ISO 11855-1:2012

INTERNATIONAL ISO
STANDARD 11855-1
First edition
2012-08-01
Building environment design — Design,
dimensioning, installation and control
of embedded radiant heating and
cooling systems —
Part 1:
Definition, symbols, and comfort criteria
Conception de l’environnement des bâtiments — Conception,
construction et fonctionnement des systèmes de chauffage et de
refroidissement par rayonnement —
Partie 1: Définition, symboles et critères de confort
Reference number
©
ISO 2012
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Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations .10
5 Comfort criteria .15
5.1 General thermal comfort .15
5.2 Local thermal comfort .17
5.3 Acoustical comfort .20
Annex A (informative) Floor surface temperature for thermal comfort .22
Annex B (informative) Draught .25
Bibliography .26
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 11855-1 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 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.
iv © ISO 2012 – All rights reserved

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, operation, and control method of embedded systems.
INTERNATIONAL STANDARD ISO 11855-1:2012(E)
Building environment design — Design, dimensioning,
installation and control of embedded radiant heating and
cooling systems —
Part 1:
Definition, symbols, and comfort criteria
1 Scope
This part of ISO 11855 specifies the basic definitions, symbols, and a comfort criteria for 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 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
ISO 7726:1998, Ergonomics of the thermal environment — Instruments for measuring physical quantities
ISO 7730:2005, Ergonomics of the thermal environment — Analytical determination and interpretation of
thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria
ISO 13731:2003, Ergonomics of the thermal environment — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
additional thermal resistance
thermal resistance representing layers added to the building structure and acting mostly as thermal resistances
because of their own low thermal inertia
EXAMPLE Carpets, moquette, and suspended ceilings.
2.2
average specific thermal capacity of the internal walls
thermal capacity related to one square metre of the internal walls
NOTE Since internal walls are shared with other rooms, then just half of the total specific thermal capacity of the wall
must be taken into account, since the second half is influenced by the opposite rooms that are considered to be at the
same thermal conditions as the one under consideration.
2.3
average surface temperature
θ
s,m
average value of all surface temperatures in the occupied or peripheral area
2.4
basic characteristic curve
curve or formula reflecting the relationship between the heat flux and the mean surface temperature difference
NOTE This depends on heating/cooling and surface (floor/wall/ceiling) but not on the type of embedded system.
2.5
calculation time step
length of time considered for the calculation of the temperatures and heat flows in the room and slab
NOTE This is typically assumed to equal 3 600 s.
2.6
circuit
section of system connected to a distributor which can be independently switched and controlled
2.7
circuit total thermal resistance
thermal resistance representing the circuit as a whole, determining a straight connection between the water
inlet temperature and the mean temperature at the pipe level
NOTE It includes the water flow thermal resistance, the convection thermal resistance at the pipe inner side, the pipe
thickness thermal resistance, and the pipe level thermal resistance.
2.8
clothing insulation
basic clothing insulation that is the resistance of a uniform layer of insulation covering the entire body that has
the same effect on sensible heat flow as the actual clothing under standardized (static, wind-still) conditions
NOTE The definition of clothing insulation also includes the uncovered parts of the body, e.g. the head. It is described
as the intrinsic insulation from the skin to the clothing surface, not including the resistance provided by the air layer around
2 2
the clothed body, and is expressed in the clo unit or in m K/W; 1 clo = 0,155 m K/W.
2.9
conductive region of the slab
region of the slab that includes the pipes with thermal conductivities of the layers higher than 0,8 W/(m·K)
NOTE Due to the subdivision of the slab into an upper slab and a lower slab, the conductive region is also subdivided
into an upper conductive region and a lower conductive region.
