CEN/TR 13582:2025

SLOVENSKI STANDARD
01-november-2025
Nadomešča:
SIST-TP CEN/TR 13582:2021
Vgradnja merilnikov toplote - Smernice za izbiro, vgradnjo in delovanje merilnikov
toplote
Installation of thermal energy meters - Guidelines for the selection, installation and
operation of thermal energy meters
Installation von thermischen Energiemessgeräten - Richtlinien für Auswahl, Installation
und Betrieb von thermischen Energiemessgeräten
Compteur d’énergie thermique Installation — Lignes directrices pour la sélection,
l’installation et le fonctionnement des compteurs d’énergie thermique
Ta slovenski standard je istoveten z: CEN/TR 13582:2025
ICS:
17.200.10 Toplota. Kalorimetrija Heat. Calorimetry
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TR 13582
TECHNICAL REPORT
RAPPORT TECHNIQUE
September 2025
TECHNISCHER REPORT
ICS 17.200.10 Supersedes CEN/TR 13582:2021
English Version
Installation of thermal energy meters - Guidelines for the
selection, installation and operation of thermal energy
meters
Compteur d'énergie thermique Installation - Lignes Installation von thermischen Energiemessgeräten -
directrices pour la sélection, l'installation et le Richtlinien für Auswahl, Installation und Betrieb von
fonctionnement des compteurs d'énergie thermique thermischen Energiemessgeräten

This Technical Report was approved by CEN on 11 August 2025. It has been drawn up by the Technical Committee CEN/TC 176.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 13582:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Selecting a metering device for thermal energy . 7
4.1 General. 7
4.2 Metrological characteristics . 8
4.3 Environmental classifications . 8
5 Dimensioning . 8
5.1 General. 8
5.2 Determining the thermal power . 9
5.3 Thermal energy load . 9
5.3.1 Standard thermal energy load in new builds . 9
5.3.2 Thermal energy load of buildings with no standard load calculation . 9
5.4 Thermal power for water heating . 10
5.5 Thermal power for ventilation and air conditioning systems. 11
5.6 Thermal power for cooling systems . 11
5.7 Thermal power for engineering purposes . 11
6 Determining the flow rate . 11
6.1 Principles of thermodynamics . 11
6.1.1 General. 11
6.1.2 Total maximum power for heating or cooling . 12
6.1.3 Inlet and outlet temperature . 12
6.1.4 Thermal coefficient . 13
7 Selecting a flow sensor for a thermal energy meter . 13
8 Checking the flow sensor design after commissioning . 13
8.1 General. 13
8.2 Operating conditions . 14
8.3 Flow sensors . 14
8.3.1 General. 14
8.3.2 Inlet and outlet pipes . 14
8.3.3 Influence of insufficient temperature mixing on measuring accuracy . 15
8.3.4 Measurement deviations due to flow disturbances caused by swirl . 15
8.3.5 Measurement deviations due to pulsation . 15
8.3.6 Measurement deviations due to the contamination of the thermal conveying medium . 15
8.3.7 Types of flow sensor . 15
8.4 Temperature sensors . 20
8.4.1 General. 20
8.4.2 Measurement deviations due to differential pressure and temperature difference . 21
8.4.3 Using pockets. 22
8.4.4 Surface mounted temperature sensors . 23
8.5 Calculators . 23
8.5.1 General . 23
8.5.2 Functionality . 23
8.5.3 Selecting a calculator. 23
8.5.4 Fast-response thermal energy measurement . 23
9 Arranging of meters for thermal energy . 24
9.1 General . 24
9.2 Environment . 24
9.2.1 Electromagnetic interference . 24
9.2.2 Thunderstorms and voltage peaks . 24
9.2.3 Temperature and humidity . 24
9.2.4 Mechanical stress . 24
9.3 Flow sensors . 25
9.3.1 Flow profile . 25
9.4 Temperature sensors . 27
9.4.1 General . 27
9.4.2 Arranging temperature sensors . 29
9.5 Calculators . 30
10 Installing thermal energy meters . 31
10.1 General . 31
10.2 Mechanics . 31
10.3 Connecting to pipes . 31
10.4 Electrical connections . 31
10.5 Commissioning . 32
11 Monitoring operation . 32
11.1 General . 32
11.2 Measuring cooling supply using water or liquids other than water . 32
11.2.1 General . 32
11.2.2 Flow sensor requirements . 33
11.2.3 Requirements for temperature measurement . 33
11.2.4 Calculator requirements . 35
11.3 Requirements for the system arrangement of cooling measurements . 36
12 Other liquids than water . 38
12.1 Introduction . 38
12.2 Physical impact . 39
12.3 Flow measurement . 41
12.4 Temperature difference measurement . 47
12.5 Calculator . 47
Bibliography . 48

