ISO 13675:2013
(Main)Heating systems in buildings — Method and design for calculation of the system energy performance — Combustion systems (boilers)
Heating systems in buildings — Method and design for calculation of the system energy performance — Combustion systems (boilers)
ISO 13675:2013 is the general standard on generation by combustion sub-systems (boilers) for oil, gas, coal and biomass burning. It specifies the required inputs, calculation method, and resulting outputs for space heating generation by combustion sub-systems (boilers) including control. ISO 13675:2013 is also intended for the case of generation for both domestic hot water production and space heating.
Systèmes de chauffage dans les bâtiments — Méthode de conception et de calcul de la performance énergétique des systèmes — Systèmes de combustion (chaudières)
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 13675
First edition
2013-11-15
Heating systems in buildings —
Method and design for calculation of
the system energy performance —
Combustion systems (boilers)
Systèmes de chauffage dans les bâtiments — Méthode de conception
et de calcul de la performance énergétique des systèmes — Systèmes
de combustion (chaudières)
Reference number
ISO 13675:2013(E)
©
ISO 2013
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ISO 13675:2013(E)
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ISO 13675:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols and units . 4
4 Alignment of the parts of the heating system standards . 5
4.1 Physical factors taken into account . 5
4.2 Input quantities from other parts of the heating system standards . 6
4.3 Output quantities for other parts of the heating system standards . 6
4.4 Heat balance of the generation sub-system, including control of heat generation . 7
4.5 Generation sub-system basic energy balance . 8
5 Generation sub-system calculation . 9
5.1 Available methodologies. 9
5.2 Boiler efficiency .10
Annex A (informative) Additional formulas and default values for parametering the boiler
efficiency method .19
Annex B (informative) General part default values and information .31
Annex C (normative) Maximum heating power in the building zone .32
Annex D (informative) Calculation examples for modulating condensing boiler .35
Annex E (informative) Generation sub-systems and gross calorific values .39
Bibliography .43
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ISO 13675:2013(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 205, Building environment design.
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ISO 13675:2013(E)
Introduction
This International Standard presents methods for calculation of the energy losses of a heat generation
system. The calculation is based on the performance characteristics of the products given in product
standards and on other characteristics required to evaluate the performance of the products as included
in the system.
This method can be used for the following applications:
— judging compliance with regulations expressed in terms of energy targets;
— optimization of the energy performance of a planned heat generation system, by applying the
method to several possible options;
— assessing the effect of possible energy conservation measures on an existing heat generation system,
by calculating the energy use with and without the energy conservation measure.
Refer to other International Standards or to regional or national documents for input data and detailed
calculation procedures not provided by this International Standard.
Heating systems also include the effect of attached systems such as hot water production systems.
This International Standard is a systems standards, i.e. it is 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 applicable 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.
Heating systems and cooling systems differ globally due to climate, traditions and national regulations.
In some cases, requirements are given as classes so national or individual needs can be accommodated.
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INTERNATIONAL STANDARD ISO 13675:2013(E)
Heating systems in buildings — Method and design
for calculation of the system energy performance —
Combustion systems (boilers)
1 Scope
This International Standard is the general standard on generation by combustion sub-systems (boilers)
for oil, gas, coal and biomass burning.
It specifies the
— required inputs,
— calculation method, and
— resulting outputs
for space heating generation by combustion sub-systems (boilers) including control.
This International Standard is also intended for the case of generation for both domestic hot water
production and space heating.
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.
ISO 7345:1987, Thermal insulation — Physical quantities and definitions
ISO 13790, Energy performance of buildings — Calculation of energy use for space heating and cooling
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7345:1987 and the following apply.
3.1.1
auxiliary energy
electrical energy used by technical building systems for heating, cooling, ventilation and/or domestic
water to support energy transformation to satisfy energy needs
Note 1 to entry: This includes energy for fans, pumps, electronics, etc. Electrical energy input to the ventilation
system for air transport and heat recovery is not considered as auxiliary energy, but as energy use for ventilation.
