Bsi bs en 15316 3 2 2007 (2008)

BRITISH STANDARD

Heating systems in
buildings —
Method for calculation
of system energy
requirements and
system efficiencies —
Part 3-2: Domestic hot water systems,
distribution

ICS 91.140.10

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BS EN
15316-3-2:2007


BS EN 15316-3-2:2007

National foreword
This British Standard is the UK implementation of EN 15316-3-2:2007.
The UK participation in its preparation was entrusted to Technical Committee
RHE/24, Central heating installations.
A list of organizations represented on this committee can be obtained on
request to its secretary.
This publication does not purport to include all the necessary provisions of a
contract. Users are responsible for its correct application.
Compliance with a British Standard cannot confer immunity from
legal obligations.

This British Standard was
published under the authority
of the Standards Policy and
Strategy Committee
on 29 August 2008

© BSI 2008

ISBN 978 0 580 55694 4

Amendments/corrigenda issued since publication
Date

Comments


EN 15316-3-2

EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM

October 2007

ICS 91.140.10

English Version

Heating systems in buildings - Method for calculation of system

energy requirements and system efficiencies - Part 3-2:
Domestic hot water systems, distribution
Systèmes de chauffage dans les bâtiments - Méthode de
calcul des besoins énergétiques et des rendements des
systèmes - Partie 3-2 : Systèmes de production d'eau
chaude sanitaire, distribution

Heizungsanlagen in Gebäuden - Verfahren zur Berechnung
der Energieanforderungen und Nutzungsgrade der Anlagen
- Teil 3-2: Trinkwassererwärmung, Verteilung

This European Standard was approved by CEN on 18 August 2007.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36

© 2007 CEN

All rights of exploitation in any form and by any means reserved
worldwide for CEN national Members.

B-1050 Brussels

Ref. No. EN 15316-3-2:2007: E


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

Contents

Page

Foreword..............................................................................................................................................................4
Introduction .........................................................................................................................................................6
1

Scope ......................................................................................................................................................7

2

Normative references ............................................................................................................................7

3

Terms and definitions ...........................................................................................................................7

4

Symbols, units and indices ................................................................................................................10

5
5.1
5.2
5.3
5.4

Domestic hot water system characteristics......................................................................................11
General..................................................................................................................................................11
Single zone and single system...........................................................................................................12
Single zone and multiple systems .....................................................................................................12
Multiple zones with single system .....................................................................................................13

6
6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.3
6.3.1
6.3.2
6.3.3

6.3.4
6.3.5
6.4
6.5

Distribution thermal losses ................................................................................................................13
Total distribution thermal losses .......................................................................................................13
Thermal losses from individual distribution pipe section...............................................................14
General..................................................................................................................................................14
Thermal losses from pipes based on dwelling area ........................................................................14
Thermal losses from pipes based on pipe lengths and number of tappings per day..................15
Thermal losses from pipes based on pipe lengths and distribution efficiencies.........................15
Thermal losses from pipes based on pipe lengths and tapping profiles ......................................16
Thermal losses from pipes based on pipe lengths and average temperature..............................16
Heat energy lost due to wasted hot water.........................................................................................16
Time periods.........................................................................................................................................16
Thermal losses from circulation loop................................................................................................16
General..................................................................................................................................................16
Thermal losses from circulation loop based on pipe length and a fixed value of heat loss .......16
Thermal losses from circulation loop based on a physical approach ...........................................17
Additional thermal losses from circulation loop during periods of no circulation ......................17
Total thermal loss from circulation loop ...........................................................................................17
Thermal losses due to accessories ...................................................................................................18
User outlets ..........................................................................................................................................18

7
7.1
7.2
7.3
7.3.1

7.3.2
7.3.3

Auxiliary energy ...................................................................................................................................18
Total auxiliary energy consumption ..................................................................................................18
Auxiliary energy consumption for ribbon heating ...........................................................................18
Auxiliary energy consumption for pumps ........................................................................................19
General..................................................................................................................................................19
Simplified method................................................................................................................................19
Detailed calculation method ...............................................................................................................20

8

Recoverable, recovered and unrecoverable system losses ...........................................................20

Annex A (informative) Calculation of thermal losses from pipes based on pipe lengths and the
number of tappings per day ...............................................................................................................22
Annex B (informative) Calculation of thermal losses from pipes based on pipe lengths and
distribution efficiencies ......................................................................................................................24
Annex C (informative) Calculation of thermal losses from pipes based on pipe lengths and
tapping profiles ....................................................................................................................................26
Annex D (informative) Calculation of thermal losses from circulation loop ...............................................28