European foreword
This document (CEN/TR 13582:2025) has been prepared by Technical Committee CEN/TC 176 “Thermal
energy meters” the secretariat of which is held by SIS.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN/TR 13582:2021.
This document includes the following significant technical changes with respect to CEN/TR 13582:2021:
— replacement of incorrect figures;
— editorial changes to the text.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
Introduction
Metering devices for thermal energy (heat and cooling meters) are only working correctly and
consistently if the system design considers the minimum and maximum ratings for temperature,
temperature difference and flow rate according to the approved ranges. The metering device is selected
for the approved legal range and the application area. The thermal energy meter is installed according to
the valid requirements. During commissioning the thermal energy meter is checked for both correct
installation and full functionality and afterwards sealed against unauthorized opening.
According to EN 1434-6, harmonized against the Measuring Instruments Directive (MID) [1], a
commissioning is obligatory to ensure that the metering device accurately measures the planned or
predicted consumption.
Installing the metering devices or their sub-assemblies incorrectly (e.g. an incorrect combination of
temperature sensors with non-approved pockets) does not guarantee the measuring accuracy. Hence,
the measurement deviations can exceed the permissible error limits. National calibration laws state that
the metering point operator ensures that the metering device is set up, connected, handled and
maintained correctly to guarantee the measuring accuracy. Incorrect measurements result in bills that
cannot be used in business transactions.
The metering point operator is in district heating networks responsible for a proper installation and
commissioning of the metering devices. The metering point operator can also delegate this task to a
service company. The building owner or the building owner’s representative (e.g. a metering service
company) is in sub metering applications responsible for a proper installation and commissioning of the
metering devices.
The EN 1434 series of standards provide technical principles and practical advice in selecting, installing
and commissioning of thermal energy meters. However, because a standard cannot cover all areas
completely, this report will assist users of thermal energy meters.
1 Scope
The EN 1434 series of standards provide technical principles and practical advice in selecting, installing
and commissioning of thermal energy meters. However, because a standard cannot cover all areas
completely, this document assists users of thermal energy meters.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 1434-1, Thermal energy meters - Part 1: General requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1434-1 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
thermal energy meter
instrument intended for measuring the energy which in a heat-exchange circuit is absorbed (cooling) or
given up (heating) by a liquid called the heat-conveying liquid
[SOURCE: EN 1434-1:2022]
3.2
water
domestic water
3.3
hot water
domestic hot water
3.4
fluid additive
fluid used to supplement a shortage of the heat transfer medium due to leaks
3.5
fluid
heat transfer medium in a district heating and/or district cooling system
4 Selecting a metering device for thermal energy
4.1 General
A thermal energy meter consists of the following three parts: a flow sensor, a temperature sensor pair
and a calculator (see Figure 1).
These sub-assemblies can be defined as complete instruments, combined instruments or hybrid
instruments (see EN 1434-1).
The calculator unit calculates the energy consumption using the signals from the temperature sensor pair
and the flow sensor.
The minimum temperature difference of the calculator does not fall below the smallest permissible value
(according to MID the minimum temperature difference is 3 K).
The temperature sensors are usually platinum resistance thermometers of type Pt 100, Pt 500 or Pt 1000.
The sensor pair determines the temperature difference between the inlet (flow) and outlet (return) of
the thermal conveying medium.
The flow sensor is granted an error limit of 2 % to 5 %. Due to faulty design, incorrect installation or wear
