized criteria for metering accuracy, installation, and operation

By adhering to this standard, utility providers, facility managers, and engineers can confidently select and install heat meters that meet performance, accuracy, and reliability requirements for their specific application environments.

Related Standards

Several international and industry standards are referenced within ASTM E3137/E3137M-18 for compatibility, metrology, and environmental testing, including:

• ITS-90 International Temperature Scale of 1990
• IAPWS-IF97: Industrial Formulation for Water and Steam Properties
• IEC 61000 Series: Electromagnetic compatibility and environmental testing
• IEC 60529 & NEMA 250: Degrees of protection and enclosure standards
• OIML R75: Heat meters - General requirements and type approval
• OIML D11: Environmental conditions for measuring instruments

These related standards collectively ensure that heat meter instrumentation is robust, accurate, and suitable for a wide range of conditions, supporting interoperability and international compliance.

Keywords: ASTM E3137/E3137M-18, heat meter instrumentation standard, heating and cooling measurement, maximum permissible error (MPE), flow sensor, temperature sensor, district heating, submetering, metrological characteristics, environmental classification.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:E3137/E3137M −18
Standard Specification for
1,2
Heat Meter Instrumentation
ThisstandardisissuedunderthefixeddesignationE3137/E3137M;thenumberimmediatelyfollowingthedesignationindicatestheyear
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This specification defines general specifications for heat 2.1 CCT Standard:
meters. Heat meters are instruments that measure heat in heat ITS-90 International Temperature Scale of 1990
exchange circuits in which energy is absorbed (cooling) or 2.2 IAPWS Standard:
given up (heating) by a flowing liquid. IAPWS-IF97 Industrial Formulation 1997 for the Thermo-
dynamic Properties of Water and Steam
1.2 For this specification, the necessary elements of a heat
2.3 IEC Standards:
meterconsistofasensortomeasureflowoftheheat-conveying
IEC 61000 Part 4-2 Electrostatic Discharge Immunity Test
liquid, a pair of temperature sensors that measure the tempera-
IEC 61000 Part 4-3 Radiated, Radio-Frequency, Electro-
ture differential across the heat exchange circuit, and a device
magnetic Field Immunity Test
that receives input from the flow and temperature sensors and
IEC61000Part4-4 ElectricalFastTransient/BurstImmunity
calculates energy.
Test
1.3 Electrical safety is not a part of this specification.
IEC 61000 Part 4-5 Surge Immunity Test
1.4 Mechanical safety (including pressure safety) is not a IEC 60068: Environmental Testing Part 2.1 Test A: Cold
IEC 60068: Environmental Testing Part 2.2 Tests B: Dry
part of this specification.
Heat
1.5 The values stated in either SI units or inch-pound units
IEC 60068: Environmental Testing Part 2-30 Tests Db:
are to be regarded separately as standard. The values stated in
Damp Heat, cyclic
each system may not be exact equivalents; therefore, each
IEC 60529 Degrees of protection provided by enclosures (IP
system shall be used independently of the other. Combining
Code)
values from the two systems may result in nonconformance
IEC 60751 Industrial platinum resistance thermometer and
with the standard.
platinum temperature sensors
1.6 This standard does not purport to address all of the
IEC 60870 Part 5-1 Telecontrol equipment and systems
safety concerns, if any, associated with its use. It is the
IEC 61107 Data exchange for meter reading, tariff and load
responsibility of the user of this standard to establish appro-
control—Direct local data exchange
priate safety, health, and environmental practices and deter-
IEC TR 61000 Electromagnetic compatibility—Part 2:
mine the applicability of regulatory limitations prior to use.
Environment—Section 7: Low frequency magnetic fields
1.7 This international standard was developed in accor-
in various environments
dance with internationally recognized principles on standard-
2.4 NEMA Standards:
ization established in the Decision on Principles for the
NEMA250 Enclosures for Electrical Equipment (1000Volts
Development of International Standards, Guides and Recom-
Maximum)
mendations issued by the World Trade Organization Technical 7
2.5 OIML Standards:
Barriers to Trade (TBT) Committee.
OIML D11 General Requirements for measuring
instruments—Environmental conditions
OIMLR 49 Part 2 Water meters intended for the metering of
This specification is under the jurisdiction of ASTM Committee E44 on Solar, cold potable water and hot water
Geothermal and OtherAlternative Energy Sources and is the direct responsibility of
Subcommittee E44.25 on Heat Metering.
Current edition approved April 1, 2018. Published August 2018. Originally AvailablefromtheConsultativeCommitteeforThermometry,www.its-90.com.
approved in 2017. Last previous edition approved in 2017 as E3137/E3137M-17. Available from the International Association for the Properties of Water and
DOI: 10.1520/E3137_E3137M–18. Steam, www.iapws.org.
2 5
Through a mutual agreement with ASTM International (ASTM), the Interna- Available from the International Electrotechnical Commission, www.iec.ch.
tional Association of Plumbing and Mechanical Officials (IAPMO) contributed its Available from National Electrical Manufacturers Association (NEMA), 1300
technical expertise to ASTM, leading to the development of this ASTM Stan- N. 17th St., Suite 900, Arlington, VA 22209, http://www.nema.org.
dard. IAPMO and its membership continue to play an active role in providing Available from the International Organization of Legal Metrology,
technical guidance to the ASTM standards development process. www.oiml.org/en.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3137/E3137M−18
OIML R75-1 Part 1 General requirements changer. In heating systems, supply liquids will normally have
a higher temperature than return liquids. In cooling systems,
supply liquids will normally have a lower temperature than
3. Terminology
return liquids.
3.1 Definitions of Terms Specific to This Standard:
3.1.9 flow sensor, n—subassembly of a heat meter designed
3.1.1 conventional true value, n—value of a quantity, which
to measure the volume or mass of a flowing liquid in a heat
for the purpose of this specification, is considered as a true
exchange circuit.
value. OIML R75-1 2002
3.1.1.1 Discussion—A conventional true value is regarded,
3.1.10 heat calculator, n—heat meter subassembly that re-
in general, as sufficiently close to the true value for the
ceives flow and temperature signals from flow and temperature
difference to be insignificant for the given purpose. OIML
sensors and calculates and displays energy.
R75-1 2002
3.1.11 influence factor, n—influence quantity having a value
3.1.2 disturbance, n—influence quantity having a value
within the rated operating conditions. OIML R75-1 2002
outside the rated operating conditions. OIML R75-1 2002
3.1.12 influence quantity, n—quantity that is not the mea-
3.1.3 electronic device, n—device using electronic compo-
surand but that affects the result of the measurement. OIML
nents and performing a specific function. OIML R75-1 2002
R75-1 2002
3.1.4 equipment under test, n—subassembly, a combination
3.1.13 meter model, n—different sizes of heat meters or
of subassemblies, or a complete meter subject to a test. OIML
subassemblies having a family similarity in the principles of
R75-1 2002
operation, construction, and materials. OIML R75-1 2002
3.1.5 error types, n—
3.1.14 minimum immersion depth of a temperature sensor,
3.1.5.1 durability error, n—difference between the intrinsic
n—depth of immersion in a thermostatic bath with a tempera-
error after a period of use and the initial intrinsic error. OIML
ture of 80 6 5°C [176 6 9°F] at an ambient temperature of
R75-1 2002
25 6 5°C [77 6 9°F], beyond which deeper immersion
3.1.5.2 error (of indication) of a measuring instrument,
changes the output value by an amount corresponding to less
n—indication of the measuring instrument minus the conven- than 0.1 K [0.18°F]. OIML R75-1 2002
tional true value of the corresponding input quantity. OIML
3.1.15 platinum resistance thermometer, PRT,
R75-1 2002
n—temperature responsive device consisting of one or more
3.1.5.3 initial intrinsic error, n—intrinsic error of a measur-
sensing platinum resistors within a protective sheath with
ing instrument as determined before performance and durabil- internal connecting wires and external terminals to permit
ity tests.
connection of electrical measurement instruments.
3.1.15.1 Discussion—Mounting means and connection
3.1.5.4 intrinsic error (of a measuring instrument), n—error
heads may be included. Not included is any separable protec-
of a measuring instrument determined under reference
tion tube or thermowell.
conditions. OIML R75-1 2002
3.1.16 platinum resistor, n—resistor made from platinum
3.1.5.5 maximum permissible error, MPE, n—extreme val-
wire or film with defined electrical characteristics, embedded
ues of the error (positive or negative) permitted by this
in an insulator (in most cases glass or ceramic), designed to be
specification. OIML R75-1 2002
assembled into a resistance thermometer or an integrated
3.1.6 fast response meter, n—heat meter designed for use in
circuit.
heat exchange circuits in which sudden or rapid changes, or
3.1.17 rated operating conditions, n—conditions of use for
both, in flow or temperature are a normal condition. OIML
which specified metrological characteristics of a measuring
R75-1 2002
instrument are intended to lie within the specified maximum
3.1.7 fault types, n—
permissible errors. OIML R75-1 2002
3.1.7.1 fault, n—difference between the error of indication
and the intrinsic error of the instrument. OIML R75-1 2002 3.1.18 rated voltage, U,n—voltage of an external power
n
supply required to operate a heat meter.
3.1.7.2 significant fault—fault greater than the absolute
3.1.19 reference conditions, n—conditions of use prescribed
value of the MPE that is not a transitory fault, for example, if
the MPE is 62 %, then a significant fault is a fault larger than for testing the performance of a measuring instrument or
2%. OIML R75-1 2002 intercomparison of results of measurements. OIML R75-1
3.1.7.3 transitory fault—momentary variations in the indi-
3.1.20 reference values of the measurand, RVM,
cation that cannot be interpreted, memorized, or transmitted as
measurements. OIML R75-1 2002 n—specified set of values of the flow rate, the return
temperature, and the temperature difference fixed to ensure
3.1.8 flow direction, n—indication of directionality for a
valid intercomparison of the results of measurements. OIML
flowing liquid within a piping system leading to and exiting
R75-1 2002
from a heat exchange circuit.
