Terms and conditions for the approval of thermal energy meters

Category: Volume
Issue date: 2018-03-07
Effective date: 2018-03-07
Revision number: N/A
Supersedes: N/A

1.0 Scope
2.0 Application
3.0 References
4.0 Definitions
5.0 Classification of thermal energy meters
6.0 Design, composition and construction
7.0 Calculation of thermal energy
- 7.1 Equations
- 7.2 Provision of heat coefficients
8.0 Performance
9.0 Seals
- 9.1 Physical seals
- 9.2 Electronic seals
10.0 Markings
11.0 Installation and use

1.0 Scope

In accordance with subsection 3(2) of the Weights and Measures Act, types of thermal energy meters may be approved on a temporary basis if:

an application is submitted which includes evidence that the device type has been tested and found to meet the requirements of the terms and conditions set out in this document; and
a sample of the device type has been evaluated in the field prior to trade use and found to be in compliance with the terms and conditions set out in this document and the applicable sections of the Weights and Measures Regulations.

Thermal energy meters will not be approved on a temporary basis once metrological requirements have been established and suitable means to conduct evaluations developed. At the discretion of Measurement Canada, types of thermal energy meters approved in accordance with subsection 3(2) of the Weights and Measures Act prior to the establishment of requirements and means to evaluate the devices may be granted full approval or may be required to be submitted for further evaluation.

2.0 Application

These terms and conditions apply to any thermal energy meter and to any of its sub-assemblies that are used in trade and measure the heat energy which, in a heat exchange circuit, is given up (heating) or absorbed (cooling) by a heat conveying liquid.

In addition to these terms and conditions, thermal energy meters must meet the applicable requirements of the Weights and Measures Act and Regulations.

3.0 References

ISO 7268:1983 Pipe components—Definition of nominal pressure
IAPWS-IF97—IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam
International Temperature Scale of 1990 (ITS-90)
IEC 61010-1—Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use - Part 1: General Requirements
IEC 60751:2008 Industrial platinum resistance thermometers and platinum temperature sensors

