prEN ISO 14505-2

SLOVENSKI STANDARD
01-julij-2025
Ergonomija toplotnega okolja - Vrednotenje toplotnega okolja v vozilih - 2. del:
Ugotavljanje ekvivalentne temperature (ISO/DIS 14505-2:2025)
Ergonomics of the thermal environment - Evaluation of thermal environments in vehicles
- Part 2: Determination of equivalent temperature (ISO/DIS 14505-2:2025)
Ergonomie der thermischen Umgebung - Beurteilung der thermischen Umgebung in
Fahrzeugen - Teil 2: Bestimmung der Äquivalenttemperatur (ISO/DIS 14505-2:2025)
Ergonomie des ambiances thermiques - Évaluation des ambiances thermiques dans les
véhicules - Partie 2: Détermination de la température équivalente (ISO/DIS 14505-
2:2025)
Ta slovenski standard je istoveten z: prEN ISO 14505-2
ICS:
13.180 Ergonomija Ergonomics
43.020 Cestna vozila na splošno Road vehicles in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 14505-2
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment — Evaluation of
Voting begins on:
thermal environments in vehicles —
2025-05-01
Part 2:
Voting terminates on:
2025-07-24
Determination of equivalent
temperature
Ergonomie des ambiances thermiques — Évaluation des
ambiances thermiques dans les véhicules —
Partie 2: Détermination de la température équivalente
ICS: 13.180; 43.020
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Reference number
ISO/DIS 14505-2:2025(en)
DRAFT
ISO/DIS 14505-2:2025(en)
International
Standard
ISO/DIS 14505-2
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment — Evaluation of
Voting begins on:
thermal environments in vehicles —
Part 2:
Voting terminates on:
Determination of equivalent
temperature
Ergonomie des ambiances thermiques — Évaluation des
ambiances thermiques dans les véhicules —
Partie 2: Détermination de la température équivalente
ICS: 13.180; 43.020
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
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Published in Switzerland Reference number
ISO/DIS 14505-2:2025(en)
ii
ISO/DIS 14505-2:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Assessment principles . 2
4.1 General description of equivalent temperature .2
4.2 General determination principle of equivalent temperature .3
5 Specific equivalent temperatures . 4
5.1 General .4
5.2 Whole body equivalent temperature . .4
5.2.1 Determination principle .4
5.2.2 Calculation .4
5.3 Segmental equivalent temperature .5
5.3.1 Determination principle .5
5.3.2 Calculation .5
5.4 Directional equivalent temperature .5
5.4.1 Determination principle .5
5.4.2 Calculation .5
5.5 Omnidirectional equivalent temperature .6
5.5.1 Determination principle .6
5.6 Calculation .6
6 Measuring instruments . 7
7 Assessment . . 7
7.1 Determination of whole body equivalent temperature .7
7.1.1 Determination with omnidirectional sensors .8
7.1.2 Determination with a thermal manikin .8
7.2 Determination of local equivalent temperature .8
7.2.1 Determination with omnidirectional sensors or flat, heated sensors .8
7.2.2 Determination with a thermal manikin .8
8 Equivalent contact temperature t . 8
eq,cont
Annex A (informative) Examples of measuring instruments .12
Annex B (informative) Characteristics and specifications of measuring instruments .15
Annex C (informative) Calibration and other determinations .21
Annex D (informative) Interpretation of equivalent temperature .23
Annex E (informative) Examples .27
Bibliography .30