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

D.1

D.2
D.2.1
D.2.2
D.2.3
D.2.4
D.2.5
D.2.6

Calculation of thermal losses based on pipe length .......................................................................28
Thermal losses based on a detailed calculation method................................................................28
General .................................................................................................................................................28
Determination of length of pipe sections..........................................................................................28
Determination of heat transfer coefficients ......................................................................................31
Tabulated method for calculation of linear thermal transmittance ................................................33
Determination of average ambient temperature...............................................................................34
Determination of average hot water temperature of pipe section..................................................34

Annex E (informative) Calculation of thermal losses from user outlets .....................................................35
Annex F (informative) Calculation of auxiliary energy requirement of a circulation pump ......................36
F.1
Simplified method for calculation of auxiliary energy requirement of a circulation pump .........36
F.2
Detailed method for calculation of auxiliary energy requirement of a circulation pump ............36
F.2.1 Hydraulic energy requirement ...........................................................................................................36
F.2.2 Hydraulic power required by the pump.............................................................................................36
F.2.3 Duration of the provision of domestic hot water .............................................................................37
F.2.4 Pump performance coefficient...........................................................................................................38
F.2.5 Intermittent pump operation...............................................................................................................39
F.2.6 Expenditure value coefficient ............................................................................................................39
F.3

Auxiliary energy recoverable factor ..................................................................................................40
Bibliography......................................................................................................................................................41

3


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

Foreword
This document (EN 15316-3-2:2007) has been prepared by Technical Committee CEN/TC 228 “Heating
systems in buildings”, the secretariat of which is held by DS.
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 April 2008, and conflicting national standards shall be
withdrawn at the latest by April 2008.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association (Mandate M/343), and supports essential requirements of EU Directive
2002/91/EC on the energy performance of buildings (EPBD). It forms part of a series of standards aimed at
European harmonisation of the methodology for calculation of the energy performance of buildings. An
overview of the whole set of standards is given in prCEN/TR 15615.
The subjects covered by CEN/TC 228 are the following:


design of heating systems (water based, electrical etc.);



installation of heating systems;



commissioning of heating systems;



instructions for operation, maintenance and use of heating systems;



methods for calculation of the design heat loss and heat loads;



methods for calculation of the energy performance of heating systems.

Heating systems also include the effect of attached systems such as hot water production systems.
All these standards are systems standards, i.e. they are based on requirements addressed to the system as a
whole and not dealing with requirements to the products within the system.
Where possible, reference is made to other European or International Standards, a.o. product standards.
However, use of products complying with relevant product standards is no guarantee of compliance with the
system requirements.
The requirements are mainly expressed as functional requirements, i.e. requirements dealing with the function
of the system and not specifying shape, material, dimensions or the like.
The guidelines describe ways to meet the requirements, but other ways to fulfil the functional requirements
might be used if fulfilment can be proved.
Heating systems differ among the member countries due to climate, traditions and national regulations. In
some cases requirements are given as classes so national or individual needs may be accommodated.
In cases where the standards contradict with national regulations, the latter should be followed.

4

BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

EN 15316 Heating systems in buildings — Method for calculation of system energy requirements and system
efficiencies consists of the following parts:
Part 1: General
Part 2-1: Space heating emission systems
Part 2-3: Space heating distribution systems
Part 3-1: Domestic hot water systems, characterisation of needs (tapping requirements)
Part 3-2: Domestic hot water systems, distribution
Part 3-3: Domestic hot water systems, generation
Part 4-1: Space heating generation systems, combustion systems (boilers)
Part 4-2: Space heating generation systems, heat pump systems
Part 4-3: Heat generation systems, thermal solar systems
Part 4-4: Heat generation systems, building-integrated cogeneration systems
Part 4-5: Space heating generation systems, the performance and quality of district heating and large volume
systems
Part 4-6: Heat generation systems, photovoltaic systems
Part 4-7: Space heating generation systems, biomass combustion systems
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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and United Kingdom.

5

BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

Introduction
This European Standard is one of a number of standards that together describe methods for calculation of
system energy requirements and system efficiencies related to domestic hot water systems. In particular this
European Standard specifies methods for calculation of the energy losses of the distribution system.
The user needs to refer to other European Standards or to national documents for input data and detailed
calculation procedures not provided by this European Standard.
Only the calculation methods are normative. Values necessary to complete the calculations should be given in
a national annex.

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

1

Scope

This European Standard is part of a set of standards covering methods for calculation of system energy
requirements and system efficiencies of heating systems in buildings. In particular this European Standard is
one of a number of standards dealing with domestic hot water systems.
The scope of this specific part is to standardise the methods for calculation of:


thermal losses from the domestic hot water distribution system;



recoverable thermal losses for space heating from the domestic hot water distribution system;



auxiliary energy of the domestic hot water distribution system.

These values are input data for calculation of the overall energy use according to prEN 15603 and
EN 15316-1.
This European Standard specifies the:


inputs;



calculation methods;



outputs.

