Building environment design - Embedded radiant heating and cooling systems - Part 2: Determination of the design heating and cooling capacity (ISO 11855-2:2021)

This document specifies procedures and conditions to enable the heat flux in water-based surface heating and cooling systems to be determined relative to the medium differential temperature for systems. The determination of thermal performance of water-based surface heating and cooling systems and their conformity to this document is carried out by calculation in accordance with design documents and a model. This enables a uniform assessment and calculation of water-based surface heating and cooling systems. The surface temperature and the temperature uniformity of the heated/cooled surface, nominal heat flux between water and space, the associated nominal medium differential temperature, and the field of characteristic curves for the relationship between heat flux and the determining variables are given as the result. This document includes a general method based on finite difference or finite element Methods and simplified calculation methods depending on position of pipes and type of building structure.

Umweltgerechte Gebäudeplanung - Flächenintegrierte Strahlheizungs- und -kühlsysteme - Teil 2: Bestimmung der Auslegungs-Heiz- bzw. Kühlleistung (ISO 11855-2:2021)

Dieses Dokument legt Verfahren und Bedingungen fest, welche die Bestimmung der Wärmestromdichte von Flächenheiz- und -kühlsystemen mit Wasserdurchströmung bezüglich der Heiz- und Kühlmittel-übertemperatur für diese Systeme ermöglichen. Die Bestimmung der Wärmeleistung von Flächenheiz- und -kühlsystemen mit Wasserdurchströmung und ihrer Übereinstimmung mit diesem Dokument wird durch Berechnung nach den Planungsdokumenten und einem Modell vorgenommen. Dies ermöglicht eine einheitliche Bewertung und Berechnung von Flächenheiz- und -kühlsystemen mit Wasserdurchströmung.
Das Ergebnis daraus sind die Oberflächentemperatur und Temperaturgleichmäßigkeit der beheizten bzw. gekühlten Oberfläche, die Nenn-Wärmestromdichte zwischen dem Wasser und dem Raum, die zugehörige Nenn-Heiz- bzw. -Kühlmittelübertemperatur und das Kennlinienfeld für die Beziehung zwischen Wärme-stromdichte und den entscheidenden Variablen.
Dieses Dokument enthält ein allgemeines Verfahren, das auf der Finite-Differenzen-Methode und der Finite-Elemente-Methode und vereinfachten Berechnungsmethoden beruht, die von der Position der Rohre und der Art der Gebäudestruktur abhängig sind.

Conception de l'environnement des bâtiments - Systèmes intégrés de chauffage et de refroidissement par rayonnement - Partie 2: Détermination de la puissance calorifique et frigorifique à la conception (ISO 11855-2:2021)

Načrtovanje notranjega okolja v stavbah - Vgrajeni sevalni ogrevalni in hladilni sistemi - 2. del: Določanje načrtovane grelne in hladilne moči (ISO 11855-2:2021)

General Information

Status
Published
Public Enquiry End Date
02-Jun-2020
Publication Date
17-Oct-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
14-Oct-2021
Due Date
19-Dec-2021
Completion Date
18-Oct-2021

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SLOVENSKI STANDARD
SIST EN ISO 11855-2:2021
01-december-2021
Nadomešča:
SIST EN ISO 11855-2:2015
Načrtovanje notranjega okolja v stavbah - Vgrajeni sevalni ogrevalni in hladilni

sistemi - 2. del: Določanje načrtovane grelne in hladilne moči (ISO 11855-2:2021)

Building environment design - Embedded radiant heating and cooling systems - Part 2:

Determination of the design heating and cooling capacity (ISO 11855-2:2021)
Umweltgerechte Gebäudeplanung - Flächenintegrierte Strahlheizungs- und -

kühlsysteme - Teil 2: Bestimmung der Auslegungs-Heiz- bzw. Kühlleistung (ISO 11855-

2:2021)

Conception de l'environnement des bâtiments - Systèmes intégrés de chauffage et de

refroidissement par rayonnement - Partie 2: Détermination de la puissance calorifique et

frigorifique à la conception (ISO 11855-2:2021)
Ta slovenski standard je istoveten z: EN ISO 11855-2:2021
ICS:
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
SIST EN ISO 11855-2:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 11855-2:2021
---------------------- Page: 2 ----------------------
SIST EN ISO 11855-2:2021
EN ISO 11855-2
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2021
EUROPÄISCHE NORM
ICS 91.040.01 Supersedes EN ISO 11855-2:2015
English Version
Building environment design - Embedded radiant heating
and cooling systems - Part 2: Determination of the design
heating and cooling capacity (ISO 11855-2:2021)

Conception de l'environnement des bâtiments - Umweltgerechte Gebäudeplanung - Flächenintegrierte

Systèmes intégrés de chauffage et de refroidissement Strahlheizungs- und -kühlsysteme - Teil 2: Bestimmung

par rayonnement - Partie 2: Détermination de la der Auslegungs-Heiz- bzw. Kühlleistung (ISO 11855-

puissance calorifique et frigorifique à la conception 2:2021)
(ISO 11855-2:2021)
This European Standard was approved by CEN on 10 September 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-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, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11855-2:2021 E

worldwide for CEN national Members.
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SIST EN ISO 11855-2:2021
EN ISO 11855-2:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 11855-2:2021
EN ISO 11855-2:2021 (E)
European foreword

This document (EN ISO 11855-2:2021) has been prepared by Technical Committee ISO/TC 205

"Building environment design" in collaboration with Technical Committee CEN/TC 228 “Heating

systems and water based cooling systems in buildings” the secretariat of which is held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by April 2022, and conflicting national standards shall be

withdrawn at the latest by April 2022.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 11855-2:2015.

