prEN 12831-1
(Main)Energy performance of buildings - Method for calculation of the design heat load - Part 1: Space heating load, Module M3-3
Energy performance of buildings - Method for calculation of the design heat load - Part 1: Space heating load, Module M3-3
This European Standard covers methods for the calculation of the design heat load for single rooms, building entities and buildings, where the design heat load is defined as the heat supply (power) needed to maintain the required internal design temperature under design external conditions.
Table 1 shows the relative position of this standard within the set of EPB standards in the context of the modular structure as set out in EN ISO 52000 -1.
NOTE 1 In CEN ISO/TR 52000 2 the same table can be found, with, for each module, the numbers of the relevant EPB standards and accompanying technical reports that are published or in preparation.
NOTE 2 The modules represent EPB standards, although one EPB standard may cover more than one module and one module may be covered by more than one EPB standard, for instance a simplified and a detailed method respectively. See also Clause 2 and Tables A.1 and B.1.
(...)
Energetische Bewertung von Gebäuden - Verfahren zur Berechnung der Norm-Heizlast - Teil 1: Raumheizlast, Modul M3-3
Performance énergétique des bâtiments - Méthode de calcul de la charge thermique nominale - Partie 1 : Charge de chauffage des locaux, module M3-3
Energijske lastnosti stavb - Metoda za izračun projektnih toplotnih obremenitev - 1. del: Toplotne obremenitve prostora - Modul M3-3
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2025
Energijske lastnosti stavb - Metoda za izračun projektnih toplotnih obremenitev -
1. del: Toplotne obremenitve prostora - Modul M3-3
Energy performance of buildings - Method for calculation of the design heat load - Part 1:
Space heating load, Module M3-3
Energetische Bewertung von Gebäuden - Verfahren zur Berechnung der Norm-Heizlast -
Teil 1: Raumheizlast, Modul M3-3
Performance énergétique des bâtiments - Méthode de calcul de la charge thermique
nominale - Partie 1 : Charge de chauffage des locaux, module M3-3
Ta slovenski standard je istoveten z: prEN 12831-1
ICS:
91.120.10 Toplotna izolacija stavb Thermal insulation of
buildings
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2025
ICS 91.140.10 Will supersede EN 12831-1:2017
English Version
Energy performance of buildings - Method for calculation
of the design heat load - Part 1: Space heating load, Module
M3-3
Performance énergétique des bâtiments - Méthode de Energetische Bewertung von Gebäuden - Verfahren zur
calcul de la charge thermique nominale - Partie 1 : Berechnung der Norm-Heizlast - Teil 1: Raumheizlast,
Charge de chauffage des locaux, module M3-3 Modul M3-3
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 228.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12831-1:2025 E
worldwide for CEN national Members.
Contents Page
European foreword . 5
Introduction . 6
1 Scope . 8
2 Normative references . 12
3 Terms and definitions . 12
4 Symbols and abbreviations . 16
4.1 Symbols . 16
4.2 Subscripts . 17
5 Description of the methods . 19
6 Standard method – Heat load of rooms, building entities and buildings . 20
6.1 Output data . 20
6.2 Input data . 21
6.3 Calculation procedure . 28
6.3.1 Design heat load . 28
6.3.2 Design transmission heat losses of a heated space (i) . 29
6.3.3 Design ventilation heat loss . 33
6.3.4 Additional heating-up power in intermittently heated spaces . 42
6.3.5 Time constant . 43
6.3.6 Heat transfer coefficients without temperature adjustment . 44
6.3.7 External design temperature (climatic data) . 45
6.3.8 Influence of the heat emission system in high rooms (ceiling height ≥ 4 m) . 47
7 Simplified method for the calculation of the design heat load of a heated space (single
rooms) . 49
7.1 Output data . 49
7.2 Input data . 49
7.3 Calculation procedure . 50
7.3.1 Design heat load of a heated space . 50
7.3.2 Design transmission heat loss of a heated space . 51
7.3.3 Design ventilation heat loss of a heated space . 51
8 Simplified method for the calculation of the building design heat load . 52
8.1 Output data . 52
8.2 Input data . 52
8.3 Calculation procedure . 53
8.3.1 Building design heat load . 53
8.3.2 Building design transmission heat loss . 53
8.3.3 Design ventilation heat loss of a building . 54
9 Compliance check . 54
9.1 General . 54
9.2 Dimensioning of heat emission systems . 55
9.3 Dimensioning of heat generators . 55
Annex A (normative) Input data, structure for default values . 56