2

Normative references

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

Not applicable

3

Terms and definitions

For the purposes of this document, the following terms and definitions apply.
3.1
auxiliary energy
electrical energy used by technical building systems for heating, cooling, ventilation and/or domestic hot water
to support energy transformation to satisfy energy needs
NOTE 1
This includes energy for fans, pumps, electronics etc. Electrical energy input to a ventilation system for air
transport and heat recovery is not considered as auxiliary energy, but as energy use for ventilation.
NOTE 2

In EN ISO 9488, the energy used for pumps and valves is called "parasitic energy".

3.2
building
construction as a whole, including its envelope and all technical building systems, for which energy is used to
condition the indoor climate, to provide domestic hot water and illumination and other services related to the
use of the building
NOTE
The term can refer to the building as a whole or to parts thereof that have been designed or altered to be used
separately.

7

BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

3.3
circulation loop
part of the domestic hot water distribution system where the water circulation is maintained by a pump
operating continuously or in cycles during a day
NOTE
Where there is a circulation loop, there are heat losses from the pipes during the whole period of water
circulation and not only related to hot water draw-offs.

3.4
calculation period
period of time over which the calculation is performed
NOTE

The calculation period can be divided into a number of calculation steps.

3.5
domestic hot water heating
process of heat supply to raise the temperature of the cold water to the intended delivery temperature
3.6
domestic hot water distribution system
distribution pipes installed between the heat generator or hot water storage vessel (if present) and the user
outlet or outlets. The domestic hot water distribution system may include a circulation loop and individual
sections
3.7
individual section of the domestic hot water distribution system
part of the domestic hot water distribution system where the circulation of the domestic hot water is not
maintained by a pump but only due to the draw offs

NOTE

The heat losses occur due to the energy used in heating up the pipes and fittings of the distribution system.

3.8
energy need for domestic hot water
heat to be delivered to the needed amount of domestic hot water to raise its temperature from the cold
network temperature to the prefixed delivery temperature at the delivery point, not taking into account the
technical building thermal systems
3.9
energy use for space heating or cooling or domestic hot water
energy input to the space heating or cooling system or the domestic hot water system to satisfy the energy
need for space heating or cooling (including dehumidification) or domestic hot water, respectively
NOTE
If the technical building system serves several purposes (e.g. space heating and domestic hot water), it can be
difficult to split the energy use into that used for each purpose. It can be indicated as a combined quantity (e.g. energy
need for space heating and domestic hot water).

3.10
heating or cooling season
period of the year during which a significant amount of energy for heating or cooling is needed
NOTE

The season lengths are used to determine the operation period of technical systems.

3.11
heat recovery
heat generated by a technical building system or linked to a building use (e.g. domestic hot water) which is
utilised directly in the related system to lower the heat input and which would otherwise be wasted (e.g.
preheating of the combustion air by flue gas heat exchanger)

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

3.12
recoverable system thermal loss
part of a system thermal loss which can be recovered to lower either the energy need for heating or cooling or
the energy use of the heating or cooling system
NOTE
This depends on the calculation approach chosen to calculate the recovered gains and losses (holistic or
simplified approach).

3.13
recovered system thermal loss
part of the recoverable system thermal loss which has been recovered to lower either the energy need for
heating or cooling or the energy use of the heating or cooling system
3.14
ribbon heating
also called trace heating. Electrical resistance enveloping the pipes (one way) used to compensate the heat
loss of the pipes in order to maintain the domestic hot water temperature in the distribution system at a
required temperature
3.15
system boundary
boundary that includes within it all areas associated with the building (both inside and outside the building)
where energy is consumed or produced
NOTE
Inside the system boundary the system losses are taken into account explicitly, outside the system boundary

they are taken into account in the conversion factor.

3.16
system thermal loss
thermal loss from a technical building system for heating, cooling, domestic hot water, humidification,
dehumidification, or ventilation or lighting that does not contribute to the useful output of the system
NOTE 1

A system loss can become an internal heat gain for the building, if it is recovered.

NOTE 2
Thermal energy recovered directly in the subsystem is not considered as a system thermal loss but as heat
recovery and directly treated in the related system standard.
NOTE 3
Heat dissipated by the lighting system or by other services (e.g. appliances of computer equipment) is not part
of the system thermal losses, but part of the internal heat gains.

3.17
tapping program
24-hour cycle that defines a number of domestic hot water draw-off requirements: succession of energy needs
corresponding to uses of domestic hot water during a day
3.18
technical building system
technical equipment for heating, cooling, ventilation, domestic hot water, lighting and electricity production
composed of sub-systems
NOTE 1
A technical building system can refer to one or to several building services (e.g. heating system, space
heating and domestic hot water system).
NOTE 2

Electricity production can include cogeneration and photovoltaic systems.