3.1.2
boiler
gas, liquid or solid fuelled appliance designed to provide hot water for space heating
Note 1 to entry: It can also be designed to provide domestic hot water heating.
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ISO 13675:2013(E)
3.1.3
biomass boiler
biomass fuelled appliance designed to provide heating medium (e.g. water, fluid)
3.1.4
condensing boiler
oil or gas boiler designed to make use of the latent heat released by condensation of water vapour in the
combustion flue products
Note 1 to entry: A condensing boiler allows the condensate to leave the heat exchanger in liquid form by way of a
condensate drain.
Note 2 to entry: Boilers not so designed, or without the means to remove the condensate in liquid form, are called
‘non-condensing’.
3.1.5
low temperature boiler
non-condensing boiler which can work continuously with a water supply temperature of 35 °C to 40 °C
3.1.6
modulating boiler
boiler with the capability to vary continuously (from a set minimum to a set maximum) the fuel burning
rate whilst maintaining continuous burner firing
3.1.7
multistage boiler
boiler with the capability to vary the fuel burning rate stepwise whilst maintaining continuous burner firing
3.1.8
on/off boiler
boiler without the capability to vary the fuel burning rate whilst maintaining continuous burner firing
Note 1 to entry: This includes boilers with alternative burning rates set once only at the time of installation,
referred to as range rating.
3.1.9
calculation period
period of time over which the calculation is performed
Note 1 to entry: The calculation period can be divided into a number of calculation steps.
3.1.10
calculation step
discrete time interval for the calculation of the energy needs and uses for heating, cooling, humidification
and dehumidification
Note 1 to entry: Typical discrete time intervals are one hour, one month or one heating and/or cooling season,
operating modes, and bins.
3.1.11
combustion power
product of the fuel flow rate and the net calorific power of the fuel
3.1.12
domestic hot water heating
process of heat supply to raise the temperature of cold water to the intended delivery temperature
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ISO 13675:2013(E)
3.1.13
external temperature
temperature of external air
Note 1 to entry: For transmission heat transfer calculations, the radiant temperature of the external environment
is supposedly equal to the external air temperature; long-wave transmission to the sky is calculated separately.
[3]
Note 2 to entry: The measurement of external air temperature is defined in ISO 15927 .
3.1.14
gross calorific value
quantity of heat released by a unit quantity of fuel, when it is burned completely with oxygen at a constant
pressure equal to 101 320 Pa, and when the products of combustion are returned to ambient temperature
Note 1 to entry: This quantity includes the latent heat of condensation of any water vapour contained in the fuel
and of the water vapour formed by the combustion of any hydrogen contained in the fuel.
[2]
Note 2 to entry: According to ISO 13602-2 , the gross calorific value is preferred to the net calorific value.
3.1.15
heat recovery
heat generated by a technical building system or linked to a building use (e.g. domestic hot water) which
is utilized directly in the related system to lower the heat input and which would otherwise be wasted
EXAMPLE Preheating of combustion air by a flue gas heat exchanger.
3.1.16
heat transfer coefficient
factor of proportionality of heat flow governed by a temperature difference between two environments
3.1.17
heated space
room or enclosure which for the purposes of the calculation is assumed to be heated to a given set-point
temperature or set-point temperatures
3.1.18
load factor
ratio between the time with the boiler on and the total generator operation time
3.1.19
modes of operation
various modes in which the heating system can operate
EXAMPLE Set-point mode, cut-off mode, reduced mode, set-back mode, boost mode.
3.1.20
net calorific value
gross calorific value minus latent heat of condensation of the water vapour in the products of combustion
at ambient temperature
3.1.21
operation cycle
time period of the operation cycle of a boiler
3.1.22
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 1 to entry: This depends on the calculation approach chosen to calculate the recovered gains and losses
(holistic or simplified approach).
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ISO 13675:2013(E)
3.1.23
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
Note 1 to entry: This depends on the calculation approach chosen to calculate the recovered gains and losses
(holistic or simplified approach).