4.0 Definitions

Calculator (calculateur): A sub-assembly which receives signals from the flow sensor and the temperature sensors to calculate and indicate the quantity of heat exchanged.
Combined device (appareil combiné): A thermal energy meter which has separable sub-assemblies.
Complete device / complete thermal energy meter (appareil complet/compteur d'énergie thermique complet): A thermal energy meter which does not have separable sub-assemblies.
Cooling meter (compteur de refroidissement): A meter and heat exchange circuit configuration in which the return temperature of the heat conveying liquid is higher than the flow temperature.
E_c: The limit of error for the heat reported by the calculator.
E_f: The limit of error for the mass and volumetric flow rate reported by the flow sensor sub-assembly.
E_t: The limit of error for the temperature difference reported by the temperature sensor pair sub-assembly.
Flow temperature (θ_f) (température d'admission): The temperature of the heat-conveying liquid at the inlet of the heat exchange circuit.
Flow rate (q) (débit)): The volumetric or mass flow rate of the heat conveying liquid through the heat exchange circuit.
Flow sensor (capteur de débit): A sub-assembly through which the heat-conveying liquid flows, at either the flow or return of a heat exchange circuit, and which emits a signal, which is a function of the volumetric or mass flow rate.
Heat conveying liquid (liquide caloporteur): The liquid in the heat exchange circuit which transmits or absorbs thermal energy, typically water.
Heat exchange circuit (circuit d'échange de la chaleur): A fluid conducting circuit that facilitates the transmission or absorption of thermal energy through the heat conveying liquid that it contains.
Heating meter (compteur de chaleur): A meter and heat exchange circuit configuration in which the return temperature of the heat conveying liquid is lower than the flow temperature.
Hybrid device (appareil hybride): A thermal energy meter which, for the purpose of type approval, can be treated as a combined device. After examination, its sub-assemblies are treated as inseparable.
Limit of error (marge de tolérance): The maximum permissible difference between the true value of a measurand and the value displayed, recorded or output by the complete device or sub-assembly.
Maximum admissible working pressure (pression maximale de service admissible): The maximum positive internal pressure that the thermal energy meter or sub-assembly can withstand permanently at the upper limit of the temperature range, expressed as a PN-series (nominal pressure) as defined in ISO 7268.
Maximum permanent flow rate (q_p) (débit maximal permanent): The maximum continuous value of the flow rate that is permitted for the thermal energy meter to function within applicable limits of error.
Maximum pressure loss (perte de pression maximale): The loss in pressure in the heat conveying liquid passing through the flow sensor when the flow sensor is operating at the maximum permanent flow rate (q_p).
Maximum short term flow rate (q_s) (débit maximal à court terme): The maximum value of the flow rate that is permitted for short periods of time (less than one hour per day and 200 hours per year) for the thermal energy meter to function within applicable limits of error.
Maximum temperature (θ_max) (température maximale): The maximum flow or return temperature for the thermal energy meter to function within applicable limits of error.
Maximum temperature difference (Δθ_max) (différence de température maximale): The maximum value of the difference between θ_f and θ_r for the thermal energy meter to function within applicable limits of error.
Maximum thermal power (P_s) (puissance thermique maximale): The highest heat exchange power that is permitted for the thermal energy meter to function within applicable limits of error.
Minimum flow rate (q_i) (débit minimal): The minimum value of the flow rate that is permitted for the thermal energy meter to function within applicable limits of error.
Minimum temperature (θ_min) (température minimale): The minimum flow or return temperature for the thermal energy meter to function within applicable limits of error.
Minimum temperature difference (Δθ_min) (différence de température minimale): The minimum value of the difference between θ_f and θ_r for the thermal energy meter to function within applicable limits of error.
Nominal meter factor (facteur de mesure nominal): The number of output pulses per unit of liquid flow.
Nominal pressure (pression nominale): The pressure in bars that a pipe can support with water at 20 °C.
Qualifying immersion depth (profondeur d'immersion admissible): The immersion depth over which a temperature sensor is considered stable.
Registration (enregistrement): The displayed and recorded thermal energy measured by the thermal energy meter.
Return temperature (θ_r) (température de retour): The temperature of the heat-conveying liquid at the outlet of the heat exchange circuit.
Sub-assembly (sous-ensemble): The flow sensor, temperature sensor pair, calculator, or a combination of these.
Sub-registration (enregistrement secondaire): A registration that only occurs when certain conditions are met.
Temperature difference (Δθ) (différence de température): The absolute value of the difference between the flow temperature (θ_f) and return temperature (θ_r).
Temperature sensor pair (paire de sondes de température): A sub-assembly which senses the temperatures of the heat conveying liquid at the flow and return of a heat exchange circuit.
Thermal energy meter (compteur d'énergie thermique): A measuring machine consisting of a flow sensor, a temperature sensor pair and a calculator that determines, records and displays the quantity of thermal energy transferred to or from a heat conveying liquid.

5.0 Classification of thermal energy meters

Thermal energy meters or sub-assemblies that contain a flow sensor are classified as Class 1, 2 or 3. This class is determined by the limits of error associated with the flow sensor set out in section 8.3.1.

6.0 Design, composition and construction

Thermal energy meters and sub-assemblies must be of a design, composition and construction that, under normal conditions of use and throughout their expected lifetime, enables them to measure accurately and does not facilitate the perpetration of fraud.

6.1 Indications and registrations

6.1.1 Provision of indicating elements

A thermal energy meter must be provided with appropriate indicating and recording elements in terms of the design, number and size of digits to permit accurate measurement.

6.1.2 Clarity and accuracy of indications

The indications and registrations generated by a thermal energy meter must be clear, accurate, reliable and easy to read under normal conditions of use.

6.1.3 Separation of figures

The figures indicating sub-multiples of a unit must be clearly distinguishable and separated from the other figures by the decimal divider or comma.

6.1.4 Identification of indications, registrations and metrologically significant annunciators

Indications, registrations and metrologically significant annunciators must be identified with suitably located words, names or symbols or abbreviations for the units of measurement that will not become obliterated or illegible under normal conditions of use of the thermal energy meter.

