EN 12831-3:2017

SLOVENSKI STANDARD
01-maj-2018
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SIST EN 15316-3-1:2007
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Energy performance of buildings - Method for calculation of the design heat load - Part 3:
Domestic hot water systems heat load and characterisation of needs, Module M8-2, M8-
Energetische Bewertung von Gebäuden - Verfahren zur Berechnung der Norm-Heizlast -
Teil 3: Trinkwassererwärmungsanlagen, Heizlast und Bedarfsbestimmung, Module M8-2,
M8-3
Performance énergétique des bâtiments - Méthode de calcul de la charge thermique
nominale - Partie 3 : Charge thermique des systèmes de production d’eau chaude
sanitaire et caractérisation des besoins, Module M8-2, M8-3
Ta slovenski standard je istoveten z: EN 12831-3:2017
ICS:
91.140.65 Oprema za ogrevanje vode Water heating equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 12831-3
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2017
EUROPÄISCHE NORM
ICS 91.140.10; 91.140.65 Supersedes EN 15316-3-1:2007
English Version
Energy performance of buildings - Method for calculation
of the design heat load - Part 3: Domestic hot water
systems heat load and characterisation of needs, Module
M8-2, M8-3
Performance énergétique des bâtiments - Méthode de Energetische Bewertung von Gebäuden - Verfahren zur
calcul des déperditions calorifiques de base - Partie 3 : Berechnung der Energieanforderungen und
Charge thermique des systèmes de production d'eau Nutzungsgrade der Anlagen - Teil 3: Dimensionierung
chaude sanitaire et caractérisation des besoins, Module von Trinkwassererwärmungsanlagen und
M8-2, M8-3 Bedarfsbestimmung, Modul M8-2, M8-3
This European Standard was approved by CEN on 27 February 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

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, Serbia, 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
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12831-3:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 11
3 Terms and definitions . 11
4 Symbols and abbreviations . 13
4.1 Symbols . 13
4.2 Subscripts . 14
5 Description of the methods . 16
5.1 General description of the method for sizing domestic hot water systems . 16
5.2 General description of the methods for calculating the energy needs for domestic
hot water . 17
6 Calculation procedures . 17
6.1 Output data . 17
6.2 Calculation time steps . 17
6.3 Input data . 18
6.3.1 General . 18
6.3.2 Product data . 18
6.3.3 System design data . 19
6.3.4 Operating data and boundary. 19
6.3.5 Other data . 19
6.4 Calculation procedure for sizing domestic hot water systems . 19
6.4.1 Calculation of the energy needs curve for DHW . 19
6.4.2 Energy supply . 22
6.4.3 Procedure for dimensioning the DHW system . 35
6.5 Calculation procedure for determining the energy needs for domestic hot water. 38
6.5.1 Energy need for domestic hot water based on draw-off or load profiles . 38
6.5.2 Energy need for domestic hot water based on volume required . 38
6.5.3 Energy need for domestic hot water based directly on floor area . 40
6.5.4 Tabulated energy need for domestic hot water . 41
7 Quality control . 41
8 Compliance check. 41
Annex A (normative) Template for input data . 42
A.1 Load profiles . 42
A.2 Parameters to calculate energy needs . 42
A.3 Parameters for sizing DHW systems . 43
A.4 General values . 45
Annex B (informative) Default input data . 46
B.1 Load profiles . 46
B.2 Parameters to calculate energy needs . 48
B.3 Parameters for sizing DHW systems . 51
B.4 General values . 56
Bibliography . 57

