FprEN ISO 11855-3

Building environment design - Embedded radiant heating and cooling systems - Part 3: Design and dimensioning (ISO/FDIS 11855-3:2021)

Umweltgerechte Gebäudeplanung - Flächenintegrierte Strahlheizungs- und -kühlsysteme - Teil 3: Planung und Auslegung (ISO/FDIS 11855-3:2021)

Dieses Dokument legt ein Systemplanungs- und  auslegungsverfahren fest, durch das die Heiz- und Kühlleistung der flächenintegrierten Strahlungsheiz- und  kühlsysteme gewährleistet wird.

Conception de l'environnement des bâtiments - Systèmes intégrés de chauffage et de refroidissement par rayonnement - Partie 3: Conception et dimensionnement (ISO/FDIS 11855-3:2021)

Načrtovanje okolja v stavbah - Vgrajeni hladilni in ogrevalni sistemi - 3. del: Načrtovanje in dimenzioniranje (ISO/FDIS 11855-3:2021)

General Information

• Status: Not Published
• ICS: 91.040.01 - Buildings in general
• ICS: 91.140.10 - Central heating systems
• ICS: 91.140.30 - Ventilation and air-conditioning systems
• Technical Committee: CEN/TC 228 - Heating systems in buildings
• Drafting Committee: CEN/TC 228 - Heating systems in buildings
• Current Stage: 6055 - CEN Ratification completed (DOR) - Publishing
• Due Date: 29-Jul-2021
• Completion Date: 29-Jul-2021
• Ref Project: kSIST FprEN ISO 11855-3:2021 - Building environment design - Embedded radiant heating and cooling systems - Part 3: Design and dimensioning (ISO/FDIS 11855-3:2021)

RELATIONS

• Revised: EN ISO 11855-3:2015 - Building environment design - Design, dimensioning, installation and control of embedded radiant heating and cooling systems - Part 3: Design and dimensioning (ISO 11855-3:2012)
• Effective Date: 21-Feb-2018

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN ISO 11855-3:2020
01-maj-2020
Načrtovanje okolja v stavbah - Vgrajeni hladilni in ogrevalni sistemi - 3. del:
Načrtovanje in dimenzioniranje (ISO/DIS 11855-3:2020)

Building environment design - Embedded radiant heating and cooling systems - Part 3:

Design and dimensioning (ISO/DIS 11855-3:2020)
Umweltgerechte Gebäudeplanung - Flächenintegrierte Strahlheizungs- und -
kühlsysteme - Teil 3: Planung und Auslegung (ISO/DIS 11855-3:2020)

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

refroidissement par rayonnement - Partie 3: Conception et dimensionnement (ISO/DIS

11855-3:2020)
Ta slovenski standard je istoveten z: prEN ISO 11855-3
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 11855-3:2020 en,fr,de

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

---------------------- Page: 1 ----------------------
oSIST prEN ISO 11855-3:2020
---------------------- Page: 2 ----------------------
oSIST prEN ISO 11855-3:2020
DRAFT INTERNATIONAL STANDARD
ISO/DIS 11855-3
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 3:
Design and dimensioning

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

rayonnement —
Partie 3: Conception et dimensionnement
ICS: 91.040.01
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 11855-3:2020(E)
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. ISO 2020
---------------------- Page: 3 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
Contents Page

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

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

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

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

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

4 Symbols and abbreviated terms ........................................................................................................................................................... 1

5 Radiant panel ........................................................................................................................................................................................................... 3

5.1 Floor heating systems ....................................................................................................................................................................... 3

5.1.1 Design procedure ............................................................................................................................................................ 3

5.1.2 Heating medium differential temperature ................................................................................................ 4

5.1.3 Characteristic curve ...................................................................................................................................................... 4

5.1.4 Field of characteristic curves ................................................................................................................................ 4

5.1.5 Limit curves .......................................................................................................................................................................... 4

5.1.6 Downwards thermal insulation .......................................................................................................................... 5

5.1.7 Procedure for determining the supply design temperature of the heating

medium .................................................................................................................................................................................... 8

5.1.8 Procedure for determining the design heating medium flow rate ....................................11

5.1.9 Peripheral areas.............................................................................................................................................................12

5.2 Ceiling heating systems ................................................................................................................................................................12

5.2.1 General...................................................................................................................................................................................12

5.2.2 Limit curves .......................................................................................................................................................................12

5.2.3 Procedure for determining the design heating medium flow rate ....................................13

5.3 Wall heating systems ......................................................................................................................................................................13

5.3.1 General...................................................................................................................................................................................13

5.3.2 Limit curves .......................................................................................................................................................................13