Any feedback and questions on this document should be directed to the users’ national standards

body/national committee. A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

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, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 11855-2:2021 has been approved by CEN as EN ISO 11855-2:2021 without any

modification.
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SIST EN ISO 11855-2:2021
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SIST EN ISO 11855-2:2021
INTERNATIONAL ISO
STANDARD 11855-2
Second edition
2021-09
Building environment design —
Embedded radiant heating and cooling
systems —
Part 2:
Determination of the design heating
and cooling capacity
Conception de l'environnement des bâtiments — Systèmes intégrés de
chauffage et de refroidissement par rayonnement —
Partie 2: Détermination de la puissance calorifique et frigorifique à la
conception
Reference number
ISO 11855-2:2021(E)
ISO 2021
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols ......................................................................................................................................................................................................................... 1

5 Concept of the method to determine the heating and cooling capacity ......................................................3

6 Heat exchange coefficient between surface and space ................................................................................................. 4

7 Simplified calculation methods for determining heating and cooling capacity or

surface temperature ......................................................................................................................................................................................... 6

7.1 Universal single power function .............................................................................................................................................. 7

7.2 Thermal resistance methods ...................................................................................................................................................... 9

8 Use of basic calculation programmes ..........................................................................................................................................12

8.1 Basic calculation programmes ...............................................................................................................................................12

8.2 Items to be included in a complete computation documentation ...........................................................13

9 Calculation of the heating and cooling capacity ...............................................................................................................13

Annex A (normative) Calculation of the heat flux ................................................................................................................................14

Annex B (informative) General resistance method ............................................................................................................................36

Annex C (informative) Pipes embedded in wooden construction .......................................................................................42

Annex D (normative) Method for verification of FEM and FDM calculation programmes ........................50

Annex E (normative) Values for heat conductivity of materials and air layers .....................................................53

Annex F (informative) Maximal surface temperatures for floor heating systems .............................................55

Bibliography .............................................................................................................................................................................................................................56

© ISO 2021 – All rights reserved iii
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(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.

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

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 205, Building environment design, in

collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC

228, Heating systems and water based cooling systems in buildings, in accordance with the Agreement on

technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 11855-2:2012), which has been

technically revised.
The main changes compared to the previous edition are as follows:
— update of the figures for type A and C,
— update of the thermal, relevant material characteristics,
— editorial corrections.
A list of all parts in the ISO 11855 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
Introduction

The radiant heating and cooling system consists of heat emitting/absorbing, heat supply, distribution,

and control systems. The ISO 11855 series deals with the embedded surface heating and cooling system

that directly controls heat exchange within the space. It does not include the system equipment itself,

such as heat source, distribution system and controller.

The ISO 11855 series addresses an embedded system that is integrated with the building structure.

Therefore, the panel system with open air gap, which is not integrated with the building structure, is

not covered by this series.

The ISO 11855 series is applicable to water-based embedded surface heating and cooling systems

in buildings. The ISO 11855 series is applied to systems using not only water but also other fluids or

electricity as a heating or cooling medium. The ISO 11855 series is not applicable for testing of systems.

The methods do not apply to heated or chilled ceiling panels or beams.

The object of the ISO 11855 series is to provide criteria to effectively design embedded systems. To do

this, it presents comfort criteria for the space served by embedded systems, heat output calculation,

dimensioning, dynamic analysis, installation, control method of embedded systems, and input

parameters for the energy calculations.

The ISO 11855 series consists of the following parts, under the general title Building environment

design — Embedded radiant heating and cooling systems:
— Part 1: Definitions, symbols, and comfort criteria
— Part 2: Determination of the design heating and cooling capacity
— Part 3: Design and dimensioning

— Part 4: Dimensioning and calculation of the dynamic heating and cooling capacity of Thermo Active

Building Systems (TABS)
— Part 5: Installation
— Part 6: Control
— Part 7: Input parameters for the energy calculation

ISO 11855-1 specifies the comfort criteria which should be considered in designing embedded radiant

heating and cooling systems, since the main objective of the radiant heating and cooling system

is to satisfy thermal comfort of the occupants. ISO 11855-2, this document, provides steady-state

calculation methods for determination of the heating and cooling capacity. ISO 11855-3 specifies design

and dimensioning methods of radiant heating and cooling systems to ensure the heating and cooling

capacity. ISO 11855-4 provides a dimensioning and calculation method to design Thermo Active

