ISO 13675:2013

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 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

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
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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The committee responsible for this document is ISO/TC 205, Building environment design.
iv © ISO 2013 – All rights reserved

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.
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.
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
2 © ISO 2013 – All rights reserved

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 t
...