iii
ISO/DIS 14505-2:2025(en)
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,
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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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
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Any trade name used in this document is information given for the convenience of users and does not
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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 159, ergonomics, Subcommittee SC 5,
ergonomics of the physical environment.
This second edition cancels and replaces the first edition (ISO 14505-2:2006), which has been technically
revised.
The main changes are as follows:
— evaluation method for the contact areas (equivalent contact temperature)
A list of all parts in the ISO 14505 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/DIS 14505-2:2025(en)
Introduction
The interaction of convective, radiative and conductive heat exchange in a vehicle compartment is very
complex. External thermal loads in combination with the internal heating and ventilation system of the
vehicle create a local climate that can vary considerably in space and time. Asymmetric thermal conditions
arise, and these are often the main cause of complaints of thermal discomfort. In vehicles without or having
a poor heating, ventilating and air-conditioning system (HVAC-system), thermal stress is determined
largely by the impact of the ambient climatic conditions on the vehicle compartment. Subjective evaluation
is integrative, as the individual combines into one reaction the combined effect of several thermal stimuli.
However, it is not sufficiently detailed or accurate for repeated use. Technical measurements provide
detailed and accurate information but require integration in order to predict the thermal effects on humans.
Since several climatic factors play a role for the final heat exchange of a person, an integrated measure of
these factors, representing their relative importance, is required. This standard includes the equivalent
temperature models t for the assessment of the thermal conditions. For special consideration of the seat,
eq
the equivalent contact temperature t can be applied for body compartments in contact to surfaces.
eq,cont
v
DRAFT International Standard ISO/DIS 14505-2:2025(en)
Ergonomics of the thermal environment — Evaluation of
thermal environments in vehicles —
Part 2:
Determination of equivalent temperature
1 Scope
This part of ISO 14505 provides guidelines for the assessment of the thermal conditions inside a vehicle
compartment. It can also be applied to other confined spaces with asymmetric climatic conditions. It is
primarily intended for assessment of thermal conditions, when deviations from thermal neutrality are
relatively small. Appropriate methodology as given in this part of ISO 14505 can be chosen for inclusion in
specific performance standards for testing of HVAC-systems for vehicles and similar confined spaces.
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 13731, Ergonomics of the thermal environment — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13731 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
equivalent temperature t
eq
temperature of a homogenous space, with mean radiant temperature equal to air temperature and zero
air velocity, in which a person exchanges the same heat loss by convection and radiation as in the actual
conditions under assessment
3.2
whole body equivalent temperature t
eq,whole
temperature of an imaginary enclosure with the same temperature in air and on surrounding surfaces and
with air velocity equal to zero in which a full-scale, human shaped, heated sensor will exchange the same
dry heat by radiation and convection as in the actual non-uniform environment
3.3
segmental equivalent temperature t
eq,segment
uniform temperature of an imaginary enclosure with the same temperature in air and on surrounding
surfaces and with air velocity equal to zero in which one or more selected zones of a thermal manikin will
exchange the same dry heat by radiation and convection as in the actual non-uniform environment