Building Systems (TABS) for energy-saving purposes, since radiant heating and cooling systems can

reduce energy consumption and heat source size by using renewable energy. ISO 11855-5 addresses the

installation process for the system to operate as intended. ISO 11855-6 shows a proper control method

of the radiant heating and cooling systems to ensure the maximum performance which was intended

in the design stage when the system is actually being operated in a building. ISO 11855-7 presents a

calculation method for input parameters to ISO 52031.
© ISO 2021 – All rights reserved v
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SIST EN ISO 11855-2:2021
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SIST EN ISO 11855-2:2021
INTERNATIONAL STANDARD ISO 11855-2:2021(E)
Building environment design — Embedded radiant heating
and cooling systems —
Part 2:
Determination of the design heating and cooling capacity
1 Scope

This document specifies procedures and conditions to enable the heat flux in water-based surface

heating and cooling systems to be determined relative to the medium differential temperature for

systems. The determination of thermal performance of water-based surface heating and cooling

systems and their conformity to this document is carried out by calculation in accordance with design

documents and a model. This enables a uniform assessment and calculation of water-based surface

heating and cooling systems.

The surface temperature and the temperature uniformity of the heated/cooled surface, nominal heat

flux between water and space, the associated nominal medium differential temperature, and the field

of characteristic curves for the relationship between heat flux and the determining variables are given

as the result.

This document includes a general method based on finite difference or finite element Methods and

simplified calculation methods depending on position of pipes and type of building structure.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 11855-1, Building environment design —Embedded radiant heating and cooling systems — Part 1:

Definitions, symbols, and comfort criteria
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11855-1 apply.

ISO and IEC maintain terminological 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/
4 Symbols
For the purposes of this document, the symbols in Table 1 apply.
Table 1 — Symbols
Symbol Unit Quantity
A m Surface of the occupied area
A m Surface of the heating or cooling surface area
© ISO 2021 – All rights reserved 1
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
Table 1 (continued)
Symbol Unit Quantity
A m Surface of the peripheral area
b — Calculation factor depending on the pipe spacing
B, B , B W/( m ⋅K) Coefficients depending on the system
G 0
D m External diameter of the pipe, including sheathing where used
d m External diameter of the pipe
d m Internal diameter of the pipe
d m External diameter of sheathing
c kJ/(kg⋅K) Specific heat capacity of water

h W/(m ⋅K) Total heat transfer coefficient (convection + radiation) between surface and space

h W/(m ⋅K) Total heat transfer coefficient (convection + radiation) between surface and space

A-F
(floor)

h W/(m ⋅K) Total heat transfer coefficient (convection + radiation) between surface and space

A-W
(wall)

h W/(m ⋅K) Total heat transfer coefficient (convection + radiation) between surface and space

A-C
(ceiling)
K W/(m ⋅K) Equivalent heat transmission coefficient
K — Parameter for heat conducting devices
k — Parameter for heat conducting layer
L m Width of heat conducting devices

L m Width of fin (horizontal part of heat conducting device seen as a heating fin)

fin
L m Length of installed pipes
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m kg/s Design heating or cooling medium flow rate
n, n — Exponents
q W/m Heat flux at the surface
q W/m Heat flux in the occupied area
q W/m Design heat flux
des
q W/m Limit heat flux
q W/m Nominal heat flux
q W/m Heat flux in the peripheral area
q W/m Outward heat flux
R m ⋅K/W Partial inwards heat transmission resistance of surface structure
R m ⋅K/W Partial outwards heat transmission resistance of surface structure
R m ⋅K/W Thermal resistance of surface covering
λ,B
R m ⋅K/W Thermal resistance of thermal insulation
λ,ins

s m In type B systems, thickness of thermal insulation from the outward edge of the

insulation to the inward edge of the pipes (see Figure 2)

s m In type B systems, thickness of thermal insulation from the outward edge of the

insulation to the outward edge of the pipes (see Figure 2)
s m Thickness of thermal insulation
ins
s m Pipe wall thickness
s m Thickness of the layer above the pipe
2 © ISO 2021 – All rights reserved
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
Table 1 (continued)
Symbol Unit Quantity
s m Thickness of heat conducting device
S m Thickness of the screed (excluding the pipes in type A systems)
W m Pipe spacing
h W/(m ⋅K) Heat exchange coefficient
α — Parameter factors for calculation of characteristic curves
λ W/(m⋅K) Heat conductivity of the heat diffusion device material
θ °C Maximum surface temperature
s,max
θ °C Minimum surface temperature
s,min
θ °C Design indoor temperature
θ °C Temperature of the heating or cooling medium
θ °C Average surface temperature
s,m
θ °C Return temperature of heating or cooling medium
θ °C Supply temperature of heating or cooling medium
θ °C Indoor temperature in an adjacent space
Δθ K Heating or cooling medium differential temperature
Δθ K Design heating or cooling medium differential temperature
H,des
Δθ K Limit of heating or cooling medium differential temperature
H,G
Δθ K Nominal heating or cooling medium differential temperature
Δθ K Heating or cooling medium differential supply temperature
Δθ K Design heating or cooling medium differential supply temperature
V,des
λ W/(m⋅K) Thermal conductivity
σ K Temperature drop θ −θ
V R
φ — Conversion factor for temperatures
ψ — Volume ratio of the attachment studs in the screed
5 Concept of the method to determine the heating and cooling capacity

A given type of surface (floor, wall, ceiling) delivers, at a given average surface temperature and indoor

temperature (operative temperature θ ), the same heat flux in any space independent of the type of

embedded system. It is, therefore, possible to establish a basic formula or characteristic curve for

cooling and a basic formula or characteristic curve for heating, for each of the type of surfaces (floor,

wall, ceiling), independent of the type of embedded system, which is applicable to all heating and

cooling surfaces (see Clause 6).
Two methods are included in this document:
— simplified calculation methods depending on the type of system (see Clause 7);
— finite element method and finite difference method (see Clause 8).

