ISO 11855-2:2021/Amd 1:2023

INTERNATIONAL ISO
STANDARD 11855-2
Second edition
2021-09
AMENDMENT 1
2023-11
Building environment design —
Embedded radiant heating and cooling
systems —
Part 2:
Determination of the design heating
and cooling capacity
AMENDMENT 1
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
AMENDEMENT 1
Reference number
ISO 11855-2:2021/Amd.1:2023(E)
ISO 11855-2:2021/Amd.1:2023(E)
© ISO 2023
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ii
ISO 11855-2:2021/Amd.1:2023(E)
Foreword
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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).
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.
iii
ISO 11855-2:2021/Amd.1:2023(E)
Building environment design — Embedded radiant heating
and cooling systems —
Part 2:
Determination of the design heating and cooling capacity
AMENDMENT 1
Clause 4, Table 1
Modify the following rows:
Table 1 — Symbols
Symbol Unit Quantity
s m In system type II, thickness of thermal insulation from the outward edge of the
h
insulation to the inward edge of the pipes (see Figure 2)
s m In system type II, thickness of thermal insulation from the outward edge of the
l
insulation to the outward edge of the pipes (see Figure 2)
S m Thickness of the screed (excluding the pipes in system type I)

Clause 7, second paragraph
Modify to the following:
A given system construction can only be calculated with one of the simplified methods. The correct
method to apply depends on the system type I to IV (position of pipes, concrete or wooden construction)
and the boundary conditions listed in Table 2.
Delete the NOTE.
Table 2
Modify to the following:
Table 2 — Criteria for selection of simplified calculation method
New Old
Reference to
Pipe position system system Figure Boundary conditions
method
type type
In screed I A, C, H, 2 a) W ≥ 0,050 m s ≥ 0,01 m 7.1
u
I, J
Thermally decoupled from the struc- 0,008 m ≤ d ≤ 0,03 m A.2.2
tural base of the building by thermal
s /λ ≥ 0,01
u e
insulation
In insulation, conductive devices II B 2 b) 0,05 m ≤ W ≤ 0,45 m 7.1
Not wooden constructions except 0,014 m ≤ d ≤ 0,022 m A.2.3
for weight bearing and thermal dif-
0,01 m ≤ s /λ ≤ 0,18 m
u e
fusion layer
ISO 11855-2:2021/Amd.1:2023(E)
TTabablele 2 2 ((ccoonnttiinnueuedd))
New Old
Reference to
Pipe position system system Figure Boundary conditions
method
type type
In concrete slab V E 4 S /W ≥ 0,3 7.2,
T
B.1
Capillary tubes in concrete surface III F 5 d /W ≤ 0,2 7.2, B.2
a
Wooden constructions, pipes in sub IV G 6 λ ≥ 10 λ 7.2, Annex C
wl
floor or under sub floor, conductive
S ≥ 0,01
WLλ
devices
7.1, second and third paragraphs
Delete the following:
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.
Replace with the following:
This calculation method is given in Annex A for the following five types of system:
— type I: pipes directly included in a thermal diffusion layer (see Figure 2);
— type II: pipes included in thermal insulation layer with additional thermal conduction layer (see
Figure 3);
— type III: capillary tubes directly included in a thermal diffusion layer (see Figure 4);
— type IV: pipes with a thermal reflection layer and an air gap to floor covering (see Figure 5);
— type V: pipes included directly in the structural construction (TABS) (see Figure 6).
Figure 3 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.

7.1, Figure 2 a)
Replace Figure 2 a) with the new Figure 2.
ISO 11855-2:2021/Amd.1:2023(E)
Key
D external diameter of the pipe
ln thermal insulation layer
Pe pipes or electric cables
Pt protection layer
Sf surface layer
St structural layer
s thickness of the layer above the pipe
u
Td thermal diffusion layer
W pipe spacing
Figure 2 — Radiant system type I: pipes directly included in a thermal diffusion layer

7.1, Figure 2 b)
Replace Figure 2 b) with the new Figure 3.
ISO 11855-2:2021/Amd.1:2023(E)
Key
ln thermal insulation layer
Pe pipes or electric cables
Pt protection layer
Sf surface layer
St structural layer
s thickness of the layer above the pipe
u
s thickness of heat conducting device
wl
Tc thermal conduction layer
Td thermal diffusion layer
W pipe spacing
Figure 3 — Radiant system type II: pipes included in a thermal insulation layer with additional
thermal conduction layer
7.1, Figure 2 c)
Replace Figure 2 c) with the new Figure 4.
ISO 11855-2:2021/Amd.1:2023(E)
Key
Ct capillary tubes
ln thermal insulation layer
Pt protection layer
Sf surface layer
St structural layer
s thickness of the layer above the pipe
u
Td thermal diffusion layer
Figure 4 — Radiant system type III: capillary tubes directly included in a thermal diffusion
layer
7.1, Figure 2 d)
Replace Figure 2 d) with the new Figure 5.
ISO 11855-2:2021/Amd.1:2023(E)
Key
Ag air gap
ln thermal insulation layer
Jt joist
l distance between the joists
p
l thickness of the joist
w
Pe pipes or electric cables
Sc structural construction
Sf surface layer (floor covering)
s thickness of thermal insulation
ins
St structural layer
Tr thermal reflection layer
Figure 5 — Radiant system type IV: pipes with a thermal reflection layer and an air gap to floor
covering
7.1, Figure 2 e)
Replace Figure 2 e) with the new Figure 6.
ISO 11855-2:2021/Amd.1:2023(E)
Key
Pe pipes or electric cables
Sf surface layer
St structural layer
Figure 6 — Radiant system type V: pipes included directly in the structure construction (TABS)