the wider error limits of this part/sub-assembly of a meter is exceeded occasionally. This case can be
avoided by selecting the correct flow sensor. An overview of the different types of flow sensors is given
in 8.3.7.
Key
1 inlet
2 outlet
3 calculator
4 flow sensor
5 inlet temperature sensor
6 outlet temperature sensor
7 thermal load
Figure 1 — Thermal energy meter
When operating the heat exchanger circuit system, one can discover that the chosen thermal energy
meter design is not applicable due to the actual requirements.
Flow sensors that are designed for higher flow rates cannot have the required accuracy at low flow rates.
If the actual flow rate is below the minimum permissible flow rate, measurements can be skipped until
the measurement fails completely.
Fast changes in energy consumption that place high demands on the dynamics of the meter can cause
significant deviations in the measurement accuracy of the accumulated energy. Fast-response meters
provide measurement characteristics that reduce this deviation (see 8.5.4)
The effects of dirt deposits and flow disturbances over the entire service life of the flow sensors is
considered when selecting a meter.
4.2 Metrological characteristics
The accuracy classes and the maximum permissible relative errors of thermal energy meters are
described in EN 1434-1. Be aware that some national regulations do not allow the use of class 3 m at all
and that other national regulations do not allow the use of class 3 meters for e.g. for q 6 m /h and higher.
p
Class 2 accuracy is the most frequently used accuracy class for flow sensors.
Due to the very high requirements on both flow sensors and test equipment, the availability of class 1
flow sensors is very limited.
4.3 Environmental classifications
The environmental classes are described in EN 1434-1. Thermal energy meters have an environmental
classification A, B and C regarding domestic and/or industrial EMC requirements and indoor and/or
outdoor ambient conditions.
Table 1 — Relationship between EN 1434-1 and MID re. EMC levels
EN 1434-1 MID (2014/32/EU)
Domestic EMC level Class A and B E1
Industrial EMC level Class C E2
Meters with Class C (E2) marking can be used also in domestic installations, but meters with Class A and B
(E1) are not used in industrial installations (see Table 1).
Classes A and C are defined for indoor installations with +5 °C to 55 °C ambient temperature.
Class B is defined for outdoor installation. Since the availability of thermal energy meters for outdoor
installation is limited, special care is taken to select a suitable meter or to select a suitable protective
cabinet.
Most thermal energy meters are installed in locations without any vibration. For such installations,
meters with the mechanical class M1 are suitable. In case some vibrations can occur at the installation
site a meter with class M2 is selected. In case of more intense vibrations a meter with class M3 is selected
(see Table 4 for more details).
5 Dimensioning
5.1 General
When selecting a thermal energy meter, it is important to determine the upper and lower flow limits for
the flow sensor as required by the operating conditions. Based on the range for nominal flow q and
p
minimum flow q one needs to select a suitable flow sensor from the various devices offered by different
i
manufacturers. This selection results in the nominal diameter of the measuring line where the flow
sensor is installed.
Simply selecting a flow sensor according to the nominal diameter of an existing pipe is not necessarily
correct. Otherwise the coverage of the lower flow range can be insufficient.
It is often good practice that flow sensor sizes of one nominal diameter smaller than the pipe are chosen
when the expected average flow rates are low.
The thermal energy output commissioned with the customer and the maximum inlet and outlet
temperature for the planned application build the base for calculating the thermal energy supply.
In transfer stations for district heating and cooling, the fluid flow rate is limited to the commissioned
value by using a flow rate limiter and/or a differential pressure controller. The controller protects the
consumer circuit and the flow sensor from overloading. Arrange the controller in series after the flow
sensor in the outlet to avoid additional disturbances in the flow profile before the flow sensor.
The expected yearly average flow rate, when known, is preferably around 2/3 of the nominal flow qp of