ISO/DIS 14505-2:2025(en)
3.4
directional equivalent temperature t
eq,direct
uniform temperature of an imaginary enclosure with the same temperature in air and on surrounding
surfaces and with air velocity equal to zero in which a small flat heated surface will exchange the same dry
heat by radiation and convection as in the actual non-uniform environment
3.5
omnidirectional equivalent temperature t
eq,omni
uniform temperature of an imaginary enclosure with the same temperature in air and on surrounding
surfaces and with air velocity equal to zero in which a heated ellipsoid will exchange the same dry heat by
radiation and convection as in the actual non-uniform environment
3.6
equivalent contact temperature t
eq,cont
uniform temperature of an imaginary contact surface, at room air speed close to zero, at which a person will
exchange the same amount of dry heat through thermal conduction for a virtual clothing insulation as in
the actual non-uniform environment, where the person experiences sensible and latent heat transfer at the
considered body parts
3.7
segment
part of a human-shaped sensor, normally corresponding to a real body-part, consisting of one or several
whole zones, for which a segmental equivalent temperature, t , is presented
eq,segment
3.8
zone
physical partition of a manikin, which is independently regulated and within which the surface temperature
and heat exchange is measured
3.9
HVAC-system
heating, ventilating and air-conditioning system of the vehicle and/or cabin
4 Assessment principles
The assessment principle is based on the measurement of the equivalent temperature. The equivalent
temperature provides a unified, physical measure of the climatic effects on the human dry heat exchange.
On the basis of the actual value for, and the variation in, equivalent temperature, it is possible to predict
the conditions for heat balance under conditions in or close to the thermoneutral zone. People’s thermal
sensation is primarily influenced by general and local levels and variations in skin surface heat flux. Values
for the equivalent temperature of a defined environment have been found to be closely related to how people
perceive thermal conditions when exposed to the same environment. This can be used for the interpretation
of the t value and assessment of the quality of the environment.
eq
The climate is assessed in terms of a total equivalent temperature, which describes the level of thermal
neutrality.
The climate is also assessed for local effects on defined parts of the human body surface. The local equivalent
temperatures determine to what extent the actual body parts fall within the range of acceptable levels of
heat loss (local discomfort).
4.1 General description of equivalent temperature
The equivalent temperature is a pure physical quantity, that in a physically sound way integrates the
independent effects of convection and radiation on human body heat exchange. This relationship is best
described for the overall (whole body) heat exchange. There is limited experience with relations between
local dry heat exchange and local equivalent temperature. The standardized definition of t applies only for
eq
the whole body. Therefore, the definition has to be modified for the purposes of this part of ISO 14505. t
eq
ISO/DIS 14505-2:2025(en)
does not take into account human perception and sensation or other subjective aspects. However, empirical
studies show that t values are well related to the subjective perception of the thermal effect.
eq
4.2 General determination principle of equivalent temperature
Determination of t is based on equations for convective and radiative heat transfer for clothed persons.
eq
Heat exchange by conduction is assumed to be small and accounted for by radiation and convection.
Rh=×()tt− (1)
rskr
Ch=×()tt− (2)
cska
where
R is heat exchange by radiation, in watts per square metre (W/m );
C is heat exchange by convection, in watts per square metre (W/m );
h is the radiation heat transfer coefficient, in watts per square metre degree Celsius [W/(m °C)];
r
h is the convection heat transfer coefficient, in watts per square metre degree Celsius [W/(m °C)];
c
t is the skin temperature, in degrees Celsius (°C);
sk
t
is the mean radiant temperature, in degrees Celsius (°C);
r
t is the ambient air temperature, in degrees Celsius (°C).
a
In practice the equivalent temperature is determined and defined by
Q
tt= − (3)
eq s
h
cal
where
t is the surface temperature, in degrees Celsius (°C);
s
t is the temperature of the standard environment, in degrees Celsius (°C);
eq
Q is the measured convective and radiative heat loss during the actual conditions, in watts per square
metre (W/m );
QR=+C (4)
h is the combined heat transfer coefficient, determined during calibration in a standard environment,
cal
in watts per square metre degree Celsius [W/(m °C)].
The standard environment comprises homogenous, uniform thermal conditions with t = t and air velocity
a r
v , < 0,1 m/s. A suitable calibration procedure is described in Annex C.
a
ISO/DIS 14505-2:2025(en)
5 Specific equivalent temperatures
5.1 General
As there is no method available for measurement of the true total or local t , four specific equivalent
eq
temperatures are calculated according to different principles, according to 5.2 to 5.5. Depending on different
measuring principles, they are defined as
1. whole body equivalent temperature,
2. segmental equivalent temperature,
3. directional equivalent temperature,
4. omnidirectional equivalent temperature.
5.2 Whole body equivalent temperature
5.2.1 Determination principle
The principle of determination is to measure the total heat flow from a human-sized test manikin consisting
of several zones, each with a specific measured surface temperature similar to that of a human being.
Theoretically whole body equivalent temperature can be measured with thermal manikins or a large
number of flat heated sensors attached to an unheated manikin. The accuracy of the result is depending
on surface temperature, size of body, number and division of zones, posture etc. An appropriate method
to use is a thermal manikin divided into separate, individually heated zones covering the whole body, with
surface temperatures close to that of a real human being. A human-sized manikin with only one zone will
not determine a realistic whole body t because the thermal conditions vary too much over the surface. The
eq
more zones the manikin has, the more correct value it will measure.
5.2.2 Calculation
Q
whole
tt= − (5)
eq,whole sk,whole
h
cal,whole
tA⋅
()
∑ sk,n n
t = (6)
sk,whole
A
∑ n
QA⋅
()
∑ nn
Q = (7)
whole
A
n
∑
where
A is a weighting factor based on the surface area;
h is determined by calibration in a standard environment (see Annex C);
cal,whole
n is the number of zones of the body (0 < n ≤ N).
In order to be able to compare results from other manikins, the measured t should be presented together
eq
with specifications of the manikin used, such as regulation principle, skin temperature, number of zones etc.
(see Annexes A and B).
ISO/DIS 14505-2:2025(en)
5.3 Segmental equivalent temperature
5.3.1 Determination principle
