ISO 13790:2004
(Main)Thermal performance of buildings — Calculation of energy use for space heating
Thermal performance of buildings — Calculation of energy use for space heating
ISO 13790:2004 gives a simplified calculation method for assessment of the annual energy use for space heating of a residential or a non-residential building, or a part of it, which will be referred to as "the building". It does not apply to buildings with air conditioning systems likely to provide space cooling during the heating season. This method includes the calculation of: the heat losses of the building when heated to constant internal temperature; the annual heat required to maintain the specified set-point temperatures in the building; the annual energy required by the heating system of the building for space heating, using heating system characteristics which are to be found in specific European or International standards, or, by default, in national documents.
Performance thermique des bâtiments — Calcul des besoins d'énergie pour le chauffage des locaux
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 13790
First edition
2004-06-15
Thermal performance of buildings —
Calculation of energy use for space
heating
Performance thermique des bâtiments — Calcul des besoins d'énergie
pour le chauffage des locaux
Reference number
ISO 13790:2004(E)
©
ISO 2004
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ISO 13790:2004(E)
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ISO 13790:2004(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 committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 13790 was prepared by the European Committee for Standardization (CEN) in collaboration with
Technical Committee ISO/TC 163, Thermal performance and energy use in the built environment,
Subcommittee SC 2, Calculation methods, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
Throughout the text of this document, read “.this European Standard.” to mean “.this International
Standard.”.
For the purposes of this International Standard, the CEN annex giving a list of EN documents corresponding
to the ISO documents mentioned as normative references has been removed.
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ISO 13790:2004(E)
Contents Page
Foreword.v
Introduction .vi
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Symbols and abbreviations.6
5 Outline of the calculation procedure and required data.8
6 Intermittent heating .12
7 Heat loss (single zone calculation).13
8 Heat gains.16
9 Heat use.18
10 Annual heat use of the building.21
11 Energy for space heating .21
12 Report.22
Annex A (normative) Application to existing buildings .24
Annex B (normative) Multi-zone calculation method .25
Annex C (normative) Intermittent heating – Calculation of adjusted internal temperature.26
Annex D (normative) Calculation with holiday period.34
Annex E (normative) Heat loss of special envelope elements .35
Annex F (normative) Solar gains of special elements.39
Annex G (informative) Ventilation airflow rates .46
Annex H (informative) Data for solar gains.50
Annex I (informative) Calculation of heat use for each heating mode.54
Annex J (informative) Accuracy of the method.56
Annex K (informative) Conventional input data .57
Bibliography .59
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ISO 13790:2004(E)
Foreword
This document EN ISO 13790:2004 has been prepared by Technical Committee CEN/TC 89 "Thermal
performance of buildings and building components”, the secretariat of which is held by SIS, in collaboration with
Technical Committee ISO/TC 163, “Thermal performance and energy use in the built environment”, sub-
committee 2, “Calculation methods”.
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 December 2004, and conflicting national standards shall be withdrawn at the latest
by December 2004.
Annexes A to F are normative. Annexes G to K are informative.
This document includes a Bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard : : Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom
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ISO 13790:2004(E)
Introduction
This standard is one of a series of calculation methods for the design and evaluation of thermal performance of
buildings and building components.
The calculation method presented in this standard is based on an energy balance taking account of internal and
external temperature variations and, through a utilisation factor, of the dynamic effect of internal and solar gains.
This method can be used for the following applications:
1) judging compliance with regulations expressed in terms of energy targets;
2) comparing the energy performance of various design alternatives for a planned building;
3) displaying a conventional level of energy performance of existing buildings;
4) assessing the effect of possible energy conservation measures on an existing building, by calculation of the
energy use with and without the energy conservation measure;
5) predicting future energy resource needs on a national or international scale, by calculating the energy uses of
several buildings representative of the building stock.
Reference can be made to other International Standards or to national documents for input data and detailed
calculation procedures not provided by this standard. In particular, this applies to the calculation of the efficiency or
the heat loss of the heating systems.
Unlike EN 832, whose scope is restricted to residential buildings, this standard can be applied to both residential
and non-residential buildings. The most important changes in EN ISO 13790 compared to EN 832:1998, “Thermal
performance of buildings - Calculation of energy use for heating - Residential buildings”, are:
1. Ventilation rates are calculated according to standards prepared by CEN/TC 156;
2. Clause 11 has been made simpler, and energy use is calculated from heat use according to existing
International Standards or, by default, to national documents;
3. A normative method has been included to calculate the effect of intermittence.
4. New input data have been included for non-residential buildings, in particular for utilisation factors.
For all these reasons, calculation using EN ISO 13790 gives results that may slightly differ from those obtained with
EN 832.