2.10
convection thermal resistance at the pipe inner side
thermal resistance associated to the convection heat transfer taking place between the water flowing in the
pipe and the pipe inner side, thus connecting the mean water temperature along the circuit with the mean
temperature of the pipe inner side
2.11
convective heating and cooling system
system that directly conditions the air in the room for the purpose of heating and cooling
2.12
convective peak load
maximum cooling load to be extracted by a virtual convective system used to keep comfort conditions in the room
2.13
daily average temperature of the conductive region of the slab
average temperature of the conductive region of the slab during the day
2.14
design cooling capacity
Q
H,c
thermal output by a cooling surface at design conditions
2 © ISO 2012 – All rights reserved

2.15
design cooling load
Q
N,c
required thermal output necessary to achieve the specified design conditions in outside summer design conditions
2.16
design sensible cooling load
required sensible thermal output necessary to achieve the specified design conditions in outside summer
design conditions
2.17
design dew point
θ
Dp,des
dew point determined for the design
2.18
design supply temperature of heating/cooling medium
θ
V,des
value of flow water temperature with the thermal resistance of the chosen floor covering, at maximum value of
heat flux q
max
NOTE The flow and the supply temperature are the same throughout the EN 1264 series.
2.19
design heat flux
q
des
heat flow divided by the heating or cooling surface, taking into account the surface temperature required to
reach the design thermal capacity of a surface heated or cooled space, Q , reduced by the thermal capacity
H
of any supplementary heating or cooling equipment, if applicable
2.20
design heating capacity
Q
H,h
thermal output from a heating surface at design conditions
2.21
design heating load
Q
N,h
required thermal output necessary to achieve the specified design conditions in outside winter design conditions
NOTE When calculating the value of the design heat load, the heat flow from embedded heating systems into
neighbouring rooms is not taken into account.
2.22
design heating/cooling medium differential temperature
Δθ
H,des
temperature difference at design heat flux
2.23
design heating medium differential supply temperature
Δθ
V,des
temperature difference between the design supply medium temperature and indoor temperature at design heat flux
2.24
design heating/cooling medium flow rate
m
H
mass flow rate in a circuit which is needed to achieve the design heat flux
2.25
design indoor temperature
θ
i
operative temperature at the centre of the conditioned space used for calculation of the design load and capacity
NOTE The operative temperature is considered relevant for thermal comfort assessment and heat loss calculations.
This value of internal temperature is used for the calculation method.
2.26
distributor
common connection point for several circuits
2.27
draught
unwanted local cooling of a body caused by movement of air and related to temperature
2.28
electric floor (wall, ceiling) heating system
several panel systems that convert electrical energy to heat, raising the temperature of conditioned indoor
surfaces and the indoor air
2.29
embedded surface heating and cooling system
system consisting of circuits of pipes embedded in floor, wall or ceiling construction, distributors and
control equipments
2.30
equivalent heat transmission coefficient
K
H
coefficient describing the relationship between the heat flux from the surface and the heating/cooling medium
differential temperature
2.31
family of characteristic curves
curves denoting the system-specific relationship between the heat flux, q, and the required heating medium
differential temperature Δθ for conduction resistance of various floor coverings
H
2.32
heat flux
q
heat flow between the space and surface divided by the heated/cooled surface
NOTE For heating it is a positive value and for cooling it is a negative value.
2.33
heat transfer coefficient
h
t
combined convective and radiative heat transfer coefficient between the heated or cooled surface and the
space operative temperature (design indoor temperature)
2.34
heating or cooling surface
surface (floor, wall, ceiling) covered by the embedded surface heating/cooling system between the pipes at the
outer edges of the system with the addition of a strip at each edge of width equal to half the pipe spacing, but
not exceeding 0,15 m
2.35
heating or cooling surface area
A
F
area of surface (floor, wall, ceiling) covered by the embedded surface heating/cooling system between the
pipes at the outer edges of the system with the addition of a strip at each edge of width equal to half the pipe
spacing, but not exceeding 0,15 m
4 © ISO 2012 – All rights reserved

2.36
heating/cooling capacity for circuit
Q
HC
heat exchange between a pipe circuit and the conditioned room
2.37
heating/cooling medium differential temperature
Δθ
H
logarithmically determined average difference between the temperature of the heating/cooling medium and the
design indoor temperature
2.38
internal convective heat gains
convective contributions by internal heat gains acting in the room
NOTE Mainly due to people or electrical equipment.
