Heat meters - Recommendations for circulation water in industrial and district heating systems and their operation

This Technical Report applies to industrial and district heating supply by means of high-temperature water heating facilities (flow temperature > 100 °C). It also applies to high-temperature water heating facilities (flow temperature ≤100 °C) that are directly connected to district heating net-works. In this Technical Report, the aforementioned supply variants will, in the following, be referred to as "district heating facilities". This Technical Report applies without limitations to new facilities. For existing district heating facilities, the application of this Technical Report is recommended in order to prevent faults due to the chemical composition of the circulation water that would affect the facilities' safe operability and availability.

Toplotni števci - Priporočila za obtočne vode v industriji in sistemih daljinskega ogrevanja ter njihovo delovanje

To tehnično poročilo se uporablja za industrijsko in daljinsko oskrbovanje s toploto s pomočjo visokotemperaturnih sistemov za ogrevanje vode (temperatura dovoda višja od 100 °C). Uporablja se tudi za visokotemperaturne sisteme za ogrevanje vode (temperatura dovoda manjša ali enaka 100 °C), ki so neposredno povezani z daljinskimi ogrevalnimi omrežji. V tem tehničnem poročilu bodo zgoraj omenjene različice oskrbovanja s toploto v nadaljevanju poimenovane »daljinski ogrevalni sistemi«. To tehnično poročilo velja za nove sisteme brez omejitev. Za obstoječe daljinske ogrevalne sisteme je uporaba tehničnega poročila priporočljiva za preprečevanje okvar, ki so posledica kemične sestave obtočne vode in ki lahko vplivajo na varno delovanje in razpoložljivost sistema.

General Information

Status
Published
Publication Date
22-Dec-2015
Current Stage
9093 - Decision to confirm - Review Enquiry
Completion Date
10-Nov-2021

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SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 16911:2015
01-oktober-2015
7RSORWQLãWHYFL3ULSRURþLOD]DREWRþQHYRGHYLQGXVWULMLLQVLVWHPLKGDOMLQVNHJD
RJUHYDQMDWHUQMLKRYRGHORYDQMH
Heat meters - Recommendations for circulation water in industrial and district heating
systems and their operation
Ta slovenski standard je istoveten z: FprCEN/TR 16911
ICS:
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
kSIST-TP FprCEN/TR 16911:2015 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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kSIST-TP FprCEN/TR 16911:2015

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kSIST-TP FprCEN/TR 16911:2015

TECHNICAL REPORT
FINAL DRAFT
FprCEN/TR 16911
RAPPORT TECHNIQUE

TECHNISCHER BERICHT

July 2015
ICS 91.140.10
English Version
Heat meters - Recommendations for circulation water in
industrial and district heating systems and their operation



This draft Technical Report is submitted to CEN members for Technical Committee Approval. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.

Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a Technical Report.


EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. FprCEN/TR 16911:2015 E
worldwide for CEN national Members.

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
Contents Page
European foreword .4
Introduction .5
1 Scope .6
2 Normative references .6
3 Terms and definitions .6
3.1 General .6
3.2 Types of water .7
3.3 Units .8
3.3.1 General .8
3.3.2 Measurands .8
4 Symbols and abbreviations .9
4.1 Chemical terms .9
4.2 Technical terms. 10
5 Water quality . 10
5.1 General . 10
5.2 Effects of the water constituents . 11
5.2.1 Gases . 11
5.2.2 Water-insoluble substances . 12
5.2.3 Water-soluble substances . 12
5.2.4 Oils/greases . 12
6 Systems engineering . 12
6.1 Systems conception . 12
6.1.1 General . 12
6.1.2 Materials . 13
6.1.3 Pressure maintenance and water supply . 14
6.2 Water treatment techniques . 15
6.2.1 General . 15
6.2.2 Filtering . 15
6.2.3 Demineralization . 16
6.2.4 Softening . 16
6.2.5 Degassing . 16
6.2.6 Catalytic and electrochemical oxygen scavenging. 16
7 Production technology . 17
7.1 Standard values for the circulation water . 17
7.2 Low-salt operation . 17
7.3 Salty operation . 17
7.4 Technical aspects related to the operation . 18
7.4.1 General . 18
7.4.2 Filling and supplementary water . 18
7.4.3 Underpressure . 19
7.4.4 Exceptional operating conditions . 20
7.4.5 Direct heating . 20
7.4.6 Indirect heating . 20
7.4.7 Partial evaporation. 20
7.5 Conditioning . 20
7.5.1 General . 20
7.5.2 pH value increase . 21
2