5.3.3 Procedure for determining the design heating medium flow rate ....................................13

5.4 Floor cooling systems ......... ............................................................................................................................................................14

5.4.1 Design procedure .........................................................................................................................................................14

5.4.2 Cooling medium differential temperature ..............................................................................................14

5.4.3 Characteristic curve ...................................................................................................................................................15

5.4.4 Field of characteristic curves .............................................................................................................................15

5.4.5 Limit curves .......................................................................................................................................................................15

5.4.6 Downwards thermal insulation .......................................................................................................................15

5.4.7 Procedure for determining the supply design temperature of cooling medium ...15

5.4.8 Procedure for determining the design cooling medium flow rate .....................................15

5.5 Ceiling cooling systems .................................................................................................................................................................15

5.6 Wall cooling systems .......................................................................................................................................................................15

Bibliography .............................................................................................................................................................................................................................16

© ISO 2020 – All rights reserved iii
---------------------- Page: 5 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(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 11855-3 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 and control of embedded radiant heating and cooling systems:

— Part 1: Definition, 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.

iv © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(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 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.
© ISO 2020 – All rights reserved v
---------------------- Page: 7 ----------------------
oSIST prEN ISO 11855-3:2020
---------------------- Page: 8 ----------------------
oSIST prEN ISO 11855-3:2020
DRAFT INTERNATIONAL STANDARD ISO/DIS 11855-3:2020(E)
Building environment design — Embedded radiant heating
and cooling systems —
Part 3:
Design and dimensioning
1 Scope

This part of ISO 11855 establishes a system design and dimensioning method to ensure the heating and

cooling capacity of the radiant heating and cooling systems.

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 applies also, 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.

EN 12831, Heating systems in buildings — Method for calculation of the design heat load

EN 15243, Ventilation for buildings — Calculation of room temperatures and of load and energy for

buildings with room conditioning systems

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

Definition, symbols, and comfort criteria

ISO 11855-2, Building environment design — Embedded radiant heating and cooling systems — Part 2:

Determination of the design heating and cooling capacity
3 Terms and definitions

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

4 Symbols and abbreviated terms

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

Table 1 — Symbols and abbreviated terms
Symbol Unit Quantity
A m Area of the heating/cooling surface
A m Area of the occupied heating/cooling surface
A m Area of the peripheral heating/cooling surface
© ISO 2020 – All rights reserved 1
---------------------- Page: 9 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
Table 1 (continued)
Symbol Unit Quantity
C J/(kg⋅K) Specific heat of medium
K W/(m ⋅K) Equivalent heat transmission coefficient
l m Distance between the joists
l m Thickness of the joist
M kg/s Design heating/cooling medium flow rate
q W/m Design heat flux
des
q W/m Design heat flux in the occupied area
des,A
q W/m Design heat flux in the peripheral area
des,R
q W/m Limit heat flux
q W/m Maximum design heat flux
max
Q W Design heating/cooling capacity
des
Q W Design heating/cooling load
Q W Design sensible cooling load
N,s
Q W Design latent cooling load
N,l
Q W Heat output of supplementary heating equipment
out
R (m K)/W Partial inwards heat transmission resistance of the surface structure
R (m K)/W Partial outwards heat transmission resistance of the surface structure
Rλ (m ⋅K)/W Thermal resistance of surface covering
Rλ (m ⋅K)/W Back side thermal resistance of insulating layer
,ins
s m Effective thickness of thermal insulating layer
ins
W m Pipe spacing
h W/(m K) Heat transfer coefficient
λ W/(m⋅K) Effective thermal conductivity of the thermal insulation layer
ins
λ W/(mK) Thermal conductivity of the thermal insulation layer between the joists
λ W/(mK) Thermal conductivity of the joist
θ °C Maximum surface temperature
F,max
θ °C Minimum surface temperature
F,min
θ °C Design indoor temperature
θ °C Return temperature of heating/cooling medium
θ °C Supply temperature of heating/cooling medium
θ °C Design supply temperature of heating/cooling medium
V,des
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 Design heating/cooling medium differential supply temperature
V,des
σ K Temperature drop/rise between supply and return medium
2 © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
5 Radiant panel
5.1 Floor heating systems
5.1.1 Design procedure

Floor heating system design requires determining heating surface area, type, pipe size, pipe spacing,

supply temperature of the heating medium, and design heating medium flow rate. The design steps are

as follows:

Step 1: Calculate the design heating load Q . The design heating load Q shall not include the adjacent

N N

heat losses. This step should be conducted in accordance with a standard for heating load calcula-

tion, such as EN 12831, based on an index such as operative temperature (OT) (see ISO 11855-1).