3.1.8.1 Discussion—The term supply (or inlet) is used to 3.1.21 response time, τ0.5, n—time interval between the
indicate liquid traveling to the heat exchanger and the term instant when the flow, the temperature, or the temperature
return (or outlet) describes the liquid exiting the heat ex- difference is subjected to a specified abrupt change and the
E3137/E3137M−18
instant when the response reaches 50 % of its final steady operating flow rate (Q). This is the turndown for the sensor.
value. OIML R75-1 2002 Whenselectingaflowsensor,itisnecessarytoidentifyfirstthe
maximum flow rate for the application. This maximum flow
3.1.22 self-heating effect, n—increase in temperature signal
rate shall be compared to the upper flow limit (Q ) and the Q
s p
that is obtained by subjecting each temperature sensor of a pair
as stated by the flow meter manufacturer for the flow sensor
to a continuous power dissipation of 5 mW when immersed to
under consideration. Next, identify the minimum flow rate for
the minimum immersion depth in a water bath having a mean
the application. Compare this value to the Q as stated by the
i
water velocity of 0.1 m/s [0.328 ft/s]. OIML R75-1 2002
flow meter manufacturer. Flow sensors should be selected that
4. Significance and Use
will operate within these upper and lower flow limits. Once the
upper and lower flow limits are defined (turndown), the
4.1 This document is based, in part, on OIML R 75-1
accuracy limits by class can be determined from Table 1.
Edition 2002, Heat meters Part 1: General requirements and
5.6.3 Table 1 shows the range of allowable error (E) for the
OIMLR 75-2 Edition 2002, Heat meters Part 2: Type approval f
flow sensor by class and turndown range for use in MPE
tests and initial verification tests. R 75 is an International
equations in 8.3. For clarity, turndown is expressed as Q /Q in
Recommendation published by OIML. International Recom- p i
Table 1.
mendations are model regulations that establish the metrologi-
cal characteristics required of certain measuring instruments
5.7 Temperature Sensor Pairs and Heat Calculator:
and which specify methods and equipment for checking their
5.7.1 The MPE of the temperature sensor pair is a function
conformity. As an OIML Member State, The United States is
of the lower limit of the temperature difference as described in
obligated to utilize these recommendations, where possible,
9.4 and 9.5. The three lower limits for the temperature
when developing standards that meet the needs of the market
difference range are 1, 2, and 3 K [1.8, 3.6, or 5.4°F]. As with
and may result in either terminology or definitions specific to
the flow sensor, the highest percentage measurement error will
this standard and deviations in standard form and style.
occur at the minimum operating level. In this case, it is the
lowest differential temperature.
5. Using this Specification
5.7.2 The heat calculator MPE is also defined by the lower
5.1 This specification is intended to provide both manufac-
limit of the temperature difference range (1, 2, or 3 K) as
turers and users of heat meters with important information.
described in 10.4. As is the case with the temperature sensor
pair,thehighestpercentagemeasurementerrorwilloccuratthe
5.2 Manufacturers will use this specification to certify that
minimum temperature differential.
their products conform to industry standards for accuracy,
5.7.3 When selecting a temperature sensor pair, it is neces-
performance, and reliability.
sary to identify the minimum and maximum operating tem-
5.3 End users and specifying engineers will use this speci-
peratures for the application and confirm that they fall within
fication as a guide in understanding how heat meters are
the operating limits of the individual temperature sensors.
defined based on performance and accuracy classifications for
Next, identify and compare the maximum and minimum
flow, temperature, and energy. They will also use this specifi-
temperature difference for the application with the upper limit
cation to ensure that the meter will be suitable for use in the
of temperature difference (∆t ) and lower limit of tempera-
max
operating environment in which it will be installed.
ture difference (∆t ) as stated by the manufacturer. Tempera-
min
5.4 End users are strongly encouraged to review carefully
ture sensor pairs should be selected that will operate within the
the requirements of their specific application and then select a
∆t and ∆t at least 75 % of the time while never exceeding
max min
heat meter that will meet their needs based on the following
the ∆t . Once the ∆t and ∆t are defined, the accuracy
max max min
criteria:
limits can be determined from Table 2.
5.4.1 Flow Sensor Accuracy Class—Class 1, Class 2, or
Class 3;
5.4.2 Lower Limit of the Temperature Difference Range—1,
TABLE 1 Allowable Flow Rate MPE by Accuracy Class and
2, or 3 K [1.8, 3.6, or 5.4°F]; and
Turndown
5.4.3 Environmental Class—A, B, C, or D.
E at Minimum Flow E at Maximum Flow
f f
Class Turndown
5.5 Overall accuracy of the heat meter is defined as the
(Q = Q ), % (Q = Q ), %
i p
additive maximum permissible errors (MPE) of the flow
Class 1 10:1 1.10 1.01
25:1 1.25 1.01
sensor, the temperature sensor pair, and the heat calculator. See
50:1 1.50 1.01
Section 7 for additional information on maximum permissible
100:1 2.00 1.01
errors.
250:1 3.50 1.01
Class 2 10:1 2.20 2.02
5.6 Flow Sensors:
25:1 2.50 2.02
5.6.1 The three flow sensor accuracy classes are Class 1, 50:1 3.00 2.02
100:1 4.00 2.02
Class2,orClass3.Ineachclass,theaccuracyisdeterminedby
250:1 5.00 2.02
the MPE at the manufacturer’s stated minimum (Q) and
i Class 3 10:1 3.50 3.05
maximum permanent flow rate (Q ). See 8.2 for additional 25:1 4.25 3.05
p
50:1 5.00 3.05
information on flow sensor operating limits.
100:1 5.00 3.05
5.6.2 The MPE for each flow sensor varies with the flow
250:1 5.00 3.05
sensor accuracy class and the ratio of the Q to the actual
p
E3137/E3137M−18
TABLE 2 Temperature Sensor Pair MPE % in -16.6°C [2°F] ∆T
7.1.1 The class of the complete instrument is determined by
Increments for the Three Lower Limits of the Temperature
the class of the flow sensor.
Difference Range
7.1.2 The maximum permissible errors of heat meters,
A
Measured ∆T,°F 1K,% 2K,% 3K,%
positive or negative, in relation to the conventional true value
2 4.60 8.20 11.80
of the heat, are defined as relative errors varying as a function
4 2.80 4.60 6.40
of the temperature difference and flow rate.
6 2.20 3.40 4.60
8 1.90 2.80 3.70
7.1.3 The maximum permissible errors of subassemblies,
10 1.72 2.44 3.16
positive or negative, are calculated from the temperature
12 1.60 2.20 2.80
difference in the case of the heat calculator and the temperature
14 1.51 2.03 2.54
16 1.45 1.90 2.35
sensorpairandfromtheflowrateinthecaseoftheflowsensor.
18 1.40 1.80 2.20
20 1.36 1.72 2.08
7.2 Relative Error—The relative error, E, is expressed as:
A ¯
1°F50.5555°C
X 2 X
d c
E 5 * 100 % (1)
X
c
where:
5.7.4 Table 2 shows the combined allowable error percent-
X = indicated value, and
d
ages for the temperature sensor pair and the heat calculator for
X = conventional true value.
c
¯
measured difference temperatures (�T)in 1.11111°C@2°F# in-
7.3 Values of Maximum Permissible Errors (MPEs)—The
crements.
MPEs of a complete instrument are calculated as a function of
5.8 Environmental Classes—Heat calculators and complete
the temperature difference ratio (�t / �t) and the flow rate
min
heat meters are defined by one of the four environmental
ratio (q /q). The MPEs of the complete instrument of accuracy
p
classifications: A, B, C, or D. These are summarized in 10.10.
Classes 1, 2, and 3 are the arithmetic sums of E (in 8.3), E (in
f t
Heatcalculatorandheatmeterenvironmentalclassesshouldbe
9.5), and E (in 10.4).The classes of heat meters are defined by
c
selectedaccordingtotheneedsoftheapplicationinwhichthey
the class of the flow sensor.
will be used.
7.3.1 Class 1, Class 2, and Class 3:
E 5 E 1E 1E (2)
f t c
6. Types of Instruments
where:
6.1 This specification defines heat meters as complete or
combined instruments. E = maximum permissible error,
6.1.1 CompleteInstrument—Aheatmeterthatdoesnothave E = flow sensor error,
f
E = temperature sensor error, and
separable subassemblies as defined in 6.1.4.
t
E = heat calculator error.
6.1.2 Combined Meter—A heat meter that has separable
c
subassemblies as defined in 6.1.4.
8. Flow Sensor
6.1.3 Hybrid Meter—A heat meter that, for the purpose of
type approval and verification, can be treated as a combined
8.1 General—Flow sensors measure the volume or mass of
instrument as defined in 6.1.2. However, after verification, its
a flowing liquid in a heat exchange circuit. Flow sensors are
subassemblies will be treated as inseparable.
defined by the following parameters:
6.1.4 Subassemblies of a Heat Meter that is a Combined
8.1.1 Flow sensor operating limits,
Instrument—The flow sensor, the temperature sensor pair, and
8.1.2 Flow sensor accuracy classes,
the heat calculator or a combination of these.
8.1.3 Operating pressure,
6.1.4.1 Flow sensor—A subassembly installed at either the
8.1.4 Pressure drop,
supply or return of a heat exchange circuit and that emits a
8.1.5 Minimum and maximum liquid temperature,
signal, which is a function of the volume or the mass or the
8.1.6 Flow sensor operation outside the stated operating
volumetric or mass flow rate.
limits,
6.1.4.2 Temperature sensor pair—A subassembly (for
8.1.7 Process connection type,
mounting with or without thermowells) that senses the tem-
8.1.8 Flow sensor installation restrictions,
peratures of the heat-conveying liquid at the inlet and outlet of
8.1.9 Materials of construction,
a heat exchange circuit.
8.1.10 Protection against fraud, and
6.1.4.3 Heat calculator—A subassembly that receives sig-
8.1.11 Flow sensor verification of design.
nals from the flow sensor and the temperature sensors and
calculates and indicates the quantity of heat exchanged.
8.2 Flow Sensor Operating Limits:
6.1.5 Equipment under Test—Asubassembly, a combination
8.2.1 Lower Flow Limit—The lower limit of the flow rate,
of subassemblies, or a complete meter subject to a test.
q, is the lowest rate the sensor can operate at without
i
exceeding the maximum permissible error. The manufacturer
7. Metrological Characteristics
shall clearly indicate the limit, q.
i
7.1 General—Flow sensors of heat meters and complete 8.2.2 Upper Flow Limit—The upper limit of the flow rate,
instruments belong to one of the following three accuracy q , is the highest flow rate the sensor can operate at for short
s
classes: Class 1, Class 2, and Class 3. periods without exceeding the maximum permissible error.