2.39
internal radiant heat gains
radiant contributions by internal heat gains acting in the room
NOTE Mainly due to people or electrical equipment.
2.40
internal thermal resistance of the slab conductive region
total thermal resistance connecting the pipe level with the middle points of the upper conductive region and
lower conductive region of the slab
2.41
limit curves
curves in the field of characteristic curves showing the pattern of the limit heat flux depending on the heating
medium differential temperature and the floor covering
2.42
limit heat flux
q
G
heat flux at which the maximum or minimum permissible surface temperature is achieved
2.43
limit heating medium temperature difference
Δθ
H,G
intersection of the system characteristic curve with the limit curve
2.44
maximum cooling power
maximum thermal power of the cooling equipment, referring only to the room under consideration
2.45
maximum permissible surface temperature
q
max
required design heat flux in the room in order to design supply medium temperature
2.46
maximum operative temperature allowed for comfort conditions
maximum operative temperature allowed in the room according to comfort requirements in cooling conditions
2.47
maximum operative temperature drift allowed for comfort conditions
maximum drift in operative temperature allowed in the room according to comfort requirements
2.48
maximum permissible surface temperature
θ
S,max
maximum temperature permissible for physiological reasons or for the physical building, for calculation of the
limit curves, which may occur at a point on the surface (floor, wall, ceiling) in the occupied or peripheral area
depending on the particular usage at a temperature drop σ of the heating medium equal to 0
2.49
mean radiant temperature
uniform surface temperature of an imaginary black enclosure in which an occupant would exchange the same
amount of radiant heat as in the actual non-uniform enclosure
2.50
mean surface temperature difference
difference between the average surface temperature θ and the design indoor temperature θ
S,m i
NOTE It determines the heat flux.
2.51
metabolic rate
rate of transformation of chemical energy into heat and mechanical work by aerobic and anaerobic metabolic
activities within an organism, usually expressed in terms of unir area of the total body surfaces
2 2
NOTE The metabolic rate varies with each activity. It is expressed in the met unit or in W/m ; 1 met = 58,2 W/m .
1 met is the energy produced per unit surface area of a sedentary person at rest. The surface area of an average person
2 0,725 0,425
can be determined by Dubois Equation, Body Surface Area (m ) = 0,20 247 × Height (m) × Weight (kg) .
2.52
minimum permissible surface temperature
θ
S,min
minimum temperature permissible for physiological reasons or for the physical building, for calculation of the
limit curves, which may occur at a point on the surface (floor, wall, ceiling) in the occupied or peripheral area
depending on the particular usage at a temperature drop σ of the heating medium equal to 0
2.53
nominal heat flux
q
N
limit heat flux achieved without surface covering
2.54
nominal heating/cooling medium differential temperature
Δθ
N
absolute temperature difference at nominal heat flux q
N
2.55
non-active area
area of the surface not covered by a heating/cooling system
2.56
number of active surfaces
number of surfaces in straight thermal connection with the pipe level, so that it distinguishes whether the slab
transfers heat both through the floor side and through the ceiling side or whether the ceiling side is much more
active than the floor side
NOTE Two active surfaces when the conductive region extends from the floor to the ceiling, one active surface otherwise.
2.57
number of operation hours of the circuit
length of time during which the system runs in the day
6 © ISO 2012 – All rights reserved

2.58
occupied area
A
A
surface area which is heated or cooled, excluding peripheral area
2.59
occupied zone
part of the conditioned zone in which persons normally reside and where requirements as to the internal
environment are satisfied
NOTE Normally, the zone between the floor and 1,8 m above the floor and 1,0 m from outside walls/windows and
heating/cooling appliances, 0,5 m from internal surfaces.
2.60
open air gap
air gap in the floor, wall, or ceiling construction, where air exchange with space or the outside may occur
2.61
operative temperature
OT
θ
o
uniform temperature of an imaginary black enclosure in which an occupant exchanges the same amount of
heat by radiation and convection as in the actual non-uniform environment
2.62
orientation of the room
orientation of the main windowed external wall: East, South or West
NOTE It is used to determine when the peak load from heat gains happens, since internal heat gains are considered
almost constant and the widest variation is expected to happen in solar heat gains.