Different simplified calculation methods are included in Clause 7 for calculation of the surface

temperature (average, maximum and minimum temperature) depending on the system construction

(type of pipe, pipe diameter, pipe distance, mounting of pipe, heat conducting devices, distribution

layer) and construction of the floor/wall/ceiling [covering, insulation layer, trapped air layer (Annex E),

etc.]. The simplified calculation methods are specific for the given type of system, and the boundary

conditions listed in Clause 7 shall be met. In the calculation report, it shall be clearly stated which

calculation method has been applied.
© ISO 2021 – All rights reserved 3
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)

In case a simplified calculation method is not available for a given type of system, either a basic

calculation using two or three dimensional finite element or finite difference method can be applied

(see Clause 8 and Annex D).
NOTE In addition, laboratory testing (for example, EN 1264) can be applied.

Based on the calculated average surface temperature at given combinations of medium (water)

temperature and space temperature, it is possible to determine the steady state heating and cooling

capacity (see Clause 9).
6 Heat exchange coefficient between surface and space

The relationship between the heat flux and mean differential surface temperature [see Figure 1 and

Formulae (1) to (4)] depends on the type of surface (floor, wall, ceiling) and whether the temperature of

the surface is lower (cooling) or higher (heating) than the space temperature.
Key
X mean differential surface temperature (θ − θ ) in K
s,m i
Y heat flux q (W/m )
Figure 1 — Basic characteristic curve for floor heating and ceiling cooling
4 © ISO 2021 – All rights reserved
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
For floor heating and ceiling cooling in Figure 1, the heat flux q is given by:
1,1
q = 8,92 (θ − θ ) (1)
S,m i
where
θ is the average surface temperature, in °C;
S,m
θ is the nominal indoor operative temperature, in °C.

For other types of surface heating and cooling systems, the heat flux q is given by:

Wall heating and wall cooling:
q = 8 (|θ − θ |) (2)
s,m i
Ceiling heating:
q = 6 (|θ − θ |) (3)
s,m i
Floor cooling:
q = 7 (|θ − θ |) (4)
s,m i
NOTE 1 Heat flux, q, is expressed in in W/m .
The heat transfer coefficient is combined convection and radiation.

NOTE 2 In many building system simulations using dynamic computer models, the heat transfer is often split

up in a convective part (between heated/cooled surface and space air) and a radiant part (between heated/

cooled surface and the surrounding surfaces or sources). The radiant heat transfer coefficient in the normal

temperature range (15-30) °C can be fixed to 5,5 W/m ·K. The convective heat transfer coefficient depends on

type of surface, heating or cooling, air velocity (forced convection) or temperature difference between surface

and air (natural convection).

By using the simplified calculation method in Annex A, the characteristic curves present the heat flux

as a function of the difference between the heating or cooling medium temperature and the indoor

temperature. For the user of Annex A, this means not to do any calculations by directly using values

of heat transfer coefficients. Consequently, Annex A does not include values for such an application or

special details or formulae concerning heat transfer coefficients on heating or cooling surfaces.

Thus, the values α of Table A.20 are not intended to calculate the heat flux directly. In fact, they are

provided exclusively for the conversion of characteristic curves in accordance with Formula (A.33). For

simplifications these calculations are based on the same heat transfer coefficient for floor cooling and

ceiling heating, 6,5 W/(m ·K).

For every surface heating and cooling system, there is a maximum allowable heat flux, the limit heat flux

q . This is determined for a selected design indoor room temperature of θ (for heating, often 20 °C and

G i

for cooling, often 26 °C) at the maximum or minimum surface temperature θ and a temperature

F,max
drop σ = 0 K.

For the calculations, the centre of the heating or cooling surface area, regardless of the type of system,

is used as a reference point for θ .
S,max

The average surface temperature, θ , which determines the heat flux (refer to the basic characteristic

S,m

curve) is linked with the maximum or minimum surface temperature: θ < θ and θ > θ

S,m S,max S,m S,min

always applies. (See Annex F for the maximal surface temperature for floor heating systems.)

The attainable value, θ , depends not only on the type of system, but also on the operating conditions

S,m

(temperature drop σ = θ −θ , outward heat flux q and heat resistance of the covering R ).

V R u λ,B
© ISO 2021 – All rights reserved 5
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SIST EN ISO 11855-2:2021
ISO 11855-2:2021(E)
The following assumptions form the basis for the calculation of the heat flux:

— the heat transfer between the heated or cooled surface and the space occurs in accordance with the

basic characteristic curve;

— the temperature drop is σ = 0 K. The dependence of the characteristic curve on the temperature

drop is determined by using the logarithmically determined mean differential heating medium

temperature Δθ [see Formula (1)];
m kg
— the turbulent
...