A.1 General . 56
A.2 Input data for the standard method (6) . 56
A.2.1 Consideration of thermal bridges . 56
A.2.2 Correction of U-values for the influence of building element properties and
meteorological conditions . 56
A.2.3 Heat loss through the ground . 56
A.2.4 Temperature adjustment for heat loss to by-design unheated spaces . 57
A.2.5 Internal temperatures of adjacent building entities . 57
A.2.6 Influence of the heat emission system in high rooms . 57
A.2.7 Volume-specific thermal storage capacity c . 58
eff
A.2.8 Specific properties of air. 58
A.2.9 Volume flow ratio between room (i) and zone (z) . 58
A.2.10 Air tightness . 58
A.2.11 Minimum air change rate . 59
A.2.12 Coefficient for the volume flow ratio f . 59
qv,z
A.2.13 Estimation of design data of external ATDs . 60
A.2.14 Pressure exponent for leakages . 60
A.2.15 Adjustment factor for the orientation of the zone (orientation factor) . 60
A.2.16 Adjustment factor for the number of exposed facades . 60
A.2.17 Air volume flow through large openings . 60
A.2.18 Additional heating-up power in intermittently heated spaces φ . 61
hu
A.2.19 Heat gains Φ . 61
gain
A.3 Input data for the simplified methods (7, 8) . 61
A.3.1 Ratio between external and internal surface areas . 61
A.3.2 Thermal bridges . 61
A.3.3 Temperature adjustment factor f . 61
x
A.3.4 Air change rate . 62
A.4 Input data for the standard method and the simplified methods . 62
A.4.1 Climatic data . 62
A.4.2 Internal design temperature . 64
A.4.3 Simplified determination of U-Values . 64
Annex B (informative) Input data, default values . 65
B.1 General . 65
B.2 Input data for the standard method (6) . 65
B.2.1 Consideration of thermal bridges . 65
B.2.2 Correction of U-values for the influence of building element properties and
meteorological conditions . 65
B.2.3 Heat loss through the ground . 65
B.2.4 Temperature adjustment for heat loss to by-design unheated spaces . 66
B.2.5 Internal temperatures of adjacent building entities . 66
B.2.6 Influence of the heat emission system in high rooms . 66
B.2.7 Volume-specific thermal storage capacity c . 67
eff
B.2.8 Specific properties of air . 68
B.2.9 Volume flow ratio between room (i) and zone (z) . 68
B.2.10 Air tightness . 68
B.2.11 Minimum air change rate . 68
B.2.12 Coefficient for the volume flow ratio f . 69
qv,z
B.2.13 Estimation of design data of external ATDs . 69
B.2.14 Pressure exponent for leakages . 70
B.2.15 Adjustment factor for the orientation of the zone (orientation factor). 70
B.2.16 Adjustment factor for the number of exposed facades . 70
B.2.17 Air volume flow through large openings . 70
B.2.18 Additional heating-up power in intermittently heated spaces φhu . 70
B.2.19 Heat gains Φgain . 70
B.3 Input data for the simplified methods (7, 8) . 70
B.3.1 Ratio between external and internal surface areas . 70
B.3.2 Thermal bridges . 71
B.3.3 Temperature adjustement factor f . 71
x
B.3.4 Air change rate . 71
B.4 Input data for the standard method and the simplified methods. 72
B.4.1 Climatic data . 72
B.4.2 Internal design temperature . 72
B.4.3 Simplified determination of U-Values . 73
Annex C (informative) Detailed consideration of thermal bridges . 76
Annex D (informative) Internal temperatures θ of adjacent building entities or adjacent by-
u
design unheated spaces within the same building . 77
Annex E (informative) Equivalent thermal transmittance of building elements against ground 80
Annex F (informative) Estimation of heating-up power in intermittently heated spaces (6.3.4) 83
F.1 General . 83
F.2 Determination of the specific heating-up power φ based on the time of disuse . 85
hu,i
F.3 Determination of the specific heating-up power φ based on the internal temperature
hu,i
drop during setback . 86
Annex G (informative) External air volume flow through large openings. 87
Bibliography . 92
European foreword
This document (prEN 12831-1:2025) has been prepared by Technical Committee CEN/TC 228 “Heating
systems and water based cooling systems in buildings”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 12831:2017.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
EN 12831, Energy performance of buildings — Method for the calculation of the design heat load, is composed
with the following parts:
— Part 1: Space heating load, Module M3-3;
— Part 2: Explanation and justification of EN 12831-1, Module M3-3 [CEN/TR];
— Part 3: Domestic hot water systems heat load and characterization of needs, Module M8-2, M8-3;
— Part 4: Explanation and justification of EN 12831-3, Module M8-2, M8-3 [CEN/TR].