3.19
technical building sub-system
part of a technical building system that performs a specific function (e.g. heat generation, heat distribution,
heat emission)

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

3.20
zone
part of a building for which the energy need for domestic hot water is to be calculated

4

Symbols, units and indices

For the purposes of this document, the following symbols and units (Table 1) and indices (Table 2) apply.
Table 1 — Symbols and units
Symbol

Name of quantity

Unit

A

area

m

b

location factor

-

c

specific heat capacity

J/(kg K)

e

system performance coefficient (expenditure factor)

-

D

diameter

m

f

conversion factor

-

h

height

m

L

length

m

m

mass

kg

n

number of operating times

-

t

time, period of time

s

Q

quantity of heat, energy

J

φ

thermal power

W

P

electrical power

W

ψ

heat loss coefficient

W/mK

V

volume

m

W

auxiliary (electrical) energy

J

α

energy loss factor

-

η

efficiency

-

θ

celsius temperature

°C

λ

heat conductivity

W/mK

2

3

Table 2 — Indices

10

amb

ambient

gen

generation

nom

nominal

avg

average

hs

heated space

on

circulation

B

building

hydr

hydraulic

off

no circulation

col

circulation loop (collective)

in

input to system

out

output from system

dis

distribution

ind

individual

pmp

pump

e

external

int

internal

rib

trace heating

em

emission

ls

losses

tap

deliveries

f

floor

nhs

non heated space

W

domestic hot water


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

5
5.1

Domestic hot water system characteristics
General

The domestic hot water distribution system is given as one or more pipes installed between the heat generator

or hot water storage vessel (if present) and the user outlet or outlets. The domestic hot water distribution
system may include a circulation loop.
The most basic system, for which this method is applied, consists of a single distribution pipe connecting a
single heat generator, or a storage vessel, and a user outlet (e.g. tap or shower head). This is shown in
Figure 1.

Key
1 generation
2 storage
3 distribution
4 emission

Figure 1 — Basic domestic hot water system components
If the building is used for different applications or is divided between different users, the method can be
applied to the entire building or to part of the building, as required. The calculation method can also be applied
to a building or to part of a building, where there is more than one domestic hot water system installed. For the

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

purposes of these calculations, the buildings are considered in terms of the number of zones into which they
are divided and the number of domestic hot water systems within these zones.
A zone is defined as a building or part of a building, for which the energy need for domestic hot water is to be
calculated.

5.2

Single zone and single system

The simplest installation is a single system within a single zone (see Figure 1).

5.3

Single zone and multiple systems

This installation corresponds to a zone in which the energy need for domestic hot water is provided by means
of more than one domestic hot water generator. In a domestic building, this may be one generator providing
domestic hot water to a bathroom and another generator providing domestic hot water to a kitchen (see
Figure 2). In non-domestic buildings, the installation depends on the building sector.

Figure 2 — Domestic hot water system, single zone and multiple systems
Calculation of system losses shall be carried out separately for each system. The total system loss for the
zone is the sum of the system losses of each system.
Each distribution system shall be kept separate in order to define the heat load on the heat generator along
with the corresponding domestic hot water demand.

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

5.4

Multiple zones with single system

This installation corresponds to a building split into a number of separate zones, for which there is a common

single domestic hot water system, e.g. a block of flats with a central boiler (see Figure 3).

Figure 3 — Domestic hot water system, multiple zones and single system
The total system loss is calculated for the system, and the total thermal loss is the sum of thermal losses of
each zone.

6

Distribution thermal losses

6.1

Total distribution thermal losses

For the calculations, the distribution system is considered divided into two parts: a circulation loop, if present,
and the individual distribution pipes to the user outlet or outlets. The thermal losses of each part are calculated
separately.
The total thermal loss

QW ,dis ,ls of the distribution system is calculated by adding the thermal losses of each

part as follows:

QW ,dis ,ls = ∑ QW ,dis ,ls ,ind + QW ,dis ,ls ,col

(MJ/day)

(1)

ind

where

∑Q

W ,dis ,ls ,ind

is the sum of thermal loss from the individual distribution pipes of the distribution system (no

ind

circulation loop), MJ/day;

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

QW ,dis ,ls ,col

is the thermal loss from the circulation loop of the distribution system (collective part), if
present, MJ/day.