The principle of determination is to measure the total heat flow from a segment consisting of one or more
zones, each with a specific measured surface temperature similar to that of a human being.
The segmental t is based on the heat flow from a certain part of the body, i.e. a segment, such as hand,
eq
head or chest. The segmental t can only be measured with a full-sized, human-shaped heated sensor,
eq
e.g. a thermal manikin. The number of zones and the partition between them must at least be such that it
corresponds to the actual segment that the segmental t should be measured for. Some segments, e.g. thigh,
eq
need to be divided into at least two zones within the segment, because the thermal conditions are different
on the front and the rear (seat contact) side in the case of the thigh.
5.3.2 Calculation
Q
segment
tt= − (8)
eq,segment sk,segment
h
cal,segment
tA⋅
()
∑ sk,n n
t = (9)
sk,segment
A
∑ n
QA⋅
()
∑ nn
Q = (10)
segment
A
∑ n
where
h is determined by calibration in a standard environment (see Annex C);
cal,segment
n is the number of zones of the body (0 < n ≤ N).
The segment can be freely chosen, but it must consist of one or more whole zones. Normally body parts
like head, hands, arms, feet, legs, chest, back and seat are chosen. To be able to compare results from other
measurements, the measured t should be presented with specifications about the segment used, such
eq
as regulation principle, surface temperature, which body part, number, size and partition of zones of the
segment (see Annexes A and B).
5.4 Directional equivalent temperature
5.4.1 Determination principle
The principle of determination is to measure the total heat flow from a small flat surface with a measured
surface temperature. The directional t can be described as a normal vector to the measuring plane in
eq
every point, defined by magnitude and direction. It refers to the heat exchange within the half-sphere in
front of the infinitesimal plane. The directional t can only be measured with a flat sensor, which might
eq
or might not be attached to an unheated manikin or other positioning device. Several sensors can be used
simultaneously to determine directional t at other locations or in other directions, provided that they are
eq
positioned so that they do not influence each other.
5.4.2 Calculation
Q
direct
tt= − (11)
eq,directsk,direct
h
cal,direct
ISO/DIS 14505-2:2025(en)
where
t is the surface temperature of the sensor;
sk,direct
Q is the heat flow from the sensor;
direct
h is determined by calibration of the sensor in a standard environment (see Annex C).
cal,direct
A local equivalent temperature, t , can be calculated as an average value from several measurements
eq,local
at the same location but in different directions. It can be calculated as an arithmetic mean value without
weighting factors (equation 12) or with weighting (equation 13) to simulate a certain body posture.
t
∑ eq,direct,n
t = (12)
eq,local
n
where n is the number of directions.
tt= ⋅A (13)
()
eq,local eq,direct,nn
∑
where n is the number of measurements, with Σ(A ) = 1, and A represents body postures.
n
A total equivalent temperature can be calculated as a weighted mean value of local equivalent temperatures.
tt= ⋅A (14)
()
eq,total ∑ eq,local,nn
where n is the number of locations, with Σ(A ) = 1.
n
In order to be able to compare results from other measurements, the measured t should be presented
eq
with specifications about the sensor used, such as regulation principle, surface temperature, size and also
location and direction of the sensor (see Annexes A and B). Whole body t and total t is not the same. In an
eq eq
asymmetric climate and with seat contact the difference between them will be considerable.
5.5 Omnidirectional equivalent temperature
5.5.1 Determination principle
The principle of determination is to measure the total heat flow from the surface of an ellipsoid with a
measured surface temperature. The omnidirectional t can be described as the weighted mean value of
eq
the directional t in all directions. The weighting factors for the different directions are dependent of the
eq
form of the ellipsoid. It refers to the heat exchange in all directions. The omnidirectional t can only be
eq
measured with an ellipsoid sensor with uniform heat flow over the surface. One or more sensors can be used
simultaneously. If more than one sensor is used, it must be pointed out that the sensors will influence each
other as hot surfaces in the sphere that is measured.
5.6 Calculation
Q
omni
tt= − (15)
eq,omnisk,omni
h
cal,omni
where
t is the surface temperature of the sensor;
sk,omni
Q is the heat flow from the sensor;
omni
h is determined by calibration of the sensor in a standard environment (see Annex C).
cal,omni
ISO/DIS 14505-2:2025(en)
Omnidirectional t determined with one ellipsoid sensor in an asymmetric climate is a local t . A total t
eq eq eq
can be calculated as an arithmetic mean value from sensors at different locations with weighting factors for
different body parts according to SAE J 2234.
tt= Σ⋅A (16)
()
eq,total eq,loca,ln n
where n is the number of locations, with Σ(A ) = 1.
n
In order to be able to compare results from other measurements, the measured t should be presented
eq
with specifications about the sensor used, such as regulation principle, surface temperature, size and also
location and direction of the sensor (see Annexes A and B).
6 Measuring instruments
Several measurement methods and instruments, representing different measuring principles, are given in
Annexes A and B. Depending on needs, a method as given in Annex A should be selected.
Measurement values obtained with principally different methods are not comparable with each other. They
represent different levels in terms of
— reliability,
— relevance,
— validity,
— repeatability,
— accuracy,
— integration,
— complexity,
— cost, and
— availability
Performance and requirements of the specific methods are given in Annex B. Requirements for calibration
procedures are given in Annex C.
7 Assessment
The equivalent temperature represents a quantitative assessment of the conditions for physical heat
exchange. The numeric value of t is a temperature level that can come close to “normal” expected room
eq
temperatures. Higher t values indicate lower heat losses (“warmer”), while lower t values indicate higher
eq eq
heat losses (“colder”).
The interpretation of equivalent temperature in terms of anticipated perceived thermal sensation is based
on series of experiments with participants in which the different types of equivalent temperature have been
measured. Examples of interpretation are given in Annex C. For some types of equivalent temperature, data
are not available for comparison with human responses. Nevertheless, these kinds of measurement can be
used for differential measurements of thermal conditions.
7.1 Determination of whole body equivalent temperature
Determination of whole body equivalent temperature should preferably be done with measurements using
a thermal manikin or by integration of discrete measurements using omnidirectional sensors placed at
defined positions in the vehicle cabin.