E3137/E3137M−18
Short periods are defined as less than 1 h/day and as less than Process connections shall comply with National Pipe Thread
200 h/year. The manufacturer shall clearly indicate the limit, (NPT), American National Standards Institute (ANSI), Ameri-
q . can Water Works Association (AWWA), or other applicable
s
U.S. standards. For instruments with threaded process connec-
8.2.3 Permanent Flow Rate—The permanent flow rate, q ,
p
tions that do not meet this requirement, it will be acceptable to
is the highest rate the sensor can operate at continuously
supply heat meters with thread adapters that meet the appli-
without exceeding the maximum permissible error. The manu-
cable U.S. standards.
facturer shall clearly indicate the limit, q .
p
8.2.4 Flow Rate Range—The manufacturer shall clearly
8.9 Flow Sensor Installation Restrictions—The manufac-
indicate the ratio of the permanent flow rate to the lower flow
turer shall declare any limitations with regard to installation of
limit, and the ratio shall be at least 10.
the flow sensor including straight, unobstructed pipe lengths
required upstream and downstream of the meter. Any restric-
8.3 Flow Sensor Accuracy Classes—Flow sensors of heat
tions relating to its orientation with respect to the vertical shall
meters and complete instruments belong to one of the follow-
also be declared.
ing three accuracy classes: Class 1, Class 2, and Class 3.
8.3.1 The class of the complete instrument is determined by 8.10 Flow Sensor Materials of Construction—Flow sensor
the class of the flow sensor.
subassemblies and complete heat meters shall be of durable
construction from materials designed to resist wear and corro-
q
p
Class1:E 56 1 1 0.01 , but not more than 63.5 % (3)
S D
f sion that may be expected to result from prolonged exposure to
q
the heat transfer liquid.
q
p
8.10.1 The enclosure for the flow sensor shall protect the
Class2:E 56 2 1 0.02 , but not more than 65 % (4)
S D
f
q
interior against the ingress of water and dust. The minimum
q
p level of protection shall conform to NEMA 3R or IP54
Class3:E 56 3 1 0.05 , but not more than 65 % (5)
S D
f
q
(heating) or IP65 (cooling) (see IEC 60529 or NEMA 250).
where: 8.11 Protection against Fraud—Flow sensors shall be pro-
tected in such a way that, after the sensor has been correctly
E = flow sensor error,
installed, there is no possibility of dismantling or altering or
q = maximum permanent flow rate, and
p
adjusting the sensor without evident damage to the sensor or a
q = actual flow rate.
security seal(s).
8.4 Operating Pressure:
8.4.1 Minimum Operating Pressure—The manufacturer
9. Temperature Sensor Pair
shall state the minimum operating pressure that shall be
9.1 General—Temperature sensor pairs measure the tem-
maintained at the meter when operating at the upper flow limit.
perature of the flowing liquid in the heat exchange circuit. The
8.4.2 Maximum Operating Pressure—The manufacturer
sensors are installed such that one sensor measures the liquid
shallstatethemaximuminternalpressurethatcanbeappliedto
temperature at supply (inlet) and the other sensor measures
the flow sensor when operating at the maximum liquid tem-
temperature at the return (outlet) of the heat exchange circuit.
perature.
Temperature sensor pairs are defined by the following param-
8.5 Maximum Pressure Loss—The loss of pressure in the
eters:
heat-conveying liquid passing through the flow sensor when
9.1.1 Limits of temperature measurement range,
theflowsensorisoperatingatthepermanentflowrate,q ,shall
p
9.1.2 Temperature sensor accuracy,
not exceed 28 kPa [4 psi].
9.1.3 Limits of temperature difference,
9.1.4 Temperature sensor pair accuracy,
8.6 Minimum and Maximum Liquid Operating
Temperature—The manufacturer shall state the minimum and 9.1.5 Direct insertion sensors and sensors used with
thermowells,
maximum temperatures at which the flow sensor will operate
without exceeding the maximum permissible error, E. 9.1.6 Minimum insertion depth,
f
9.1.7 Sensor lengths,
8.7 Flow Sensor Operation outside the Stated Operating
9.1.8 The influence on a temperature sensor pair when
Limits—When the flow rate is less than a threshold value
installed in thermowells,
declared by the supplier, no registration is allowed.
9.1.9 Materials of construction,
NOTE 1—The flow rate through a “nominally” closed valve or the 9.1.10 Protection against fraud,
movement of liquid in the pipe behind a closed valve caused by thermal
9.1.11 Process connection type,
expansion and contraction shall not be recorded.
9.1.12 Maximum operating pressure,
8.7.1 For flow rates greater than q , the behavior of the
9.1.13 Sensing element types, and
s
meter, for example, the production of spurious or zero signals, 9.1.14 Restrictions on the use of platinum resistance tem-
shall be declared by the manufacturer. Flow rates greater than
perature sensors.
q shall not result in a positive error greater than 10 %.
s
9.2 Limits of Temperature Measurement Range:
8.8 Flow Sensor Process Connections—Complete heat me- 9.2.1 Lower Temperature Limit—The lower temperature
ters and flow sensor subassemblies are provided with threaded limit of the temperature measurement range, t , is the lowest
min
or flanged process connections as required by the application. temperature of the heat-conveying liquid at which the heat
E3137/E3137M−18
meter will function without exceeding the maximum permis- heat-conveying liquid flowing in the pipes transfers heat to the
sibleerrors.Thistemperaturelimitshallbeclearlystatedbythe thermowell and the thermowell transfers heat to the tempera-
manufacturer. ture sensor.
9.6.2 The manufacturer shall declare if the temperature
9.2.2 Upper Temperature Limit—The upper temperature
sensor pair provided is designed for use with thermowells.
limit of the temperature measurement range, t , is the highest
max
9.6.3 Temperature sensor pair installation methods shall be
temperature of the heat-conveying liquid at which the heat
symmetrical. The use of one direct insertion sensor and one
meter will function without exceeding the maximum permis-
thermowell is not permitted.
sible errors. The manufacturer shall clearly indicate the upper
9.6.4 The use of clamp-on temperature sensors is not
temperature limit, t .
max
permitted.
9.3 Temperature Sensor Absolute Accuracy—The relation-
9.6.5 Temperature Sensor Pair Immersion Depths—The
ship between the output of each individual temperature sensor
minimum allowable insertion depth for temperature sensors
of a pair and the conventional true value of temperature shall
shall be stated by the manufacturer based on the nominal pipe
not be greater than 2 K [3.6°F].
diameter and the length of the insertion temperature sensors.
Thepreferredimmersiondepthistothecenterofthepipe.This
9.4 Limits of Temperature Difference—The temperature
may not be practical in larger pipes. In all cases, the minimum
difference, �t, is the absolute value of the difference between
insertion depth shall be sufficient to ensure that further in-
the temperatures of the heat-conveying liquid at the supply and
creases in the insertion depth will not produce a change in
return of the heat-exchange circuit.
temperature measurement greater than 0.1 K [0.18°F]. (Refer
9.4.1 Lower Limit of Temperature Difference—The lower
to Annex A2.)
limit of the temperature difference, �t , is the lowest tem-
min
9.6.6 Temperature Sensor Lengths—The manufacturer shall
perature difference at which the heat meter shall clearly
provide the appropriate length temperature sensors according
function without the maximum permissible errors being ex-
to 9.6.5 based on the nominal pipe diameter in use in the heat
ceeded. The manufacturer shall indicate the lower limit of the
exchange piping system where the sensors are installed.
temperature difference, �t .
min
9.6.6.1 Temperaturesensordimensions—Sensordimensions
9.4.2 Upper Limit of Temperature Difference—The upper
are not defined by this specification.
limit of the temperature difference, �t , is the highest
max
9.6.6.2 Thermowell dimensions—The temperature sensor
temperature difference at which the heat meter shall function
manufacturer shall specify the length and diameter of ther-
without the maximum permissible errors being exceeded. The
mowell(s) to match the temperature sensor(s) if used.
manufacturer shall clearly indicate the upper limit of the
9.6.6.3 Influence on a temperature sensor pair when in-
temperature difference, �t .
max
stalled in thermowells—The difference in the temperature
9.4.3 Temperature Difference Range—The ratio of the upper
measurement with and without thermowells shall not exceed
and lower limits of the temperature difference shall clearly not
one third of the maximum permissible error.
be less than ten, with the exception of heat meters intended for
9.7 Methods and Materials of Construction—Direct inser-
cooling applications.The manufacturer shall indicate the lower
tion sensors and thermowells shall be constructed from mate-
limit of the temperature difference as 1, 2, or 3 K [1.8, 3.6, or
rials designed to resist wear and corrosion that may be
5.4°F].
expected to result from prolonged exposure to the heat-
9.5 Temperature Sensor Pair Accuracy—Temperature sen-
conveying liquid. The materials shall be suitable for use at the
sor pair accuracy is defined as:
heat-conveying liquid’s operating temperatures and pressures.
∆t
Thesensorsandthermowellsshallbedesignedtowithstandthe
min
E 56 0.5 1 3 (6)
S D
t
∆t
forces applied from the flowing liquid, and they shall have the
requisite thermal conductivity for the application.
where:
9.8 Protection against Fraud—Temperaturesensorsshallbe
E = temperature sensor pair accuracy,
t
protected in such a way that, after the sensor has been correctly
∆t = lower limit temperature difference, and
min
installed, there is no possibility of dismantling, altering, or
∆t = temperature difference measured across the heat
adjusting the sensor without evident damage to the sensor or a
exchange circuit.
security seal(s).
9.6 Direct Insertion Sensors and Thermowells—Direct in-
9.9 Process Connection Type—The temperature sensor pro-
sertion temperature sensors are designed to be immersed
cess connection type is not defined by this specification. NPT,
directly into the heat-conveying liquid. They are provided with
ANSI, or AWWA process connections are preferred. For
a process connection suitable for installation into the heat
instrumentswiththreadedprocessconnectionsthatdonotmeet
exchange piping system. Direct insertion sensors should be
this requirement, it will be acceptable to supply heat meters
used for heat exchange pipes with a nominal diameter of less
1 with thread adapters that meet the applicable U.S. standards.
than3cm[1 ⁄4 in.] (DN32) whenever possible as they provide
the most accurate temperature measurement.
9.10 Maximum Operating Pressure—The manufacturer
9.6.1 Thermowells are tubes closed at one end that are shall state the maximum operating pressure for the temperature
inserted into the heat exchange circuit pipes. The temperature sensor or thermowell when operating at maximum fluid tem-
sensors are inserted into the open end of the tubes. The perature.