7.1, Figure 2 f)
Remove Figure 2 f).
7.2
Modify to the following:
The concept is shown in Figure 7.
This calculation method, using the general resistance concept, is given in Annex B for the following two
types of system:
— system type V with pipes embedded in massive concrete slabs (see Figure 6);
— system type III with capillary pipes embedded in a layer at the inside surface (see Figure 4).
ISO 11855-2:2021/Amd.1:2023(E)
Key
R external resistance
e
R equivalent resistance
HC
R internal resistance
i
Figure 7 — Basic network of thermal resistance
Dimensions and other relevant parameters for these constructions are given in Figures 8 and 9.
Key
θ temperature
θ temperature of the thermal diffusion layer
Td
λ thermal conductivity
d external diameter of the pipe
a
s thickness
s thickness of the pipe wall
r
U heat transfer coefficient
W pipe spacing
1 space 1
ISO 11855-2:2021/Amd.1:2023(E)
2 space 2
Figure 8 — Pipes embedded in a massive concrete layer, type V
Key
θ temperature
temperature of the heat pipes
θ
c
θ temperature of the thermal diffusion layer
Td
λ thermal conductivity
d external diameter of the pipe
a
h distance between the surface and the undisturbed room temperature
R heat resistance of the wall
R resistance between the pipes
ib
s thickness
s thickness of the pipe wall
r
U heat transfer coefficient
W pipe spacing
1 space 1
2 space 2
Figure 9 — Capillary pipes embedded in a layer at the inner surface, type III

A.2.1, Table A.1
Modify to the following:
ISO 11855-2:2021/Amd.1:2023(E)
Table A.1 — Criteria for selection of the simplified calculation method
System Figure Boundary conditions Reference to meth-
type od
I Figure 2 T ≥ 0,050 m A.2.2
s ≥ 0,01 m
u
0,008 m ≤ D ≤ 0,03 m
s /λ ≥ 0,01
u e
II Figure 3 0,05 m ≤ T ≤ 0,45 m A.2.3
0,014 m ≤ D ≤ 0,022 m
0,01 m ≤ s /λ ≤ 0,18 m
u e
A.2.2, first paragraph
Modify to the following:
A.2.2  Systems with pipes inside the screed (system type I)
For these systems (see Figure 2), the characteristic curves are calculated by:
m m m
W U D
qB=⋅aa⋅⋅aa⋅⋅Δθ (A.3)
B WU D H
where B = B = 6,7 in W/m ⋅K.
A.2.3, first paragraph
Modify to the following:
A.2.3   Systems with pipes below the screed or timber floor (system type II)
For these systems (see Figure 3), the variable thickness s of the weight bearing layer and its
u
variable thermal conductivity λ are represented by a factor a . The pipe diameter has no effect.
WL U
However, the contact between the heating pipe and the heat conducting device or any other heat
distribution device is an important parameter. The characteristic curve is calculated from Formula
(A.11):
A.2.4, first paragraph
Modify to the following:
Formula (A.17) applies to surfaces fully covered with embedded heating or cooling elements (see
Figure 4):
A.2.5
Replace with the following:
The procedure for the determination of the limits of the heat flux is shown in principle within Figure A.2.
The limit curve (see Figure A.2) gives the relationship between the specific thermal output and the
temperature difference between the heating medium and the room for cases where the maximum
permissible difference between surface temperature and indoor room temperature (9 K or 15 K,
respectively; see Table A.21) is achieved.
ISO 11855-2:2021/Amd.1:2023(E)
The limit curve is calculated using the following expression in form of a product.
The limit curves are calculated by Formula (A.19):
n
G
Δθ
 
H
qB=⋅φ ⋅ in W/m (A.19)
GG
 
φ
 
where B is a coefficient in accordance with:
G
— for system type I systems: Tables A.5, A.6, A.7 or A.8, depending on the ratio s /λ ;
uE
— for system type II systems: Table A.18;
— for plane section systems: B = 100 W/(m ⋅K);
G
n  is an exponent in accordance with:
G
— for system type I systems: Table A.9 or A.10, depending on the ratio s /λ ;
uE
— for system type II systems: Table A.19;
— for plane section systems: n = 0.
G
φ is the factor for conversion to any values of temperatures θ and θ and is calculated according to
F,max i
Formula (A.20):
11,
θθ−
 
Fi,max
φ = (A.20)
 
Δθ
 
o
where Δθ =9K .
o
The intersection of the characteristic curve with the limit curve is calculated using Formula (A.21),
expressed in K:
 1−n
G
 
B
G
 
Δθφ=⋅ (A.21)
H,G
m
i
 
Ba⋅
∏ i
 
 
i
The limit curves for system type I systems, for T > 0,375 m, are calculated according to Formulae (A.22)
to (A.24):
0,375 m
qq=⋅f (A.22)
GG;,0 375 G
W
ΔΔθθ=⋅ f (A.23)
HG,;H,GG0,375
where
q is the limit heat flux in W/m , calculated for a spacing W = 0,375 m;
G;0,375
θ is the limit temperature di
...