6.2
6.2.1

Thermal losses from individual distribution pipe section
General

Where there is no circulation loop, thermal losses occur due to the energy used for heating up the pipes and
fittings of the distribution system. This contributes also to a delay in reaching the required minimum
temperature of the domestic hot water at the user outlet.
When the desired temperature is reached in the distribution system, thermal losses from the distribution
system occur during the period of draw-off of domestic hot water.
The heat content within the distribution system, after a draw-off of domestic hot water has been completed, is
lost to the surrounding environment, i.e. heat content of the hot water in the distribution system and thermal
capacity of the material of the distribution system.
Insulation on the distribution pipes reduces the heat loss rate during a hot water draw-off and thus reduces the
total thermal losses during a hot water demand period.
Further, insulation on the distribution pipes reduces the heat loss rate regarding the heat content within the
distribution system, after a hot water draw-off has been completed. The effect of the insulation in this respect
depends on the time periods between consecutive draw-offs. If the time period is sufficiently long, pipe
insulation does not affect the thermal loss of the heat content and the hot water temperature drops to the
ambient temperature around the pipe. If the time period is short, pipe insulation reduces the thermal loss of
the heat content, as the hot water temperature does not drop to the ambient temperature around the pipe.
Thus, depending on the tapping pattern, the reduced thermal losses and effect of insulation should be taken
into account.
Different methods for calculation of thermal losses are described in the following. The methods differ in the
detail of the calculations and the input data required. The method applied can be chosen based on the data
available and the objectives of the user. The level of detail chosen should reflect the level of detail used in
defining the domestic hot water needs.
A national annex may specify which calculation method should be used for different types of buildings. A
national annex may also specify which calculation method is applicable for the purpose of energy labelling or
any other specific use.
The calculations are based on daily domestic hot water needs.
6.2.2

Thermal losses from pipes based on dwelling area

This method is a simplified method relating the thermal loss of individual distribution pipes only to building
floor area and, thus, detailed knowledge of the domestic hot water distribution system is not required for this
method.
This method can only be applied in a limited number of situations and is usually restricted to domestic
buildings with a domestic hot water distribution system that does not involve a circulation loop.
If this method is applicable, details for the calculation and limitations for its use shall be given in a national
annex. Although detailed knowledge of the domestic hot water distribution system is not required, the pipe
lengths shall be kept to a minimum. The maximum acceptable distribution pipe length for this method may be
given in a national annex.

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

6.2.3

Thermal losses from pipes based on pipe lengths and number of tappings per day

This method takes into account the thermal losses from the pipes and the thermal losses from the water within
the pipes. It is necessary to know the pipe diameters and pipe lengths for each individual section of the
domestic hot water distribution system.
This method is applicable only for domestic hot water distribution pipes that are not part of a circulation loop.
The thermal loss is calculated by:

QW ,dis ,ls ,ind =

ρ w * cw
1000

* VW ,dis * (θW ,dis ,nom − θ amb ) * ntap

(MJ/day)

(2)

where

ρw

is the specific mass of water (kg/m );

cw

is the specific heat capacity of water (kJ/kg⋅K);

VW ,dis

is the volume of water contained in the pipes (m );

θ amb

is the average ambient temperature around the pipes (°C);

θW ,dis,nom

is the nominal hot water temperature in the pipes (°C);

ntap

is the number of hot water draw-offs during a day.

3

3

Details on this method shall be given in a national annex. It is possible to take into account other parameters,
e.g. the thermal capacity of the pipes. An example is described in Annex A.
It is possible also to include the thermal losses from the user outlets in this method.
A reduction of thermal losses in case of short intervals between the tapping cycles is not taken into account in
this calculation method. If this is to be considered, details shall be given in a national annex, and for this
purpose, the effect of pipe insulation on thermal losses shall be taken into account. An example is described
in Annex A.
6.2.4

Thermal losses from pipes based on pipe lengths and distribution efficiencies

This method is based on estimates of proportion of the heat energy reaching the user outlets for different pipe
lengths. A distinction is made between supplies to kitchens and supplies to bathrooms. Detailed knowledge of
the domestic hot water distribution system is not required for this method, however, an approximation of the
length and diameter of each of the delivery pipes shall be made. The proportion of heat energy reaching the
user outlets is tabulated against pipe lengths and diameters.
This method is applicable only for domestic hot water distribution pipes that are not part of a circulation loop.
If this method is applicable, details for the calculation and suitable tabulated values shall be given in a national
annex. A table of default values is given in Annex B.