Introduction
This document is part of a series of standards aiming at international harmonization of the methodology for
the assessment of the energy performance of buildings, called “set of EPB standards”.
All EPB standards follow specific rules to ensure overall consistency, unambiguity and transparency.
All EPB standards provide a certain flexibility with regard to the methods, the required input data and
references to other EPB standards, by the introduction of a normative template in Annex A and Annex B with
informative default choices.
For the correct use of this standard a normative template is given in Annex A to specify these choices.
Informative default choices are provided in Annex B.
The EPB set of standards deals with energy performance calculation and other related aspects (like system
sizing) to provide the building services considered in the EPBD.
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.
Use by or for regulators: In case the standard is used in the context of national or regional legal requirements,
mandatory choices may be given at national or regional level for such specific applications. These choices
(either the informative default choices from Annex B or choices adapted to national / regional needs, but in
any case following the template of this Annex A) can be made available as national annex or as separate (e.g.
legal) document (national data sheet).
NOTE So in this case:
— the regulators will specify the choices;
— the individual user will apply the standard to assess the energy performance of a building, and thereby use
the choices made by the regulators.
Topics addressed in this standard can be subject to public regulation. Public regulation on the same topics
can override the default values in Annex B of this standard. Public regulation on the same topics can even,
for certain applications, override the use of this standard. Legal requirements and choices are in general not
published in standards but in legal documents. To avoid double publications and difficult updating of double
documents, a national annex may refer to the legal texts where national choices have been made by public
authorities. Different national annexes or national data sheets are possible, for different applications.
It is expected, if the default values, choices and references to other EPB standards in Annex B are not
followed due to national regulations, policy or traditions, that:
— national or regional authorities prepare data sheets containing the choices and national or regional
values, according to the model in Annex A. In this case the national annex (e.g. NA) refers to this text;
— or, by default, the national standards body will consider the possibility to add or include a national annex
in agreement with the template of Annex A, in accordance with the legal documents that give national
or regional values and choices.
Further target groups are parties wanting to motivate their assumptions by classifying the building energy
performance for a dedicated building stock.
More information is provided in the Technical Report accompanying this standard (CEN/TR 12831-2).
1 Scope
This document covers methods for the calculation of the design heat load for single rooms, building entities
and buildings, where the design heat load is defined as the heat supply (power) needed to maintain the
required internal design temperature under design external conditions.
Table 1 shows the relative position of this document within the set of EPB standards in the context of the
modular structure as set out in EN ISO 52000-1.
NOTE In CEN ISO/TR 52000-2 the same table can be found, with, for each module, the numbers of the relevant
EPB standards and accompanying technical reports that are published or in preparation.
The modules represent EPB standards, although one EPB standard may cover more than one module and
one module may be covered by more than one EPB standard, for instance a simplified and a detailed method
respectively. See also Clause 2 and Tables A.1 and B.1.