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
7.5.3 Hardness stabilizing . 22
7.5.4 Oxygen scavenging . 22
7.5.5 Corrosion inhibitors . 23
7.5.6 Water tracing dyes for the circulation water . 24
7.5.7 Antifreezing agents . 24
7.6 Monitoring . 24
7.6.1 General . 24
7.6.2 Assessment criteria . 24
7.6.3 Measurement frequency . 26
7.6.4 Dosing of conditioning agents . 27
7.6.5 Sampling. 28
7.6.6 Measurement procedures . 30
8 Hygienic, toxicological and environmental aspects . 30
8.1 General . 30
8.2 Hygienic and toxicological aspects . 30
8.3 Environmental aspects . 31
Bibliography . 32

3

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
European foreword
This document (FprCEN/TR 16911:2015) has been prepared by Technical Committee CEN/TC 176 “Heat
meters”, the secretariat of which is held by SIS.
This document is currently submitted to the Technical Committee Approval.
4

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
Introduction
This document is based on the German Guideline AGFW FW 510 prepared by the German Heat and Power
Association (AGFW) that represents the state of the art but does not have a normative status has been
reproduced in this Technical Report with the permission of AGFW.
This Technical Report is an informative document that describes a process that may be applied for the
operation of district heating facilities and gives recommendations for the water used in such facilities. The
water quality described in this Technical Report can be used also during testing of heat meters.
5

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
1 Scope
This Technical Report applies to industrial and district heating supply by means of high-temperature water
heating facilities (flow temperature > 100 °C). This also applies to high-temperature water heating facilities
(flow temperature ≤ 100 °C) that are directly connected to district heating networks. In this Technical Report,
the aforementioned supply variants will, in the following, be referred to as “district heating facilities”.
This document applies without limitations to new facilities. For existing district heating facilities, the application
of this Technical Report is recommended in order to prevent faults due to the chemical composition of the
circulation water that would affect the facilities' safe operability and availability.
NOTE Informative notes in the form of guidance and recommendations are identified correspondingly and set in
italics for better differentiation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 1717, Protection against pollution of potable water in water installations and general requirements of
devices to prevent pollution by backflow
ISO 11466, Soil quality — Extraction of trace elements soluble in aqua regia
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 General
3.1.1
district heating
heat (regardless of its origin) which is supplied by means of a transfer medium (mostly hot water or steam)
commercially on the basis of a supply agreement and from the delivery of which no collateral duties arise with
regard to leasing regulations
3.1.2
hot-/warm-water heating plants
hot-/warm-water generating facility in connection with a district heating network
3.1.3
water treatment
measures taken to remove solid particles, water-soluble substances (salts) and gases from the filling-,
supplementary- or circulation water
3.1.4
primary network
district heating network in indirect (e. g. heat exchanger) or direct connection with the heat generator
3.1.5
secondary network
district heating network separated from the primary district heating network by a substation with different
system parameters
6

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
3.1.6
tertiary network
end-user's domestic installation
3.1.7
heat exchanger with intermediary medium
heat exchanger with a safety system for the indirect heating of drinking water and in which the heating side
and the drinking water side are separated by two walls; the space between the two walls is filled with a
medium
3.1.8
chalk/carbonic acid equilibrium
if calciferous water is heated up, the concentration of bonded calcium hydrogen carbonate decreases with
increasing temperature, and the so called “chalk/carbonic acid equilibrium” shifts from the side of the calcium
hydrogen carbonate through the escaping carbon dioxide towards the side of the calcium carbonate:

Ca (HCO ) ⇔ CaCO ↓+ CO ↑+ H O
3 2 3 2 2
3.1.9
bicarbonate decomposition
after sofenting and in cause of higher temperature, sodium bicarbonate gradually decomposes into at least
sodium hydroxid, water and carbon dioxide (at about 55°C, higher pressure)
2 NaHCO → Na CO + CO ↑ + H O
3 2 3 2 2
Na CO + 2H O → 2 NaOH + H CO
2 3 2 2 3
H CO → CO ↑ + H O
2 3 2 2
3.1.10
boiler scale
conglomerate of low-solubility alkaline earth salts which form at temperatures < 100 °C, mainly CaCO3 and
MgCO3
3.1.11
limescale
conglomerate of low-solubility alkaline earth salts, mainly CaCO3, MgCO3, CaSO4 and CaSiO3
Note 1 to entry: They form either by heat conversion of the alkaline earth salts dissolved in the water (carbonate
hardness) or by overstepping the point of solubility which is also temperature-dependent. Soluble alkaline earth salts are
available as hardness components or neutral salts in drinking water.
3.1.12
heat transfer medium according to Class 4 pursuant to EN 1717
heat transfer medium which contains toxic, very toxic, carcinogenic or radioactive substances
3.1.13
water conditioning
improving certain quality parameters of the circulation water (e.g. increasing the pH value) by means of
conditioning chemicals
3.2 Types of water
3.2.1
untreated water
water available upstream from the treatment plant, regardless of a possible previous treatment outside the
plant
7