ISO/DIS 14505-2:2025(en)
7.1.1 Determination with omnidirectional sensors
Omnidirectional sensors are described in Annexes A and B. Sensors are placed on a stand simulating a person
and placed in a seat of the vehicle. At least six sensors are placed in relevant positions and measurements
are made when steady state is achieved. Whole body equivalent temperature is determined as the area-
weighted average of the individual sensors. Interpretation of values should be made according to Annex D.
7.1.2 Determination with a thermal manikin
Requirements for the manikin and procedures are described in Annexes A and B. The manikin is placed in a
seat in the vehicle and whole body heat loss is measured when steady state conditions are achieved. Whole
body heat loss is the area-weighted average of the independent segments of the manikin. Interpretation of
values should be made according Annex D.
7.2 Determination of local equivalent temperature
Determination of whole body equivalent temperature should preferably be done with measurements using a
thermal manikin or by the integration of discrete measurements using omnidirectional sensors.
7.2.1 Determination with omnidirectional sensors or flat, heated sensors
Omnidirectional sensors are described in Annex A. Sensors are placed on a stand simulating a person and
placed in a seat of the vehicle or at defined spots on the surface of the clothing of a person or a manikin.
Measurements are made when steady state is achieved. Local equivalent temperature is determined as the
value of the individual sensor. The more sensors located in the space, the better resolution of the variation in
the thermal field around the human body.
7.2.2 Determination with a thermal manikin
Requirements for the manikin and procedures are described in Annexes A and B. The manikin is placed
in a seat in the vehicle and heat loss is measured from a local segment of the manikin when steady state
conditions are achieved. Local equivalent temperature is determined by the measured value of the individual
segment and represent that particular segment only. Interpretation of values should be made according to
Annex D.
8 Equivalent contact temperature t
eq,cont
The heat exchange between a person and a contacting surface by heat conduction as well as moisture is
not negligible and has a significant influence on the thermal sensation. The calculation of the equivalent
contact temperature t is based on the equations for heat conduction as well as latent and sensible heat
eq,cont
exchange between a clothed person and the contacting surfaces.
As shown in Figure 1, the principles for definition of the equivalent contact temperature t and
eq,cont
equivalent temperature t are similar to each other and both depend on the air velocity v in the real
eq air
environment. In the equivalent temperature model, the equivalent heat flux q depends on the convective
eq
q and radiant heat fluxes q in the real environment with the determined radiant temperature t , air
conv rad r
temperature t and skin temperature t . The equivalent contact temperature t includes the detailed
air skin eq,cont
description of the thermodynamic situation at the contact interface between a seat and the human body
surface. Here, the equivalent heat flux q depends on the combined effect of heat conduction through
eq,cont
the clothing q and the seat q as well as the change in enthalpy due to sensible and latent heat transfer
clo seat
in the real environment, such as by the moisture flow from skin to contact area q . These mechanisms can
evp
be influenced by the use of mechanically induced air flow rates (e.g. seat ventilation, q - q ) or heat
air,out air,in
sources (e.g. seat heating, q ).
heat
This chapter describes an index for evaluating the thermal comfort of seats. This evaluation method is
basically based on experiments with participants, but it can also be applied to evaluations using thermal
manikins, as described in the previous chapter, by replacing the evaporation effects of perspiration on the