SLOVENSKI STANDARD
oSIST prEN ISO 11855-2:2020
01-maj-2020
Načrtovanje okolja v stavbah - Vgrajeni hladilni in ogrevalni sistemi - 2. del:
Določanje načrtovane grelne in hladilne moči (ISO/DIS 11855-2:2020)

Building environment design - Embedded radiant heating and cooling systems - Part 2:

Determination of the design heating and cooling capacity (ISO/DIS 11855-2:2020)
Umweltgerechte Gebäudeplanung - Flächenintegrierte Strahlheizungs- und -
kühlsysteme - Teil 2: Bestimmung der Auslegungs-Heiz- bzw. Kühlleistung (ISO/DIS
11855-2:2020)

Conception de l'environnement des bâtiments - Systèmes intégrés de chauffage et de

refroidissement par rayonnement - Partie 2: Détermination de la puissance calorifique et

frigorifique à la conception (ISO/DIS 11855-2:2020)
Ta slovenski standard je istoveten z: prEN ISO 11855-2
ICS:
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
oSIST prEN ISO 11855-2:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 11855-2:2020
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oSIST prEN ISO 11855-2:2020
DRAFT INTERNATIONAL STANDARD
ISO/DIS 11855-2
ISO/TC 205 Secretariat: ANSI
Voting begins on: Voting terminates on:
2020-03-16 2020-06-08
Building environment design — Embedded radiant heating
and cooling systems —
Part 2:
Determination of the design heating and cooling capacity

Conception de l'environnement des bâtiments — Systèmes intégrés de chauffage et de refroidissement par

rayonnement —

Partie 2: Détermination de la puissance calorifique et frigorifique à la conception

ICS: 91.040.01
THIS DOCUMENT IS A DRAFT CIRCULATED
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THEREFORE SUBJECT TO CHANGE AND MAY
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STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
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Reference number
NATIONAL REGULATIONS.
ISO/DIS 11855-2:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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ii © ISO 2020 – All rights reserved
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols and abbreviations ....................................................................................................................................................................... 1

5 Concept of the method to determine the heating and cooling capacity ......................................................3

6 Heat exchange coefficient between surface and space ................................................................................................. 4

7 Simplified calculation methods for determining heating and cooling capacity or

surface temperature ......................................................................................................................................................................................... 5

7.1 Universal single power function .............................................................................................................................................. 6

7.2 Thermal resistance methods ...................................................................................................................................................... 9

8 Use of basic calculation programmes ..........................................................................................................................................11

8.1 Basic calculation programmes ...............................................................................................................................................11

8.2 Items to be included in a complete computation documentation ...........................................................12

9 Calculation of the heating and cooling capacity ...............................................................................................................12

Annex A (normative) Calculation of the heat flux ................................................................................................................................13

Annex B (normative) General resistance method ...............................................................................................................................34

Annex C (normative) Pipes embedded in wooden construction ..........................................................................................40

Annex D (normative) Method for verification of FEM and FDM calculation programmes ........................48

Annex E (normative) Values for heat conductivity of materials and air layers .....................................................52

Bibliography .............................................................................................................................................................................................................................54

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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(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 11855-2 was prepared by Technical Committee ISO/TC 205, Building environment design.

ISO 11855 consists of the following parts, under the general title Building environment design —

Design, dimensioning, installation, control and input parameters for the energy calculation of embedded

radiant heating and cooling systems:
— Part 1: Defintion, symbols, and comfort criteria
— Part 2: Determination of the design and heating and cooling capacity
— Part 3: Design and dimensioning

— Part 4: Dimensioning and calculation of the dynamic heating and cooling capacity of Thermo Active

Building Systems (TABS)
— Part 5: Installation
— Part 6: Control
— Part 7: Input parameters for the energy calculation

Part 1 specifies the comfort criteria which should be considered in designing embedded radiant

heating and

cooling systems, since the main objective of the radiant heating and cooling system is to satisfy thermal

comfort of the occupants. Part 2 provides steady-state calculation methods for determination of the

heating and cooling capacity. Part 3 specifies design and dimensioning methods of radiant heating

and cooling systems to ensure the heating and cooling capacity. Part 4 provides a dimensioning and

calculation method to design Thermo Active Building Systems (TABS) for energy-saving purposes,

since radiant heating and cooling systems can reduce energy consumption and heat source size by using

renewable energy. Part 5 addresses the installation process for the system to operate as intended. Part

6 shows a proper control method of the radiant heating and cooling systems to ensure the maximum

performance which was intended in the design stage when the system is actually being operated in a

building. Part 7 presents a calculation method for input parameters to ISO 52031.

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oSIST prEN ISO 11855-2:2020
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Introduction

The radiant heating and cooling system consists of heat emitting/absorbing, heat supply, distribution,

and control systems. The ISO 11855 series deals with the embedded surface heating and cooling system

that directly controls heat exchange within the space. It does not include the system equipment itself,

such as heat source, distribution system and controller.