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
3.2.2
soft water
oxygenated water that has been treated by ion exchange to remove earth alkali (the process is called
softening)
3.2.3
demineralized water
oxygenated water that has been treated to remove the major part of dissociated, water-soluble substances
and is characterized by a pH value < 7, a conductance < 20 µS/cm and a silicic acid concentration < 0,5 mg/l
3.2.4
distilled water
deionized water
oxygenated water that has been treated by ion exchange to fully remove all dissociated, water-soluble
substances
3.2.5
filling water
conditioned water with which district heating facilities are initially, partly or re-filled
3.2.6
supplementary water
conditioned water with which temperature-related volume differences and losses due to evaporation and
leakage are compensated
3.2.7
circulation water
water that flows through the heat generator/heat exchanger, the piping network, heat transfer stations and, if
applicable, radiators. The term not only applies to primary networks, but also to water in a secondary network
3.2.8
feedwater
water that is used to feed a steam generator. It consists of supplementary water and condensate water after
full treatment and conditioning
Note 1 to entry: Feedwater is considered as salt-free if its cation conductance is < 0,2 µS/cm and the silicic acid
concentration is < 0,02 mg/l (not to mistake for distilled water!).
3.2.9
boiler water
water contained in water piping and large-scale water boilers and whose properties differ from those of
feedwater due to densification processes during use
3.3 Units
3.3.1 General
Pursuant to the “Units in Metrology Act”, the below-mentioned water-chemical terms and units apply.
3.3.2 Measurands
3.3.2.1
molar amount
concentration of substances contained in the water is stated in mmol/l or in mg/l
8

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
3.3.2.2
pH value
index for the acidic, neutral or alkaline reaction of water
Note 1 to entry: At a reference temperature of 25 °C, the pH value scale from 0 to 14 applies. Water is acidic at pH
values < 7, neutral at a pH value = 7, and alkaline at pH values > 7.
3.3.2.3
electrical conductivity
the salt concentration is generally determined by measuring the electrical conductivity which includes all
dissociated elements of the investigated medium, i.e. bases, acids and salts. In water chemistry, the reference
temperature used to measure electrical conductivity is 25 °C, the unit of measurement is µS/cm
3.3.2.4
sum of alkaline earth (hardness)
the former term “hardness” has been replaced by the term “sum of alkaline earth“
Note 1 to entry: The former units for the alkaline earth concentration (°d and mval/l) have been replaced by mmol/l,
3
mol/m and mg/l. The following applies to the conversion of the units:
1 mmol/l = 1 mol/m3 corresponding to 2 mval/l that will give 56 mg CaO/l
Note 2 to entry: Example of calculation for the conversion of the former units:
3,4 mval/l: 2 = 1,7 mmol/l
Note 3 to entry: Contrary to the concentration indications derived from the term “hardness” (°dH), technical
expressions such as “water softening” and “softened water” remain in usage.
4 Symbols and abbreviations
4.1 Chemical terms
3+
Al aluminium ion
2+
Ca calcium ion
CaCO3 calcium carbonate
CaSiO3 calcium silicate
CaSO4 calcium sulphate

Cl chloride ion
CO carbon dioxide
2
2+
Cu+ / Cu copper(I) ion / copper(II) ion
EDTA ethylenediaminetetraacetic acid or ethylenediaminetetraacetate
Fe iron
Fe 2+ / Fe 3+ iron(II) ion / iron(III) ion
KS4.3 acid capacity up to pH value 4,3
KS8.2 acid capacity up to pH value 8,2
2+
Mg magnesium ion
MgCO3 magnesium carbonate
N nitrogen
2
NaCl sodium chloride (common salt)
9

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
NaHCO3 sodium hydrogen carbonate
NaOH sodium hydroxide (caustic soda)
Na3PO4 trisodium phosphate
Na2SO3 sodium sulphite
Na2SO4 sodium sulphate
NTA nitrilotriacetic acid
O oxygen
2
PO43- orthophosphate ion
S2- sulphide ion
SO32- sulphite ion
SO42- sulphate ion
2+
Zn zinc ion
4.2 Technical terms
EV expansion vessel
DEV diaphragm expansion vessel
MIF magnetic inductive flow measurement
DFR differential pressure regulator
DOC dissolved organic carbon
TOC total organic carbon
5 Water quality
5.1 General
Untreated water may contain insoluble and, especially, soluble substances as well as gases.
Insoluble substances are frequent in surface water, infrequent in groundwater, whereas water from public
supply networks only contains traces of them.
Soluble substances occur in untreated water in the form of inorganic salts (especially calcium-, magnesium-
and sodium salts) and organic substances. The soluble gases are mostly oxygen, nitrogen from the air, and
carbon dioxide.
In district heating facilities, these water constituents can lead to malfunctions and either have to be removed,
or their effects to be limited.
The use of insufficiently treated filling or supplementary water or the inflow of water and/or air into district
heating facilities from the outside can lead to system malfunctions due to deposits and corrosion.
When assessing the cost-effectiveness of protective measures to prevent the diverse types of damages, the
fact that damage may, under certain circumstances, lead to considerable costs that cannot be calculated in
advance has to be taken into account.
When complying with the standard values, the alkalinization of the water on metallic surfaces furthers the
formation of homogeneous oxidic covering layers which are highly resistant against corrosion. A prerequisite
is, however, that the filling and supplementary water be treated correctly.
10