European foreword
This document (EN 12831-3:2017) has been prepared by Technical Committee CEN/TC 228 “Heating
systems and water based cooling systems in buildings”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2018, and conflicting national standards shall
be withdrawn at the latest by January 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15316-3-1:2007.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
The changes made to the previous edition are minor editorial corrections:
a) minor improvement readability of Figure 4;
b) correction of an incorrect term in Formula (14);
c) correction of an incorrect symbol in Figure 14.
EN 12831, Energy performance of buildings — Method for the calculation of the design heat load, is
composed with the following parts:
— Part 1: Space heating load, Module M3-3;
— Part 2: Explanation and justification of EN 12831-1, Module M3-3 [CEN/TR];
— Part 3: Domestic hot water systems heat load and characterisation of needs, Module M8-2, M8-3;
— Part 4: Explanation and justification of EN 12831-3, Module M8-2, M8-3 [CEN/TR].
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: 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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Introduction
CEN/TC 228 deals with heating systems in buildings. Subjects covered by CEN/TC 228 are:
— energy performance calculation for heating systems;
— inspection of heating systems;
— design of heating systems;
— installation and commissioning of heating systems.
This European Standard was developed to cover hourly and minutely time-steps.
This European Standard is part of a series of standards aiming at international harmonization of the
methodology for the assessment of the energy performance of buildings, called “set of EPB standards”.
All EPB standards follow specific rules to ensure overall consistency, unambiguity and transparency.
All EPB standards provide a certain flexibility with regard to the methods, the required input data and
references to other EPB standards, by the introduction of a normative template in Annex A and Annex B
with informative default choices.
For the correct use of this standard a normative template is given in Annex A to specify these choices.
Informative default choices are provided in Annex B.
Use by or for regulators: In case the standard is used in the context of national or regional legal
requirements, mandatory choices may be given at national or regional level for such specific
applications. These choices (either the informative default choices from Annex B or choices adapted to
national / regional needs, but in any case following the template of this Annex A) can be made available
as national annex or as separate (e.g. legal) document (national data sheet).
NOTE So in this case:
— the regulators will specify the choices;
— the individual user will apply the standard to assess the energy performance of a building, and thereby use
the choices made by the regulators.
Topics addressed in this standard can be subject to public regulation. Public regulation on the same
topics can override the default values in Annex B of this standard. Public regulation on the same topics
can even, for certain applications, override the use of this standard. Legal requirements and choices are
in general not published in standards but in legal documents. In order to avoid double publications and
difficult updating of double documents, a national annex may refer to the legal texts where national
choices have been made by public authorities. Different national annexes or national data sheets are
possible, for different applications.
It is expected, if the default values, choices and references to other EPB standards in Annex B are not
followed due to national regulations, policy or traditions, that:
— national or regional authorities prepare data sheets containing the choices and national or regional
values, according to the model in Annex A. In this case the national annex (e.g. NA) refers to this
text;
— or, by default, the national standards body will consider the possibility to add or include a national
annex in agreement with the template of Annex A, in accordance to the legal documents that give
national or regional values and choices.
Further target groups are parties wanting to motivate their assumptions by classifying the building
energy performance for a dedicated building stock.
More information is provided in the Technical Report accompanying this standard (EN 12831-4).
1 Scope
This European Standard describes a method to calculate the power and the storage volume required for
the dimensioning of domestic hot water systems (DHW). The applicability ranges from direct water
heaters (no storage volume and a comparatively large effective heating power) to larger storage
systems with a comparatively small heating power and large storage volumes.
This European Standard is applicable to the following water storage systems:
— storage systems characterized by a minimal mixing zone, (such as stratified charging storage tanks
or storage tanks with external heat exchangers): these systems are nominated in this standard as
“charging storage systems”;
— storage tank water heaters and warm water storage tanks with a pronounced mixing zone (such as
DHW storage tanks with internal heat exchangers), nominated in this standard as “mixed storage
systems”;
and for different uses.
The Scope also includes standardization methods for determining the energy need for domestic hot