The ISO 11855 series addresses an embedded system that is integrated with the building structure.

Therefore, the panel system with open air gap, which is not integrated with the building structure, is

not covered by this series.

The ISO 11855 series shall be applied to systems using not only water but also other fluids or electricity

as a heating or cooling medium.

The object of the ISO 11855 series is to provide criteria to effectively design embedded systems. To do

this, it presents comfort criteria for the space served by embedded systems, heat output calculation,

dimensioning, dynamic analysis, installation, control method of embedded systems, and input

parameters for the energy calculations.
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oSIST prEN ISO 11855-2:2020
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oSIST prEN ISO 11855-2:2020
DRAFT INTERNATIONAL STANDARD ISO/DIS 11855-2:2020(E)
Building environment design — Embedded radiant heating
and cooling systems —
Part 2:
Determination of the design heating and cooling capacity
1 Scope

This part of ISO 11855 specifies procedures and conditions to enable the heat flow in water based

surface heating and cooling systems to be determined relative to the medium differential temperature

for systems. The determination of thermal performance of water based surface heating and cooling

systems and their conformity to this part of ISO 11855 is carried out by calculation in accordance with

design documents and a model. This should enable a uniform assessment and calculation of water based

surface heating and cooling systems.

The surface temperature and the temperature uniformity of the heated/cooled surface, nominal heat

flux between water and space, the associated nominal medium differential temperature, and the field

of characteristic curves for the relationship between heat flux and the determining variables are given

as the result.

This part of ISO 11855 includes a general method based on Finite Difference or Finite Element Methods

and simplified calculation methods depending on position of pipes and type of building structure.

The ISO 11855 series is applicable to water based embedded surface heating and cooling systems in

residential, commercial and industrial buildings. The methods apply to systems integrated into the

wall, floor or ceiling construction without any open air gaps. It does not apply to panel systems with

open air gaps which are not integrated into the building structure.

The ISO 11855 series also applies, as appropriate, to the use of fluids other than water as a heating or

cooling medium. The ISO 11855 series is not applicable for testing of systems. The methods do not apply

to heated or chilled ceiling panels or beams.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 11855-1, Building environment design — Design, dimensioning, installation, control and input

parameters for the energy calculation of embedded radiant heating and cooling systems — Part 1:

Vocabulary, symbols, and comfort criteria
EN 1264, Water based surface embedded heating and cooling systems (2012)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11855-1 apply.

4 Symbols and abbreviations

For the purposes of this document, the symbols and abbreviations in Table 1 apply.

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oSIST prEN ISO 11855-2:2020
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Table 1 — Symbols and abbreviations
Symbol Unit Quantity
α — Parameter factors for calculation of characteristic curves
A m Surface of the occupied area
A m Surface of the heating/cooling surface area
A m Surface of the peripheral area
b — Calculation factor depending on the pipe spacing
B, B , B W/(m ⋅K) Coefficients depending on the system
G 0
D m External diameter of the pipe, including sheathing where used
d m External diameter of the pipe
d m Internal diameter of the pipe
d m External diameter of sheathing
c kJ/(kg⋅K) Specific heat capacity of water

h W/(m ⋅K) Total heat transfer coefficient (convection + radiation) between surface and space

K W/(m ⋅K) Equivalent heat transmission coefficient
K — Parameter for heat conducting devices
k — Parameter for heat conducting layer
L m Width of heat conducting devices

L m Width of fin (horizontal part of heat conducting device seen as a heating fin)

fin
L m Length of installed pipes
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m — Exponents for determination of characteristic curves
m kg/s Design heating/cooling medium flow rate
n, n — Exponents
q W/m Heat flux at the surface
q W/m Heat flux in the occupied area
q W/m Design heat flux
des
q W/m Limit heat flux
q W/m Nominal heat flux
q W/m Heat flux in the peripheral area
q W/m Outward heat flux
R m ⋅K/W Partial inwards heat transmission resistance of surface structure
R m ⋅K/W Partial outwards heat transmission resistance of surface structure
R m ⋅K/W Thermal resistance of surface covering
λ,B
R m ⋅K/W Thermal resistance of thermal insulation
λ,ins

s m In Type B systems, thickness of thermal insulation from the outward edge of the

insulation to the inward edge of the pipes (see Figure 2)

s m In Type B systems, thickness of thermal insulation from the outward edge of the

insulation to the outward edge of the pipes (see Figure 2)
s m Thickness of thermal insulation
ins
s m Pipe wall thickness
s m Thickness of the layer above the pipe
s m Thickness of heat conducting device
S m Thickness of the screed (excluding the pipes in type A systems)
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
Table 1 (continued)
Symbol Unit Quantity
W m Pipe spacing
h W/(m ⋅K) Heat exchange coefficient
λ W/(m⋅K) Heat conductivity of the heat diffusion device material
θ °C Maximum surface temperature
s,max
θ °C Minimum surface temperature
s,min
θ °C Design indoor temperature
θ °C Temperature of the heating/cooling medium
θ °C average surface temperature
s,m
θ °C Return temperature of heating/cooling medium
θ °C Supply temperature of heating/cooling medium
θ °C Indoor temperature in an adjacent space
Δθ K Heating/cooling medium differential temperature
Δθ K Design heating/cooling medium differential temperature
H,des
Δθ K Limit of heating/cooling medium differential temperature
H,G
Δθ K Nominal heating/cooling medium differential temperature
Δθ K Heating/cooling medium differential supply temperature
Δθ K Design heating/cooling medium differential supply temperature
V,des
λ W/(m⋅K) Thermal conductivity
σ K Temperature drop θ −θ
V R
φ — Conversion factor for temperatures
ψ — Volume ratio of the attachment studs in the screed
5 Concept of the method to determine the heating and cooling capacity