E3137/E3137M−18
9.11 Sensing Element Types—The type of temperature sens- where:
ing element is not defined by this specification.
E = maximum permissible heat calculator error,
c
9.11.1 Restrictions on the Use of Resistance Temperature
∆t = lower limit temperature difference, and
min
Sensors—Resistance temperature sensors may be used in two-, ∆t = temperature difference.
three-, or four-wire resistance bridge circuits.
10.5 TypesofTemperatureSensors—Themanufacturershall
9.11.2 Resistance Temperature Sensor Signal Leads—
clearly indicate the type of temperature-sensing element that
Stranded or solid wire leads may be used. Stranded wire lead
shall be used with the heat calculator.
ends shall be trimmed and provided with lead end sleeves.
Signal wire lead ends coated with solder to prevent fraying are
10.6 Limits of Ambient Temperature—The manufacturer
not permitted.
shall clearly indicate the allowable ambient temperature range
9.11.3 Two-Wire Resistance Temperature Sensors—The
that the heat calculator can operate in without exceeding the
lengthandcross-sectionalareaofsignalwiresofpairedsensors
maximum permissible error.
of separable subassemblies shall be equal. The maximum lead
10.7 Heat-Conveying Liquid Type—For heat calculators in-
length shall be as shown in Table 3. For sensors with a higher
tended for use with heat-conveying liquids other than water,
nominal resistance, the lead lengths can be proportionally
the manufacturer shall clearly state the heat coefficient(s) used
longer.
as a function of temperature and pressure.
10. Heat Calculator
10.8 Heat Transmission Formula—Heat transmitted to or
from a body of liquid can be determined from knowledge of its
10.1 General—Heat calculators receive signals from the
mass, specific heat capacity, and change in temperature.
flow sensor and the temperature sensors and calculate and
10.8.1 In a heat meter, the rate of change of enthalpy
indicate the quantity of heat exchanged. Heat calculators are
defined by the following parameters: between the supply and return through a heat exchanger is
10.1.1 Limits of thermal power, integrated with respect to time. The equation for its operation
10.1.2 Heat calculator accuracy classes, is:
10.1.3 Maximum permissible error,
t
Q 5 q ∆hdt (8)
*
m
10.1.4 Types of temperature sensors, t
10.1.5 Limits of ambient temperature,
where:
10.1.6 Heat-conveying liquid type,
Q = quantity of heat given up,
10.1.7 Heat transmission formula,
q = mass flow rate of the heat-conveying liquid passing
m
10.1.8 Supply voltage,
through the heat meter,
10.1.9 Environmental class,
∆h = difference between the specific enthalpies of the heat-
10.1.10 Protection against fraud,
conveying liquid at the supply and return temperatures
10.1.11 Display, and
of the heat-exchange circuit, and
10.1.12 Materials of construction.
t = time.
10.2 Limits of Thermal Power—The upper limit of thermal
10.8.2 If the instrument determines the volume instead of
power, P , is the highest power at which the heat meter shall
s
the mass, its equation becomes:
function without the maximum permissible errors being ex-
V
ceeded. The manufacturer shall clearly indicate the upper limit
Q 5 k∆tdV (9)
*
V
of thermal power, P .
s
where:
10.3 Heat Calculator Accuracy Classes—Heat calculators
Q = quantity of heat given up,
and heat meters are defined by the accuracy class of the flow
V = volume of liquid passed
sensor and shall be Class 1, Class 2, or Class 3.
k = function of the properties of the heat-conveying liquid
10.4 Heat Calculator Maximum Permissible Error—The
at the relevant temperatures and pressure, called the
heat calculator maximum permissible error is defined as:
heat coefficient, and
∆t = temperature difference between the flow and return of
∆t
min
E 56 0.5 1 (7)
S D
c
the heat exchange circuit.
∆t
10.8.3 Where water is used as the system heat-conveying
liquid, the conventional true value of the heat coefficient, k,
shall be obtained from the formulas from AnnexA1, where the
TABLE 3 Maximum Lead Cross Section and Length
pressure shall be set to 1.6 MPa [232.1 psi].
Requirements
Lead Cross Section in Minimally Acceptable Maximum Length for 100 10.8.4 For heat calculators intended for use with heat-
mm [cmil] AWG Wire Sizes Ω Sensors in metres
conveying liquids other than water, the manufacturer shall
[feet]
clearly declare the heat coefficient used as a function of
0.22 [434.2] 22 2.5 [8.2]
temperature and pressure.
0.5 [986.7] 20 5.0 [16.4]
0.75 [1480.1] 18 7.5 [24.6]
10.9 Supply Voltage—Heat calculators shall be powered
1.50 [2960.3] 16 15.0 [49.2]
frombatteries,low-voltageacordcsupplies,orfromacmains.
E3137/E3137M−18
10.9.1 Battery Power—If a heat calculator has interchange- 10.10.3.3 High electrical and electromagnetic conditions as
able batteries, they shall be replaceable without damaging defined in OIML D11, Section 8.4, at a test level for Class E2.
verification seals. The battery(s) lifetime shall be clearly stated
10.10.3.4 Low-level mechanical conditions as defined in
by the manufacturer.
OIML D11, Section 8.3, at a test level index for Class M2.
10.9.2 Remote Low-Voltage Power (<50 V)—Heat calcula-
10.10.3.5 NEMA 3R or IP54 (heating) or IP65 (cooling) or
tors intended for use with remote low-voltage ac/dc power
better enclosure (see IEC 60529 or NEMA 250).
shall operate at a nominal voltage and shall tolerate the
10.10.4 Environmental Class D (Domestic/Light Commer-
following variations:
cial Use, Outdoor Installations):
10.9.2.1 Voltage variations of 610 % of the nominal stated
10.10.4.1 Ambient temperature— -40 to 55°C [-40 to
value, or
131°F].
10.9.2.2 ac frequency variations of 62 % from the nominal
10.10.4.2 Normal electrical and electromagnetic conditions.
stated frequency.
10.9.2.3 The manufacturer shall clearly indicate the maxi- 10.10.4.3 Low-level mechanical conditions.
mum input current.
10.10.4.4 NEMA 3R or IP54 (heating) or IP65 (cooling) or
10.9.3 ac Mains Power—Heat calculators intended for use
better enclosure (see IEC 60529 or NEMA 250).
with ac mains power shall operate at a nominal voltage of
10.11 Protection against Fraud—Heat calculators shall be
120 V and shall tolerate the following variations:
protectedinsuchawaythat,afterthedevicehasbeencorrectly
10.9.3.1 Voltage variations of -15 to +10 % of the nominal
installed, there is no possibility of dismantling, altering, or
stated value or
adjusting it without evident damage to the sensor or a security
10.9.3.2 ac frequency variations of 62 Hz from the nominal
seal(s).
stated frequency.
10.9.3.3 The manufacturer shall clearly indicate the maxi-
10.12 Display (Indicating Device)—The heat calculator
mum input current.
shall include a device that indicates the quantity of heat. The
display shall include a numerical or semi-numerical scale and
10.10 Environmental Class—Heat calculators and complete
shall provide an easily read, reliable, and unambiguous indi-
heat meters shall conform to one or more of the following
cation. The real or apparent character height shall be at least 4
environmental classifications according to the application.
mm [0.16 in.]. The quantity of heat shall be indicated in Btus,
10.10.1 Environmental Class A (Domestic/Light Commer-
watt-hours, or decimal multiples of those units. The figures
cial Use, Indoor Installations):
indicating decimal fractions of a unit shall be separated from
10.10.1.1 Ambient temperature—5 to 55°C [41 to 131°F].
the others by the decimal divider. The name or symbol of the
10.10.1.2 Low-level humidity conditions as defined in
unit in which the quantity of heat is given shall be indicated
OIML D11, Section 8.2.2, at a test level index for Class H1.
adjacent to the display.
10.10.1.3 Normal electrical and electromagnetic conditions
10.12.1 Retention of Data—Heat calculators shall be so
as defined in OIML D11, Section 8.4, at a test level for Class
designed that, in the event of an external power supply failure
E1.
(mains or external ac or dc), the meter indication of energy at
10.10.1.4 Low-level mechanical conditions as defined in
the time of failure is not lost and remains accessible for a
OIML D11, Section 8.3, at a test level index for Class M2.
minimum of one year.
10.10.1.5 NEMA 12 or IP52 or better enclosure (off the
pipe) (see IEC 60529 or NEMA 250).
NOTE 2—Compliance with 10.12.1 will not necessarily ensure that the
10.10.1.6 NEMA3R or IP54 (heating) or IP65 (cooling) (on
heat meter will continue to register the heat consumed in the event of a
the pipe) or better (see IEC 60529 or NEMA 250).
power supply failure.
10.10.2 Environmental Class B (Domestic/Light Commer-
10.12.2 Scaling and Resolution—The display indicating the
cial Use, Outdoor Installations):
quantity of heat shall be able to register, without overflow, a
10.10.2.1 Ambient temperature—-25to55°C[-13to
quantity of heat at least equal to the transfer of energy that
131°F].
corresponds to a continuous operation for 3000 h at the upper
10.10.2.2 Normal level humidity conditions as defined in
limit of the thermal power, P , of the heat meter.
s
OIML D11, Section 8.2.2, at a test level index for Class H2.
10.12.2.1 The quantity of heat, measured by a heat meter
10.10.2.3 Normal electrical and electromagnetic conditions
operating at the upper limit of the thermal power for 1 h shall
as defined in OIML D11, Section 8.4, at a test level for Class
correspond to at least one digit of lowest significance of the
E1.
display.
10.10.2.4 Low-level mechanical conditions as defined in
OIML D11, Section 8.3, at a test level index for Class M2.
10.13 Materials of Construction—The heat calculator shall
10.10.2.5 NEMA 3R or IP54 (heating) or IP65 (cooling) or
be constructed from materials designed to resist wear and
better enclosure (see IEC 60529 or NEMA 250).
corrosion that may be expected to result from exposure to the
10.10.3 Environmental Class C (Industrial Installations): heat-conveying liquid. The materials shall also be suitable for
10.10.3.1 Ambient temperature—-25to55°C[-13to
the environmental class of the instrument. The heat calculator
131°F]. enclosure shall meet NEMA 3R or IP54 (heating) or IP65
10.10.3.2 Normal level humidity conditions as defined in (cooling) requirements when installed on the piping system
OIML D11, Section 8.2.2, at a test level index for Class H2. (see IEC 60529 or NEMA 250).