ISO/DIS 14505-2:2025(en)
seat contact surface with a theoretical model. This means a suitable theoretical sweating model is available
for evaluating t with a thermal manikin instead of a participant.
eq,cont
Calculation methodology:
As can be seen from Figure 1, the calculation of t is based on the balance of heat flux densities at an
eq,cont
infinitesimal volume element (green area). The equivalent heat flux q (Figure 1b, right-hand side)
eq,cont
depends on the heat fluxes in the real environment (Figure 1b, left-hand side) according to the equations
in the centre of Figure 1b. The volume element is represented by node K at which the energy balance is
performed. Furthermore, K represents the contact interface between the human body and any kind of
contacting surface.
Figure 1 — Definition and physical interpretation of the equivalent temperature (a) and equivalent
contact temperature (b). The t is described using a nodal energy balance at node K (left-hand
eq,cont
side: heat fluxes in real environment, right-hand side: heat flux in equivalent environment with a
calibrated insulation value R ).
calib
The energy balance at node K is described by (17), where negative quantities leave K and positive ones enter K.
q+qq−−+q q+q=0 (17)
cloevp seat air,in air,outheat

ISO/DIS 14505-2:2025(en)
where
q is the heat flux density through the clothing, in watts per square metre (W/m );
clo
q is the heat flux density of the moisture flow through the clothing, in watts per square metre (W/m );
evp
q is the heat flux density through the seat, in watts per square metre (W/m );
seat
q is the heat flux density of the incoming mass air flow by seat fan, in watts per square metre (W/m );
air,in
q is the heat flux density of the outgoing mass air flow by seat fan, in watts per square metre (W/
air,out out
m );
q is the heat flux density of an optional internal heat source, in watts per square metre (W/m ).
heat
The heat flux densities in the real environment, visualized on the left-hand side of Figure 1b are subsequently
described with the heat flux density through the clothing layer q (18), the evaporative heat flux density
clo
between skin and contact area q (19), the conductive heat flux density through the seat q (20), the
evp seat
outgoing heat flux density due to the seat ventilation q (21) as well as the incoming heat flux density
air,out
due to the seat ventilation q (22) and the heat flux generated by the use of a heat source q (23).
air,in heat
tt−
skin nod
q= (18)
clo
R
clo

