ISO/DTR 23672

Ergonomics of the thermal environment: Adaptive methods for achieving thermal comfort

Titre manquant

General Information

• Status: Not Published
• ICS: 13.180 - Ergonomics
• Technical Committee: ISO/TC 159/SC 5 - Ergonomics of the physical environment
• Drafting Committee: ISO/TC 159/SC 5 - Ergonomics of the physical environment
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 01-Dec-2025
• Completion Date: 01-Dec-2025

Standards Content (Sample)

FINAL DRAFT
Technical
Report
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment: Adaptive methods for
Voting begins on:
achieving thermal comfort
2025-12-01
Titre manquant
Voting terminates on:
2026-01-26
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 SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
Technical
Report
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment: Adaptive methods for
Voting begins on:
achieving thermal comfort
Titre manquant
Voting terminates on:
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 SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Approaches to adaptive thermal comfort models . 3
5 Regression based adaptive comfort models . 3
5.1 Background and model formulation .3
5.2 Model development . . .4
5.3 Values for model coefficients .4
5.4 Model application in national and international standards.4
6 Adaptive PMV (aPMV) model . 5
6.1 General .5
6.2 Background and model formulation .5
6.3 Model development . . .7
6.4 Values for model coefficients .8
6.5 Model application in national and international standards.8
7 The adaptive thermal heat balance (ATHB) model . 8
7.1 General .8
7.2 Background and model formulation .8
7.3 Model development . . .9
7.4 Values for model coefficients .9
7.5 Model application in national and international standards.9
Annex A (informative) Derivation and recommendations of adaptive coefficients for aPMV .10
Annex B (informative) Derivation of equations and coefficients for ATHB .12
PMV
Bibliography .15

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document 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
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5,
Ergonomics of the physical environment.
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
Introduction
This document is one of a series of standards, specifying methods of measuring and evaluating moderate
and extreme thermal environments to which people are exposed at working practices.
In this series of standards, there already exist several documents related to moderate thermal environments
at working practices.
— ISO 7726, Ergonomics of the thermal environment — Instruments for measuring physical quantities;
— ISO 7730, 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 8996, Ergonomics of the thermal environment — Determination of a metabolic rate;
— ISO 9920, Ergonomics of the thermal environment — Estimation of thermal insulation and water vapour
resistance of a clothing ensemble;
— ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols
— ISO/TS 13732-2, Ergonomics of the thermal environment — Methods for the assessment of human responses
to contact with surfaces — Part 2: Human contact with surfaces at moderate temperature;
— ISO 14505 (series), Ergonomics of the thermal environment — Evaluation of thermal environments in
vehicles;
— ISO 17772-1, Energy performance of buildings — Indoor environmental quality — Part 1: Indoor
environmental input parameters for the design and assessment of energy performance of buildings;
— ISO 17772-2, Energy performance of buildings — Overall energy performance assessment procedures —
Part 2: Guideline for using indoor environmental input parameters for the design and assessment of energy
performance of buildings.
These standards give methods for evaluation of the thermal environment. This document covers the
evaluation of thermal sensation and comfort considering seasonal adaptive mechanisms to moderate
thermal environments.
A human being’s thermal sensation is mainly related to the thermal balance of their body as a whole.
This balance is influenced by physical activity and clothing, as well as the environmental parameters: air
temperature, mean radiant temperature, air velocity and air humidity. At the same time, thermal sensation
and comfort are additionally affected among others by seasonal differences in the human being’s state
of thermal adaptation. The mechanisms leading to thermal adaptation are grouped into physiological,
behavioural, and psychological. These effects are only partially considered in other methods for determining
thermal sensation. Adaptive thermal comfort models consider all known adaptive mechanisms in the
prediction of thermal sensation votes or comfort ranges. Therefore, in this document, first, an overview of
existing approaches is presented. Second, three examples of adaptive thermal comfort models are featured in
this document. For each example, the background and model formulation, steps towards model development
and implementation and the application in national and international standards are described.
This document is intended to be used with reference to ISO 28803, when considering persons with special
requirements, such as those with physical disabilities. Ethnic, national or geographical differences must also
to be taken into account.
v
FINAL DRAFT Technical Report ISO/DTR 23672:2025(en)
Ergonomics of the thermal environment: Adaptive methods
for achieving thermal comfort
1 Scope
This document defines adaptive thermal comfort and its mechanisms, and describes current approaches to
predict adaptive thermal comfort.
This document applies to human thermal comfort in indoor built environments and seasonal adaptive
processes. It is applicable to healthy humans exposed to indoor environments where thermal comfort is
desirable, but where moderate deviations from thermal comfort occur, in the design of new environments or
the assessment of existing ones.
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
thermoregulation
accommodation
acute response to a (thermal) stimuli supporting homeostatic regulation
3.2
adaptation
changes that reduce the (physiological or psychological) strain produced by stressful components of the
total environment
Note 1 to entry: This change can occur within the lifetime of an organism (phenotypic) or be the result of genetic
selection in a species or subspecies (genotypic).
[SOURCE: Glossary of terms for thermal physiology]
3.2.1
adaptation
behavioural changes like changing posture or activity, clothing level adjustments or
adjustments to the indoor thermal environment (e.g. window opening or using a fan) that affect the human
body’s heat balance
3.2.2
adaptation
altered response of the thermoregulation system through adjustments in physiological
parameters, such as the onset of sweating as a consequence of repeated warm or cold stimuli that reduces
thermal stress on the human body
3.2.3
adaptation
changes in perception of, and reaction to, sensory information from thermoreceptors
due to habituation, changed expectations, or perceived control influenced by a person’s longer history of
experiences with indoor and outdoor climate
3.3
adaptive thermal comfort
all known adaptive mechanisms in the prediction of thermal sensation votes or comfort ranges
3.4
mean daily outdoor air temperature
t
mda
arithmetic mean of outdoor air temperature for a 24-hour period used to calculate prevailing mean outdoor
air temperature (t )
pma
3.5
mean monthly outdoor air temperature
t
a(out)
arithmetic average of the mean daily minimum and mean daily maximum outdoor (dry-bulb) temperatures
for the month in question when used as an input variable for the adaptive model
3.6
neutral operative temperature
t
o n
operative temperature at which the average person will be thermally neutral
3.7
prevailing mean outdoor air temperature
t
pma
arithmetic average of the mean daily outdoor temperatures over some period of days, which are no fewer
than seven and no more than 30 sequential days prior to the day in question in the adaptive model
3.8
running mean outdoor temperature
t
rm
exponentially weighted running mean of the daily mean outdoor air temperature in the adaptive model
3.9
predictive mean vote
PMV
standard index that predicts the mean value of the votes of a large group of persons on the 7 point thermal
sensation scale based on the heat balance of the human body
3.10
predicted percentage of dissatisfied
PPD
standard index that establishes a quantitative index related to the percentage of thermally dissatisfied
people who feel too cool or too warm