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ISO 13790:2004(E)
1 Scope
This standard gives a simplified calculation method for assessment of the annual energy use for space heating of a
residential or a non-residential building, or a part of it, which will be referred to as "the building".
It does not apply to buildings with air conditioning systems likely to provide space cooling during the heating
season.
This method includes the calculation of:
1. the heat losses of the building when heated to constant internal temperature;
2. the annual heat required to maintain the specified set-point temperatures in the building;
3. the annual energy required by the heating system of the building for space heating, using heating system
characteristics which are to be found in specific European or International Standards, or, by default, in
national documents.
The building can have several zones with different set-point temperatures, and can have intermittent heating.
The calculation period is the month. For residential buildings the calculation can also be performed for the heating
season. Monthly calculation gives correct results on an annual basis, but the results for individual months close to
the beginning and the end of the heating season can have large relative errors. Annex J provides some information
on the accuracy of the method.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN ISO 7345:1995, Thermal insulation – Physical quantities and definitions (ISO 7345:1987).
EN ISO 13370:1998, Thermal performance of buildings – Heat transfer via the ground – Calculation methods
(ISO 13370:1998).
EN ISO 13789, Thermal performance of buildings – Transmission heat loss coefficient – Calculation method
(ISO 13789:1999).
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ISO 13790:2004(E)
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN ISO 7345:1995 and the
following apply.
3.1
calculation period
time period for the calculation of heat losses and gains
NOTE The calculation period is the month. For residential buildings the calculation can also be performed for the heating season.
3.2
external temperature
temperature of external air
NOTE For transmission heat loss calculations, the radiant temperature of the external environment is supposed equal to the external air
temperature; long-wave transmission to the sky is considered in F.5.
3.3
internal temperature
arithmetic average of the air temperature and the mean radiant temperature at the centre of the occupied zone
NOTE This is the approximate operative temperature according to ISO 7726, Ergonomics of the thermal environment - Instruments for
measuring physical quantities.
3.4
set-point temperature
internal temperature, as fixed by the control system in normal heating mode
3.5
set-back temperature
minimum internal temperature to be maintained during reduced heating periods
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ISO 13790:2004(E)
3.6
adjusted internal temperature
constant virtual internal temperature leading to the same heat loss as intermittent heating
3.7
heated space
room or enclosure heated to a given set-point temperature
3.8
unheated space
room or enclosure which is not part of the heated space
3.9
heat use
heat to be delivered to the heated space by an ideal heating system to maintain the set-point temperature during a
given period of time
NOTE The heat use can include additional building heat loss resulting from non-uniform temperature distribution and non-ideal temperature
control, if they are taken into account by increasing the set-point temperature and not included in the heat loss due to the heating system.
3.10
energy use for space heating
thermal energy to be delivered to the heating system to satisfy the heat use
3.11
intermittent heating
heating pattern where normal heating periods alternate with reduced heating periods
3.12
modes of intermittence
during intermittent heating, the heating system is operated according to either of the following modes:
3.12.1 normal mode: the heating system functions to maintain the internal temperature at the value it would have
with continuous heating;
3.12.2 cut-off mode: the heating system does not provide heat;
3.12.3 reduced heating power mode: the heating system provides a heat flow rate lower than in normal heating;
3.12.4 set-back mode: heat flow rate is controlled to maintain a set-back temperature;
3.12.5 boost mode: the heating system runs at full power in order to reach the set-point temperature at or before
the end of the reduced heating period
NOTE Depending on the control system, the boost mode can start according to two different strategies:
a) fixed time boost: the start of the boost mode is fixed by the user;
b) optimised boost: the time when the set-point internal temperature is recovered is fixed by the user, and the control system
optimises the start of the boost mode, taking account of the external and internal temperatures.
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ISO 13790:2004(E)
3.13
heated zone
part of the heated space with a given set-point temperature, throughout which the internal temperature is assumed
to have negligible spatial variations
3.14
heat transfer coefficient
heat flow rate between two zones divided by the temperature difference between both zones
3.15
heat loss coefficient
heat transfer coefficient from the heated space to the external environment
NOTE The heat loss coefficient of the building cannot be used when the multi-zone calculation method according to annex B is applied
3.16
building heat loss
heat transferred from heated space to the external environment by transmission and by ventilation, during a given
period of time
3.17
ventilation heat loss
heat lost with the air leaving the heated space either by exfiltration or ventilation
3.18
transmission heat loss
heat loss by transmission through the building envelope and through the ground
3.19
heat gains
heat generated within or entering into the heated space from heat sources other than the space and hot water
heating systems
NOTE These include internal heat gains and solar gains.
3.20
internal heat gains
heat provided within the building by occupants (sensible metabolic heat) and by appliances other than the space
and hot water heating systems (lighting, domestic appliances, office equipment, etc.)