6.1.5 Units of measure

The quantity of thermal energy measured must be indicated in units of joules, watt-hours, or in decimal multiples of those units.

6.1.6 Interval format

The interval of a thermal energy meter must be presented in a decimal format and must be equal to 1 × 10ⁿ, 2 × 10ⁿ or 5 × 10ⁿ, where the power "n" is a positive or negative whole number or zero.

6.1.7 Display capacity

The display indicating the quantity of heat must be able to record, without overflow, a quantity of heat at least equal to the transfer of energy which corresponds to a continuous operation for 3,000 h at the maximum of the thermal power of the thermal energy meter.

6.1.8 Digit of lowest significance

The quantity of heat measured by a thermal energy meter operating at maximum thermal power for 1 h must correspond to at least one digit of lowest significance of the display.

6.1.9 Indication of flow rate and temperature difference

A thermal energy meter or calculator must be capable of indicating the mass or volumetric flow rate and temperature difference of the heat conveying liquid in addition to the heat exchanged.

6.1.10 High resolution mode

A thermal energy meter must be provided with a high resolution mode in which indications of the thermal energy, temperature and flow rate are displayed to a resolution sufficient to establish its conformance to the applicable limits of error.

6.2 Auxiliary equipment and interfaces

A thermal energy meter that is equipped with interfaces that allow the connection of auxiliary equipment must be designed so that

the metrological functions of the device are not adversely affected by either the operation of the auxiliary equipment, or by disturbances or influence factors acting on the auxiliary equipment or interfaces; and
the interfaces do not allow access to the metrological functions and adjustable components of the device.

6.3 Allowable operating parameters

6.3.1 Ratio of Δθ_max to Δθ_min

Except for cooling meters, the ratio of Δθ_max to Δθ_min must not be less than 10.

6.3.2 Value of minimum temperature difference

Δθ_min must be 1, 2 or 3 K.

6.3.3 Ratio of q_p to q_i

The ratio of the permanent flow rate (q_p) to the minimum flow rate (q_i) must be equal to or greater than 10.

6.3.4 Pressure loss

The maximum pressure loss through the flow sensor at the permanent flow rate must not exceed 0.25 bar, except where the thermal energy meter includes a flow controller or also acts as a pressure reducing device.

6.4 Registration

6.4.1 Proper incrementation of registration

The registration of a thermal energy meter must not increment when the flow rate is lower than the minimum flow rate.

6.4.2 Sub-registrations

A complete thermal energy meter or a calculator may include multiple sub-registrations of thermal energy, in addition to the primary registration, for the separation of heating and cooling energy, time-of-use billing or other purposes provided that

they are in mathematical agreement with the primary registration and any other sub-registrations;
they clearly indicate their function and when they are active;
any means or conditions used to switch the sub-registration that is being recorded do not affect device accuracy.

6.4.3 Non-resettable registrations

The primary registration of the total quantity of thermal energy supplied or the sub-registrations from which the total quantity of thermal energy supplied can be derived must not be able to be reset during use.

6.4.4 Power failure

In the event of external power supply failure, the recorded quantity of energy in all registrations and sub-registrations at the time of failure must not be lost and must remain accessible for a minimum of one year.

6.5 Protection of interior parts

Casings of thermal energy meters must protect the interior parts against the ingress of water and dust. The minimum protection rating of enclosures must be IP54 for enclosures that are to be installed into pipework and IP52 for other enclosures, in accordance with IEC 61010-1.

6.6 Design of temperature sensors

Temperature sensors must be designed to be installed in the flow sensor or within the heat exchange circuit, either directly or in thermal wells.

6.7 Assumption of quantities

A thermal energy meter must be designed to measure temperature differences and flow rates and these quantities must not be assumed.

6.8 Software version number

A complete thermal energy meter or calculator must be equipped with a feature to indicate the software and any version of the software that it is using.

7.0 Calculation of thermal energy

7.1 Equations

The measured heat energy registered by the meter (Q) must be calculated from the temperature difference and flow rate using the following heat transmission equations.