2.63
outward heat flux
q
U
heat flow which is exchanged through the construction with unconditioned spaces, another building entity, the
ground or outdoor air
2.64
peak load
maximum cooling load to be extracted by the system used to keep comfort conditions in the room
2.65
peripheral area
A
R
surface area which is heated or cooled to a higher or lower temperature
NOTE It is generally an area of 1 m maximum in width along exterior walls. It is not an occupied area.
2.66
pipe level
virtual plane where the pipe circuit lies
2.67
pipe level thermal resistance
thermal resistance associated to the 2-D conduction heat transfer taking place between the pipes and the
embedding layer, virtually referred to the pipe level, thus connecting the mean temperature of the pipe outer
side with the mean temperature at the pipe level
2.68
pipe spacing
spacing or distance between pipes embedded in the surface
2.69
pipe thickness thermal resistance
thermal resistance associated to the conduction heat transfer taking place through the pipe wall, thus connecting
the mean temperature of the pipe inner side with the mean temperature of the pipe outer side
2.70
predicted mean vote
PMV
index that predicts the mean value of the thermal sensation votes of a large group of persons on a 7-point
thermal sensation scale
2.71
predicted percentage of dissatisfied
PPD
index that establishes a quantitative prediction of the percentage of thermally dissatisfied people who are either
too warm of too cool
2.72
primary air convective heat gains
heat gains acting in the room due to the infiltration or primary air inflow
2.73
radiant surface heating and cooling system
heating and cooling system that controls the temperature of indoor surfaces on the floor, walls, or ceiling
2.74
radiant temperature asymmetry
difference between the plane radiant temperature of the two opposite sides of a small plane element
2.75
relative air velocity
air velocity relative to the occupant, including body movements
2.76
regional dew point
θ
Dp,R
dew point specified depending on the climatic conditions of the region
2.77
running mode
running mode of the circuit that defines whether the system is currently switched on or off
2.78
slab
horizontal building structure separating two rooms placed one below the other, hence being the ceiling for one
and the floor for the other
2.79
solar heat gains
solar heat gains acting in the room due to high-frequency radiation transmission through windows
2.80
specific daily energy gains
total energy to be extracted during the day in order to avoid a net increase in internal energy in the room and
maintain comfort conditions
2.81
supplementary heating equipment
additional heating facility with the additional heat output Q
out
EXAMPLE Convector, radiators.
8 © ISO 2012 – All rights reserved

NOTE It may have its own control equipment.
2.82
surface heating and cooling components
insulating layer (for thermal and/or impact noise insulation), protection layer (to protect the insulating layer), the pipes
or plane sections, the load and thermal distribution layer where pipes are embedded, covering and other items
NOTE 1 Other items include conducting devices, peripheral strips, attachment items, etc.
NOTE 2 Components may differ depending on the system.
2.83
system insulation
insulation with the thermal resistance R according to ISO 11855-5:2012, Table 2, to limit the heat loss of
λ,ins
heating and cooling systems
NOTE For floor heating and cooling systems, as a rule the thermal resistance R is provided by the insulation
λ,ins
layers which are integral parts of the system. National rules shall be consulted for this subject. For wall and ceiling heating
and cooling systems, the thermal resistance R may be determined taking into account the effective thermal resistance
λ,ins
of the building structure.
2.84
Thermally Active Building System
TABS
water based heating and cooling system where the pipes are embedded in the central concrete core of a
building construction
2.85
temperature drop
σ
difference between the supply and return temperature of the heating/cooling medium in a circuit
2.86
temperature of the heating/cooling medium
θ
m
average temperature between the supply and the return temperature defined as θ = θ + Δθ
m i H
2.87
thermal node
node summarizing the thermal behavior of a material or air volume as regards heat transfer calculations
2.88
thermal output of surface system
Q
S
sum of the products of the heating or cooled surfaces of a space with the associated design heat fluxes
NOTE For heating it is a positive value. For cooling it is a negative value.