3.1.24
space heating
process of heat supply for thermal comfort
3.1.25
system thermal loss
thermal loss from a technical building system for heating, cooling, domestic hot water, humidification,
dehumidification or ventilation that does not contribute to the useful output of the system
Note 1 to entry: A system loss can become an internal heat gain for the building if it is recoverable.
Note 2 to entry: 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.
3.1.26
total system thermal loss
total of the technical system thermal loss, including recoverable system thermal losses
3.2 Symbols and units
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
D day d/mth
2
A area m
b
J or
energy in general [except quantity of heat, mechanical work and auxil-
E
iary (electrical) energy]
a
Wh
f factor -
P power in general including electrical power kW, W
J or
Q quantity of heat
a
Wh
s or
t time, period of time
a
H/d, h/mth
J or
W auxiliary (electrical) energy
a
Wh
X gas content Vol-%
2
α heat transfer coefficient W/(m K)
β load factor —
η efficiency —
θ temperature °C
a
If seconds (s) is used as the unit of time, the unit for energy shall be J; if hours (h) is used as the unit of time, the unit for
energy shall be Wh.
b
The unit depends on the type of energy carrier.
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ISO 13675:2013(E)
Table 2 — Indices
C cooling day day od operating day
CO carbon dioxide del delivered on running
2
H heating dis distribution system op operational
HC heating circuit dry dry gases out output
O oxygen e external pa partial area
2
Pn at nominal load env envelope prio priority
Pint at intermediate load fg flue gas ren renewable energy
P0 at zero load gen generation, generator rbl recoverable
RT return i,j,k indices res reheating
V ventilation in input rvd recovered
W hot water int internal sat saturation
Hs/Hi ratio of gross calorific/net calorific value ls loss sim simultaneous
an annual m mean sink sink
air air max maximum st stoichiometric
aux auxiliary mech mechanical (ventilation system) test test
brm boiler room min minimum th thermal
ch chimney meas measured tr transmission
cond condensation mth month use use
corr corrected/correction nrbl non recoverable ve ventilation
ctr control n radiator index wfg water to fluegas
4 Alignment of the parts of the heating system standards
4.1 Physical factors taken into account
The calculation method of the generation sub-system takes into account heat losses and/or recovery due
to the following physical factors:
a) heat losses to the chimney (or flue gas exhaust) and through the envelope of the storage tank and
the generator(s) during total time of generator operation (running and stand-by);
b) heat losses through the generator(s) envelope during total time of generator operation (running
and stand-by);
c) auxiliary energy.
The relevance of these effects on the energy requirements depends on:
— type of heat generator(s);
— type of buffer tank(s);
— location of heat generator(s);
— type of buffer tank(s);
— part load ratio;
— operating conditions (temperature, control, etc.);
— control strategy (on/off, multistage, modulating, cascading, etc.).
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ISO 13675:2013(E)
4.2 Input quantities from other parts of the heating system standards
Table 3 — Input quantities
Notation Meaning Reference
H heat transfer coefficient of transmission see ISO 13790
tr
H heat transfer coefficient of ventilation see ISO 13790
ve
P heat load see heat load calculation
H,max
t heating hours (in the calculation interval), in h/mth see ISO 13790
H
availability period for hot water production – when connected, in
t see input data
W
h/mth
d number of days per month, in d/mth see project data
mth
β load factor at full load see input data
Pn
β load factor at intermediate load see input data
Pint
β actual load factor see input data
H,gen
see external climate
θ external air temperature, in °C
e
data
see external climate
θ daily average design temperature, in °C;
e,min
data
generator average water temperature (or return temperature to
θ the generator for condensing boilers) as a function of the specific see input data
HC,m
operating conditions
average return temperature to the generator for condensing
θ
HC,RT
boilers as a function of the specific operating conditions
θ ambient temperature, in °C
int
θ space temperature during the operation time, in °C see project data
nt,H,op
a
θ is to be used for system components in a heated zone, taking into account reduced heating operation (without
int,H
taking into account weekends and holidays).