E3137/E3137M−18
11. Data Exchange and Communications Protocols istrative phases. If the instrument passes all required tests and
examinations in Section 15, it is given legal character by its
11.1 General—Heat meters may use either none or a num-
acceptance as evidenced by stamping, or issue of a certificate
ber of interfaces to communicate with remote readout devices.
of verification, or both. Unless otherwise stated in the type
11.1.1 Hardware Interface and Communications
approval certificate, the verification shall be carried out in
Protocols—The hardware interface and communications pro-
accordance with this specification, the provisions of which also
tocols should meet internationally recognized standards for
apply to the subsequent verification of heat meters.
interoperability. Recognized standards organizations include
12.3.2 Combined Instrument—When verifying a heat meter
theInstituteofElectricalandElectronicsEngineers(IEEE),the
as a combined instrument, the flow sensor, the temperature
International Organization for Standardization (ISO), Ameri-
sensor pair, the heat calculator or a combination of these shall
can National Standards Institute, (ANSI), the European Tele-
each be verified separately.
communications Standards Institute (ETSI), the European
Committee for Standardization (CEN), and the International
12.4 Requirements—Under rated operating conditions, the
Electrotechnical Commission (IEC).
errors of heat meters or their subassemblies shall not exceed
11.1.2 Data Element Structure and Definitions—Heat me-
the MPE specified in Section 7. When heat meters or their
ters that use one or more communications interfaces shall at
subassemblies are exposed to disturbances, significant faults
least,ataminimum,transmitvaluesforheatandvolumetotals.
shall not occur.
Other recommended values would include volume flow,
temperature(s), and heat rate.
13. Specification of Operating Conditions During Testing
13.1 Rated Operating Conditions—Theratedoperatingcon-
12. Heat Meter Testing
ditions are those given in Table 4.
12.1 Heat meters that comply with the general requirements
of this specification and are submitted for type approval and 13.2 Reference Conditions:
undergoinitialverificationshallcomplywiththespecifiedtests
13.2.1 Range of Ambient Temperature—15 to 35°C [59 to
in
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E3137/E3137M − 17 E3137/E3137M − 18
Standard Specification for
1,2
Heat Meter Instrumentation
This standard is issued under the fixed designation E3137/E3137M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This specification defines general specifications for heat meters. Heat meters are instruments that measure heat in heat
exchange circuits in which energy is absorbed (cooling) or given up (heating) by a flowing liquid.
1.2 For this specification, the necessary elements of a heat meter consist of a sensor to measure flow of the heat-conveying
liquid, a pair of temperature sensors that measure the temperature differential across the heat exchange circuit, and a device that
receives input from the flow and temperature sensors and calculates energy.
1.3 Electrical safety is not a part of this specification.
1.4 Mechanical safety (including pressure safety) is not a part of this specification.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in nonconformance with the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 CCT Standard:
ITS-90 International Temperature Scale of 1990
2.2 IAPWS Standard:
IAPWS-IF97 Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam
2.3 IEC Standards:
IEC 61000 Part 4-2 Electrostatic Discharge Immunity Test
IEC 61000 Part 4-3 Radiated, Radio-Frequency, Electromagnetic Field Immunity Test
IEC 61000 Part 4-4 Electrical Fast Transient/Burst Immunity Test
IEC 61000 Part 4-5 Surge Immunity Test
IEC 60068: Environmental Testing Part 2.1 Test A: Cold
IEC 60068: Environmental Testing Part 2.2 Tests B: Dry Heat
IEC 60068: Environmental Testing Part 2-30 Tests Db: Damp Heat, cyclic
IEC 60529 Degrees of protection provided by enclosures (IP Code)
IEC 60751 Industrial platinum resistance thermometer and platinum temperature sensors
This specification is under the jurisdiction of ASTM Committee E44 on Solar, Geothermal and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.25 on Heat Metering.
Current edition approved Nov. 1, 2017April 1, 2018. Published December 2017August 2018. Originally approved in 2017. Last previous edition approved in 2017 as
E3137/E3137M-17. DOI: 10.1520/E3137_E3137M–17.10.1520/E3137_E3137M–18.
Through a mutual agreement with ASTM International (ASTM), the International Association of Plumbing and Mechanical Officials (IAPMO) contributed its technical
expertise to ASTM, leading to the development of this ASTM Standard. IAPMO and its membership continue to play an active role in providing technical guidance to the
ASTM standards development process.
Available from the Consultative Committee for Thermometry, www.its-90.com.
Available from the International Association for the Properties of Water and Steam, www.iapws.org.
Available from the International Electrotechnical Commission, www.iec.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3137/E3137M − 18
IEC 60870 Part 5-1 Telecontrol equipment and systems
IEC 61107 Data exchange for meter reading, tariff and load control—Direct local data exchange
IEC TR 61000 Electromagnetic compatibility—Part 2: Environment—Section 7: Low frequency magnetic fields in various
environments
2.4 NEMA Standards:
NEMA 250 Enclosures for Electrical Equipment (1000 Volts Maximum)
2.5 OIML Standards:
OIML D11 General Requirements for measuring instruments—Environmental conditions
OIML R 49 Part 2 Water meters intended for the metering of cold potable water and hot water
OIML R75-1 Part 1 General requirements
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 conventional true value, n—value of a quantity, which for the purpose of this specification, is considered as a true value.
OIML R75-1 2002
3.1.1.1 Discussion—
A conventional true value is regarded, in general, as sufficiently close to the true value for the difference to be insignificant for the
given purpose. OIML R75-1 2002
3.1.2 disturbance, n—influence quantity having a value outside the rated operating conditions. OIML R75-1 2002
3.1.3 electronic device, n—device using electronic components and performing a specific function. OIML R75-1 2002
3.1.4 equipment under test, n—subassembly, a combination of subassemblies, or a complete meter subject to a test. OIML
R75-1 2002
3.1.5 error types, n—
3.1.5.1 durability error, n—difference between the intrinsic error after a period of use and the initial intrinsic error. OIML R75-1
3.1.5.2 error (of indication) of a measuring instrument, n—indication of the measuring instrument minus the conventional true
value of the corresponding input quantity. OIML R75-1 2002
3.1.5.3 initial intrinsic error, n—intrinsic error of a measuring instrument as determined before performance and durability tests.
3.1.5.4 intrinsic error (of a measuring instrument), n—error of a measuring instrument determined under reference conditions.
OIML R75-1 2002
3.1.5.5 maximum permissible error, MPE, n—extreme values of the error (positive or negative) permitted by this specification.
OIML R75-1 2002
3.1.6 fast response meter, n—heat meter designed for use in heat exchange circuits in which sudden or rapid changes, or both,
in flow or temperature are a normal condition. OIML R75-1 2002
3.1.7 fault types, n—
3.1.7.1 fault, n—difference between the error of indication and the intrinsic error of the instrument. OIML R75-1 2002
3.1.7.2 significant fault—fault greater than the absolute value of the MPE that is not a transitory fault, for example, if the MPE
is 62 %, then a significant fault is a fault larger than 2 %. OIML R75-1 2002
3.1.7.3 transitory fault—momentary variations in the indication that cannot be interpreted, memorized, or transmitted as
measurements. OIML R75-1 2002
3.1.8 flow direction, n—indication of directionality for a flowing liquid within a piping system leading to and exiting from a heat
exchange circuit.
3.1.8.1 Discussion—
The term supply (or inlet) is used to indicate liquid traveling to the heat exchanger and the term return (or outlet) describes the
liquid exiting the heat exchanger. In heating systems, supply liquids will normally have a higher temperature than return liquids.
In cooling systems, supply liquids will normally have a lower temperature than return liquids.
Available from National Electrical Manufacturers Association (NEMA), 1300 N. 17th St., Suite 900, Arlington, VA 22209, http://www.nema.org.
Available from the International Organization of Legal Metrology, www.oiml.org/en.
E3137/E3137M − 18
3.1.9 flow sensor, n—subassembly of a heat meter designed to measure the volume or mass of a flowing liquid in a heat
exchange circuit.
3.1.10 heat calculator, n—heat meter subassembly that receives flow and temperature signals from flow and temperature sensors
and calculates and displays energy.
3.1.11 influence factor, n—influence quantity having a value within the rated operating conditions. OIML R75-1 2002
3.1.12 influence quantity, n—quantity that is not the measurand but that affects the result of the measurement. OIML R75-1
3.1.13 meter model, n—different sizes of heat meters or subassemblies having a family similarity in the principles of operation,
construction, and materials. OIML R75-1 2002
3.1.14 minimum immersion depth of a temperature sensor, n—depth of immersion in a thermostatic bath with a temperature of
80 6 5°C [176 6 9°F] at an ambient temperature of 25 6 5°C [77 6 9°F], beyond which deeper immersion changes the output
value by an amount corresponding to less than 0.1 K [0.18°F]. OIML R75-1 2002
3.1.15 platinum resistance thermometer, PRT, n—temperature responsive device consisting of one or more sensing platinum
resistors within a protective sheath with internal connecting wires and external terminals to permit connection of electrical
measurement instruments.
3.1.15.1 Discussion—
Mounting means and connection heads may be included. Not included is any separable protection tube or thermowell.
3.1.16 platinum resistor, n—resistor made from platinum wire or film with defined electrical characteristics, embedded in an
insulator (in most cases glass or ceramic), designed to be assembled into a resistance thermometer or an integrated circuit.
3.1.17 rated operating conditions, n—conditions of use for which specified metrological characteristics of a measuring
instrument are intended to lie within the specified maximum permissible errors. OIML R75-1 2002
3.1.18 rated voltage, U , n—voltage of an external power supply required to operate a heat meter.
n
3.1.19 reference conditions, n—conditions of use prescribed for testing the performance of a measuring instrument or
intercomparison of results of measurements. OIML R75-1 2002
3.1.20 reference values of the measurand, RVM, n—specified set of values of the flow rate, the return temperature, and the
temperature difference fixed to ensure valid intercomparison of the results of measurements. OIML R75-1 2002
3.1.21 response time, τ0.5, n—time interval between the instant when the flow, the temperature, or the temperature difference
is subjected to a specified abrupt change and the instant when the response reaches 50 % of its final steady value. OIML R75-1
3.1.22 self-heating effect, n—increase in temperature signal that is obtained by subjecting each temperature sensor of a pair to
a continuous power dissipation of 5 mW when immersed to the minimum immersion depth in a water bath having a mean water
velocity of 0.1 m/s [0.328 ft/s]. OIML R75-1 2002
4. Significance and Use
4.1 This document is based, in part, on OIML R 75-1 Edition 2002, Heat meters Part 1: General requirements and OIML R 75-2
Edition 2002, Heat meters Part 2: Type approval tests and initial verification tests. R 75 is an International Recommendation
published by OIML. International Recommendations are model regulations that establish the metrological characteristics required
of certain measuring instruments and which specify methods and equipment for checking their conformity. As an OIML Member
State, The United States is obligated to utilize these recommendations, where possible, when developing standards that meet the
needs of the market and may result in either terminology or definitions specific to this standard and deviations in standard form
and style.