A given type of surface (floor, wall, ceiling) delivers, at a given average surface temperature and indoor

temperature (operative temperature θ ), the same heat flux in any space independent of the type of

embedded system. It is therefore possible to establish a basic formula or characteristic curve for cooling

and a basic formula or characteristic curve for heating, for each of the type of surfaces (floor, wall,

ceiling), independent of the type of embedded system, which is applicable to all heating and cooling

surfaces (see Clause 6).
Two methods are included in this part of ISO 11855:
— simplified calculation methods depending on the type of system (see Clause 7);
— Finite Element Method and Finite Difference Method (see Clause 8).

Different simplified calculation methods are included in Clause 7 for calculation of the surface

temperature (average, maximum and minimum temperature) depending on the system construction

(type of pipe, pipe diameter, pipe distance, mounting of pipe, heat conducting devices, distribution

layer) and construction of the floor/wall/ceiling (covering, insulation layer, trapped air layer, etc.). The

simplified calculation methods are specific for the given type of system, and the boundary conditions

listed in Clause 7 shall be met. In the calculation report, it shall be clearly stated which calculation

method has been applied.

In case a simplified calculation method is not available for a given type of system, either a basic

calculation using two or three dimensional finite element or finite difference method can be applied

(see Clause 8 and Annex D).
NOTE In addition, laboratory testing (for example EN 1264:2012) may be applied.
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)

Based on the calculated average surface temperature at given combinations of medium (water)

temperature and space temperature, it is possible to determine the steady state heating and cooling

capacity (see Clause 9).
6 Heat exchange coefficient between surface and space

The relationship between the heat flux and mean differential surface temperature [see Figure 1 and

Equations (1) to (4)] depends on the type of surface (floor, wall, ceiling) and whether the temperature

of the surface is lower (cooling) or higher (heating) than the space temperature.

Figure 1 — Basic characteristic curve for floor heating and ceiling cooling
For floor heating and ceiling cooling in Figure 1, the heat flux q is given by:
1,1 2
q = 8,92 (θ −θ ) (W/m) (1)
S,m i
where
θ is the average surface temperature in°C;
S,m
θ is the nominal indoor operative temperature in °C.

For other types of surface heating and cooling systems, the heat flux q is given by:

Wall heating and wall cooling: q = 8 (|θ −θ |) (W/m ) (2)
s,m i
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
Ceiling heating: q = 6 (|θ −θ |) (W/m ) (3)
s,m i
Floor cooling: q = 7 (|θ −θ |) (W/m ) (4)
s,m i
The heat transfer coefficient is combined convection and radiation.

NOTE In many building system simulations using dynamic computer models, the heat transfer is often split

up in a convective part (between heated/cooled surface and space air) and a radiant part (between heated/

cooled surface and the surrounding surfaces or sources). The radiant heat transfer coefficient may in the normal

temperature range 15-30 °C be fixed to 5,5 W/m K. The convective heat transfer coefficient depends on type of

surface, heating or cooling, air velocity (forced convection) or temperature difference between surface and air

(natural convection).

For using the simplified calculation method in Annex A the characteristic curves present the heat

flux as a function of the difference between the heating/cooling medium temperature and the indoor

temperature. For the user of Annex A, this means not to do any calculations by directly using values

of heat transfer coefficients. Consequently, Annex A does not include values for such an application or

special details or equations concerning heat transfer coefficients on heating or cooling surfaces.

Thus, the values α of Table A.12 of Annex A are not intended to calculate the heat flux directly. In

fact, they are provided exclusively for the conversion of characteristic curves in accordance with

Equation (A.32) in Clause A.3. For simplifications these calculations are based on the same heat transfer

coefficient for floor cooling and ceiling heating, 6,5 W/m K.

For every surface heating and cooling system, there is a maximum allowable heat flux, the limit heat flux

q . This is determined for a selected design indoor room temperature of θ (for heating, often 20 °C and

G i

for cooling, often 26 °C) at the maximum or minimum surface temperature θ and a temperature

F,max
drop σ = 0 K.

For the calculations, the centre of the heating or cooling surface area, regardless of the type of system,

is used as a reference point for θ .
S,max

The average surface temperature, θ , which determines the heat flux (refer to the basic characteristic

S,m

curve) is linked with the maximum or minimum surface temperature: θ < θ and. θ > θ

S,m S,max S,m S,min
always applies.

The attainable value, θ , depends not only on the type of system, but also on the operating conditions

S,m

(temperature drop σ = θ −θ , outward heat flow q and heat resistance of the covering R ).