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BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

6.2.5

Thermal losses from pipes based on pipe lengths and tapping profiles

This method is based on estimates of the thermal losses expressed as a proportion of the domestic hot water
energy demand at the user outlets. Data on domestic hot water energy demand is required for this method,
but detailed knowledge of the domestic hot water distribution system is not required, as long as sufficient data
is available to estimate the average pipe lengths. Additionally, data is required on the location of the domestic
hot water distribution system, i.e. as to lengths of pipe sections installed within the heated space and lengths
of pipe sections installed outside the heated space.
This method is described in Annex C. Details on this method, including the equivalent energy loss factors,
shall be given in a national annex.
6.2.6

Thermal losses from pipes based on pipe lengths and average temperature

This method is based on the same calculation principles as for the thermal losses from a circulation loop
based on a physical approach (see 6.3.3). The only difference is the average temperature of the domestic hot
water taken into account, which is normally lower for the individual section of the domestic hot water
distribution system than for the circulation loop.
Appropriate values shall be given in a national annex. An example is given in D.2.
6.2.7

Heat energy lost due to wasted hot water

For most uses, a minimum domestic hot water temperature is required at the user outlet, before it is
considered useful. The energy content of the water tapped, until the water at the user outlet has reached the

minimum required temperature, is wasted and is considered as a thermal loss. These thermal losses may be
reduced if there is a high demand on the distribution system, i.e. a large number of hot water draw-offs occur
over a short time period.
If the domestic hot water demand is defined in accordance with EN 15316-3-1 on the basis of tapping
programs, the conditions for the minimum domestic hot water temperatures and flow rates are given.
If the domestic hot water performance of the generator unit is measured in accordance with EN 13203-2, the
energy content of the wasted domestic hot water is also measured.
If the domestic hot water performance of the generator is not measured in accordance with EN 13203-2, the
energy content of the wasted domestic hot water may be calculated. A national annex should give details on
this method and the assumptions to be made.
6.2.8

Time periods

The weekly, monthly or annual thermal losses are obtained by multiplying the thermal loss per day by the
appropriate number of days.

6.3
6.3.1

Thermal losses from circulation loop
General

For a circulation loop, there are thermal losses from the pipes during the whole period of water circulation, i.e.
not restricted to domestic hot water draw-offs.
6.3.2

Thermal losses from circulation loop based on pipe length and a fixed value of heat loss

A fixed value of heat loss from the circulation loop may be assumed. This method is applicable if exact design

of the domestic hot water distribution system is not available or the pipe insulation thickness is not known. The
value should be given in a national annex. If a national annex is not provided or does not include this value, a
default value is given in D.1.

16


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

6.3.3

Thermal losses from circulation loop based on a physical approach

The general determination of thermal losses of a circulation loop comprising a number of pipe sections i is
given by:

QW ,dis ,ls ,col ,on =

∑Q

W ,dis ,ls ,col ,on ,i

i

=∑
i

3.6
* U W ,i * LW ,i * (θW ,dis ,avg ,i − θ amb,i ) * tW

1000

(MJ/day)

(3)

where

QW ,dis ,ls ,col ,on ,i is the thermal losses of pipe section i (during periods of circulation) (MJ/day);
U W ,i

is the linear thermal transmittance of pipe section i (W/mK);

LW ,i

is the length of pipe section i (m);

θW ,dis ,avg ,i

is the average hot water temperature of pipe section i ( C);

θ amb,i

is the average ambient temperature around pipe section i ( C);

tW

is the daily utilisation period at the corresponding temperatures,

o

o

θW ,dis ,avg ,i

(h/day).

The individual components of the equation are obtained from the method given in D.2.
6.3.4

Additional thermal losses from circulation loop during periods of no circulation

If the circulation loop is not operated continuously, the heat energy within each pipe section of the circulation
loop is lost to the surrounding environment. This thermal loss is calculated by:

QW ,dis ,ls ,col ,off =

∑Q

W ,dis ,ls ,col ,off ,i

i

=

∑
i

ρ w * cw
1000

* VW ,dis ,i * (θW ,dis ,avg ,i − θ amb,i ) * nnorm

(MJ/day)

(4)

where

ρw

is the specific mass of water (kg/m );

cw

is the specific heat capacity of water (kJ/kg⋅K);

VW ,dis ,i

is the volume of water contained in pipe section i (m );

nnorm

is the number of circulation pump operating cycles during a day.

6.3.5

3

3

Total thermal loss from circulation loop

The total thermal loss from a circulation loop is the sum of thermal losses during periods of circulation and
thermal losses during periods of no circulation:

QW ,dis,ls,col = QW ,dis,ls,col ,on + QW ,dis ,ls ,col ,off

(MJ/day)

(5)

The weekly, monthly or annual thermal losses are obtained by multiplying the thermal loss per day by the
appropriate number of days.

17


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

6.4

Thermal losses due to accessories

The thermal losses from the circulation loop and from individual distribution pipes are increased by the thermal
losses through fittings, i.e. valves and flanges, as well as thermal losses through pipe hangers.
These thermal losses are estimated by introducing an additional equivalent pipe length. If these additional
thermal losses are to be included in the analysis, details shall be given in a national annex.