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
In district heating facilities, one fundamentally differentiates between low-salt and salty operation, depending
on the quality of the circulation water.
Further plant-specific prescriptions and guidance can be found in the Technical Connection Conditions (TCC).
5.2 Effects of the water constituents
5.2.1 Gases
5.2.1.1 General
Gases enter the circulation water due to the following processes:
— utilization of non-degassed filling and supplementary water;
— air leakage into the system in the event of underpressure (e.g. insufficient pressure maintenance);
— air inclusion during the initial, partial or new filling of the system;
— external water inflow;
— diffusion through permeable components (e.g. diaphragms, plastic pipes, seals).
5.2.1.2 Oxygen
Oxygen (O ) causes unalloyed and low-alloy ferrous materials to corrode. Oxygen inflow therefore has to be
2
prevented as far as this is technically justifiable.
Damage directly due to corrosion can manifest in the form of perforations in heat generators, pipes and
radiators made of unalloyed or low-alloy ferrous materials. The blinding of sieves, measuring equipment and
filters due to corrosion products is considered as an indirect consequence of corrosion.
5.2.1.3 Nitrogen
Nitrogen (N ) is an inert gas and, as a water constituent, only causes problems when its concentration is so
2
high that free nitrogen fractions (gas bubbles) form inside the system. Gas bubbles may occur, since the
solubility of gases decreases with increasing temperature and decreasing pressure. Circulation faults,
disturbing noises and erosion of protection layers (erosion corrosion) are the consequences.
Experience has shown that no system malfunctions due to nitrogen bubbles have to expected with nitrogen
contents of < 10 mg N per litre of water at a positive excess pressure of min. 0,5 bar (at the highest point of
2
the system).
5.2.1.4 Carbon dioxide
If the circulation water is not sufficiently alkalinized, the quantity of water-soluble carbon dioxide (CO )
2
influences the pH value – i.e. increasing CO cause the pH value to drop. Due to the in-creasing solubility of
2
iron(II)-hydroxide occurring at decreasing pH values, deposited corrosion products can be partially dissolved
by water having a relatively low pH value (<8). The increased iron(II) ion concentration can lead to an
increased formation of magnetite (Fe O ) in the form of hard, black deposits on the hot side of heat exchanger
3 4
surfaces.
This causes the increase of the overall heat transfer resistance and, thus, the thermal performance to
decrease. In particularly critical cases, this may even lead to overheating which, in turn, may lead to crack
formation.
11

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kSIST-TP FprCEN/TR 16911:2015
FprCEN/TR 16911:2015 (E)
5.2.2 Water-insoluble substances
Insoluble substances cause deposits and blockages and have to be removed from the untreated water by
means of suitable techniques (mud flaps, filters).
5.2.3 Water-soluble substances
5.2.3.1 Hardness components (alkaline earth)
When using unsoftened filling water, especially the alkaline earth ions contained in the water in connection
with the hydrogen carbonate ions lead to the formation of hard deposits, mainly containing calcium carbonate
(limescale, boiler scale). This causes the increase of the overall heat transfer resistance and, thus, the thermal
performance to decrease. In particularly critical cases, this may even lead to overheating which, in turn, may
lead to crack formation in heat generators (e.g. heat exchanger, vessels).
5.2.3.2 Chloride and sulphate
From all the water-soluble anions contained in the water, especially chloride and sulphate, in the presence of
oxygen, further local corrosion (e.g. crevice corrosion) in unalloyed ferrous materials.
Under critical conditions (e.g. concentration under deposits or in crevices), chloride ions can lead to pitting
corrosion or stress-corrosion cracking in non-corroding steels.
In addition, chlorides can cause corrosion in aluminium materials.
5.2.3.3 Hydrogen carbonate
The anion hydrogen carbonate primary react with the cations calcium and magnesium and form hardness-
causing salt (see 5.2.3.1). By means of a softening unit with a weakly acidic cation exchanger calcium- and
magnesium ions will be substituted against sodium ions. This results to sodium bicarbonate which reacts at
higher temperature and raised pressure to sodiumcarbonate. As result of so-called soda decomposition arise,
that means sodiumcarbonate decompose into soda lye and carbon dioxide gas, which escape out of the
system. The formed soda lye result in a selfalkalinization of the circulating water and can cause an increase of
the pH-value up to a value of > 10.
5.2.3.4 Organic substances
Insoluble and soluble organic substances – analytically determined as TOC or DOC – can both affect the
water treatment techniques and further microbiological reactions in the circulation water.
5.2.4 Oils/greases
The contamination of circulation water by oils or greases – e.g. due to the inflow of operating fluids or due to
valves, pipes, heating surfaces, etc. that have been treated with a temporary corrosion protection and with
processing aids – can cause massive malfunctions. As a film or coating on heated surfaces, oils and greases
hamper heat transfer and can, alone or in connection with other substances, cause malfunctions of the
regulation and safety devices. Oils and greases are nutrients for microorganisms and therefore increase the
probability of microbiologically influenced corrosion processes.
6 Systems engin
...