water. This European Standard covers the domestic hot water needs in buildings.
The calculation of the energy needs for DHW-Systems applies to residential and non-residential
buildings, a building or a zone of a building.
Figure 1 shows the relative position of this standard within the set of EPB standards in the context of
the modular structure as set out in EN ISO 52000-1.
NOTE 1 In CEN ISO/TR 52000-2 the same table can be found, with, for each module, the numbers of the
relevant EPB standards and accompanying technical reports that are published or in preparation.
NOTE 2 The modules represent EPB standards, although one EPB standard may cover more than one module
and one module may be covered by more than one EPB standard, for instance a simplified and a detailed method
respectively. See also Clause 2 and Tables A.1 and B.1.
Table 1 shows the relative position of this standard within the EPB package of standards.
Table 1 — Position of this standard, within the modular structure of the set of EPB standards
Building
Overarching Technical Building Systems
(as such)
Building
Sub Humidif Dehumidifi Domestic Electricity
Descriptions  Descriptions  Descriptions Heating Cooling Ventilation Lighting automation
module ication cation Hot water production
and control
sub1  M1  M2  M3 M4 M5 M6 M7 M8 M9 M10 M11
1 General  General  General 15316–1     15316–1
Common
terms and
definitions; Building Energy
2   Needs      12831–3
symbols, Needs
units and
subscripts
(Free) Indoor
Maximum
Conditions
3 Applications   Load and 12831–1     12831–3
without
Power
Systems
Ways to Ways to
Ways to
Express Express
4  Express Energy  15316–1     15316–1
Energy Energy
Performance
Performance Performance
Building
Heat Transfer
categories Emission and
5  by  15316–2 15316–2
and Building control
Transmission
Boundaries
Building
Occupancy Heat Transfer
Distribution
6 and  by Infiltration  15316–3 15316–3    15316–3
and control
Operating and Ventilation
Conditions
Aggregation
of Energy 15316–5
Internal Storage and
7 Services and   15316–5     15316–4–
Heat Gains control
Energy 3
Carriers
Building
Overarching Technical Building Systems
(as such)
Building
Sub Humidif Dehumidifi Domestic Electricity
Descriptions  Descriptions  Descriptions Heating Cooling Ventilation Lighting automation
module ication cation Hot water production
and control
sub1  M1  M2  M3 M4 M5 M6 M7 M8 M9 M10 M11
Building Solar
8   Generation
zoning Heat Gains
Combustion 15316– 15316–4–
8–1
boilers 4–1 1
15316– 15316– 15316–4–
8–2     Heat pumps
4–2 4–2 2
Thermal solar
15316– 15316–4–
8–3           15316–4–3
4–3 3
Photovoltaics
On-site 15316– 15316–4–
8–4           15316–4–4
cogeneration 4–4 4
District
15316– 15316–
8–5     heating and       15316–4–5
4–5 4–5
cooling
Direct
15316– 15316–4–
8–6     electrical
4–8 8
heater
15316–4–
8–7     Wind turbines
Radiant
15316–
8–8     heating,
4–8
stoves
Load
Calculated Building
dispatching
9 Energy  Dynamics
and operating
Performance (thermal mass)
conditions
Measured  Measured Measured
10 Energy Energy  Energy 15378–3     15378–3
Performance Performance Performance
Building
Overarching Technical Building Systems
(as such)
Building
Sub Humidif Dehumidifi Domestic Electricity
Descriptions  Descriptions  Descriptions Heating Cooling Ventilation Lighting automation
module ication cation Hot water production
and control
sub1  M1  M2  M3 M4 M5 M6 M7 M8 M9 M10 M11
11 Inspection  Inspection  Inspection 15378–1     15378–1
Ways to
Express
12  – BMS
Indoor
Comfort
External
13 Environment
Conditions
Economic 15459–
Calculation 1
NOTE The shaded modules are not applicable.
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 12897, Water supply — Specification for indirectly heated unvented (closed) storage water heaters
EN 50440, Efficiency of domestic electrical storage water heaters and testing methods
EN ISO 52000-1:2017, Energy performance of buildings — Overarching EPB assessment — Part 1:
General framework and procedures (ISO 52000-1:2017)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 52000-1:2017 and the
following apply.
3.1
energy storage tank
storage tank for providing thermal energy amongst others for use in domestic hot water systems
(DHW)
Note 1 to entry: The storage medium is not potable water.
3.2
centralized DHW system
DHW system where water for several building units is heated centrally and then distributed to each
building unit
3.3
potable water, cold (PWC)
water that has not been heated by the DHW system
3.4
decentralized, individual DHW system
DHW System in which PWC is distributed to each draw-off point, dwelling or building unit and then
individually heated (e.g. via a separate DHW module), in which case hot water is only distributed within
individual building units)
Note 1 to entry: In this case, hot water is only distributed within individual building units.
3.5
domestic hot water
DHW
potable water, the temperature of which has been increased by means of heat transfer
Note 1 to entry: In this standard, the term domestic hot water (DHW) is equivalent to the term potable water
hot (PWH). The usage of the term DHW also applies to non-domestic buildings and their systems.
3.6
DHW storage tank
tank for storage of domestic hot water (DHW)
3.7
mixed storage system
tank (energy storage or DHW storage tank) which is characterized by a pronounced mixing zone during
the charging phase and a minimal mixing zone during the exclusive discharging phase
Note 1 to entry: E.g. storage systems with internal heat exchangers.
Note 2 to entry: As an example see Figure 1:

a) Charging phase of a mixed storage system b) Discharging phase of a mixed storage system
Figure 1 — Phases of a mixed storage system
3.8
charging storage system
tank (energy storage or DHW storage tank) which is characterized by a minimal mixing zone during
charging and discharging phases
Note 1 to entry: Examples are: stratified charging tanks and tanks with external heat exchangers.
Note 2 to entry: As an example see Figure 2:

a) Charging phase of a charging storage b) Discharging phase of a charging storage
system system
Figure 2 — Phases of a charging storage system
3.9
summation curve
cumulated course of a time-dependent element over time
Note 1 to entry: The needs curve and the supply curve are summation curves.
3.10
needs curve
cumulated course of energy needs which is to be supplied by the DHW system
3.11
supply curve
cumulated course of energy supplied by the DHW system including the losses thereof
3.12
residual capacity curve
cumulated course of useful energy in the storage tank at the switch-ON point
3.13
distribution system
piping sections connecting the heat generator, storage system (energy- and DHW storage tanks) and
tapping points
3.14
draw-off temperature
temperature measured at the draw-off point (tapping point) of the DHW system
3.15
minimal useable draw-off temperature
minimal withdrawal temperature at a draw-off point which can still be seen as a fulfilment of the
specified temperature needs
Note 1 to entry: In systems with different temperature needs, the highest temperature needs to be applied.
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this document, the symbols given in EN ISO 52000-1:2017 and the specific symbols
listed in Table 2 apply. Symbols and subscripts may have more than one denotation.
Table 2 — Symbols and units
Symbol Name Unit
Φ Power/Wattage (Heat power) W
ϑ Temperature on the Celsius scale °C
Q Energy kWh or J/3,6x10 also
depending on context, absolute or time-specific kWh/[unit of time]
q´ heat loss per unit length of pipe W/m