6.5

User outlets

The domestic hot water is supplied to the user through a user outlet, e.g. a tap, showerhead or similar device.
Depending on the design and the material of construction, the user outlet absorbs heat energy during the
supply of hot water and causes a delay in reaching the required minimum hot water temperature at the user
outlet.
Depending on the characteristics of the user outlet, the user needs more or less time to adjust the required
temperature (e.g. thermostatic user outlets). These delays increase thermal losses in the domestic hot water
distribution system.
The additional heat energy lost due to wasted hot water (according to 6.2.7) may be combined with the
thermal losses due to user outlets and, thus, no additional calculation is required to take user outlets into
account.
If the thermal losses from user outlets are to be considered separately, the need for this calculation shall be
indicated in a national annex. The basis of the calculation method is given in Annex E. These thermal losses
are dependent on the number of hot water draw-offs. This dependence shall be detailed in the national annex.
Default values for the thermal losses from different types of user outlets may be used in place of a calculation.
If default values are applicable, these shall be given in a national annex.

7
7.1

Auxiliary energy
Total auxiliary energy consumption

For the domestic hot water distribution system, auxiliary energy may be used for ribbon heating and for pumps,
and the total auxiliary energy consumption is determined by:

WW ,dis ,aux = WW ,dis ,rib + WW ,dis , pmp

(MJ//day)

(6)

where

WW ,dis ,rib

is the auxiliary energy consumption for the ribbon heater (MJ/day);

WW ,dis , pmp

is the auxiliary energy consumption for pumps (MJ/day).

7.2

Auxiliary energy consumption for ribbon heating

Where ribbon heating or trace heating is applied to reduce the heat losses, it is assumed that the auxiliary
energy consumption for the ribbon heater is equal to what the heat losses from the pipe would have been
without the heater.
The ribbon heater does not contribute to the generation of hot water. The heat losses compensated by the
ribbon heater shall not be added to the heat losses of other individual parts of the domestic hot water

18


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

distribution system, used to determine the heat demand and the load on the heat generator. The ribbon heater
is supplied by electricity and should thus be considered as part of the auxiliary energy requirements.
The auxiliary energy consumption for the ribbon heater is calculated by:

WW ,dis ,rib =

3.6
* LW ,rib * U W ,dis * (θW ,dis ,avg − θ amb ) * tW
1000

(MJ/day)

(7)

where

LW ,rib

is the length of pipe section heated by trace heating (m);

U W ,dis

is the linear thermal transmittance of pipe section (W/mK);

θW ,dis ,avg

is the average hot water temperature of pipe section ( C);

θ amb

is the average ambient temperature around pipe section ( C);

tW

is the duration of the provision of hot water (h/day).

o

o

It is assumed that the ribbon heater operates during the same time periods as the domestic hot water heating
programme setting, if this is not continuous.
The weekly, monthly or annual auxiliary energy consumptions are obtained by multiplying the auxiliary energy
consumption per day by the appropriate number of days.

7.3

Auxiliary energy consumption for pumps

7.3.1

General

Electrical energy is required for the pump to overcome the hydraulic losses within the domestic hot water
distribution system. A simplified method or a detailed calculation method may be applied to estimate the
auxiliary energy consumption for pumps in domestic hot water distribution systems.
The proportion of the auxiliary energy consumption for a pump, which is transferred as heat to the circulating
water, should be given in a national annex. If a national annex is not provided or does not include this value,
the default value given in Annex F may be applied. For the purpose of the calculations, the auxiliary energy

recovered as heat to the circulating water is subtracted from the total thermal losses of the circulation loop.
7.3.2

Simplified method

The auxiliary energy consumption for the pump may be estimated from the pump power rating as follows:

WW ,dis , pmp = 3.6 * Ppmp * t pmp

(MJ/day)

(8)

where
Ppmp

is the power rating of the pump (kW);

tpmp

is the pump running time (h/day).

Values for tpmp should be given in a national annex. If a national annex is not provided or does not include this
value, a default value is given in F.1.

19


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

The weekly, monthly or annual auxiliary energy consumptions are obtained by multiplying the auxiliary energy
consumption per day by the appropriate number of days.
7.3.3

Detailed calculation method

If the design of the domestic hot water distribution system is available, a detailed calculation method can be
applied. The auxiliary energy consumption for the pump can be calculated from the hydraulic energy
requirement and the performance of the pump.
The general calculation of the auxiliary energy consumption for the circulation pump is:
WW ,dis, pmp = WW ,dis,hydr * eW ,dis, pmp

(MJ/day)

(9)

where

WW ,dis ,hydr
eW ,dis , pmp

is the hydraulic energy requirement (MJ/day);
is the performance coefficient for circulation pump (-).

Details of the method are given in F.2.
The weekly, monthly or annual auxiliary energy consumptions are obtained by multiplying the auxiliary energy
consumption per day by the appropriate number of days.