the flow sensor. As for each flow sensor size the nominal flow q corresponds with about 2 m/s average
p
flow velocity. This is the basis for the relationship between DN and q , and it minimizes the risk of
p
cavitation as well as loss of accuracy due to wrong meter size.
5.2 Determining the thermal power
The metering point operator performs calculations to determine the thermal power only as a check.
5.3 Thermal energy load
5.3.1 Standard thermal energy load in new builds
The standard heat load in new buildings and major redevelopments are determined by a qualified project
engineer, e.g. according to EN 12831-1:2017, Clause 6.
5.3.2 Thermal energy load of buildings with no standard load calculation
If existing buildings are being connected to a thermal energy supply with no standard load calculation,
one could use an approximation or estimation method to determine the thermal energy load for
dimensioning the flow sensor.
If a building connected to a district heating supply already contains a central heating system, an
approximate thermal energy load can be e.g. calculated from an average of the last three years’ annual
consumption, an outside-temperature (see Figure 2) and the expected full usage hours.
Maximum values stored in the thermal energy meter can also be used to determine the output.
Key
X hours per year
Y temperature, °C
1 Palermo, Italy
2 Florence, Italy
3 Strasbourg, France
4 Helsinki, Finland
5 Kiruna, Sweden
6 effective indoor temperature 17 °C
Distribution of outdoor temperatures for five European locations, 1881–2000. An indoor temperature has
been added as example.
Figure 2 — Outdoor temperature duration in Europe
5.4 Thermal power for water heating
The thermal power for water heating usually needs to be determined by a qualified project engineer.
Using a priority control for the water heating and taking advantage of the building’s heat storage capacity
it can be possible to provide the required thermal energy output for short-term peaks of water heating
without having a significant drop in room temperature.
If a priority control is used the qualified project engineer can select the higher value of the required
thermal power between the thermal power output for central heating or cooling and the thermal power
for water heating. The higher value is the deciding factor in the selection of the flow sensor.
Parallel operations are considered separately.
See Figure 3 for dimensioning of thermal power for hot water as a function of the number of normal
apartments.
Source reference: Svend Frederiksen, Svend Werner. 2013. District Heating and Cooling. Studenterlitteratur AB,
Lund. Source reference: Figure 4.2 from “District Heating and Cooling” Svend Frederiksen, Svend Werner ISBN
978-91-44-08530-2.
Key
X number of normal apartments
Y required power (kW)
Figure 3 — Dimensioning thermal power for hot water as a function of the number of normal
apartments.
5.5 Thermal power for ventilation and air conditioning systems
The thermal power required for ventilation and air conditioning systems are calculated by a qualified
project engineer.
Depending on climatic requirements, the flow sensor can encounter flow rate peaks during the low load
season if there are ambient inlet temperatures in the district thermal energy network. These peaks are
investigated and considered for dimensioning the flow sensor.
5.6 Thermal power for cooling systems
In bifunctional systems the flow sensor is selected by the maximum flow required for either heat or
cooling. The power is calculated by a qualified project engineer.
5.7 Thermal power for engineering purposes
When supplying heating or cooling for industrial and commercial engineering, it is recommended that
the requirements of the customer and the customer’s qualified project engineer regarding the flow sensor
design are checked. A modulating operating curve in the district thermal energy network can cause
increased flow rate values, especially when there are power peaks in the low load season. This is
considered when dimensioning the flow sensor.
6 Determining the flow rate
6.1 Principles of thermodynamics
6.1.1 General
The nominal heat or cooling load specifies the thermal power required at the measuring point in the
(projected) application.
The maximum thermal power released or absorbed by a thermal conveying medium in a heating or
cooling circuit is calculated as follows:

Q= kV⋅⋅θθ− (1)
( )
io
where

is the thermal power, e.g. kW;
Q
 is the flow rate of the thermal conveying medium, in m /h;
V
k is the thermal coefficient, in kWh/m K;
θ is the design temperature in inlet, in °C;
i
θ is the design temperature in outlet, in °C.
o
Convert the formula to calculate the flow rate for the design case.


Q
(2)
V=
k⋅−θθ
( )
io
6.1.2 Total maximum power for heating or cooling
Add the outputs specified in Clause 5 to calculate the total thermal power.
n

Q = Q
(3)
tot
i
∑
i=1
where

is the total thermal power, in kW;
Q
tot

is the standard thermal load, in kW;
Q

is the thermal power for hot water heating, in kW;
Q
 
NOTE If using priority control, use only the larger value, either Q or Q .
1 2

is the thermal power for ventilation and air conditioning systems, in kW;
Q

is the thermal power for engineering purposes, in kW.
Q
For cooling systems, the thermal load will be added the same way (identical).
6.1.3 Inlet and outlet temperature
The difference between inlet and outlet temperatures is the temperature difference.
∆=Θθ −θ K (4)
inlet outlet 
In general, the inlet temperature of the heating or cooling medium is regulated depending on the outside
temperature and the outlet temperature is based on the design and operating mode of the heating system.
6.1.4 Thermal coefficient
The thermal coefficient k is determined according to EN 1434-1. For example, with θ = 100 °C,
inlet
θ = 50 °C the approximate value of 1,15 [kWh/(m K)] can be expected for meters installed in the inlet
outlet
and 1,12 [kWh/(m K)] for meters installed in the outlet.
7 Selecting a flow sensor for a thermal energy meter
Because the design case described above occurs only for a few days of the year, a flow sensor is selected
so that it ensures that the smallest possible deviation occurs over the whole range of the year.
The range of the most frequent flow values (main operation range) at the measuring point is the deciding
factor for selecting the flow sensor.
The operating range of the flow sensor is within the approved range which is spread between the smallest
flow q and the nominal flow q .
i p
A flow sensor is selected to fulfil all the following criteria:
— the nominal flow q of the flow sensor is as close as possible to the calculated flow rate;
p
— the minimum flow q of the flow sensor is smaller than/equal to the minimum flow of the thermal
i
energy circuit;
— the maximum flow qs of the flow sensor is reserved for short term overload (1 hour per day;
200 hours per year) in the thermal energy circuit.
If the minimum flow rate of the thermal energy circuit is not covered by the minimum flow q of the flow
i
sensor, it is checked whether a smaller flow sensor will cover the design case better.
To achieve the minimum flow rate of the thermal energy circuit, a flow sensor with a higher dynamic
range, q /q , is selected.
p i
The nominal flow q is not exceeded when selecting the flow sensor.
p
Selecting a flow sensor can be easier if technical measures are taken to reduce the fluctuation range of
the flow.
When selecting a flow sensor statutory regulations and standards, such as the EN 1434 series, the
operating conditions, the manufacturer’s installation instructions and nationally applicable requirements
are all considered.
The nominal pressure level (PN/PS) of the flow sensor corresponds to the pressure class at the measuring
point. In praxis the average pressure is well below PN.
The permissible temperature range of the flow sensor complies with the temperature range of the
thermal conveying medium as well as the ambient temperature at the measuring point. Because of
temperature stress, the flow sensor is generally installed in the outlet. This is the cooler pipe for flow
sensors in heat meters and this is the warmer pipe for cooling meters.
In combination with low temperature heating installations flow sensors are also installed in the inlet pipe
which is done to avoid measurement drop outs due to water loss in the installation.
8 Checking the flow sensor design after commissioning
8.1 General
The actual operating conditions of the heating circuit can deviate significantly from the calculated or
specified volumes.
Regular intermediate readings and plausibility checks are performed when evaluating the readings to
detect any deviations.
If minimum or maximum flow rates deviate significantly, the size of the flow sensor is adapted.
The maximum flow value stored in the thermal energy meter’s calculator can be used to check the actual
flow level. However, it is remembered that the value was determined as an average over a thermal energy
meter-specific measuring (integration) period (e.g. one hour).
A plausibility check can also be performed based on the annual full usage hours using regional
temperature values.
If there are any doubts about the plausibility of the heat measurement, an on-site investigation is
recommended.
8.2 Operating conditions
To determine the maximum thermal power demand of the building, one needs to select the higher value
between the thermal energy output for generating hot water and the thermal energy output for central