mr⋅⋅+ct ⋅()xx−
()
da 0 P,vapskinnod env
q= (19)
evp
A
cont
tt−
nodenv
q= (20)
seat
R
seat

mc×+⋅⋅tx (r +ct⋅ )
()
da P,da nodnod 0P,vap nod
q= (21)
air,out
A
cont
mc ⋅⋅tx+(⋅⋅rc+)t
()
da P,da envenv 0P,vap env
q= (22)
air,in
A
cont
A Q
cont el
q= ⋅⋅η (23)
heat
A A
tot tot
where
A is the contacting surface area related to a person’s body, in square metres (m );
cont
A is the total heated seat surface area, in square metres (m );
tot
c is the specific heat capacity of water vapor (= 2 080 J/(kg °C)), in joules per kilogram degree Celsius
p,vap
[J/(kg °C)];
c is the specific heat capacity of dry air (= 1 005 J/(kg °C)), in joules per kilogram degree Celsius [J/
p,da
(kg °C)];

m is the mass flow rate generated by the seat fans, in kilograms per second (kg/s);
da
Q is the electrical power consumed by the seat heating, in watts (W);
el
r is the specific heat for vaporization of water (= 2 256 kJ/kg), in joules per kilogram (J/kg);
ISO/DIS 14505-2:2025(en)
R is the thermal resistance of the clothing combination, in square metres degree Celsius per watt
clo
[(m °C)/W];
R is the thermal resistance of the seat or the contacting surface, in square metres degree Celsius per
seat
watt [(m °C)/W];
t is the ambient temperature, in degrees Celsius (°C);
env
t is the local skin temperature, in degrees Celsius (°C);
skin
t is the contact area temperature in the real environment, in degrees Celsius (°C);
nod
x is the specific humidity of the surrounding air, in kilograms per kilogram (kg/kg);
env
x is the specific humidity at contact area, in kilograms per kilogram (kg/kg);
nod
is the electrical efficiency of the seat heating (-).
η

If m = 0 , evaporative heat (e.g. sweating and insensible perspiration) is ignored.
da
Replacing the single terms in (17) by equations (18) – (23) and rearranging the terms, finally leads to (24),
which holds the mathematical model for the calculation of t .
nod
mx ⋅ −xc⋅
()
 
1 da nodenv P,vap
+ ⋅t
 
skin
R A
clo cont
 
t =
nod
mc ⋅⋅+xc
()
1 1 da P,da nodP,vap
+ +
R RR A
clo seat cont
(24)
  
mc⋅ +x ⋅c
()
da P,da envvP,vap
 + ⋅tq+
envheat
 
R A
seat cont
 
+

mc⋅ ++xc⋅
()
1 1 da P,da nodP,vap
+ +
RR A
closeat cont
Since the equivalent heat flux depends on the heat fluxes in the real thermal environment, as described in
Figure 1, it can be calculated by application of the heat fluxes on the environmental-side or skin-surface-
side of the balance with equations (25) or (26), respectively. R is a fixed, calibrated insulation value
calib
corresponding to a generally defined virtual clothing insulation.
tt=−Rq⋅+qq−−q (25)
()
eq ,,cont skin calibseatair outair ,in heat
tt=−Rq⋅+q (26)
()
eq ,cont skin calibclo evp
where R is the virtual thermal resistance between t and t , in square metres Kelvin per watt
calib eq,cont skin
[(m °C)/W].
As mentioned in the introduction to this chapter, x should be measured by experiments with participants,
nod
but it can also be estimated using a theoretical sweating model instead of a thermal manikin. As a result, it
can also be used to evaluate air conditioning seats of a blow-out type, which are difficult to measure with.

ISO/DIS 14505-2:2025(en)
Annex A
(informative)
Examples of measuring instruments
A.1 Thermal manikins
A thermal manikin comprises a human-sized and -shaped sensor with its surface covered with numerous,
individually controlled, heated zones. It is suitable for measurement of whole body as well as local t . The
eq
independent zones of the manikin are heated to a controlled and measured temperature. Low-voltage
power is pulsed to each zone at a rate that allows the maintenance of a chosen constant or variable surface
temperature. It is also possible to main
...