8

Recoverable, recovered and unrecoverable system losses

The calculated system losses are not all necessarily lost. Some of the system losses are recoverable for
space heating and a proportion of these may actually be recovered and contribute to the space heating.
The recoverable system losses are expressed as a fraction of the distribution thermal losses and a fraction of
the distribution auxiliary energy consumption:

QW ,dis ,ls ,rbl = QW ,dis ,ls * fW ,dis ,ls ,rbl + WW ,dis ,aux * fW ,dis ,aux ,rbl

(MJ/day)

(9)

where

fW ,dis ,ls ,rbl

is the fraction of distribution thermal losses recoverable for space heating;

fW ,dis ,aux ,rbl

is the fraction of distribution auxiliary energy consumption recoverable for space heating.

The fractions depend on e.g. location of the pipes, location of the pump, duration of the heating season. If the
pipes are installed in the heated space of the building, the thermal losses may be recoverable. However,
recoverable losses can only be considered during periods of the year where there is a significant space
heating demand.
The proportion of the total recoverable system losses that can be recovered is determined according to other
standards (e.g. EN ISO 13790 and prEN 15603) for which the total recoverable system losses are provided as

an input.
The fractions shall be specified in a national annex. If a national annex is not provided or does not include
these values, it is considered that no system losses are recoverable for the space heating. ( QW ,dis ,ls ,rbl = 0).
Under some circumstances, the recoverable system losses may add to the cooling load required in a building.

20


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

In some situations, the system losses may be reduced by an energy gain from the building to the cold water
supply or by heat recovery from the wastewater. These energy transfers may be ignored, unless otherwise
required by a national annex.
Some of the auxiliary energy may be recovered as heat in the domestic hot water system, see 7.3.1.

21


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

Annex A
(informative)
Calculation of thermal losses from pipes based on pipe lengths and the
number of tappings per day

This calculation method takes into account the thermal losses from the pipes and the thermal losses from the
water within the pipes. It is necessary to know the pipe diameters and pipe lengths for each individual section
of the domestic hot water distribution system.

This annex is only applicable for domestic hot water distribution pipes that are not part of a circulation loop.
For every pipe section i, the maximum thermal losses are given by:

QW ,dis ,ls ,ind ,i = {

ρ w * cw * VW ,dis ,i + c p * m p ,dis ,i
1000

} * {θW ,dis ,nom,i − θ amb,i } * ntap

(MJ/day)

(A.1)

where

ρw

is the specific mass of water (kg/m );

cw

is the specific heat capacity of water (kJ/kg⋅K);

VW , dis ,i

is the volume of water contained in pipe section i (m );

cp

is the specific heat capacity of pipe material (kJ/kg⋅K);

m p ,dis ,i

is the mass of pipe section i (kg);

θW ,dis ,nom ,i

is the nominal hot water temperature in pipe section i (°C);

θ amb,i

is the average ambient temperature around pipe section i (°C);

ntap

number of tappings per day using pipe section i.

3

3

A reduction of thermal losses in case of short intervals between the tapping cycles is not taken into account in
this calculation method.
Thermal losses due to energy content of wasted hot water at the user outlets, while the desired domestic hot
water temperature has not been reached, are not included in this calculation method.
If the thermal losses from user outlets, i.e. materials of shower heads or taps, are to be included, a further
contribution is added to Equation (A.1) taking into account the mass and specific heat capacity of the user
outlet material.
Influence of pipe insulation in case of short tapping intervals

In case of short tapping intervals, the effect of pipe insulation on thermal losses should be taken into account.
The following calculation method can be applied.

22


BS EN 15316-3-2:2007
EN 15316-3-2:2007 (E)

For every pipe section i, the thermal losses for each tapping, which is followed by a short interval ttap, are
given by:

QW ,dis ,ls ,ind ,i ,tap = {
and θW ,i

ρ w * cw * VW ,dis ,i + c p * m p ,dis ,i
1000

= θ amb,i + (θW , dis ,nom ,i − θ amb,i ) * e

} * {θW ,dis ,nom ,i − θW ,i }

[MJ]

− ( qi * Li * t tap ) / {( ρ w * c w * VW ,dis ,i + c p * m p ,dis ,i ) * (θW ,dis ,nom ,i − θ amb ,i )*1000}

(A.2)

(°C)

(A.3)

where

θ W ,i

is the final hot water temperature in pipe section i before the next tapping (°C);

qi

is the density of heat flow rate of pipe section i (W/m);

Li

is the length of pipe section i (m);

ttap

is the time interval before the next tapping (s).

The density of heat flow rate is given by:

qi = U R * (θW ,dis ,nom ,i − θ amb ,i )

(W/m)

(A.4)

where
UR

is the linear thermal transmittance (W/m⋅K) according to Equation (D.1).

23