θ is to be used for system components in a cooled zone (the user shall decide whether a cooled zone exists).
int,C
θ is to be used for system components in an unheated and uncooled zone.
e
If a zone is heated and cooled in the same month, it shall be determined which occurred more often and the appropriate
temperature used.
The daily operation is taken into account by the heating time (operating hours/period of duration), t .
H,op
The assumption is made that there is always only one user. Where there are a number of different loads,
a differentiation must be made between the individual requirements for each case.
Only if the useful heat demand Q > 1 kWh (in the calculation interval) is heating necessary.
H,dis,in
4.3 Output quantities for other parts of the heating system standards
The calculation of the values takes place basically for the zones defined in ISO 13790.
If a number of parts of systems are contained in the various process domains then the values are to be
added together for further analysis.
Here it is to be taken into account that the heating data are to be related to the gross calorific value.
In the following sections the thermal and auxiliary energy components of the different process domains
are determined for further analysis.
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ISO 13675:2013(E)
Table 4 — Output quantities
Notation Description Reference
E Fuel heat requirement see 4.5
H,gen,in
Recoverable generation heat losses for heating system (in the calculation
Q see 5.2.4.2
H,gen,ls,rbl
interval), in kWh
W heat generation auxiliary energy for the heating system (in the calculation
H,gen,
see 5.2.3
interval), in kWh
4.4 Heat balance of the generation sub-system, including control of heat generation
Figure 1 shows the calculation inputs and outputs of the generation sub-system.
NOTE For commercial purpose, Figure 1 can be simplified by grouping the different type of losses.
Key
SUB Generation sub-system balance boundary
HF Heating fluid balance boundary (see Formula 1)
Q Generation sub-system heat output [input to distribution sub-system(s)]
H,gen,out
E Generation sub-system fuel input (energyware)
H,gen,in
W Generation sub-system total auxiliary energy
H,gen
Q Generation sub-system recovered auxiliary energy
H,gen,aux,rvd
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ISO 13675:2013(E)
Q Generation sub-system total thermal losses
H,gen,ls
Q Generation sub-system thermal loss recoverable for space heating
H,gen,ls,rbl
Q Generation sub-system thermal loss (thermal part) recoverable for space heating
H,gen,ls,rbl,th
Q Generation sub-system recoverable auxiliary energy
H,gen, rbl,aux
Q Generation sub-system thermal loss (thermal part) non recoverable
H,gen,ls,nrbl,th
Q Generation sub-system non recoverable auxiliary energy
H,gen,nrbl,,aux,
NOTE Figures shown are sample percentages.
Figure 1 — General generation sub-system inputs, outputs and energy balance
4.5 Generation sub-system basic energy balance
The basic energy balance of the generation sub-system is given by
EQ=−QQ+−Q (1)
gen,in gen,outgen,aux,rvd gen,ls gen,ren
where
E is the energy input of the generation sub-system (fuel input) (in the calculation inter-
gen,in
val), in kWh;
Q is the energy supplied to the distribution sub-systems (e.g. space heating and domes-
gen,out
tic hot water) (in the calculation interval), in kWh;
Q is the auxiliary energy recovered by the generation sub-system (e.g. pumps, burner
gen,aux,rvd
fan, etc.) (in the calculation interval), in kWh;
Q is the thermal losses of the generation sub-system (e.g. through the chimney, genera-
gen,ls
tor envelope, etc.) (in the calculation interval), in kWh;
Q is the regenerative energy contribution (in the calculation interval), in kWh.
gen,ren
NOTE 1 Q takes into account flue gas and generator envelope losses, part of which may be recoverable for
gen,ls
space heating according to location of the generator. See 5.2.2.
NOTE 2 Generally biomass boilers are not designed for controlling the emission part of heating systems.