5. Using this Specification
5.1 This specification is intended to provide both manufacturers and users of heat meters with important information.
5.2 Manufacturers will use this specification to certify that their products conform to industry standards for accuracy,
performance, and reliability.
5.3 End users and specifying engineers will use this specification as a guide in understanding how heat meters are defined based
on performance and accuracy classifications for flow, temperature, and energy. They will also use this specification to ensure that
the meter will be suitable for use in the operating environment in which it will be installed.
5.4 End users are strongly encouraged to review carefully the requirements of their specific application and then select a heat
meter that will meet their needs based on the following criteria:
5.4.1 Flow Sensor Accuracy Class—Class 1, Class 2, or Class 3;
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5.4.2 Lower Limit of the Temperature Difference Range—1, 2, or 3 K [1.8, 3.6, or 5.4°F]; and
5.4.3 Environmental Class—A, B, C, or D.
5.5 Overall accuracy of the heat meter is defined as the additive maximum permissible errors (MPE) of the flow sensor, the
temperature sensor pair, and the heat calculator. See Section 7 for additional information on maximum permissible errors.
5.6 Flow Sensors:
5.6.1 The three flow sensor accuracy classes are Class 1, Class 2, or Class 3. In each class, the accuracy is determined by the
MPE at the manufacturer’s stated minimum (Q ) and maximum permanent flow rate (Q ). See 8.2 for additional information on
i p
flow sensor operating limits.
5.6.2 The MPE for each flow sensor varies with the flow sensor accuracy class and the ratio of the Q to the actual operating
p
flow rate (Q). This is the turndown for the sensor. When selecting a flow sensor, it is necessary to identify first the maximum flow
rate for the application. This maximum flow rate shall be compared to the upper flow limit (Q ) and the Q as stated by the flow
s p
meter manufacturer for the flow sensor under consideration. Next, identify the minimum flow rate for the application. Compare
this value to the Q as stated by the flow meter manufacturer. Flow sensors should be selected that will operate within these upper
i
and lower flow limits. Once the upper and lower flow limits are defined (turndown), the accuracy limits by class can be determined
from Table 1.
5.6.3 Table 1 shows the range of allowable error (E ) for the flow sensor by class and turndown range for use in MPE equations
f
in 8.3. For clarity, turndown is expressed as Q /Q in Table 1.
p i
5.7 Temperature Sensor Pairs and Heat Calculator:
5.7.1 The MPE of the temperature sensor pair is a function of the lower limit of the temperature difference as described in 9.4
and 9.5. The three lower limits for the temperature difference range are 1, 2, and 3 K [1.8, 3.6, or 5.4°F]. As with the flow sensor,
the highest percentage measurement error will occur at the minimum operating level. In this case, it is the lowest differential
temperature.
5.7.2 The heat calculator MPE is also defined by the lower limit of the temperature difference range (1, 2, or 3 K) as described
in 10.4. As is the case with the temperature sensor pair, the highest percentage measurement error will occur at the minimum
temperature differential.
5.7.3 When selecting a temperature sensor pair, it is necessary to identify the minimum and maximum operating temperatures
for the application and confirm that they fall within the operating limits of the individual temperature sensors. Next, identify and
compare the maximum and minimum temperature difference for the application with the upper limit of temperature difference
(Δt ) and lower limit of temperature difference (Δt ) as stated by the manufacturer. Temperature sensor pairs should be selected
max min
that will operate within the Δt and Δt at least 75 % of the time while never exceeding the Δt . Once the Δt and Δt
max min max max min
are defined, the accuracy limits can be determined from Table 2.
5.7.4 Table 2 shows the combined allowable error percentages for the temperature sensor pair and the heat calculator for
¯
measured difference temperatures (T) in –17°C1.11111°C@2°F# [2°F] increments.
5.8 Environmental Classes—Heat calculators and complete heat meters are defined by one of the four environmental
classifications: A, B, C, or D. These are summarized in 10.10. Heat calculator and heat meter environmental classes should be
selected according to the needs of the application in which they will be used.
6. Types of Instruments
6.1 This specification defines heat meters as complete or combined instruments.
6.1.1 Complete Instrument—A heat meter that does not have separable subassemblies as defined in 6.1.4.
TABLE 1 Allowable Flow Rate MPE by Accuracy Class and
Turndown
E at Minimum Flow E at Maximum Flow
f f
Class Turndown
(Q = Q ), % (Q = Q ), %
i p
Class 1 10:1 1.10 1.01
25:1 1.25 1.01
50:1 1.50 1.01
100:1 2.00 1.01
250:1 3.50 1.01
Class 2 10:1 2.20 2.02
25:1 2.50 2.02
50:1 3.00 2.02
100:1 4.00 2.02
250:1 5.00 2.02
Class 3 10:1 3.50 3.05
25:1 4.25 3.05
50:1 5.00 3.05
100:1 5.00 3.05
250:1 5.00 3.05
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TABLE 2 Temperature Sensor Pair MPE % in -16.6°C [2°F] ΔT
Increments for the Three Lower Limits of the Temperature
Difference Range
A
Measured ΔT, °F 1 K, % 2 K, % 3 K, %
2 4.60 8.20 11.80
4 2.80 4.60 6.40
6 2.20 3.40 4.60
8 1.90 2.80 3.70
10 1.72 2.44 3.16
12 1.60 2.20 2.80
14 1.51 2.03 2.54
16 1.45 1.90 2.35
18 1.40 1.80 2.20
20 1.36 1.72 2.08
A ¯
1°F 1°F50.5555°C= –17.2°C.
6.1.2 Combined Meter—A heat meter that has separable subassemblies as defined in 6.1.4.
6.1.3 Hybrid Meter—A heat meter that, for the purpose of type approval and verification, can be treated as a combined
instrument as defined in 6.1.2. However, after verification, its subassemblies will be treated as inseparable.
6.1.4 Subassemblies of a Heat Meter that is a Combined Instrument—The flow sensor, the temperature sensor pair, and the heat
calculator or a combination of these.
6.1.4.1 Flow sensor—A subassembly installed at either the supply or return of a heat exchange circuit and that emits a signal,
which is a function of the volume or the mass or the volumetric or mass flow rate.
6.1.4.2 Temperature sensor pair—A subassembly (for mounting with or without thermowells) that senses the temperatures of
the heat-conveying liquid at the inlet and outlet of a heat exchange circuit.
6.1.4.3 Heat calculator—A subassembly that receives signals from the flow sensor and the temperature sensors and calculates
and indicates the quantity of heat exchanged.
6.1.5 Equipment under Test—A subassembly, a combination of subassemblies, or a complete meter subject to a test.
7. Metrological Characteristics
7.1 General—Flow sensors of heat meters and complete instruments belong to one of the following three accuracy classes: Class
1, Class 2, and Class 3.
7.1.1 The class of the complete instrument is determined by the class of the flow sensor.
7.1.2 The maximum permissible errors of heat meters, positive or negative, in relation to the conventional true value of the heat,
are defined as relative errors varying as a function of the temperature difference and flow rate.
7.1.3 The maximum permissible errors of subassemblies, positive or negative, are calculated from the temperature difference
in the case of the heat calculator and the temperature sensor pair and from the flow rate in the case of the flow sensor.
7.2 Relative Error—The relative error, E, is expressed as:
X 2 X
d c
E 5 * 100 % (1)
X
c
where:
X = indicated value, and
d
X = conventional true value.
c
7.3 Values of Maximum Permissible Errors (MPEs)—The MPEs of a complete instrument are calculated as a function of the
temperature difference ratio (t /t) and the flow rate ratio (q /q). The MPEs of the complete instrument of accuracy Classes
min p
1, 2, and 3 are the arithmetic sums of E (in 8.3), E (in 9.5), and E (in 10.4). The classes of heat meters are defined by the class
f t c
of the flow sensor.
7.3.1 Class 1, Class 2, and Class 3:
E 5 E 1E 1E (2)
f t c
where:
E = maximum permissible error,
E = flow sensor error,
f
E = temperature sensor error, and
t
E = heat calculator error.
c
8. Flow Sensor
8.1 General—Flow sensors measure the volume or mass of a flowing liquid in a heat exchange circuit. Flow sensors are defined
by the following parameters:
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8.1.1 Flow sensor operating limits,
8.1.2 Flow sensor accuracy classes,
8.1.3 Operating pressure,
8.1.4 Pressure drop,
8.1.5 Minimum and maximum liquid temperature,
8.1.6 Flow sensor operation outside the stated operating limits,
8.1.7 Process connection type,
8.1.8 Flow sensor installation restrictions,
8.1.9 Materials of construction,
8.1.10 Protection against fraud, and
8.1.11 Flow sensor verification of design.
8.2 Flow Sensor Operating Limits:
8.2.1 Lower Flow Limit—The lower limit of the flow rate, q , is the lowest rate the sensor can operate at without exceeding the
i
maximum permissible error. The manufacturer shall clearly indicate the limit, q .
i
8.2.2 Upper Flow Limit—The upper limit of the flow rate, q , is the highest flow rate the sensor can operate at for short periods
s
without exceeding the maximum permissible error. Short periods are defined as less than 1 h/day and as less than 200 h/year. The
manufacturer shall clearly indicate the limit, q .
s
8.2.3 Permanent Flow Rate—The permanent flow rate, q , is the highest rate the sensor can operate at continuously without
p
exceeding the maximum permissible error. The manufacturer shall clearly indicate the limit, q .
p
8.2.4 Flow Rate Range—The manufacturer shall clearly indicate the ratio of the permanent flow rate to the lower flow limit,
and the ratio shall be at least 10.
8.3 Flow Sensor Accuracy Classes—Flow sensors of heat meters and complete instruments belong to one of the following three
accuracy classes: Class 1, Class 2, and Class 3.