SLOVENSKI STANDARD
SIST-TP CEN/TR 16911:2016
01-marec-2016
7RSORWQLãWHYFL3ULSRURþLOD]DREWRþQHYRGHYLQGXVWULMLLQVLVWHPLKGDOMLQVNHJD
RJUHYDQMDWHUQMLKRYRGHORYDQMH
Heat meters - Recommendations for circulation water in industrial and district heating
systems and their operation
Ta slovenski standard je istoveten z: CEN/TR 16911:2015
ICS:
17.200.10 Toplota. Kalorimetrija Heat. Calorimetry
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
SIST-TP CEN/TR 16911:2016 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 16911:2016

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SIST-TP CEN/TR 16911:2016


CEN/TR 16911
TECHNICAL REPORT

RAPPORT TECHNIQUE

December 2015
TECHNISCHER BERICHT
ICS 91.140.10
English Version

Heat meters - Recommendations for circulation water in
industrial and district heating systems and their operation



This Technical Report was approved by CEN on 16 November 2015. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16911:2015 E
worldwide for CEN national Members.

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SIST-TP CEN/TR 16911:2016
CEN/TR 16911:2015 (E)
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
3.1 General . 6
3.2 Types of water . 8
3.3 Units . 9
3.3.1 General . 9
3.3.2 Measurands . 9
4 Symbols and abbreviations . 9
4.1 Chemical terms . 9
4.2 Technical terms . 10
5 Water quality . 10
5.1 General . 10
5.2 Effects of the water constituents . 11
5.2.1 Gases . 11
5.2.2 Water-insoluble substances . 12
5.2.3 Water-soluble substances . 12
5.2.4 Oils/greases . 13
6 Systems engineering . 13
6.1 Systems conception . 13
6.1.1 General . 13
6.1.2 Materials . 13
6.1.3 Pressure maintenance and water supply . 14
6.2 Water treatment techniques . 15
6.2.1 General . 15
6.2.2 Filtering . 16
6.2.3 Demineralization . 16
6.2.4 Softening . 16
6.2.5 Degassing . 16
6.2.6 Catalytic and electrochemical oxygen scavenging . 16
7 Production technology . 17
7.1 Standard values for the circulation water . 17
7.2 Low-salt operation . 18
7.3 Salty operation . 18
7.4 Technical aspects related to the operation . 19
7.4.1 General . 19
7.4.2 Filling and supplementary water . 19
7.4.3 Underpressure . 20
7.4.4 Exceptional operating conditions . 21
7.4.5 Direct heating . 21
7.4.6 Indirect heating . 21
7.4.7 Partial evaporation . 21
2

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SIST-TP CEN/TR 16911:2016
CEN/TR 16911:2015 (E)
7.5 Conditioning . 22
7.5.1 General . 22
7.5.2 pH value increase . 22
7.5.3 Hardness stabilizing . 23
7.5.4 Oxygen scavenging . 23
7.5.5 Corrosion inhibitors . 24
7.5.6 Water tracing dyes for the circulation water . 25
7.5.7 Antifreezing agents . 25
7.6 Monitoring . 25
7.6.1 General . 25
7.6.2 Assessment criteria. 25
7.6.3 Measurement frequency . 27
7.6.4 Dosing of conditioning agents . 28
7.6.5 Sampling . 29
7.6.6 Measurement procedures . 31
8 Hygienic, toxicological and environmental aspects . 31
8.1 General . 31
8.2 Hygienic and toxicological aspects . 31
8.3 Environmental aspects . 32
Bibliography . 33
3