Table 1 — Position of this standard, within the modular structure of the set of EPB standards
Building
Overarching Technical Building Systems
(as such)
Building
Humidifi Dehumid Domestic Electricity
Sub module Descriptions Descriptions Descriptions Heating Cooling Ventilation Lighting automation
cation ification Hot water production
and control
sub1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
15316–
1 General General General 15316–1
Common
terms and
Building
2 definitions; Needs 12831–3
Energy Needs
symbols, units
and subscripts
(Free) Indoor
Maximum
Conditions 12831–
3 Applications Load and 12831–3
without 1
Power
Systems
Ways to Ways to Ways to
Express Express Express 15316–
4 15316–1
Energy Energy Energy 1
Performance Performance Performance
Building
Heat Transfer
categories and Emission and 15316–
5 by 15316–2
Building control 2
Transmission
Boundaries
Building Heat Transfer
Occupancy by Infiltration Distribution 15316–
6 15316–3 15316–3
and Operating and and control 3
Conditions Ventilation
Building
Overarching Technical Building Systems
(as such)
Building
Humidifi Dehumid Domestic Electricity
Sub module Descriptions Descriptions Descriptions Heating Cooling Ventilation Lighting automation
cation ification Hot water production
and control
sub1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
Aggregation of
Energy 15316–5
Internal Storage and 15316–
7 Services and 15316–4–
Heat Gains control 5
Energy 3
Carriers
Building Solar
8 Generation
zoning Heat Gains
Combustion 15316– 15316–4–
8–1
boilers 4–1 1
15316– 15316– 15316–4–
8–2 Heat pumps
4–2 4–2 2
Thermal solar
15316– 15316–4–
8–3 15316–4–3
4–3 3
Photovoltaics
On-site 15316– 15316–4–
8–4 15316–4–4
cogeneration 4–4 4
District
15316– 15316–
8–5 heating and 15316–4–5
4–5 4–5
cooling
Direct
15316– 15316–4–
8–6 electrical
4–8 8
heater
8–7 Wind turbines 15316–4–10
Radiant 15316–
8–8
heating, stoves 4–8
Building
Overarching Technical Building Systems
(as such)
Building
Humidifi Dehumid Domestic Electricity
Sub module Descriptions Descriptions Descriptions Heating Cooling Ventilation Lighting automation
cation ification Hot water production
and control
sub1 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
Building Load
Calculated
Dynamics dispatching
9 Energy
(thermal and operating
Performance
mass) conditions
Measured Measured Measured
15378–
10 Energy Energy Energy 15378–3
Performance Performance Performance
15378–
11 Inspection Inspection Inspection 15378–1
Ways to
Express
12 – BMS
Indoor
Comfort
External
13 Environment
Conditions
Economic
14 15459–1
Calculation
NOTE The shaded modules are not applicable.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 6946, Building components and building elements - Thermal resistance and thermal transmittance
- Calculation methods (ISO 6946)
EN ISO 7345, Thermal performance of buildings and building components - Physical quantities and
definitions (ISO 7345)
EN ISO 9972, Thermal performance of buildings - Determination of air permeability of buildings - Fan
pressurization method (ISO 9972)
EN ISO 10077-1, Thermal performance of windows, doors and shutters - Calculation of thermal
transmittance - Part 1: General (ISO 10077-1)
EN ISO 13370, Thermal performance of buildings - Heat transfer via the ground - Calculation methods (ISO
13370)
EN ISO 13789, Thermal performance of buildings - Transmission and ventilation heat transfer coefficients
- Calculation method (ISO 13789)
EN ISO 52000-1, Energy performance of buildings - Overarching EPB assessment - Part 1: General
framework and procedures (ISO 52000-1)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN ISO 7345 and EN ISO 52000-1,
and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org
3.1
air terminal device
ATD
air out-/inlets allowing air transfer between external and internal air (external ATD) or between
separate rooms (internal ATD)
Note 1 to entry: In the field, the term ATD is used for a broad variety of air out- and inlets. Within this standard,
the term refers only to passive devices allowing air flow through a building element (walls, etc.) in a defined
manner. It does not include air out-/inlets of fan-assisted ventilation system.
Note 2 to entry: Within this standard, it is assumed that external ATDs are only applied in unbalanced ventilation.
Note 3 to entry: Within this standard, the term/index only refers for external ATDs.
3.2
annual mean external temperature
mean value of the external temperature during the year
3.3
balanced ventilation
fan-assisted ventilation where the sum of all supply air volume flows equals the sum of all exhausted air
volume flows in quantity and over the course of time
3.4
building element
internal or external component of the building structure and/or thermal envelope or a portion thereof
where the thermal conditions on each side of the element can differ from each other, but are uniform
over the whole surface of each side
EXAMPLE Wall between two rooms of the same or different temperatures.
3.5
building entity
certain portion of a building (one or more rooms) used as one unit by one party/occupant, such as:
— one apartment / flat;
— one office unit…
where the heat supply to that unit can be controlled individually by the occupant (usually by means of
room temperature control devices)
Note 1 to entry: For the definition of building entities within application of this standard, it is not relevant if the
heat supplied to building entities is generated centralized per building or separately in each building entity.