8.3.1 The class of the complete instrument is determined by the class of the flow sensor.
q
p
Class1:E 56 1 1 0.01 , but not more than 63.5 % (3)
S D
f
q
q
p
Class2:E 56 2 1 0.02 , but not more than 65 % (4)
S D
f
q
q
p
Class3:E 56 3 1 0.05 , but not more than 65 % (5)
S D
f
q
where:
E = flow sensor error,
q = maximum permanent flow rate, and
p
q = actual flow rate.
8.4 Operating Pressure:
8.4.1 Minimum Operating Pressure—The manufacturer shall state the minimum operating pressure that shall be maintained at
the meter when operating at the upper flow limit.
8.4.2 Maximum Operating Pressure—The manufacturer shall state the maximum internal pressure that can be applied to the
flow sensor when operating at the maximum liquid temperature.
8.5 Maximum Pressure Loss—The loss of pressure in the heat-conveying liquid passing through the flow sensor when the flow
sensor is operating at the permanent flow rate, q , shall not exceed 28 kPa [4 psi].
p
8.6 Minimum and Maximum Liquid Operating Temperature—The manufacturer shall state the minimum and maximum
temperatures at which the flow sensor will operate without exceeding the maximum permissible error, E .
f
8.7 Flow Sensor Operation outside the Stated Operating Limits—When the flow rate is less than a threshold value declared by
the supplier, no registration is allowed.
NOTE 1—The flow rate through a “nominally” closed valve or the movement of liquid in the pipe behind a closed valve caused by thermal expansion
and contraction shall not be recorded.
8.7.1 For flow rates greater than q , the behavior of the meter, for example, the production of spurious or zero signals, shall be
s
declared by the manufacturer. Flow rates greater than q shall not result in a positive error greater than 10 %.
s
8.8 Flow Sensor Process Connections—Complete heat meters and flow sensor subassemblies are provided with threaded or
flanged process connections as required by the application. Process connections shall comply with National Pipe Thread (NPT),
American National Standards Institute (ANSI), American Water Works Association (AWWA), or other applicable U.S. standards.
For instruments with threaded process connections that do not meet this requirement, it will be acceptable to supply heat meters
with thread adapters that meet the applicable U.S. standards.
E3137/E3137M − 18
8.9 Flow Sensor Installation Restrictions—The manufacturer shall declare any limitations with regard to installation of the flow
sensor including straight, unobstructed pipe lengths required upstream and downstream of the meter. Any restrictions relating to
its orientation with respect to the vertical shall also be declared.
8.10 Flow Sensor Materials of Construction—Flow sensor subassemblies and complete heat meters shall be of durable
construction from materials designed to resist wear and corrosion that may be expected to result from prolonged exposure to the
heat transfer liquid.
8.10.1 The enclosure for the flow sensor shall protect the interior against the ingress of water and dust. The minimum level of
protection shall conform to NEMA 3R or IP54 (heating) or IP65 (cooling) (see IEC 60529 or NEMA 250).
8.11 Protection against Fraud—Flow sensors shall be protected in such a way that, after the sensor has been correctly installed,
there is no possibility of dismantling or altering or adjusting the sensor without evident damage to the sensor or a security seal(s).
9. Temperature Sensor Pair
9.1 General—Temperature sensor pairs measure the temperature of the flowing liquid in the heat exchange circuit. The sensors
are installed such that one sensor measures the liquid temperature at supply (inlet) and the other sensor measures temperature at
the return (outlet) of the heat exchange circuit. Temperature sensor pairs are defined by the following parameters:
9.1.1 Limits of temperature measurement range,
9.1.2 Temperature sensor accuracy,
9.1.3 Limits of temperature difference,
9.1.4 Temperature sensor pair accuracy,
9.1.5 Direct insertion sensors and sensors used with thermowells,
9.1.6 Minimum insertion depth,
9.1.7 Sensor lengths,
9.1.8 The influence on a temperature sensor pair when installed in thermowells,
9.1.9 Materials of construction,
9.1.10 Protection against fraud,
9.1.11 Process connection type,
9.1.12 Maximum operating pressure,
9.1.13 Sensing element types, and
9.1.14 Restrictions on the use of platinum resistance temperature sensors.
9.2 Limits of Temperature Measurement Range:
9.2.1 Lower Temperature Limit—The lower temperature limit of the temperature measurement range, t , is the lowest
min
temperature of the heat-conveying liquid at which the heat meter will function without exceeding the maximum permissible errors.
This temperature limit shall be clearly stated by the manufacturer.
9.2.2 Upper Temperature Limit—The upper temperature limit of the temperature measurement range, t , is the highest
max
temperature of the heat-conveying liquid at which the heat meter will function without exceeding the maximum permissible errors.
The manufacturer shall clearly indicate the upper temperature limit, t .
max
9.3 Temperature Sensor Absolute Accuracy—The relationship between the output of each individual temperature sensor of a pair
and the conventional true value of temperature shall not be greater than 2 K [3.6°F].
9.4 Limits of Temperature Difference—The temperature difference,t, is the absolute value of the difference between the
temperatures of the heat-conveying liquid at the supply and return of the heat-exchange circuit.
9.4.1 Lower Limit of Temperature Difference—The lower limit of the temperature difference,t , is the lowest temperature
min
difference at which the heat meter shall clearly function without the maximum permissible errors being exceeded. The
manufacturer shall indicate the lower limit of the temperature difference,t .
min
9.4.2 Upper Limit of Temperature Difference—The upper limit of the temperature difference,t , is the highest temperature
max
difference at which the heat meter shall function without the maximum permissible errors being exceeded. The manufacturer shall
clearly indicate the upper limit of the temperature difference,t .
max
9.4.3 Temperature Difference Range—The ratio of the upper and lower limits of the temperature difference shall clearly not be
less than ten, with the exception of heat meters intended for cooling applications. The manufacturer shall indicate the lower limit
of the temperature difference as 1, 2, or 3 K [1.8, 3.6, or 5.4°F].
9.5 Temperature Sensor Pair Accuracy—Temperature sensor pair accuracy is defined as:
Δt
min
E 56 0.5 1 3 (6)
S D
t
Δt
where:
E = temperature sensor pair accuracy,
t
Δt = lower limit temperature difference, and
min
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Δt = temperature difference measured across the heat exchange circuit.
9.6 Direct Insertion Sensors and Thermowells—Direct insertion temperature sensors are designed to be immersed directly into
the heat-conveying liquid. They are provided with a process connection suitable for installation into the heat exchange piping
system. Direct insertion sensors should be used for heat exchange pipes with a nominal diameter of less than 3 cm [1 ⁄4 in.] (DN32)
whenever possible as they provide the most accurate temperature measurement.
9.6.1 Thermowells are tubes closed at one end that are inserted into the heat exchange circuit pipes. The temperature sensors
are inserted into the open end of the tubes. The heat-conveying liquid flowing in the pipes transfers heat to the thermowell and
the thermowell transfers heat to the temperature sensor.
9.6.2 The manufacturer shall declare if the temperature sensor pair provided is designed for use with thermowells.
9.6.3 Temperature sensor pair installation methods shall be symmetrical. The use of one direct insertion sensor and one
thermowell is not permitted.
9.6.4 The use of clamp-on temperature sensors is not permitted.
9.6.5 Temperature Sensor Pair Immersion Depths—The minimum allowable insertion depth for temperature sensors shall be
stated by the manufacturer based on the nominal pipe diameter and the length of the insertion temperature sensors. The preferred
immersion depth is to the center of the pipe. This may not be practical in larger pipes. In all cases, the minimum insertion depth
shall be sufficient to ensure that further increases in the insertion depth will not produce a change in temperature measurement
greater than 0.1 K [0.18°F]. (Refer to Annex A2.)
9.6.6 Temperature Sensor Lengths—The manufacturer shall provide the appropriate length temperature sensors according to
9.6.5 based on the nominal pipe diameter in use in the heat exchange piping system where the sensors are installed.
9.6.6.1 Temperature sensor dimensions—Sensor dimensions are not defined by this specification.
9.6.6.2 Thermowell dimensions—The temperature sensor manufacturer shall specify the length and diameter of thermowell(s)
to match the temperature sensor(s) if used.
9.6.6.3 Influence on a temperature sensor pair when installed in thermowells—The difference in the temperature measurement
with and without thermowells shall not exceed one third of the maximum permissible error.
9.7 Methods and Materials of Construction—Direct insertion sensors and thermowells shall be constructed from materials
designed to resist wear and corrosion that may be expected to result from prolonged exposure to the heat-conveying liquid. The
materials shall be suitable for use at the heat-conveying liquid’s operating temperatures and pressures. The sensors and thermowells
shall be designed to withstand the forces applied from the flowing liquid, and they shall have the requisite thermal conductivity
for the application.
9.8 Protection against Fraud—Temperature sensors shall be protected in such a way that, after the sensor has been correctly
installed, there is no possibility of dismantling, altering, or adjusting the sensor without evident damage to the sensor or a security
seal(s).
9.9 Process Connection Type—The temperature sensor process connection type is not defined by this specification. NPT, ANSI,
or AWWA process connections are preferred. For instruments with threaded process connections that do not meet this requirement,
it will be acceptable to supply heat meters with thread adapters that meet the applicable U.S. standards.
9.10 Maximum Operating Pressure—The manufacturer shall state the maximum operating pressure for the temperature sensor
or thermowell when operating at maximum fluid temperature.
9.11 Sensing Element Types—The type of temperature sensing element is not defined by this specification.
9.11.1 Restrictions on the Use of Resistance Temperature Sensors—Resistance temperature sensors may be used in two-, three-,
or four-wire resistance bridge circuits.
9.11.2 Resistance Temperature Sensor Signal Leads—Stranded or solid wire leads may be used. Stranded wire lead ends shall
be trimmed and provided with lead end sleeves. Signal wire lead ends coated with solder to prevent fraying are not permitted.
9.11.3 Two-Wire Resistance Temperature Sensors—The length and cross-sectional area of signal wires of paired sensors of
separable subassemblies shall be equal. The maximum lead length shall be as shown in Table 3. For sensors with a higher nominal
resistance, the lead lengths can be proportionally longer.