V R u λ,B
The following assumptions form the basis for calculation of the heat flux:

— heat transfer between the heated or cooled surface and the space occurs in accordance with the

basic characteristic curve;

— the temperature drop σ = 0. The dependence of the characteristic curve on the temperature drop is

determined by using the logarithmically determined mean differential heating medium temperature

Δθ [see Equation (1)];
m kg
— turbulent flow in pipe: > 4000 ;
d hm⋅
— no lateral heat flow.
7 Simplified calculation methods for determining heating and cooling capacity
or surface temperature

Two types of simplified calculation methods can be applied according to this part of ISO 11855:

— one method is based on a single power function product of all relevant parameters developed from

the finite element method (FEM);
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)

— another method is based on calculation of equivalent thermal resistance between the temperature

of the heating or cooling medium and the surface temperature (or room temperature).

A given system construction can only be calculated with one of the simplified methods. The correct

method to apply depends on the type of system, A to G (position of pipes, concrete or wooden

construction) and the boundary conditions listed in Table 2.
Table 2 — Criteria for selection of simplified calculation method
Type of Reference to
Pipe position Figure Boundary conditions
system method
In screed A, C 2 a) W ≥ 0,050 m s ≥ 0,01 m 7.1
Thermally decoupled from the structural 0,008 m ≤ d ≤ 0,03 m A.2.2
base of the building by thermal insulation
s /λ ≥ 0,01
u e
In insulation, conductive devices B 2 b) 0,05 m ≤ W ≤ 0,45 m 7.1
Not wooden constructions except for 0,014 m ≤ d ≤ 0,022 m A.2.3
weight bearing and thermal diffusion layer
0,01 m ≤ s /λ ≤ 0,18
u e
Plane section system D 2 c) 7.1,
A.2.4
In concrete slab E 4 S /W ≥ 0,3 7.2,
B.1
Capillar tubes in concrete surface F 5 d /W ≤ 0,2 7.2, B.2
Wooden constructions, pipes in sub floor G 6 λ ≥ 10 λ 7.2, Annex C
wl surroundingmaterial
or under sub floor, conductive devices
S λ ≥ 0,01
7.1 Universal single power function

The heat flux between embedded pipes (temperature of heating or cooling medium) and the space is

calculated by the general equation:
i 2
qB=⋅ ()a ⋅” θ (W/m) (5)
∏ i H
where

B is a system-dependent coefficient in W/(m ⋅K). This depends on the type of system;

i is the power product, which links the parameters of the structure (surface covering, pipe

()a
∏ i
spacing, pipe diameter and pipe covering).

This calculation method is given in Annex A for the following four types of systems:

— Type A with pipes embedded in the screed or concrete (see Figure 2 and A.2.2);
— Type B with pipes embedded outside the screed (see Figure 2 and A.2.3);
— Type C with pipes embedded in the screed (see Figure 2 and A.2.2);
— Type D plane section systems (see A.2.4).

Figure 2 shows the types as embedded in the floor, but the methods can also be applied for wall and

ceiling systems with a corresponding position of the pipes.

This method shall only be used for system configurations meeting the boundary conditions listed for

the different types of systems in Annex A.
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
a) Type A and C
Key
1 floor covering

2 weight bearing and thermal diffusion layer (cement screed, anhydrite screed, asphalt screed)

3 thermal insulation
4 structural bearing
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
b) Type B
Key
1 floor covering

2 weight bearing and thermal diffusion layer (cement screed, anhydrite screed, asphalt screed, wood)

3 heat diffusion devices
4 thermal insulation
5 structural bearing
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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
c) Type D
Key
1 floor covering R , B

2 weight bearing and thermal diffusion layer (cement screed, anhydrite screed, asphalt screed, timber)

3 thermal insulation
4 structural bearing
Figure 2 — System types A, B and C covered by the method in Annex A
7.2 Thermal resistance methods

The heat flux between embedded pipes (temperature of heating or cooling medium) and the space or

surface is calculated using thermal resistances.
The concept is shown in Figure 3.

An equivalent resistance, R , between the heating or cooling medium to a fictive core (or heat

conduction layer) at the position of the pipes is determined. This resistance includes the influence of

type of pipe, pipe distance and method of pipe installation (in concrete, wooden construction, etc.).

In this way a fictive core temperature is calculated. The heat transfer between this fictive layer and

the surfaces, R and R (or space and neighbour space) is calculated using linear resistances (adding of

i e
resistance of the layers above and below the heat conductive layer).

The equivalent resistance of the heat conductive layer is calculated in different ways depending on the

type of system.

This calculation method, using the general resistance concept, is given in Annex B for the following two

types of systems:
— Type E with pipes embedded in massive concrete slabs (see Figure 4 and B.1);

— Type F with capillary pipes embedded in a layer at the inside surface (see Figure 5 and B.2).

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oSIST prEN ISO 11855-2:2020
ISO/DIS 11855-2:2020(E)
Figure 3 — Basic network of thermal resistance
Figure 4 — Pipes embedded in a massive concrete layer, Type E
10 © ISO
...

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