For devices recording a mass flow rate:
$Q = \int_{t_{o}}^{t_{1}} q_{m} Δh dt$
For devices recording a volumetric flow rate:
$Q = \int_{V_{o}}^{V_{1}} k Δθ dV$
$k = \frac{(h_{f} - h_{r})}{v (θ_{f} - θ_{r})}$

where:

V is the volume of the heat conveying liquid passed through the heat exchange circuit
q_m is the mass flow rate of the heat conveying liquid passed through the heat exchange circuit
k is the heat coefficient, which is a function of the specific volume and specific enthalpies of the heat conveying liquid
Δh is the difference between the specific enthalpies of the heat conveying liquid at the flow θ_f and θ_r temperatures of the heat exchange circuit
v is the specific volume of the heat conveying liquid
h_f and h_r are the specific enthalpies of the heat conveying liquid at the flow and return locations, respectively
t is time

Note: The quantities of v, h_f and h_r must be calculated according to IAPWS-IF97—APWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam using the International Temperature Scale of 1990 (ITS-90).

7.2 Provision of heat coefficients

Thermal energy meters intended for use with heat conveying liquids other than water must be provided with documentation stating the heat coefficient used as a function of temperature and pressure.

8.0 Performance

8.1 Acceptance limits of error

The acceptance limit of error for the thermal energy reported by a thermal energy meter, expressed in percent of the true value, is the sum of the acceptance limit of error for each sub-assembly, as defined in sections 8.3.1, 8.3.2 and 8.3.3.

$E = E_{f} + E_{t} + E_{c}$

8.2 Acceptance limits of error for combined and hybrid meters

Combined and hybrid devices will be subject to acceptance limits of error equal to the sum of the acceptance limits of error specified for their constituent sub-assemblies in sections 8.3.1, 8.3.2 and 8.3.3.

8.3 Acceptance limits of error for sub-assemblies

A sub-assembly tested separately for approval will be subject to the acceptance limits of error specified for that sub-assembly in sections 8.3.1, 8.3.2 and 8.3.3. Where the sub-assembly is composed of a combination of a flow sensor and calculator, or a temperature sensor pair and calculator, its outputs will be subject to the sum of the limits of error specified for each component of that sub-assembly in sections 8.3.1, 8.3.2 and 8.3.3.

8.3.1 Acceptance limits of error for flow sensors

The acceptance limits of error for the volumetric or mass flow rate output by a flow sensor sub-assembly, expressed in percent of the true value for each accuracy class, are:

Class 1: $E_{f} = (1 + 0.01 \frac{q_{p}}{q})$ , not to exceed 5%
Class 2: $E_{f} = (2 + 0.02 \frac{q_{p}}{q})$ , not to exceed 5%
Class 3: $E_{f} = (3 + 0.05 \frac{q_{p}}{q})$ , not to exceed 5%

8.3.2 Acceptance limits of error for temperature sensors

The acceptance limit of error for the temperature difference output by a temperature sensor pair sub-assembly, expressed in percent of the true value, is:

$E_{t} = (\frac{0.5 + 3 Δ θ_{min}}{Δθ})$

8.3.3 Acceptance limits of error for calculators

The acceptance limit of error for the thermal energy output by a calculator expressed in percent of the true value is:

$E_{c} = (\frac{0.5 + Δ θ_{min}}{Δθ})$

8.4 In-service limits of error

The in-service limits of error for complete, combined and hybrid meters and associated sub-assemblies are two times the acceptance limits of error set out in sections 8.1, 8.2 and 8.3.

8.5 Repeatability

The repeated application of the same measurand under the same conditions to the same thermal energy meter or sub-assembly must produce measurements differing by no more than one third of the applicable limit of error.

8.6 Durability

8.6.1 Difference in flow rate

The difference in volumetric or mass flow rate reported by a thermal energy meter or flow sensor sub-assembly before and after being subjected to 2,400 hours of continuous fluid flow may differ by no more than the absolute value of E_f.

8.6.2 Difference in temperature

The difference in temperature reported by a thermal energy meter or temperature sensor sub-assembly before and after being subjected to 10 heating and cooling cycles must not be greater than 0.1 °C.