volume flow rate (water) l/s
V
U (Linear) Thermal transmittance of the piping W/mK
l Length of the piping m
f Adjustment/correction factor or term -
ρ Density 3
kg/m or kg/l
c Specific heat capacity kJ/kgK
V Volume m
n number –
h Height m
x Relative amount of water drawn within a certain period of time -
t Depending on context, a period of time or a time step (e.g. 1 min) eg. min
S standing loss value [W]
4.2 Subscripts
For the purposes of this document, the subscripts given in EN ISO 52000-1:2017, and the specific
subscripts listed in Table 3 apply. Subscripts may have several denotations.
Table 3 — Subscripts
Index Meaning/Use
W Water
a Ambient
b Building needs
c Cold; referring to cold water
ch Charging
D Design
A Draw-off flow rate
sto Storage
sb Standby
dis Distribution
d, day Per day, daily
t Time; referring to a period of time or one time step within the calculation
draw Drawn; referring to properties of the water drawn-off at the tap
i General numbering index
i Loop cycle / calculation step (one cycle per each minute of the period under consideration); referring
to cumulated items
t Time step, one minute; referring to non-cumulated items
l Load, loading
h Hourly, per hour, over the time of an hour
sensor Temperature sensor of the storage tank
sup Supply
start Start; referring to (estimated) start values for iterative calculation approaches
ON Switch on point; setting, at which the temperature sensor turns on the heat generator (reheat)
OFF Switch off point; setting, at which the temperature sensor turns off the heat generator
eff Effective
HE Heat exchanger
HG Heat generator
min Minimum
max Maximum
m Mean
N Net floor area
N Nominal
lag (Time) lag
5 Description of the methods
5.1 General description of the method for sizing domestic hot water systems
This standard describes a method to determine the power and the storage volume required for
designing and dimensioning DHW systems. The method is based on a comparison of the curves of the
energy needs for domestic hot water and the energy supply from the hot water system as a function of
time.
The sizing of DHW systems can be depicted graphically. The graphical approach is called summation
curve method. Here, the energy need for DHW (needs curve) as well as the energy supply from the hot
water system (supply curve) are depicted in the form of cumulative curves for a certain time period
(usually 24 h). The hot water system is adequately designed as long as:
— the supply curve does not intersect with or fall below the needs curve in systems with a minimal
mixing zone (charging storage systems) or
— the supply curve always lies above the needs curve while maintaining a minimal distance in
systems with a distinct mixing zone (mixed storage systems).
Both curves are determined with a time step of 1 min. The input data for the needs curve can also be
given on a different time basis, such as an hourly basis. In this case, the data are broken down into equal
minutely values.
The design steps are as follows:
a) determination of the hot water needs:
1) by measuring the volume flow rate of hot water on a minutely basis and considering the hot
and cold water temperatures;
2) on the basis of statistical methods (characteristic needs);
3) on the basis of published and accepted characteristic load profiles (to be determined on a
national basis. In the absence of national values default profiles are given in Annex B);
b) calculation and depiction of the needs curve;
c) definition of the design parameters of the hot water system:
1) selection of the hot water system;
2) type and power of the available heat source and other required data such as thermal losses of
the storage and distribution systems;
d) dimensioning of the hot water system. Calculate and depict the supply curve, starting alternatively
by either:
1) defining the power on the basis of the available power of the heat generator;
2) defining the storage volume (storing the peaks in the hot water needs or via daily, half-daily or
hourly energy needs);
3) using a starting value for either the power of the heat generator or the storage volume by
evaluating the mean slope of the needs curve in cases where no distinct data on heat generator
power or storage volume is available;
e) determination of the missing parameter (volume or power) by modification of the supply curve;
f) optimization of the system by using manufacturers' data and by considering further boundary
conditions (e.g. restricted periods, work cycles and hygienically aspects).
5.2 General description of the methods for calculating the energy needs for domestic hot
water
This clause describes several methods for calculating the energy needs of domestic hot water. The
methods differ as to the level of detail assumed for the domestic hot water demand; for example
whether the conditions relating to the different uses of the hot water are taken into account. The energy
needs per day may also be used to size the DHW system according to Clause 5, provided an appropriate
load profile is used. When using this approach it should be considered that the energy needs and the
load profile do not necessarily reflect a worst-case scenario.
A National Annex may specify which method should be used for different building categories. A national
Annex may also specify which method is acceptable for the purpose of energy labelling or any other
specific use.
The calculations are based on a daily domestic hot water requirement.
6 Calculation procedures
6.1 Output data
This standard provides a method or (default) values to determine the following items. Note that the
method presented here may require first estimates (start values) of some items considered output data.
Therefore, some items may be both output and input data (see Table 4).
Table 4 — Output data
Description Symbol Unit Intended use Intended
destination module
Effective power Φ W Dimensioning of M8–8, M3–8
W,eff
required for DHW components for DHW, as
heat generators
Storage volume of V 3 M8–7
sto m
hot water tanks
the hot water tank
Energy needs for Q kWh/t Energy demand calculation M8–1
W;nd;i
DHW in time step
Volume of water Vt m /ti  M8–6
drawn at the
current time step
6.2 Calculation time steps
The calculation time step for the purpose of sizing the DHW system is one minute. The input data for the
energy needs can however also be given on a different time basis (usually an hourly basis) and can then
be converted.
6.3 Input data
6.3.1 General
The following data are required and shall be obtained from the sources named hereafter. In case of
multiple sources for one item, all sources are arranged in order of priority from highest to lowest.
6.3.2 Product data
Table 5 — Product Input data
Symbol Name Unit Origin
V Effective size of the hot water storage l Depending on application case
sto
tank
Manufacturer data or
Estimate (start value)
h Height of the temperature sensor in m Manufacturer data / design
sensor
the storage tank
National annex to this standard
Informative Annex B
f loading factor – Manufacturer data / design
l
National annex to this standard
Informative Annex B
q Standby heat loss of the hot water kWh/d Manufacturer data
sb,sto
tank
Estimation in accordance with EN 12897
t time lag of the heat generation min Manufacturer data / design
lag
system (from the perspective of
National annex to this standard
water-heating)
Informative Annex B
6.3.3 System design data
Table 6 — System design input data
Symbol Name Unit Origin
V Volume of water drawn per day; l Building data / design
w,,f,day
optional: may be used to determine
National annex to this standard
V
t
Informative Annex B
f number of units to be taken into - Building data / design
account
A floor area m Building data / design
n number of persons to be taken into - Building data / design
P
account
x Relative amount of water drawn each - Building data / design
h
hour of a day; optional: may be used
National annex to this standard
to determine V
t
Informative Annex B
ϑ maximal water temperature in the °C National annex to this standard
w;sto,max
storage tank used for design
Informative Annex B
purposes
ϑ Water temperature of the mixed °C Building data / design
w;draw
(cold and hot) water drawn at the
National annex to this standard
tap (e.g. 42 °C) - as used for the
Informative Annex B
calculation of the energy needs
type of building (building category); List Building data