TABLE 3 Maximum Lead Cross Section and Length
Requirements
Lead Cross Section in Minimally Acceptable Maximum Length for 100
mm [cmil] AWG Wire Sizes Sensors in metres
[feet]
0.22 [434.2] 22 2.5 [8.2]
0.5 [986.7] 20 5.0 [16.4]
0.75 [1480.1] 18 7.5 [24.6]
1.50 [2960.3] 16 15.0 [49.2]
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10. Heat Calculator
10.1 General—Heat calculators receive signals from the flow sensor and the temperature sensors and calculate and indicate the
quantity of heat exchanged. Heat calculators are defined by the following parameters:
10.1.1 Limits of thermal power,
10.1.2 Heat calculator accuracy classes,
10.1.3 Maximum permissible error,
10.1.4 Types of temperature sensors,
10.1.5 Limits of ambient temperature,
10.1.6 Heat-conveying liquid type,
10.1.7 Heat transmission formula,
10.1.8 Supply voltage,
10.1.9 Environmental class,
10.1.10 Protection against fraud,
10.1.11 Display, and
10.1.12 Materials of construction.
10.2 Limits of Thermal Power—The upper limit of thermal power, P , is the highest power at which the heat meter shall function
s
without the maximum permissible errors being exceeded. The manufacturer shall clearly indicate the upper limit of thermal power,
P .
s
10.3 Heat Calculator Accuracy Classes—Heat calculators and heat meters are defined by the accuracy class of the flow sensor
and shall be Class 1, Class 2, or Class 3.
10.4 Heat Calculator Maximum Permissible Error—The heat calculator maximum permissible error is defined as:
Δt
min
E 56 0.5 1 (7)
S D
c
Δt
where:
E = maximum permissible heat calculator error,
c
Δt = lower limit temperature difference, and
min
Δt = temperature difference.
10.5 Types of Temperature Sensors—The manufacturer shall clearly indicate the type of temperature-sensing element that shall
be used with the heat calculator.
10.6 Limits of Ambient Temperature—The manufacturer shall clearly indicate the allowable ambient temperature range that the
heat calculator can operate in without exceeding the maximum permissible error.
10.7 Heat-Conveying Liquid Type—For heat calculators intended for use with heat-conveying liquids other than water, the
manufacturer shall clearly state the heat coefficient(s) used as a function of temperature and pressure.
10.8 Heat Transmission Formula—Heat transmitted to or from a body of liquid can be determined from knowledge of its mass,
specific heat capacity, and change in temperature.
10.8.1 In a heat meter, the rate of change of enthalpy between the supply and return through a heat exchanger is integrated with
respect to time. The equation for its operation is:
t
Q 5 q Δh dt (8)
*
m
t
where:
Q = quantity of heat given up,
q = mass flow rate of the heat-conveying liquid passing through the heat meter,
m
Δh = difference between the specific enthalpies of the heat-conveying liquid at the supply and return temperatures of the
heat-exchange circuit, and
t = time.
10.8.2 If the instrument determines the volume instead of the mass, its equation becomes:
V
Q 5 kΔt dV (9)
*
V
where:
Q = quantity of heat given up,
V = volume of liquid passed
k = function of the properties of the heat-conveying liquid at the relevant temperatures and pressure, called the heat coefficient,
and
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Δt = temperature difference between the flow and return of the heat exchange circuit.
10.8.3 Where water is used as the system heat-conveying liquid, the conventional true value of the heat coefficient, k, shall be
obtained from the formulas from Annex A1, where the pressure shall be set to 1.6 MPa [232.1 psi].
10.8.4 For heat calculators intended for use with heat-conveying liquids other than water, the manufacturer shall clearly declare
the heat coefficient used as a function of temperature and pressure.
10.9 Supply Voltage—Heat calculators shall be powered from batteries, low-voltage ac or dc supplies, or from ac mains.
10.9.1 Battery Power—If a heat calculator has interchangeable batteries, they shall be replaceable without damaging verification
seals. The battery(s) lifetime shall be clearly stated by the manufacturer.
10.9.2 Remote Low-Voltage Power (<50 V)—Heat calculators intended for use with remote low-voltage ac/dc power shall
operate at a nominal voltage and shall tolerate the following variations:
10.9.2.1 Voltage variations of 610 % of the nominal stated value, or
10.9.2.2 ac frequency variations of 62 % from the nominal stated frequency.
10.9.2.3 The manufacturer shall clearly indicate the maximum input current.
10.9.3 ac Mains Power—Heat calculators intended for use with ac mains power shall operate at a nominal voltage of 120 V and
shall tolerate the following variations:
10.9.3.1 Voltage variations of -15 to +10 % of the nominal stated value or
10.9.3.2 ac frequency variations of 62 Hz from the nominal stated frequency.
10.9.3.3 The manufacturer shall clearly indicate the maximum input current.
10.10 Environmental Class—Heat calculators and complete heat meters shall conform to one or more of the following
environmental classifications according to the application.
10.10.1 Environmental Class A (Domestic/Light Commercial Use, Indoor Installations):
10.10.1.1 Ambient temperature—5 to 55°C [41 to 131°F].
10.10.1.2 Low-level humidity conditions as defined in OIML D11, Section 8.2.2, at a test level index for Class H1.
10.10.1.3 Normal electrical and electromagnetic conditions as defined in OIML D11, Section 8.4, at a test level for Class E1.
10.10.1.4 Low-level mechanical conditions as defined in OIML D11, Section 8.3, at a test level index for Class M2.
10.10.1.5 NEMA 12 or IP52 or better enclosure (off the pipe) (see IEC 60529 or NEMA 250).
10.10.1.6 NEMA 3R or IP54 (heating) or IP65 (cooling) (on the pipe) or better (see IEC 60529 or NEMA 250).
10.10.2 Environmental Class B (Domestic/Light Commercial Use, Outdoor Installations):
10.10.2.1 Ambient temperature— -25 to 55°C [-13 to 131°F].
10.10.2.2 Normal level humidity conditions as defined in OIML D11, Section 8.2.2, at a test level index for Class H2.
10.10.2.3 Normal electrical and electromagnetic conditions as defined in OIML D11, Section 8.4, at a test level for Class E1.
10.10.2.4 Low-level mechanical conditions as defined in OIML D11, Section 8.3, at a test level index for Class M2.
10.10.2.5 NEMA 3R or IP54 (heating) or IP65 (cooling) or better enclosure (see IEC 60529 or NEMA 250).
10.10.3 Environmental Class C (Industrial Installations):
10.10.3.1 Ambient temperature— -25 to 55°C [-13 to 131°F].
10.10.3.2 Normal level humidity conditions as defined in OIML D11, Section 8.2.2, at a test level index for Class H2.
10.10.3.3 High electrical and electromagnetic conditions as defined in OIML D11, Section 8.4, at a test level for Class E2.
10.10.3.4 Low-level mechanical conditions as defined in OIML D11, Section 8.3, at a test level index for Class M2.
10.10.3.5 NEMA 3R or IP54 (heating) or IP65 (cooling) or better enclosure (see IEC 60529 or NEMA 250).
10.10.4 Environmental Class D (Domestic/Light Commercial Use, Outdoor Installations):
10.10.4.1 Ambient temperature— -40 to 55°C [-40 to 131°F].
10.10.4.2 Normal electrical and electromagnetic conditions.
10.10.4.3 Low-level mechanical conditions.
10.10.4.4 NEMA 3R or IP54 (heating) or IP65 (cooling) or better enclosure (see IEC 60529 or NEMA 250).
10.11 Protection against Fraud—Heat calculators shall be protected in such a way that, after the device has been correctly
installed, there is no possibility of dismantling, altering, or adjusting it without evident damage to the sensor or a security seal(s).
10.12 Display (Indicating Device)—The heat calculator shall include a device that indicates the quantity of heat. The display
shall include a numerical or semi-numerical scale and shall provide an easily read, reliable, and unambiguous indication. The real
or apparent character height shall be at least 4 mm [0.16 in.]. The quantity of heat shall be indicated in Btus, watt-hours, or decimal
multiples of those units. The figures indicating decimal fractions of a unit shall be separated from the others by the decimal divider.
The name or symbol of the unit in which the quantity of heat is given shall be indicated adjacent to the display.
10.12.1 Retention of Data—Heat calculators shall be so designed that, in the event of an external power supply failure (mains
or external ac or dc), the meter indication of energy at the time of failure is not lost and remains accessible for a minimum of one
year.
NOTE 2—Compliance with 10.12.1 will not necessarily ensure that the heat meter will continue to register the heat consumed in the event of a power
supply failure.
E3137/E3137M − 18
10.12.2 Scaling and Resolution—The display indicating the quantity of heat shall be able to register, without overflow, a
quantity of heat at least equal to the transfer of energy that corresponds to a continuous operation for 3000 h at the upper limit
of the thermal power, P , of the heat meter.
s
10.12.2.1 The quantity of heat, measured by a heat meter operating at the upper limit of the thermal power for 1 h shall
correspond to at least one digit of lowest significance of the display.
10.13 Materials of Construction—The heat calculator shall be constructed from materials designed to resist wear and corrosion
that may be expected to result from exposure to the heat-conveying liquid. The materials shall also be suitable for the
environmental class of the instrument. The heat calculator enclosure shall meet NEMA 3R or IP54 (heating) or IP65 (cooling)
requirements when installed on the piping system (see IEC 60529 or NEMA 250).
11. Data Exchange and Communications Protocols
11.1 General—Heat meters may use either none or a number of interfaces to communicate with remote readout devices.
11.1.1 Hardware Interface and Communications Protocols—The hardware interface and communications protocols should meet
internationally recognized standards for interoperability. Recognized standards organizations include the Institute of Electrical and
Electronics Engineers (IEEE), the International Organization for Standardization (ISO), American National Standards Institute,
(ANSI), the European Telecommunications Standards Institute (ETSI), the European Committee for Standardization (CEN), and
the International Electrotechnical Commission (IEC).
11.1.2 Data Element Structure and Definitions—Heat meters that use one or more communications interfaces shall at least, at
a minimum, transmit values for heat and volume totals. Other recommended values would include volume flow, temperature(s),
and heat rate.
12. Heat Meter Testing
12.1 Heat meters that comply with the general requirements of this specification and are submitted for type approval and
undergo initial verification shall comply with the specified tests in this section. Initial verification is intended to ensure that
instruments that are put into service will have specified metrological characteristics within the limits of the maximum permissible
errors and will function properly.
12.2 Type Approval Tests—The type approval procedure will ascertain that the design and construction of the instrument type
conforms to the metrological requirements of this specification. In addition to verifying documentation provided by the
manufacturer (see 14.18) and comparison of the type with the metrological requirements of this specification, the tests in Section
14 shall be performed.
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