2.89
total convective heat gains
sum of all convective contributions from heat gains acting in the room, hence it is the sum of internal convective
heat gains, primary air convective heat gains and a fraction of transmission heat gains
2.90
total radiant heat gains
sum of all radiant contributions from heat gains acting in the room (internal radiant heat gains, solar heat gains
and a fraction of transmission heat gains)
2.91
transmission heat gains
heat gains acting in the room due to conductive heat transmission through the external walls and windows
2.92
vertical air temperature difference
difference in air temperature measured at 1,1 m and 0,1 m above the floor
NOTE The distances 1,1 m and 0,1 m are theoretical average values for head and ankle height of a sedentary person.
2.93
wall surface thermal resistance
thermal resistance representing the connection between the core of the internal walls and their surface on
the room side
NOTE It usually corresponds to the layer of plaster covering the internal side of the walls.
2.94
water based floor (wall, ceiling) heating and cooling system
floor (wall, ceiling) system where pipes carrying water with or without additives as a medium are laid in the floor
(wall, ceiling)
2.95
water flow thermal resistance
thermal resistance that expresses the variation in temperature of the water flowing in the pipe along the circuit,
so it connects the water inlet temperature with the mean water temperature along the circuit
4 Symbols and abbreviations
For the purposes of this part of ISO 11855, the symbols and abbreviations in Table 1 apply.
Table 1 — Symbols and abbreviations
Symbol Unit Quantity
A m Area of the occupied surface
A
A m Area of the heating/cooling surface
F
A m Area of the peripheral surface
R
A m Total area of internal vertical walls (i.e. vertical walls, external façades excluded)
W
a - Parameter factors for calculation of characteristic curves
i
B, B , B W/(m ·K) Coefficients depending on the system
G 0
b - Calculation factor depending on the pipe spacing
u
C J/(m ·K) Specific thermal capacity of the thermal node under consideration
C J/(m ·K) Average specific thermal capacity of the internal walls
W
c J/(kg·K) Specific heat of the material constituting the j-th layer of the slab
j
c J/(kg·K) Specific heat of water
W
D
m External diameter of the pipe, including sheathing where used
d m External diameter of the pipe
a
d m Internal diameter of the pipe
i
d m External diameter of sheathing
M
E kWh/m Specific daily energy gains
Day
F - View factor between the floor and the ceiling
v F-C
F - View factor between the floor and the external walls
v F-EW
F - View factor between the floor and the internal walls
v F-W
f - Design safety factor
s
Running mode (1 when the system is running; 0 when the system is switched off) in the
h
-
f
rm
h-th hour
10 © ISO 2012 – All rights reserved

Table 1 (continued)
Symbol Unit Quantity
Heat transfer coefficient between the thermal node under consideration and the air
H W/K
A
thermal node (“A”)
Heat transfer coefficient between the thermal node under consideration and the ceiling
H W/K
C
surface thermal node (“C”)
H W/K Heat transfer coefficient between the thermal node under consideration and the circuit
Circuit
H W/K Heat transfer coefficient between the thermal node under consideration and the next one
CondDown
Heat transfer coefficient between the thermal node under consideration and the previous
H W/K
CondUp
one
H - Fraction of internal convective heat gains acting on the thermal node under consideration
conv
Heat transfer coefficient between the thermal node under consideration and the floor
H W/K
F
surface thermal node (“F”)
H W/K Coefficient connected to the inertia contribution at the thermal node under consideration
Inertia
Heat transfer coefficient between the thermal node under consideration and the internal
H W/K
IWS
wall surface thermal node (“IWS”)
H - Fraction of total radiant heat gains impinging on the thermal node under consideration
Rad
h W/(m ·K) Convective heat transfer coefficient between the air and the ceiling
A-C
h W/(m ·K) Convective heat transfer coefficient between the air and the floor