6.3.4 Operating data and boundary
ϑ Cold-water temperature (e.g. 10 °C) °C From M1–13
w;c
6.3.5 Other data
ρ Density of water 3 National annex to this standard
w kg/m
Informative Annex B
c Specific thermal capacity of water kJ/kgK National annex to this standard
w
Informative Annex B
6.4 Calculation procedure for sizing domestic hot water systems
6.4.1 Calculation of the energy needs curve for DHW
The energy needs curve is determined by cumulating the energy needs of the individual hot water
draw-off sequences. The needs curve is, amongst others, dependent on the type of building and its use.
The cumulative energy need for hot water is calculated in accordance with Formula (1) on a minutely
basis over a period of time (usually 24 h) and is depicted as cumulative values in a diagram. The total
energy need for DHW over a certain time period Q can be determined according to Clause 6. It can
W;b
also be calculated from every-minute values.
i
 
Q Q with i 1, 2,., i (1)
W;b;i ∑ W;b;t max
 
t1=
where
Q cumulative energy need for water heating from time period t = 1 to i [kWh]
W;b;i
Q energy need for water heating at the time t (minute), either taken from a [kWh/min]
W;b;t
national annex to this standard or calculated in accordance with Formula (3)
t time step, one minute [min] [min]
i loop cycle / calculation step [-]
i maximum number of loops [-]
max
The method requires one loop per every-minute value of energy need. Thus, the evaluation over the
period of one day requires 1 440 loops. [-]

Key
X time [h]
Y cumulated energy [kWh]
Figure 3 — Exemplary needs curve (summation curve diagram)
The energy need for DHW in time steps of one minute can be calculated from the water volume drawn
every minute (see Formula (2)):
Qx⋅
1 W;b h
QV= ⋅ρ⋅⋅c ϑϑ− ⋅ = (2)
( )
W;b;t t w w w;draw w;c
3600 60
==
where
Q energy demand for DHW at the time t (minute) [kWh/min]
W;b;t
V volume of water at ϑ , drawn in the time interval t (minute) [l]
w,draw
t
ρ density of water [kg/l]
w
c specific heat capacity of water [kJ/kgK]
w
ϑ minimum temperature of the mixed water drawn at the tap (needs [°C]
w;draw
temperature)
ϑ cold-water temperature [°C]
w;c
Q energy needs for DHW over the considered period (e.g. one day) [kWh/d]
W;b
x relative amount of water drawn each hour. x is the ratio between the hot -
h
h
water volume drawn during the hour h and the total daily hot water
volume in % (Σx = 1)
h
The basis of V is a load profile which gives the percentage of DHW volume withdrawn at a certain time
t
x . Examples of such load profiles based on a minutely basis are given in EN 50440. Individual
h
measurements are also possible. Where such detailed every-minute data on the drawn-off water
volume is not available, V may be calculated from data based on hourly tapping patterns as shown in
t
Formula (3) and Figure 4:
xV⋅
h day
V = . (3)
t
where
V volume of DHW drawn at the time t (minute) [l]
t
V total volume of DHW drawn in a day [l]
day
x relative amount of DHW drawn each hour. x is the ratio between the hot water volume -
h h
drawn during the hour h and the total daily hot water volume in % (Σx = 1)
h
Key
X time [h]
Y relative amount of daily DHW needs drawn in each hour -
Figure 4 — Exemplary needs profile, relative hot-water demand over the day given in hourly
values
The load profiles can be depicted based both on drawn-off volume as well as energy. They shall be given
on a national basis. In the absence of such national data, typical profiles are given in Annex B.
6.4.2 Energy supply
6.4.2.1 General
The supply curve is determined by cumulating the energy supplied by the DHW system. The supply
curve is dependent upon the type of DHW-System and its components.
6.4.2.2 DHW systems
6.4.2.2.1 General
The different systems for hot water production covered by this standard are classified according to
their heating principle.
6.4.2.2.2 DHW mixed storage systems
Characteristics:
- central system
- directly or indirectly heated
- monovalent hot water tank
- with distinct mixing zone
while charging
- internal heat exchanger
- with or without circulation
- with or without space heating

Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 5 — Monovalent DHW- mixed storage systems
This system diagram is also suited for a bivalent storage system with heat exchangers connected in
series.
Characteristics:
- central system
- bivalent hot water tank
- with distinct mixing zone in
the stand-by volume of the
tank while charging
- internal heat exchanger
- with or without circulation
- with or without space heating

Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 6 — Bivalent DHW- mixed storage systems
6.4.2.2.3 DHW charging systems
Characteristics:
- central system
- charging storage system
(minimal mixing zone
during charging and
discharging of the DHW
tank)
- with or without circulation
in DHW loop
- with or without space
heating
Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 7 — DHW charging system
6.4.2.2.4 DHW direct flow system with energy storage tank
Characteristics:
- central system
- DHW production in direct
flow
- energy storage tank as a
charging system (minimal
mixing zone during charging
and discharging)
- external or internal heat
exchangers
- with or without circulation
in DHW loop
- with or without space
heating
Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 8 — DHW direct flow with energy storage tank, central system
Characteristics:
- decentralized DHW system
- DHW production in direct
flow
- energy storage tank as a
charging system (minimal
mixing zone during charging
and discharging)
- external heat exchangers
- DHW loop without
circulation
- circulation within the
charging system
- with or without space
heating
Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 9 — DHW direct flow with energy storage tank, decentralized system
6.4.2.2.5 DHW direct flow system
Characteristics:
- centralized DHW system
- DHW production in direct flow
- centralized heat exchangers
- with or without circulation in DHW
loop
- with or without space heating

Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 10 — DHW direct flow, centralized system
Characteristics:
- decentralized DHW system
- DHW production in direct flow
- decentralized heat exchangers
- without circulation in DHW loop
- with or without space heating

Key
1 potable water hot, PWH
2 potable water cold, PWC
Figure 11 — Decentralized system
The storage tanks (DHW storage and energy storage tanks) are categorized and calculated according to
their mixing characteristics during charging and discharging phases. In this standard, a mixed storage
tank maintains its temperature layering while in discharge mode (hot water withdrawal) and has a
minimal mixing zone in this mode. In the loading phase (reheating), the storage tank is ideally mixed
due to convection. The principle is shown in 3.7.
A charging storage tank is characterized as a tank which maintains its temperature layering both in
charging and discharging mode. The principle is shown in 3.8.
6.4.2.3 Procedure for the determination of the supply curve
6.4.2.3.1 General
The main elements of the supply curve are the utilizable energy content of the storage tank (depicted in
the diagram as the vertical distance between the supply curve and the needs curve), the effective
reheating power of the system Φ (depicted in the diagram as a line with a positive slope) and the
eff
thermal losses of the system (depicted in the diagram as a line with a negative slope).
The thermal losses, arising mainly from the storage and distribution systems, result in a continual
decrease of the useful energy content of the storage system (see Figure 12). The hot water withdrawal
(represented by a rising needs curve) further decreases the utilizable energy content of the storage
system which also results in the rising of the cold water layer in the tank. A temperature sensor (often
positioned in the middle of the storage tank) registers the sudden drop in temperature and activates the
reheating system (switch-ON-point). The useful thermal energy in the storage tank at this point in time
is defined as the residual capacity Q Q can be depicted in the summation diagram as a
Sto,ON Sto,ON
characteristic curve. The reheating system is always activated, when the supply curve falls below the
Q curve.
Sto,ON
Depending on the DHW system, there is a time lag t between the switch ON point and the time where
lag
the full reheating power of the heat generation system is available in the storage system. The effe
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