Step 2: Determine the area of the heating surface A , excluding any area covered by immovable objects

or objects fixed to the building structure.

Step 3: Establish a maximum permissible surface temperature in accordance with ISO 11855-1.

Step 4: Determine the design heat flux q according to Equation (1). For floor heating systems includ-

des

ing a peripheral area, the design heat flux of peripheral area q and the design heat flux of

des,R

occupied area q shall be calculated respectively on the area of the peripheral heating surface

des,A
A and on the area of the occupied heating surface A complying with Equation (2).
R A
(1)
q =
des
Qq=⋅Aq+⋅A (2)
Ndes,R Rdes,A A

Step 5: For the design of the floor heating systems, determine the room used for design with the max-

imum design heat flux q = q .
max des

Step 6: Determine the floor heating system such as the pipe spacing and the covering type, and design

heating medium differential temperature Δθ based on the maximum design heat flux q

H,des max

and the maximum surface temperature θ from the field of characteristic curves according

F,max
to ISO 11855-2 and 5.1.7 in this part of ISO 11855.

Step 7: If the design heat flux q cannot be obtained by any pipe spacing for the room used for the

des

design, it is recommended to include a peripheral area and/or to provide supplementary heating

equipment. In this case, the maximum design heat flux q for the embedded system may now

max

occur in another room. The amount of heat output of supplementary heating equipment Q is

out
determined by the following equation:
QQ=−Q (3)
outN des
where design heating capacity Q is calculated by:
des
Qq=×A (4)
desdes F

Step 8: Determine the backside thermal resistance of insulating layer R and the design heating

λ,ins
medium flow rate m (see 5.1.6 and 5.1.8).
Step 9: Estimate the total length of heating circuit.

If intermittent operation is common, the characteristics of the increase of the heat flow and the surface

temperature and the time to reach the allowable conditions in rooms just after switching on the system

shall be considered.
© ISO 2020 – All rights reserved 3
---------------------- Page: 11 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
5.1.2 Heating medium differential temperature

Heating medium differential temperature Δθ is calculated as follows (refer to ISO 11855-2):

θθ−
Δθ = (5)
θθ−
θθ−

In this equation, the effect of the temperature drop of the heating medium is taken into account.

5.1.3 Characteristic curve

The characteristic curve describes the relationship between the heat flux q and the heating medium

differential temperature Δθ . For simplicity, the heat flux q is taken to be proportional to the heating

medium differential temperature Δθ :
qK=⋅Δθ (6)

where K is the equivalent heat transmission coefficient determined in ISO 11855-2 depending on the

type of the system.
5.1.4 Field of characteristic curves

The field of characteristic curves of a floor heating system with a specific pipe spacing W shall at least

contain the characteristic curves for values of the thermal resistance of surface covering R = 0,

λ,B

R = 0,05, R = 0,10 and R = 0,15 (m K/W), in accordance with ISO 11855-2 (see Figure 1). Values of

λ,B λ,B λ,B
R > 0,15 (m K/W) shall not be used if possible.
λ,B
5.1.5 Limit curves

The limit curves in the field of characteristic curves describe, in accordance with ISO 11855-2, the

relationship between the heating medium differential temperature Δθ and the heat flux q in the case

where the physiologically agreed limit values of surface temperatures are reached. For design purposes,

i.e. the determination of design values of the heat flux and the associated heating medium differential

temperature Δθ , the limit curves are valid for temperature drop between supply and return medium

σ in a range of:
0 K < σ < 5 K (7)

The limit curves are used to specify the limit of heating medium differential temperature Δθ and

H,G
supply temperature (refer to Figure 6).
4 © ISO 2020 – All rights reserved
---------------------- Page: 12 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
Key
1 limit curves
2 performance characteristic curves
Peripheral area.
Occupied area.

Figure 1 — Field of characteristic curves, including limit curves for floor heating, for constant

pipe spacing

This example is for floor heating, indoor temperature = 20 °C and the maximum temperature is 29 °C

(occupied areas) and 35 °C (peripheral area). For bathrooms (the indoor temperature is 24 °C), the limit

curve for (θ – θ ) = 9K also applies.
F,max i
5.1.6 Downwards thermal insulation

In order to limit the heat flow through the floor towards the space below, the required back side thermal

resistance of the insulating layer R shall be specified in the design to be not lower than the value in

λ,ins
Table 2 in ISO 11855-4.

For systems which have a flat insulating layer (Types A, B, C, D and G in ISO 11855-2), the back-side

thermal resistance of the insulating layer R is calculated by Equation (8-1) where there is no stud.