heating. The higher value represents the output demand. It is generally not necessary to add both values
due to the usual priority control and if a priority control is not applied due to the short hot water heating
time. If a meter that stores the maximum value is commissioned, it can be used to check the calculation
against the measured values and it can be used to determine the appropriate flow range when changing
the meter.
The energy output demand for generating hot water can be calculated using the “Guidelines for hot water
preparation”. These guidelines provide an established European procedure developed by Euroheat and
Power (UNICHAL). The energy output demand can also be determined using the stored maximum values
if a thermal energy meter is available for generating hot water.
The following factors influence the choice of a meter:
— change in temperature difference;
— operating mode of the heat conveying medium circuit;
— quality of installation;
— speed of change (dynamics) in the temperature difference;
— actual required thermal energy demand and flow rate.
It is therefore important for the metering point operator to perform a plausibility check of the
measurement results.
8.3 Flow sensors
8.3.1 General
To optimize the application conditions for flow sensors, the recommendations below are considered,
regardless of the used sensor type.
8.3.2 Inlet and outlet pipes
A straight inlet pipe of at least 5 × diameter and an outlet pipe of 2 × diameter in the same dimensions as
the flow sensor is recommended to reduce any effect on the measurement deviation caused by the flow
profile. This recommendation enables most thermal energy meters on the market to be installed
correctly.
The inlet and outlet pipes do not contain any fittings that change the flow profile, e.g. flow limiters,
differential pressure regulators, dirt traps, filters, pipe bends, cross-sectional changes. Temperature
sensors are not allowed in the straight inlet pipe before the flow sensor but can be installed in the straight
outlet pipe after the flow sensor. Gaskets do not protrude into the settling section and connection fittings
have the same nominal diameter as the flow sensors.
The straight inlet pipeis optimized for maximum length, as some disturbances are reduced significantly
over long distances. All structural design options are used to achieve straight inlet pipes. If the measuring
equipment was planned in the design stage, it is usually possible to design straight inlet pipes of sufficient
length.
To fulfil the legal metrology, the minimum inlet and outlet pipes comply with the specifications in the
approval documents.
In case of narrow installation conditions, which only leave space for an installation of the flow sensor
directly after a tube bend, it is ensured that the flow sensor selected is approved for a 0x diameter inlet
pipe.
8.3.3 Influence of insufficient temperature mixing on measuring accuracy
Any kind of a strand formation caused by the combination of two flow circuits with different fluid
temperatures are eliminated sufficiently by having a long inlet pipe (at least 10 × diameters) or by using
mixing fittings. This applies to both flow measurement and temperature measurement.
8.3.4 Measurement deviations due to flow disturbances caused by swirl
Flow disturbances caused by swirl are difficult to reduce and are therefore avoided with a suitable pipe
design. If the course of a pipe cannot be changed, a flow rectifier with a following inlet pipe is used. Dirt
traps also reduce flow distortions caused by swirl. At least at the change of the flow sensor the dirt trap
is cleaned. The increased pressure drop of these installations is considered. Massively contaminated dirt
traps can also cause heavy flow disturbances.
8.3.5 Measurement deviations due to pulsation
Pulsations can be caused by pumps and air accumulations. The resulting measurement deviations can be
avoided by arranging the flow sensor with a certain minimum distance to pumps, high points in pipes or
other flow disturbance sources.
8.3.6 Measurement deviations due to the contamination of the thermal conveying medium
Any form of contamination of solid or gaseous particles in the thermal conveying medium will lead to
measurement deviations. A flow sensor is not installed at a position in a pipe system where air or gas
bubbles usually occur (e.g. at the highest points in the pipe circuit).
The thermal transfer medium changes over time due to the interaction between the fluid and the
materials in the system. It has a significant effect on the ageing behaviour of the flow sensor.
8.3.7 Types of flow sensor
a) Turbine flow sensor
This group of flow sensors includes several sensor types, e.g. impeller single-beam sensors, impeller
multi-beam sensors and Woltman sensors.
Inside single or multi-beam sensors the fluid flows against the impeller blades from one or more inlet
nozzles. Inside Woltman sensors the fluid flows axially against the rotor with helical blades, like turbine
wheel.
The transmission of the rotary motion can be magnetic, mechanical, inductive, capacitive, optical or
ultrasonic.
Some examples are shown in the following Figures 4, 5, 6 and 7:

Figure 4 — Single-beam sensor
Figure 5 — Woltman sensor for vertical or horizontal installation
Figure 6 — Multi-beam sensor
Figure 7 — Woltman sensor for horizontal installation only
b) Ultrasonic flow sensor
This type of flow sensor consists of a housing with integrated piezoelectric ultrasonic transducers that
are positioned opposite or staggered to each other. The piezoelectric ultrasonic transducers can operate
both as transmitters and as receivers.
The ultrasonic measuring technology is based on the runtime behaviour of ultrasonic signals in the fluid
flow. The sound is transmitted in the flowing water between the transducers at a velocity that is increased
or decreased by the amount of the flow velocity of the fluid flow, depending on whether it was measured
within or against the direction of the flow. There are several measuring principles for the application of
this technology (see Figures 8 and 9).
Figure 8 — Ultrasonic flow sensor

Figure 9 — Ultrasonic flow sensor
c) Magnetic-inductive flow sensor
The Magnetic-inductive flow sensor determines the flow velocity according to Faraday’s law of induction:
If an electrical conductor moves in a magnetic field in such a way that it intersects the magnetic field lines,
it will induce an electrical current. The flowing water acts as the electrical conductor, requiring a minimum
conductivity of the medium. If a desalinated fluid (like e.g. well-treated district heating water) is used as
the thermal conveying medium, the specific electrical conductivity can be too low to use this measuring
technology.
The flow sensor consists of a pipe which is lined with insulating material in which two electrodes are
embedded directly opposite each other. Two magnetic coils generate a magnetic field in the pipe cross-
section. The induced voltage is measured at the electrodes and is proportional to the average flow
velocity. This voltage is fed to an amplifier, which generates a usable signal to determine the flow rate
(see Figure 10).
Figure 10 — Magnetic-inductive flow sensor
d) Fluidic oscillation flow sensor
The fundamental basis for a fluidic oscillator as static meter is the creation of a fluid jet by means of an
acceleration through a nozzle. Successively the jet is confronted with a splitter (bi-stable) or target
(instable). Either two feedback loops or a relaxation loop will make the jet oscillate with a geometry-
determined frequency. Its oscillating frequency is proportional with the volume flow passing through the
nozzle. This frequency can be detected by a variety of methods, i.e. by differential pressure (e.g. piezo-
electric) or by flow velocity (e.g. magnetic inductive, hot wire anemometry, ultrasonic). There are several
types of fluidic oscillators, depending on their geometric design. Examples can be found in the
Figure below. Both left ones concern a bounded jet using the Coanda wall attachment and the right one
uses a free jet avoiding wall attachment for
...