A-F
h W/(m ·K) Convective heat transfer coefficient between the air and the internal walls
A-W
h W/(m ·K) Convective heat transfer coefficient
c
h W/(m ·K) Radiant heat transfer coefficient between the floor and the ceiling
F-C
h W/(m ·K) Radiant heat transfer coefficient between the floor and the internal walls
F-W
h W/(m ·K) Radiant heat transfer coefficient
r
h W/(m ·K) Total heat transfer coefficient (convection + radiation) between surface and space
t
J - Number of layers constituting the slab as a whole
J - Number of layers constituting the upper part of the slab
J - Number of layers constituting the lower part of the slab
K W/(m ·K) Equivalent heat transmission coefficient
H
K - Parameter for heat conducting devices
WL
k - Parameter for heat conducting layer
CL
k - Parameter for heat conducting devices
fin
L m Width of fin (horizontal part of heat conducting device seen as a heating fin)
fin
L m Length of installed pipes
R
L m Width of heat conducting devices
WL
m - Exponents for determination of characteristic curves
m kg/s Design heating/cooling medium flow rate
H

m
kg/(m ·s) Specific water flow in the circuit, calculated on the area covered by the circuit
H,sp
m Number of partitions of the j-th layer of the slab
j
n - Actual number of iteration in iterative calculations
n, n - Exponents
G
n h Number of operation hours of the circuit
h
Max
n - Maximum number of iterations allowed in iterative calculations
W Maximum cooling power reserved to the circuit under consideration in the h-th hour
Max
P W Maximum specific cooling power (per floor square metre)
Circuit,Spec
PB - Polybutylene
Table 1 (continued)
Symbol Unit Quantity
PE-MDX - Cross-linked polyethylene, medium density
PE-RT-
- Polyethylene of raised temperature resistance
Systems
PE-X - Cross-linked polyethylene
PP - Polypropylene
PVC-C - Chlorinated polyvinyl chloride
h
Q W Heat flow impinging on the ceiling surface (“C”) in the h-th hour
C
h
Q W Heat flow extracted by the circuit in the h-th hour
Circuit
h
Q W Total convective heat gains in the h-th hour
Conv
Q W Design capacity
des
h
Q W Heat flow impinging on the floor surface (“F”) in the h-th hour
F
h
Q W Internal convective heat gains in the h-th hour
IntConv
h
Q W Internal radiant heat gains in the h-th hour
IntRad
h
Q W Heat flow impinging on the internal wall surface (“IWS”) in the h-th hour
IWS
Q W Design load
N
Q W Design cooling load
N,c
Q W Design heating load
N,h
Q W Design latent cooling load
N,l
Q W Design sensible cooling load
N,s
Q W Heat output of supplementary heating equipments
out
h
Q W Primary air convective heat gains in the h-th hour
PrimAir
h
W Total radiant heat gains in the h-th hour
Q
Rad
Q W Thermal output of surface heating-cooling
s
h
Q W Solar heat gains in the room in the h-th hour
Sun
h
Q W Transmission heat gains in the h-th hour
Transm
Q W/m Average specific cooling power
W
q W/m Heat flow density at the surface
q W/m Heat flow density in the occupied area
A
q W/m Design heat flow density
des
q W/m Design heat flow density of occupied area
des,A
q W/m Design heat flow density of peripheral area
des,R
q W/m Limit heat flow density
G
q W/m Inward specific heat flow
i
q W/m Maximum design heat flow density
max
q W/m Nominal heat flow density
N
q W/m Heat flow density in the peripheral area
R
q W/m Outward heat flow density
U
12 © ISO 2012 – All rights reserved

Table 1 (continued)
Symbol Unit Quantity
R (m ·K)/W Additional thermal resistance covering the lower side of the slab
Add C
R (m ·K)/W Additional thermal resistance covering the upper side of the slab
Add F
Convection thermal resistance connecting the air thermal node (“A”) with the ceiling
RCAC K/W
surface thermal node (“C”)
Convection thermal resistance connecting the air thermal node (“A”) with the floor
RCAF K/W
surface thermal node (“F”)
Convection thermal resistance connecting the air thermal node (“A”) with the internal wall
RCAW K/W
surface thermal node (“IWS”)
R (m ·K)/W Internal thermal resistance of the slab conductive region
int
Conduction thermal resistance connecting the p-th thermal node with the boundary of
R (m ·K)/W
L,p