NOTE 3 Q is normally not used with boilers.
gen,ren
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ISO 13675:2013(E)
The heat output from the boiler equals the sum of heat input to the connected distribution systems:
Qf=⋅ QQ+ (2)
gen,outctr,lsH∑∑,dis,in,i W,dis,in,j
i j
where
f is the factor taking into account emission control losses. Default value of f is given
ctr,ls ctr,ls
in Table B.1. Other values may be specified in a national annex, provided that emission
control losses have not been already taken into account in the emission part or in the
distribution part;
Q is the heat input to the connected heat distribution system (in the calculation interval),
H,dis,in
in kWh;
Q is the heat input to the connected DHW distribution system (in the calculation interval),
W,dis,in
in kWh.
If there are multiple generation sub-systems or multiple boilers, see input data “generator systems”.
If the generator provides heat for heating, cooling, ventilation and domestic hot water, the index H shall
be replaced by C, V or W. In the following only H is used for simplicity.
The heat load calculation will be written in another standard.
5 Generation sub-system calculation
5.1 Available methodologies
This subclause describes the calculation method for the heat generation sub-system.
This method takes into account the specific operation conditions of the individual installation by taking
the certified product value provided either by the manufacturer or taken from informative Annex A, or
by measuring the needed values on-site.
The considered calculation step can be the heating season but may also be a shorter period (month,
week and/or the operation modes according to ISO 13790). The method is not limited and can be used
with the default values given in informative Annex A.
For existing boilers the calculation by measured values takes the losses of a generator which occurs
during boiler cycling (i.e. combustion losses) in consideration. This method is well adapted for existing
buildings and to take into account condensation heat recovery according to operating conditions.
The calculation methods for biomass combustion systems differ with respect to:
— type of stoking device (automatic or by hand);
— type of biomass fuel (pellets, chipped wood or log wood).
Data to characterize the boiler shall be taken from one of the following sources, listed in priority order:
a) measured data (see 5.2.1);
b) product data from the manufacturer, if the boiler has been tested and certified (see 5.2.2);
c) default data from Annex A (see 5.2.2).
It shall be recorded if the efficiency values include or not auxiliary energy recovery.
NOTE Biomass boilers with automatic stocking fired by pellets or chipped wood.
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ISO 13675:2013(E)
5.2 Boiler efficiency
5.2.1 Generator thermal losses measurement
5.2.1.1 Thermal losses through the chimney with the burner on at full load f
ch,on
Thermal losses through the chimney with the burner on f can be calculated according to the flue gas
ch,on
analysis results:
Measuring O
2
c
10
f =−θθ ⋅ +c (3)
()
ch,on,meas ch brm 11
21%−X
O2
where measured values are as follows:
θ is the flue gas temperature, in °C;
ch
θ is the installation room (combustion air) temperature (see Table A.7), in °C;
brm
X is the flue gas oxygen contents, in Vol%.
O2
The constants c and c are given in Table A.9.
10 11
The measured value shall be corrected to reference conditions according to water temperature
using the formula:
ff=− θθ− ⋅ f (4)
()
ch,onch,on,meas gen,refgen,meas corr,ch,on
where
f is the measured losses through the chimney with burner on;
ch,on,meas
θ is the reference average water temperature in the boiler at test conditions (average
gen,ref
of flow and return temperature, usually flow temperature 80 °C, return temperature
60 °C);
θ is the average water temperature in the boiler during measurement of f ;
gen,meas ch,on,meas
f is the correction factor for f . Default values for f = 0,045 [%/°C].
corr,ch,on ch,on corr,ch,on
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ISO 13675:2013(E)
5.2.1.2 Thermal losses through the generator envelope, f
gen,env
Actual specific thermal losses through the generator envelope, f , are given by measurement in site:
gen,env
()A ⋅⋅αθΔ
pa pa
∑
f = (5)
gen,env
1000⋅P
gen,del
where
2
A is the partial area of the envelop of the boiler, in m ;
pa
α is the heat transfer coefficient, normally α = 10 [for a more exact calculation see Fig-
2
ure A.1], in W/(m K);
Δθ is the average temperature difference of
...
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