3.6
design heat load
heat flow (power) required to achieve/maintain the specified internal design temperature under
external design conditions
Note 1 to entry: The design heat load covers transmission and ventilation heat losses and, if any, an additional
heating-up power.
3.7
design heat loss
heat loss (power) leaving the building, building entity or room to the external environment under
specified standard and design conditions
3.8
design transmission heat loss
heat loss under specified standard conditions to the exterior and between heated and other heated or
unheated spaces inside a building as a result of thermal conduction through the surrounding surfaces
Note 1 to entry: The design transmission heat loss is a portion of the design heat loss.
3.9
design ventilation heat loss
heat loss under specified standard conditions to the exterior by ventilation and infiltration through the
building envelope and the heat transferred by ventilation from one heated space to another heated or
unheated space
Note 1 to entry: The design ventilation heat loss is a portion of the design heat loss.
3.10
external design temperature
(minimal) external air temperature which is used for the calculation of the design heat losses
3.11
heated space
space which, per design, is heated to the specified internal design temperature and separated from other
spaces and/or the exterior by building elements such as walls, etc
Note 1 to entry: Usually each single (heated) room is considered a separate heated space.
3.12
internal air temperature
temperature of the air inside the considered heated space
3.13
internal design temperature
temperature-value required for the intended use of a heated space and that is used to calculate the
design heat loss
Note 1 to entry: The internal design temperature is an operative temperature and, therefore, depends, among
other parameters, on the air temperature and the radiant temperature – usually defined in a simplified manner as
arithmetic average between both.
Note 2 to entry: Default values for the internal design temperature are subject to national regulations.
3.14
large openings
openings of the enveloping surface of a room/building that are kept open for significant periods over
the day on a regular basis; usually, but not necessarily, (large) doors or gates
EXAMPLE Gates in logistics and industrial halls.
3.15
mean internal air temperature
mean air temperature of a heated space
Note 1 to entry: With low room heights (h < 4 m), the mean internal air temperature can be assumed to equal the
internal design temperature; with larger room heights, the mean internal air temperature is calculated based on
the internal design temperature, specifically for the heating system to be used.
3.16
mean internal surface temperature
mean temperature of a building element’s inner surface
Note 1 to entry: With low room heights (h < 4 m), the mean internal surface temperature can be assumed to equal
the internal design temperature; with larger room heights, the mean internal surface temperature is calculated
based on the internal design temperature, specifically for the heating system to be used.
3.17
minimum air change rate
number of air changes (exchange of room air) per hour that needs to be ensured in order to maintain an
appropriate level of air hygiene (reduction of air pollutants, CO , moisture, etc.), which depends on type
of the room (use); subject to national regulation
3.18
regularly unheated space
space that, by design, is unheated; e.g. unheated attic, unheated corridor, unheated winter garden, etc
Note 1 to entry: Within this standard, adjacent building entities (neighbouring apartment, etc.) are, for
calculational purposes, assumed to be unheated – these, however, do not belong to regularly unheated spaces.
3.19
unbalanced ventilation
fan-assisted ventilation where the sums of all supply air volume flows and all exhausted air volume flows
differ significantly in quantity or over the course of time
3.20
ventilation
entirety of all processes transporting air, including fan-assisted ventilation by ventilation systems,
natural ventilation (“airing”), infiltration through leakages, etc
3.21
zone (ventilation zone)
group of rooms that are air-connected by design, either directly or indirectly (through other rooms there
between); e.g. through internally mounted air transfer devices / shortened door leafs, etc
Note 1 to entry: By design, there is no air transfer between ventilation zones. Usually, each building entity is
considered a separate zone.
4 Symbols and abbreviations
4.1 Symbols
For the purposes of this document, the symbols given in EN ISO 52000-1 and the specific symbols listed
in Table 2 apply.