3.21
solar gains
heat provided by solar radiation entering into the building through windows or passive solar devices such as
sunspaces, transparent insulation and solar walls
NOTE Active solar devices such as solar collectors are considered as part of the heating system.
3.22
solar irradiation
incident solar heat per area over a given period
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ISO 13790:2004(E)
3.23
utilisation factor
factor reducing the total monthly or seasonal heat gains to obtain the resulting reduction of the heat use
3.24
recovered heat
heat recovered from the environment or from heating and hot water systems (including auxiliary equipment), if not
directly taken into account in a reduction of the heating system losses
3.25
ventilation heat recovery
heat recovered from the exhaust air
3.26
heating system losses
total of the heat lost by the heating system, including recovered system heat loss
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ISO 13790:2004(E)
4 Symbols and abbreviations
Table 1 — Symbols and units
Symbol Quantity Unit
A area m²
a
numerical parameter in utilisation factor -
b correction factor for unheated zones -
C
effective heat capacity of a heated space J/K
c specific heat capacity J/(kg·K)
d
layer thickness m
F factor -
g
total solar energy transmittance of a building element -
I solar irradiance J/m²
H
heat transfer coefficient, heat loss coefficient W/K
h surface coefficient of heat transfer W/(m²·K)
L
length m
N number
Q
quantity of heat or energy J
R thermal resistance m²·K/W
T
thermodynamic temperature K
t time, period of time s
U
thermal transmittance W/(m²·K)
V volume of air in a heated zone m³
V airflow rate m³/s
Fheat flow rate, heating power W
heat loss parameter for solar walls W/(m²·K)Z
absorption coefficient of a surface for solar radiation -a
gain/loss ratio -g
ratio of the accumulated internal-external temperature difference when the -d
ventilation is on to its value over the calculation period
emissivity of a surface for thermal radiation -e
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ISO 13790:2004(E)
Symbol Quantity Unit
efficiency, utilisation factor for the gains -h
factor related to heat losses of ventilated solar walls -k
Celsius temperature °Cq
density kg/m³r
4
8
-sW/(m²·K )
Stefan-Boltzmann constant (s = 5,67 · 10 )
time constant st
heat capacity per area J/(m²·K)c
ratio of the effects of a change in heating flow rate on the internal temperature -x
and on the structure temperature
effective part of the heat capacity -z
ratio of the total solar radiation falling on the element when the air layer is open -w
to the total solar radiation during the calculation period
NOTE Hours can be used as the unit of time instead of seconds for all quantities involving time (i.e. for time periods as well as for air change
rates), but in that case the unit of energy is Watt-hours [Wh] instead of Joules.
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ISO 13790:2004(E)
Table 2 — Subscripts
C capacity, calculation, f form, final r radiative, recovered,
convective reduced
F frame g gains s solar, sunspace
G ground h heating, heated, hemispherical sb set back
L loss hol holidays se surface external
P related to power hw hot water si surface internal
S shading i internal ss surface-sky average
T transmission ih intermittent heating sw solar wall
V ventilation i,j,k,m,n dummy integers t transparent insulation
a air l layer th heating system
ad adjusted m metabolic, month u unheated
ap appliances nh no heating v ventilation
bh boost heating o overall w window
c structure p partition wall y, z zone number
d design, daily, direct pp peak power perpendicular^
e exterior, envelope ps permanent shading 0 base, reference
5 Outline of the calculation procedure and required data
5.1 Energy balance
The energy balance includes the following terms (only sensible heat is considered):
5. transmission and ventilation heat loss from the heated space to the external environment;
6. transmission and ventilation heat transfer between adjacent zones;
7. internal heat gains;
8. solar gains;
9. generation, distribution, emission and control losses of the space heating system;
10. energy input to the space heating system.
It may also include recovered energy from various sources.
NOTE As heat gains may induce internal temperature to rise above the set-point, the resulting additional heat loss is taken into account
through a utilisation factor reducing heat gains.
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ISO 13790:2004(E)
The main terms of the energy balance are schematically illustrated in Figure 1.
4
Q
m
Q
s
Q
Vr
1 Q
g
hQ
g
Q
Q
i
V
Q
oa
Q
L
Q
h
Q
T
3
Q
Q
hw
Q
Q 2
hs
r
Key
Q Energy use for heating Q Heat use
h
Q Heat from other appliances Q Ventilation heat loss
oa V
Q Recovered energy Q Ventilation heat recovery
r Vr
Q Losses from the heating system Q Transmission heat loss
hs T
Q Metabolic heat Q Heat for hot water preparation
m hw
Q Passive solar gains Q Total heat loss
s L
Q Internal gains
1 Boundary of the heated zone
i
Q Total gains 2 Boundary of the hot water system
g
h Q Useful gains 3 Boundary of the heating plant
g
4 Boundary of the building
Figure 1 – Energy balance of a building
5.2 Calculation procedure
The calculation procedure is summarised below. In addition, the special approach given in annex A shall be
followed when applying this standard to existing buildings.