the (p+1)-th thermal node
R (m ·K)/W Generic thermal resistance
R (m ·K)/W Partial inwards heat transmission resistance of surface structure
o
R (m ·K)/W Pipe thickness thermal resistance
r
R (m ·K)/W Circuit total thermal resistance
t
R (m ·K)/W Partial outwards heat transmission resistance of surface structure
u
Conduction thermal resistance connecting the p-th thermal node with the boundary of
R (m ·K)/W
U,p
the (p-1)-th thermal node
R (m ·K)/W Wall surface thermal resistance
Walls
R (m ·K)/W Water flow thermal resistance
W
R (m ·K)/W Pipe level thermal resistance
X
R (m ·K)/W Convection thermal resistance at the pipe inner side
Z
R (m ·K)/W Thermal resistance of surface covering
λ,B 2
R (m ·K)/W Thermal resistance of thermal insulation
λ,ins
S m Thickness of the screed (excluding the pipes in type A systems)
In Type B systems, thickness of thermal insulation from the outward edge of the
s m
h
insulation to the inward edge of the pipes (see Figure 2)
s m Thickness of thermal insulation
ins
In Type B systems, thickness of thermal insulation from the outward edge of the
s m
l
insulation to the outward edge of the pipes (see Figure 2)
s m Thickness of the pipe wall
r
s m Thickness of the layer inward from the pipe
u
s m Thickness of heat conducting device
WL
s m Thickness of the upper part of the slab
s m Thickness of the lower part of the slab
v m/s Maximum air velocity
max
W m Pipe spacing
x m Distance to the surface
α W/(m ·K) Heat exchange coefficient
δ m Thickness of the j-th layer of the slab
j
η - Rate of the extra capacity of the heat source
Δt s Calculation time step
Δθ K Generic temperature difference
Max
Δθ °C Maximum operative temperature drift allowed for comfort conditions
Comfort
Δθ K Heating/cooling medium differential temperature
H
Table 1 (continued)
Symbol Unit Quantity
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
N
Δθ K Heating/cooling medium differential supply temperature
V
Δθ K Design heating/cooling medium differential supply temperature
V,des
h
θ °C Temperature of the air thermal node (“A”) in the h-th hour
A
θ °C Maximum operative temperature allowed for comfort conditions in the reference case
Comfort,Ref
h
θ °C Temperature of the ceiling surface thermal node (“C”) in the h-th hour
c
Max
θ °C Maximum operative temperature allowed for comfort conditions
Comfort
θ °C External design temperature
d
θ °C Maximum surface temperature
F,max
θ °C Minimum surface temperature
F,min
h
°C Temperature of the floor surface thermal node (“F”) in the h-th hour
θ
F
h
θ °C Temperature of the core of the internal walls thermal node (“IW”) in the h-th hour
IW
h
°C Temperature of the internal wall surface thermal node (“IWS”) in the h-th hour
θ
IWS
θ °C Design indoor temperature
i
h
θ °C Room mean radiant temperature in the h-th hour
MR
θ °C Temperature of the heating/cooling medium
m
h
θ
°C Room operative temperature in the h-th hour
Op
h
θ
°C Temperature of the p-th thermal node in the h-th hour
p
h
θ °C Temperature of the pipe level thermal node (“PL”) in the h-th hour
PL
Av
θ °C Daily average temperature of the conductive region of the slab
Slab
θ °C Minimum indoor air temperature
i,min
θ °C Operative temperature
o
θ °C Mean radiant temperature
r
θ °C Average surface temperature
s,m
θ °C Maximum surface temperature
s,max
θ °C Minimum surface temperature
s,min
θ °C Return temperature of heating/cooling medium
R
θ °C Supply temperature of heating/cooling medium
V
θ °C Design supply temperature of heating/cooling medium
V,des
θ °C Maximum heating water flow temperature
V,des,max
θ °C Indoor temperature in an adjacent space
u
h
θ
°C Water inlet actual temperature in the h-th hour
Water,In
14 © ISO 2012 – All rights reserved

Table 1 (continued)
Symbol Unit Quantity
Setp,h
θ °C Water inlet set-point temperature in the h-th hour
Water,In
Setp
θ °C Water inlet set-point temperature in the reference case
Water,In,Ref
h
θ °C Water outlet temperature in the h-th hour
Water,Out
λ W/(m·K) Thermal conductivity
λ W/(m·K) Thermal conductivity of the material of the pipe embedded layer
b
λ W/(m·K) Thermal conductivity of the thermal insulation layer
ins