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SIST-TP CEN/TR 16911:2016
CEN/TR 16911:2015 (E)
European foreword
This document (CEN/TR 16911:2015) has been prepared by Technical Committee CEN/TC 176 “Heat
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 [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
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Introduction
This document is based on the German Guideline AGFW FW 510 prepared by the German Heat and
Power Association (AGFW) that represents the state of the art but does not have a normative status has
been reproduced in this Technical Report with the permission of AGFW.
This Technical Report is an informative document that describes a process that may be applied for the
operation of district heating facilities and gives recommendations for the water used in such facilities.
The water quality described in this Technical Report can be used also during testing of heat meters.
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1 Scope
This Technical Report applies to industrial and district heating supply by means of high-temperature
water heating facilities (flow temperature > 100 °C). This also applies to high-temperature water
heating facilities (flow temperature ≤ 100 °C) that are directly connected to district heating networks.
In this Technical Report, the aforementioned supply variants will, in the following, be referred to as
“district heating facilities”.
This document applies without limitations to new facilities. For existing district heating facilities, the
application of this Technical Report is recommended in order to prevent faults due to the chemical
composition of the circulation water that would affect the facilities' safe operability and availability.
NOTE Informative notes in the form of guidance and recommendations are identified correspondingly and
set in italics for better differentiation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 1717, Protection against pollution of potable water in water installations and general requirements of
devices to prevent pollution by backflow
ISO 11466, Soil quality — Extraction of trace elements soluble in aqua regia
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 General
3.1.1
district heating
heat (regardless of its origin) which is supplied by means of a transfer medium (mostly hot water or
steam) commercially on the basis of a supply agreement and from the delivery of which no collateral
duties arise with regard to leasing regulations
3.1.2
hot-/warm-water heating plants
hot-/warm-water generating facility in connection with a district heating network
3.1.3
water treatment
measures taken to remove solid particles, water-soluble substances (salts) and gases from the filling-,
supplementary- or circulation water
3.1.4
primary network
district heating network in indirect (e. g. heat exchanger) or direct connection with the heat generator
3.1.5
secondary network
district heating network separated from the primary district heating network by a substation with
different system parameters
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3.1.6
tertiary network
end-user's domestic installation
3.1.7
heat exchanger with intermediary medium
heat exchanger with a safety system for the indirect heating of drinking water and in which the heating
side and the drinking water side are separated by two walls; the space between the two walls is filled
with a medium
3.1.8
chalk/carbonic acid equilibrium
if calciferous water is heated up, the concentration of bonded calcium hydrogen carbonate decreases
with increasing temperature, and the so called “chalk/carbonic acid equilibrium” shifts from the side of
the calcium hydrogen carbonate through the escaping carbon dioxide towards the side of the calcium
carbonate:

Ca (HCO )⇔ CaCO↓+ CO↑+ H O
32 3 2 2
3.1.9
bicarbonate decomposition
after sofenting and in cause of higher temperature, sodium bicarbonate gradually decomposes into at
least sodium hydroxid, water and carbon dioxide (at about 55°C, higher pressure)
2 NaHCO → Na CO + CO ↑ + H O
3 2 3 2 2
Na CO + 2H O → 2 NaOH + H CO
2 3 2 2 3
H CO → CO ↑ + H O
2 3 2 2
3.1.10
boiler scale
conglomerate of low-solubility alkaline earth salts which form at temperatures < 100 °C, mainly CaCO3
and MgCO3
3.1.11
limescale
conglomerate of low-solubility alkaline earth salts, mainly CaCO3, MgCO3, CaSO4 and CaSiO3
Note 1 to entry: They form either by heat conversion of the alkaline earth salts dissolved in the water
(carbonate hardness) or by overstepping the point of solubility which is also temperature-dependent. Soluble
alkaline earth salts are available as hardness components or neutral salts in drinking water.
3.1.12
heat transfer medium according to Class 4 pursuant to EN 1717
heat transfer medium which contains toxic, very toxic, carcinogenic or radioactive substances
3.1.13
water conditioning
improving certain quality parameters of the circulation water (e.g. increasing the pH value) by means of
conditioning chemicals
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3.2 Types of water
3.2.1
untreated water
water available upstream from the treatment plant, regardless of a possible previous treatment outside
the plant
3.2.2
soft water
oxygenated water that has been treated by ion exchange to remove earth alkali (the process is called
softening)
3.2.3
demineralized water
oxygenated water that has been treated to remove the major part of dissociated, water-soluble
substances and is characterized by a pH value < 7, a conductance < 20 µS/cm and a silicic acid
concentration < 0,5 mg/l
3.2.4
distilled water
deionized water
oxygenated water that has been treated by ion exchange to fully remove all dissociated, water-soluble
substances
3.2.5
filling water
conditioned water with which district heating facilities are initially, partly or re-filled
3.2.6
supplementary water
conditioned water with which temperature-related volume differences and losses due to evaporation
and leakage are compensated
3.2.7
circulation water
water that flows through the heat generator/heat exchanger, the piping network, heat transfer stations
and, if applicable, radiators. The term not only applies to primary networks, but also to water in a
secondary network
3.2.8
feedwater
water that is used to feed a steam generator. It consists of supplementary water and condensate water
after full treatment and conditioning
Note 1 to entry: Feedwater is considered as salt-free if its cation conductance is < 0,2 µS/cm and the silicic acid
concentration is < 0,02 mg/l (not to mistake for distilled water!).
3.2.9
boiler water
water contained in water piping and large-scale water boilers and whose properties differ from those of
feedwater due to densification processes during use
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3.3 Units
3.3.1 General
Pursuant to the “Units in Metrology Act”, the below-mentioned water-chemical terms and units apply.
3.3.2 Measurands
3.3.2.1
molar amount
concentration of substances contained in the water is stated in mmol/l or in mg/l
3.3.2.2
pH value
index for the acidic, neutral or alkaline reaction of water
Note 1 to entry: At a reference temperature of 25 °C, the pH value scale from 0 to 14 applies. Water is acidic at
pH values < 7, neutral at a pH value = 7, and alkaline at pH values > 7.
3.3.2.3
electrical conductivity
the salt concentration is generally determined by measuring the electrical conductivity which includes
all dissociated elements of the investigated medium, i.e. bases, acids and salts. In water chemistry, the
reference temperature used to measure electrical conductivity is 25 °C, the unit of measurement is
µS/cm
3.3.2.4
sum of alkaline earth (hardness)
the former term “hardness” has been replaced by the term “sum of alkaline earth“
Note 1 to entry: The former units for the alkaline earth concentration (°d and mval/l) have been replaced by
3
mmol/l, mol/m and mg/l. The following applies to the conversion of the units:
1 mmol/l = 1 mol/m3 corresponding to 2 mval/l that will give 56 mg CaO/l
Note 2 to entry: Example of calculation for the conversion of the former units:
3,4 mval/l: 2 = 1,7 mmol/l
Note 3 to entry: Contrary to the concentration indications derived from the term “hardness” (°dH), technical
expressions such as “water softening” and “softened water” remain in usage.
4 Symbols and abbreviations
4.1 Chemical terms
3+
Al aluminium ion
2+
Ca calcium ion
CaCO3 calcium carbonate
CaSiO3 calcium silicate
CaSO4 calcium sulphate