λ,ins

And the effective thickness of thermal insulating layer s is identical to the thickness of the thermal

ins

insulating panel and the effective thermal conductivity of the thermal insulation layer λ is calculated

ins
by Equation (8-2) where there are studs.
ins
R = (8-1)
λ,ins
ins
ll−
pws
λλ= +λ (8-2)
insi ws
ls l
p ps
where:
© ISO 2020 – All rights reserved 5
---------------------- Page: 13 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
λ is thermal conductivity of the thermal insulation layer between the studs;
λ is thermal conductivity of the stud;
l is the distance between the studs (see Figure 2);
l is the thickness of the stud (see Figure 2).

Depending on the construction of the floor heating system, the effective thickness of thermal insulating

layer s and effective thermal conductivity of the thermal insulation layer λ are determined

ins ins
differently.

For floor heating systems with flat thermal insulating panels of types A and C in ISO 11855-2, the

effective thickness of thermal insulating layer s is identical to the thickness of the thermal insulation,

ins

and the effective thermal conductivity of the thermal insulation layer λ is identical to the thermal

ins
conductivity of the thermal insulation [Figure 2 a)].

For the system with profiled thermal insulating panels of type B in ISO 11855-2 [Figure 2 b)], the

effective thickness of the insulating layer shall be determined by Equation (9).
sW⋅−()Ds+⋅D
s = (9)
ins

For the system with the light wooden radiant panel on the joist of type G in ISO 11855-2 [Figure 2 c)], the

effective thickness of thermal insulating layer s is identical to the thickness of the thermal insulating

ins

panel, and the effective thermal conductivity of the thermal insulation layer λ is:

ins
ll−
λλ= +λ (10)
insi w
l l
p p
where:
λ is thermal conductivity of the thermal insulation layer between the joists;
λ is thermal conductivity of the joist;
l is the distance between the joist (see Figure 5);
l is the thickness of the joist (see Figure 5).
For type G systems with air cavities see Annex C and E in ISO 11855-2.
6 © ISO 2020 – All rights reserved
---------------------- Page: 14 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
Key
1 floor covering

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

3 thermal insulation
4 structural bearing

Figure 2 — Effective thickness and effective thermal conductivity of thermal insulating layer of

flat thermal insulating panel — Types A and C
Key
1 floor covering

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

3 plane section
4 thermal insulation
5 structural bearing

Figure 3 — Effective thickness and effective thermal conductivity of thermal insulating layer of

flat thermal insulating panel — Type D
© ISO 2020 – All rights reserved 7
---------------------- Page: 15 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)
Key
1 floor covering

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

3 heat diffusion devices
4 thermal insulation
5 structural bearing

Figure 4 — Effective thickness and effective thermal conductivity of thermal insulating layer of

profiled thermal insulating panel — Type B

Figure 5 — Effective thickness and effective thermal conductivity of thermal insulating layer of

flat thermal insulating panel with joist — Type G

The insulating layers of a floor heating shall comply with the minimum thermal resistances given in

national building codes.

5.1.7 Procedure for determining the supply design temperature of the heating medium

The design supply temperature of the heating medium θ is determined for the room with the

V,des

maximum design heat flux q = q . In the rooms being heated, it is assumed that floor coverings

max des
8 © ISO 2020 – All rights reserved
---------------------- Page: 16 ----------------------
oSIST prEN ISO 11855-3:2020
ISO/DIS 11855-3:2020(E)

(carpet, tiles, acoustic plates, etc.) with a uniform thermal conduction resistance are used. The thermal

resistance of the covering used for the design shall be documented. For the room used for design, the

temperature drop between supply and return medium σ ≤ 5K is specified. If necessary, a subdivision of

the room into heating circuits shall be performed. Under these conditions, the maximum design heat

flux q may reach until the limit heat flux q (see Figure 6).
max G

For the room with q , a pipe spacing is chosen with which q remains less than or equal to the limit

max max

heat flux q , specified by the limit curves: (q ≤ q ; see Figure 6). In case of q < q , design heating

G max G max G

medium differential supply temperature is Δθ ≤ Δθ + 2,5 K. The maximum permissible design

V,des H,G
heating medium differential supply temperature is determined by Equation 11:
””θθ=+ (11)
V,desH,des
where ””θθ≤ .
H,desH,G

Equation (11) applies if σ/Δθ ≤ 0,5. For the ratio (σ/Δθ ) > 0,5, the following applies:

H H
””θθ=+ + K (12)
V,desH,des
212”θ
H,des
The temperature drop σ in Equations
...