λj W/(m·K) Thermal conductivity of the material constituting the j-th layer of the slab
λ W/(m·K) Thermal conductivity of the material constituting the pipe
r
σ
K Temperature drop θ -θ
V R
ξ
°C Actual tolerance in iterative calculations
ξ °C Maximum tolerance allowed in iterative calculations
max
ρ kg/m Density of the material constituting the j-th layer of the slab
j
φ - Conversion factor for temperatures
ψ - Content by volume of the attachment burrs in the screed
ω various Slope of correlation curves
5 Comfort criteria
An occupant’s thermal comfort would be the primary objective that any HVAC system pursues. Radiant heating
and cooling systems can be used as primary or hybrid systems which are combined with an air system and
provide unique and cost-effective approaches to dealing with numerous conditions affecting human thermal
comfort. Radiant heating and cooling systems directly transfer heat in order to condition a space to a specific
temperature. Meanwhile, radiant heating and cooling systems can be used to directly provide heat to humans
as well as to spaces.
As long as the occupants are radiantly heated in a radiant heating system, the same comfort level can be
maintained with a lower air temperature in comparison to a convective heating system. For radiant cooling
systems, with a higher air temperature in comparison to convective cooling, maintaining the same comfort level
is possible. Therefore, compared with conventional heating and cooling systems, it is possible to reduce the
energy loss due to ventilation, and infiltration is possible while maintaining the same comfort level.
Thermal comfort can be defined as the psychological condition that expresses satisfaction with the thermal
environment. Therefore, thermal comfort would be evaluated by asking all the occupants if they are satisfied
with their thermal environment. However, in order to design and control radiant heating and cooling systems, it
is necessary to predict the thermal comfort in a room without resorting to a polling result.
To provide an acceptable thermal environment to the occupants, the requirements for general thermal comfort,
e.g. predicted mean vote (PMV), operative temperature, and local thermal comfort (surface temperature,
vertical air temperature differences, radiant temperature asymmetry, draft, etc.) shall be taken into account.
5.1 General thermal comfort
Operative temperature and PMV can be used as a single index to evaluate general thermal comfort. For sizing
and dimensioning of radiant heating and cooling systems, operative temperature can be chosen as general
thermal comfort because the systems use radiative heat transfer from the surfaces. In order to design a hybrid
system combined with convective systems or to design considering factors related to the occupant such as
metabolic rate and clothing, a more comprehensive index, PMV can be used as a general thermal comfort
criterion. Meanwhile, when operative temperature and PMV are used in the control as well as the design, it is
possible not only to obtain a better comfort condition but also to save energy in buildings.
5.1.1 Operative temperature
In order to provide acceptable thermal conditions, two parameters, air temperature and mean radiant
temperature, should be taken into account. The combined influence of these two temperatures is expressed as
the operative temperature. In a place where air velocities are low (< 0,2m/s) or the difference between mean
radiant temperature and air temperature is small (< 4°C), the operative temperature can be approximated with
the simple average of air and mean radiant temperature. This means that air temperature and mean radiant
temperature have an equal importance with respect to the level of thermal comfort in a space. Compared with
a convective heating and cooling system, a radiant heating system can achieve the same level of operative
temperature at a lower air temperature and a radiant cooling system at a higher air temperature.
5.1.2 Definition
Operative temperature is defined as the temperature of a uniform isothermal black enclosure in which the
occupant
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