8.7 Influence factors

A thermal energy meter must perform within the applicable limits of error when it is tested under controlled conditions for the following influence factors:

for devices that use mains electricity as a power source, any voltage from −15% to +10% of the nominal voltage, or, for devices that operate over a range of voltages, −15% from the low end of the range to +10% from the high end of the range;
for devices that use non-mains alternating current electricity of less than 50 V as a power source, any voltage from −50% to +50% of the nominal voltage, or, for devices that operate over a range of voltages, −50% from the low end of the range to +50% from the high end of the range;
for devices that have a frequency range or for any AC-powered device (if the AC frequency is used for measurement), any frequency from −2% to +2% of the nominal frequency, or, for devices that operate over a range of frequencies, −2% from the low end of the range to +2% from the high end of the range;
for devices powered by internal batteries, any voltage below the nominal voltage at which the device is capable of displaying measurement registrations and at +10% of the nominal voltage;
for devices that use direct current electricity with a nominal voltage of less than 50 V as a power source, any voltage from −50% to +75% of the nominal voltage;
any temperature within the ambient temperature range marked on the device.

8.8 Disturbances

A thermal energy meter, when disturbed by interference such as the effects of electromagnetic or electrostatic fields, a short time power reduction, voltage spikes, electrostatic discharges, damp heat or other disturbances that may be encountered under normal conditions of use, must:

provide an indication or registration that does not differ from the value of the indication or registration that would be provided without interference by more than the absolute value of the applicable limit of error;
blank the indication and prevent the transmission, printing and storage of measured values;
provide an error message and prevent the transmission, printing and storage of measured values; or
provide an indication that is so completely unstable that it cannot be interpreted, stored or printed as a correct measurement value.

8.9 Temperature sensors

8.9.1 Immersion beyond qualifying immersion depth

Immersion of a temperature sensor beyond its qualifying immersion depth must change the resistance by an amount corresponding to no more than 0.1 K.

8.9.2 Relationship between temperature and resistance

The relationship between temperature and resistance of each single sensor of a pair must not differ from the values of the formula given in IEC 60751 (using the standard values of the constants A, B and C) by more than an amount equivalent to 2 K.

8.9.3 Difference in results with and without thermal wells

The difference in the measuring result reported by the temperature sensor with and without thermal wells must not exceed one third of the applicable limit of error.

9.0 Seals

9.1 Physical seals

Subject to 9.2, a thermal energy meter must be protected by means of readily accessible and observable physical seals that make apparent any:

accessing of the metrological functions and the adjustable components;
dismantling, removing or altering of the thermal energy meter or sub-assemblies;
disconnection from the external power source, for devices not incorporating an internal battery supply with automatic changeover.

9.2 Electronic seals

Electronic means of sealing may be used in place of a physical seal for protection of programmable or configurable components of a thermal energy meter or calculator.

10.0 Markings

10.1 Markings for complete devices or sub-assemblies

The information set out in column I of Table 1 to this section must be marked, using appropriate words or the symbols set out in column II of the table, on the complete meter or sub-assembly described in columns III to VI of the table.

Table 1: Required markings
Column I: information to be marked	Column II: symbols	Column III: complete device	Column IV: flow sensor	Column V: temperature sensor pair	Column VI: calculator
Manufacturer, applicant or importer's name or trademark	-	yes	yes	yes	yes
Model or type number	-	yes	yes	yes	yes
Distinctive serial number	-	yes	yes	yes	yes
Approval number	-	yes	yes	yes	yes
Accuracy class	-	yes	yes	-	-
Ambient temperature range	-	yes	yes	-	yes
Limits of temperature of heat conveying liquid	θ	yes	yes	yes	yes
Limits of temperature difference of heat conveying liquid	Δθ	yes	-	yes	yes
Indication of sensor for flow and return temperature, if applicable	-	yes	-	yes	-
Limits of flow rate	q_i, q_p, q_s	yes	yes	-	-
Maximum admissible working pressure	-	yes	yes	yes^{Footnote 1}	-
Flow sensor installation location: inlet or outlet	-	yes	-	-	yes
Indication of flow direction	-	yes	yes	-	-
Heat conveying liquid (if other than water)	-	yes	yes	-	yes
Nominal meter factor	-	-	yes	-	yes
Voltage (external supply)	-	yes	yes	-	yes
Type of temperature sensor	-	-	-	yes	yes
Orientation limitations	-	yes	yes	-	-
Nominal pressure	-	yes	yes	-	-

10.2 Markings for combined and hybrid devices

Subject to 10.3, each sub-assembly of a combined or hybrid device must be marked according to the requirements in 10.1 pertaining to that particular sub- assembly.