Table 2 — Symbols and units
Symbol Name Unit
Φ Heat power (heat loss, heat load) W
H Heat transfer coefficient W/K
θ Temperature on the Celsius scale °C
U Thermal transmittance, U-value W/(m ∙K)
f Adjustment/correction factor or term -
Δ… Delta/difference -
A Area m
a, b, c Calculation parameters -
B’ Geometric parameter of the floor slab m
z Depth of the floor slab below ground level m
P Exposed periphery of the floor slab m
n Calculation parameters (exponent) -
1…3
−1
n Air change rate 1/h, h
ρ Density (of air) kg/m
c Specific heat capacity of air (constant pressure) Wh/(kg∙K)
p
q Air volume flow m /h
(v)
3 2
q Specific air permeability of the building envelope m /(m ∙h)
V Volume m
v Pressure exponent for leakages -
a ATD authority -
(ATD…)
ϕ Specific heat power W/m
τ Building time constant h
t time, timespan h
C Thermal storage capacity Wh/K
c Volume-specific thermal storage capacity Wh/(m ∙K)
G Temperature gradient over height K/m
k Calculation parameter (factor) -
h Height
Symbol Name Unit
λ Thermal conductivity
R Heat transmission resistance m K/W
l Length (of a linear thermal bridge) m
T Thermodynamic temperature on the Kelvin scale K
v Wind velocity m/s
η efficiency -
Ψ Thermal transmittance of a linear thermal bridge W/(m∙K)
4.2 Subscripts
For the purposes of this document, the subscripts given in EN ISO 52000-1, any TC LEVEL GENERAL
DEFINITIONS STANDARD and the specific subscripts listed in Table 3 apply.
Table 3 — Indices
Index Meaning/Use
50 Referring to a pressure difference of 50 Pa
air Air
ann Annual
ATD Air transfer device; refers to externally mounted air transfer devices unless
otherwise specified
BE a
Numbering index for building entities
bottom Referring to the underneath of the building or a portion hereof
build Building
bw basement wall
comb Combustion
D Discharge (coefficient)
design Referring to a design condition or technical property
dir Direction, orientation
du Disuse
e, ext External air, exterior; usually refers to an external design condition
e,m (Annual) mean external
eff Effective
env Envelope
equiv Equivalent (U-value)
exh Exhaust
fac Facade; vertical external walls
Index Meaning/Use
floor Floor
g Ground, referring to ground level
gain Heat gains
GW Groundwater
HL Heat load
hu Heating-up
i, j a
Numbering indices for heated spaces; where (i) is normally used for heated spaces
in consideration and (j) for other heated space interrelating to (i), such as a
neighbouring room, etc.
ia From the considered space (i) to an adjacent (heated) space (a)
iaBE From the considered space (i) to an adjacent Building entity (aBE)
iae From the considered space (i) to the exterior through an adjacent unheated space
(ae)
ie From the considered space (i) to the exterior (e)
ig From the considered space (i) to the ground (g)
inf Infiltration
inf-add Additional infiltration
inner Inner/internal, Referring to internal dimensions
int Internal; often refers to an internal design condition
ix From the considered space (i) to another space; x being a placeholder for e, a, g, etc.
ju From a space (j) to a space (u) that is looked upon as being unheated, although,
design-wise, (u) may be heated or containing heated spaces
k a
Numbering index for building elements (walls, windows, ceilings, etc.)
l a
Numbering index for linear thermal bridges
leak Leakage(s)
m a
Numbering index for punctiform thermal bridges
max Maximum, upper limit
measure Measured or obtained on the basis of a measurement
min Minimum, lower limit
occup Occupied; referring to the occupied zone as the height level that internal design
conditions shall be achieved for
open Openings (e.g. open gates)
p Constant pressure
rad Radiant
rec Heat recovery
Index Meaning/Use
Ref Reference site
sb Setback
shield Shielding
si, se Internal and external heat transmission (e.g.: internal air to building element,
building element to external air)
small_open Small openings
sup Supply air
surf Surface
T (Heat) Transmission
TB Thermal bridge
techn Technical, technically required or caused
th Thermally induced
transfer Referring to air volume flows between rooms
u Referring to a space (u) that is looked upon as being unheated although, design-wise,
(u) may be a heated space or an entity containing heated spaces
U Referring to a quality or condition regarding the thermal transmittance (U-value)
ue From a space (u) that is looked upon as being unheated to the exterior (e)
v Volume or volume flow
V Ventilation
w Wind-induced
z Numbering index for (ventilation) zones
a
Note that, within this standard, the ranges of numbering indices (k, i, j, etc.) are not defined explicitly (e.g.
n
x with n = …). They shall be defined depending on context, e.g.:
∑ i
i =1
— All building elements (k) that are walls to the exterior;
— all building elements (k) that belong to the room (i);
— all rooms (i) tha
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