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
Public Enquiry End Date
09-Nov-2015
Publication Date
14-Feb-2016
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
27-Jan-2016
Due Date
02-Apr-2016
Completion Date
15-Feb-2016

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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.

---------------------- Page: 1 ----------------------
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.
---------------------- Page: 3 ----------------------
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

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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

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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.
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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.

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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
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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
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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

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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,

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
Al aluminium ion
Ca calcium ion
CaCO3 calcium carbonate
CaSiO3 calcium silicate
CaSO4 calcium sulphate
Cl chloride ion
CO carbon dioxide
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
Mg magnesium ion
MgCO3 magnesium carbonate
N nitrogen
NaCl sodium chloride (common salt)
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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
PO43- orthophosphate ion
S2- sulphide ion
SO32- sulphite ion
SO42- sulphate ion
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.
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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

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

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

the system).
5.2.1.4 Carbon dioxide

If the circulation water is not sufficiently alkalinized, the quantity of water-soluble carbon dioxide (CO )

influences the pH value – i.e. increasing CO cause the pH value to drop. Due to the in-creasing solubility 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 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.
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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.

---------------------- Page: 1 ----------------------
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.
---------------------- Page: 3 ----------------------
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

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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

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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

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
Al aluminium ion
Ca calcium ion
CaCO3 calcium carbonate
CaSiO3 calcium silicate
CaSO4 calcium sulphate
Cl chloride ion
CO carbon dioxide
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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
Mg magnesium ion
MgCO3 magnesium carbonate
N nitrogen
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
PO43- orthophosphate ion
S2- sulphide ion
SO32- sulphite ion
SO42- sulphate ion
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

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

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 )

influences the pH value – i.e. increasing CO cause the pH value to drop. Due to the in-creasing solubility

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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