10.3 Markings for inseparable hybrid devices

Hybrid devices in which all sub-assemblies are physically inseparable, or sealed together so as to be inseparable, may be marked as a complete device.

10.4 Markings for dual use meters

Where a device is intended for use as both a heating and cooling meter, it must bear two sets of markings indicating the parameters for each meter configuration, if different.

10.5 Legibility and permanence of markings

All markings must meet the following criteria:

they are distinct, easily readable and of such nature that they will not become obliterated or illegible;
they are of a height appropriate to the size of the device; and
the height of capital letters is at least 2 mm.

10.6 Visibility of markings

All markings must be located in a clearly visible place on a part of the meter or on a marking plate affixed to it.

10.7 Marking plates

Marking plates must be made of durable material and must be permanently affixed to the device.

10.8 Area for verification markings

There must be an area on every thermal energy meter that is suitable for the application of verification markings.

11.0 Installation and use

11.1 Manner of installation, maintenance and use

A thermal energy meter and any equipment or accessories connected to or used in conjunction with it must be installed, maintained and used in a manner that:

ensures accurate measurement;
respects the parameters, restrictions, limitations and conditions of use set out in the notice of approval issued for the device;
complies with the manufacturer's or importer's instructions;
does not detrimentally affect the performance of the device; and
does not facilitate the perpetration of fraud.

11.2 Suitability

A thermal energy meter must be suitable for its intended use with respect to the elements of its design, composition and construction.

11.3 Commercial, industrial and residential applications

11.3.1 Commercial and industrial applications

A thermal energy meter intended for use in commercial or industrial applications must be of a Class 1 or 2.

11.3.2 Residential applications

A thermal energy meter intended for use in residential applications must be of a Class 1, 2 or 3.

11.3.3 Mixed use applications

A thermal energy meter intended for use in a combined commercial and residential application must be of a Class 1 or 2.

11.4 Required ambient temperature range

11.4.1 Indoor use

Devices intended for indoor use must have an approved ambient temperature range extending from 5 °C to 55 °C.

11.4.2 Outdoor use

Devices intended for outdoor use must have an approved ambient temperature range extending from −25 °C to 55 °C.

11.5 Minimization of condensation in cooling applications

Meters intended for use as a cooling meter or as a cooling and heating meter must be installed so as minimize the effects of condensation on device performance.

11.6 Heat exchange circuit

The heat exchange circuit must

be properly maintained and pressurized so as to avoid cavitation, water hammering and surge within the heat conveying liquid flow, or contain means to minimize these effects.
have suitable provisions (thermal wells) for the application of temperature reference standards used during examinations, except where such provisions would have an adverse effect on device accuracy. These must be installed in close proximity to the location of each element of the temperature sensor pair sub-assembly.

11.7 Heat conveying liquid

The heat conveying liquid must

be maintained so as to avoid the build-up of solid particulates
meet the minimum quality standards specified by the thermal energy meter manufacturer
not be substituted with another liquid with a different heat coefficient after the installation of the thermal energy meter

11.8 Temperature sensors

The temperature sensors must be

installed directly within the heat exchange circuit or flow sensor, or in thermal wells. If thermal wells are used then both temperature sensors of a temperature sensor pair must be mounted in a well.
replaced as a pair, whenever replacement is necessary.
located at a sufficient distance from external heat sources, with the exception of the heat exchange circuit itself.
located so as to ensure the relevance of the thermal energy metered to the entity being billed.

11.9 Flow sensor

The flow sensor must be installed so as to minimize any adverse effects on the flow pattern resulting from the pipe configuration or construction.