1) Define the boundaries of the heated space and, if appropriate, of different zones and unheated spaces,
according to 5.3.
2) In case of intermittent heating or intermittent ventilation define, within the calculation period, the periods having
different heating and ventilation patterns (e.g. day, night, weekend) according to clause 6.
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ISO 13790:2004(E)
3) For a single zone calculation, calculate the heat loss coefficient of the heated space according to clause 7; or
for a multi-zone calculation, follow the procedure in annex B.
4) For seasonal calculation, define or calculate the length and climatic data of the heating season, according
to 9.2.
Then, for each calculation period (month or heating season):
5) calculate the adjusted internal temperature for each period according to clause 6;
6) calculate the heat loss, Q , according to clause 7;
L
7) calculate the internal heat gains, Q , according to 8.1;
i
8) calculate the solar gains, Q , according to 8.2;
s
9) calculate the utilisation factor for heat gains, h, according to 9.2;
10) calculate the heat use, Q , for all calculation periods, according to clause 9;
h
11) calculate the annual heat use, Q , according to clause 10;
h
12) calculate the energy use for heating taking into account the losses of the heating system, according to
clause 11.
5.3 Definition of boundaries and zones
5.3.1 Boundary of the heated space
The boundary of the heated space consists of all the building elements separating the considered heated space
from external environment or from adjacent heated zones or unheated spaces.
5.3.2 Thermal zones
5.3.2.1 Single zone calculation
When the heated space is heated to the same temperature throughout, and when internal and solar gains are
relatively small or evenly distributed throughout the building, the single zone calculation applies.
The division in zones is not required when:
a) set-point temperatures of the zones never differ by more than 4 K, and it is expected that the gain/loss ratios
differ by less than 0,4 (e.g. between south and north zones), or
b) doors between zones are likely to be frequently open.
In such cases, even if the set-point temperature is not uniform, the single zone calculation applies. Then the
internal temperature to be used is:
Hq∑
z iz
z
q= (1)
i
H
∑ z
z
where
qis the set-point temperature of zone z;
iz
H is the heat loss coefficient, according to clause 6, but calculated separately for each zone z.
z
In this case, a unique intermittence pattern shall be chosen.
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ISO 13790:2004(E)
5.3.2.2 Multi-zone calculation
In other cases with significant differences in set-point temperatures or heat gains, the building is divided into
several zones.
If the purpose of the calculation is to assess heat use for each zone individually, then the calculation procedure
given in annex B shall be used.
Otherwise, each zone may be calculated independently using the single zone procedure and assuming adiabatic
boundaries between zones. The energy use for the building is the sum of the energy use calculated for the
individual zones.
5.4 Input data
5.4.1 Source and type of input data
When no International Standard is given as a reference, the necessary information may be obtained from national
standards or other suitable documents, and these should be used where available. The informative annexes give
values or methods to obtain values when the required information is otherwise not available.
For predicting the energy needs or judging compliance with regulations or specifications, conventional values shall
be used, in order to make the results comparable between different buildings.
For optimisation of a planned building or retrofitting an existing building, the best available estimate for that
particular building shall be used (see annex A). However, if no better estimates are available, conventional values
may be used as first approximations.
The physical dimensions of the building construction shall be consistent throughout the calculation. Internal,
external or overall internal dimensions can be used, but the same type shall be kept for the whole calculation and
the type of dimensions used shall be clearly indicated in the report.
NOTE 1 Some linear thermal transmittances of thermal bridges depend on the type of dimensions used.
The input data required for single zone calculation are listed below. Some of these data may be different for each
calculation period (e.g. shading correction factors, airflow rates in cold months) and for each period of an
intermittence pattern (e.g. air flow rate, thermal transmittance of windows due to closing of shutters during night
periods). Input data for heat loss are
H transmission heat loss coefficient according to EN ISO 13789.
T
NOTE 2 In contrast with EN ISO 13789, daily average values of the thermal transmittance of windows with shutters can be determined on the
basis of the values given by EN ISO 10077-1, Thermal performance of windows, doors and shutters - Calculation of thermal transmittance –
Part 1: Simplified method.
.
V air flow rate through the building, including airflows to and from unheated spaces.
5.4.2 Input data for heat gains
Faverage internal heat gains during the calculation period.
i
For glazed envelope elements, the following data shall be collected separately for each orientation (e.g. horizontal,
pitched, and vertical south and north):
A area of opening in the building envelope for each window
...
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