Cl chloride ion
CO carbon dioxide
2
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2+
Cu+ / Cu copper(I) ion / copper(II) ion
EDTA ethylenediaminetetraacetic acid or ethylenediaminetetraacetate
Fe iron
Fe 2+ / Fe 3+ iron(II) ion / iron(III) ion
KS4.3 acid capacity up to pH value 4,3
KS8.2 acid capacity up to pH value 8,2
2+
Mg magnesium ion
MgCO3 magnesium carbonate
N nitrogen
2
NaCl sodium chloride (common salt)
NaHCO3 sodium hydrogen carbonate
NaOH sodium hydroxide (caustic soda)
Na3PO4 trisodium phosphate
Na2SO3 sodium sulphite
Na2SO4 sodium sulphate
NTA nitrilotriacetic acid
O oxygen
2
PO43- orthophosphate ion
S2- sulphide ion
SO32- sulphite ion
SO42- sulphate ion
2+
Zn zinc ion
4.2 Technical terms
EV expansion vessel
DEV diaphragm expansion vessel
MIF magnetic inductive flow measurement
DFR differential pressure regulator
DOC dissolved organic carbon
TOC total organic carbon
5 Water quality
5.1 General
Untreated water may contain insoluble and, especially, soluble substances as well as gases.
Insoluble substances are frequent in surface water, infrequent in groundwater, whereas water from
public supply networks only contains traces of them.
Soluble substances occur in untreated water in the form of inorganic salts (especially calcium-,
magnesium- and sodium salts) and organic substances. The soluble gases are mostly oxygen, nitrogen
from the air, and carbon dioxide.
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In district heating facilities, these water constituents can lead to malfunctions and either have to be
removed, or their effects to be limited.
The use of insufficiently treated filling or supplementary water or the inflow of water and/or air into
district heating facilities from the outside can lead to system malfunctions due to deposits and
corrosion.
When assessing the cost-effectiveness of protective measures to prevent the diverse types of damages,
the fact that damage may, under certain circumstances, lead to considerable costs that cannot be
calculated in advance has to be taken into account.
When complying with the standard values, the alkalinization of the water on metallic surfaces furthers
the formation of homogeneous oxidic covering layers which are highly resistant against corrosion. A
prerequisite is, however, that the filling and supplementary water be treated correctly.
In district heating facilities, one fundamentally differentiates between low-salt and salty operation,
depending on the quality of the circulation water.
Further plant-specific prescriptions and guidance can be found in the Technical Connection Conditions
(TCC).
5.2 Effects of the water constituents
5.2.1 Gases
5.2.1.1 General
Gases enter the circulation water due to the following processes:
— utilization of non-degassed filling and supplementary water;
— air leakage into the system in the event of underpressure (e.g. insufficient pressure maintenance);
— air inclusion during the initial, partial or new filling of the system;
— external water inflow;
— diffusion through permeable components (e.g. diaphragms, plastic pipes, seals).
5.2.1.2 Oxygen
Oxygen (O ) causes unalloyed and low-alloy ferrous materials to corrode. Oxygen inflow therefore has
2
to be prevented as far as this is technically justifiable.
Damage directly due to corrosion can manifest in the form of perforations in heat generators, pipes and
radiators made of unalloyed or low-alloy ferrous materials. The blinding of sieves, measuring
equipment and filters due to corrosion products is considered as an indirect consequence of corrosion.
5.2.1.3 Nitrogen
Nitrogen (N ) is an inert gas and, as a water constituent, only causes problems when its concentration is
2
so high that free nitrogen fractions (gas bubbles) form inside the system. Gas bubbles may occur, since
the solubility of gases decreases with increasing temperature and decreasing pressure. Circulation
faults, disturbing noises and erosion of protection layers (erosion corrosion) are the consequences.
Experience has shown that no system malfunctions due to nitrogen bubbles have to expected with
per litre of water at a positive excess pressure of min. 0,5 bar (at the
nitrogen contents of < 10 mg N2
highest point of the system).
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5.2.1.4 Carbon dioxide
If the circulation water is not sufficiently alkalinized, the quantity of water-soluble carbon dioxide (CO )
2
influences the pH value – i.e. increasing CO cause the pH value to drop. Due to the in-creasing solubility
2
of iron(II)-hydroxide occurring at decreasing pH values, deposited corrosion products can be partially
dissolved by water having a relatively low pH value (<8). The increased iron(II) ion concentration can
lead to an increased formation of magnetite (Fe O ) in the form of hard, black deposits on the hot side of
3 4
heat exchanger surfaces.
This causes the increase of the overall heat transfer resistance and, thus, the thermal performance to
decrease. In particularly critical cases, this may even lead to overheating which, in turn, may lead to
crack formation.
5.2.2 Water-insoluble substances
Insoluble substances cause deposits and blockages and have to be removed from the untreated water
by means of suitable techniques (mud flaps, filters).
5.2.3 Water-soluble substances
5.2.3.1 Hardness components (alkaline earth)
When using unsoftened filling water, especially the alkaline earth ions contained in the water in
connection with the hydrogen carbonate ions lead to the formation of hard deposits, mainly containing
calcium carbonate (limescale, boiler scale). This causes the increase of the overall heat transfer
resistance and, thus, the thermal performance to decrease. In particularly critical cases, this may even
lead to overheating which, in turn, may lead to crack formation in heat generators (e.g. heat exchanger,
vessels).
5.2.3.2 Chloride and sulphate
From all the water-soluble anions contained in the water, especially chloride and sulphate, in the
presence of oxygen, further local corrosion (e.g. crevice corrosion) in unalloyed ferrous materials.
Under critical conditions (e.g. concentration under deposits or in crevices), chloride ions can lead to
pitting corrosion or stress-corrosion cracking in non-corroding steels.
In addition, chlorides can cause corrosion in aluminium materials.
5.2.3.3 Hydrogen carbonate
The anion hydrogen carbonate primary react with the cations calcium and magnesium and form
hardness-causing salt (see 5.2.3.1). By means of a softening unit with a weakly acidic cation exchanger
calcium- and magnesium ions will be substituted against sodium ions. This results to sodium
bicarbonate which reacts at higher temperature and raised pressure to sodiumcarbonate. As result of
so-called soda decomposition arise, that means sodiumcarbonate decompose into soda lye and carbon
dioxide gas, which escape out of the system. The formed soda lye result in a selfalkalinization of the
circulating water and can cause an increase of the pH-value up to a value of > 10.
5.2.3.4 Organic substances
Insoluble and soluble organic substances – analytically determined as TOC or DOC – can both affect the
water treatment techniques and further microbiological reactions in the circulation water.
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5.2.4 Oils/greases
The contamination of circulation water by oils or greases – e.g. due to the inflow of operating fluids or
due to valves, pipes, heating surfaces, etc. that have been treated with a temporary corrosion protection
and with processi
...

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