4 Approaches to adaptive thermal comfort models
Approaches to model human thermal comfort include:
a) the heat balance (e.g. PMV) or thermophysiological (e.g. Gagge’s 2-node) approach,
b) adaptive models based on regression-analysis, and
[1]
c) a combination of heat balance and thermophysiological models with the adaptive approach.
The heat balance approach focuses on the heat balance between the human body and the surrounding
[2]
environment, while thermophysiological approaches include the physiological responses of the human
[3]
body such as vasoconstriction, vasodilation, sweat secretion, skin wettedness, and blood flow rate. The
latter two modelling approaches b) and c) including the adaptive views on human thermal perception
consider the human being as an active player in the relationship between environmental conditions
and individual perception. Thermal adaptation in contrast to accommodation is considering long-term
[4]
adjustments and includes three mechanisms: physiological, behavioural and psychological adaptations.
Physiological adaptation includes a variety of processes that altered the response of the thermoregulation
system to thermal stimuli. These processes include adjustments in physiological parameters, such as
the onset of sweating or altered body core temperatures. Behavioural adaptation consists of changes in
behavioural reactions like changing posture or activity, clothing level adjustments or adjustments to the
indoor thermal environment (e.g. window opening or using a fan) that affect the human body’s heat balance.
Psychological adaptation is used to describe changes in perception of, and reaction to, sensory information
from thermoreceptors due to habituation, changed expectations, or perceived control influenced by a
person’s longer history of experiences with indoor and outdoor climate.
[1]
A large variety of adaptive thermal comfort models exists. The adaptive thermal comfort models based
on regression analysis (Clause 5) establish the indoor thermal comfort temperature or neutral operative
temperature as a function of outdoor air temperatures and are mainly based on data from field studies.
[5]
Combinations of heat balance or thermophysiological models with the adaptive approach are based on
[1]
combinations of field and laboratory work (Clauses 6 and 7). These approaches can differ in the underlying
heat balance and thermoregulation model, and in the way the adaptive processes are modelled.
This document presents three examples focusing on adaptive approaches:
[4]
— the regression based adaptive comfort models, which do not explicitly consider the human heat balance
nor thermoregulation (Clause 5),
[6]
— the adaptive PMV (aPMV) model, which is based on the heat balance equations of the PMV index and
quantifies occupants’ feedback loop of thermal adaptations with coefficient lambda (Clause 6),
[7],[8]
— the adaptive thermal heat balance model (ATHB), which is a framework for models based on the heat
balance equations of the PMV index, and considers each adaptive mechanisms individually (Clause 7).
5 Regression based adaptive comfort models
5.1 Background and model formulation
Regression models consider that all three adaptive mechanisms are driven by seasonal changes, which can
be represented by the outdoor environmental conditions. Hence, the neutral operative temperature for
occupants who have the opportunity to interact with the building and its devices relates primarily to the
outdoor environmental conditions.

This relationship is commonly expressed as shown in Formula (1):
t = a *·T + b, (1)
o n o
where
t is the neutral operative temperature;
o n
T is the outdoor reference temperature;
o
a is the slope of the function, proportional to the degree of adaption to the regional climatic
[4]
conditions ;
b is the y-intercept.
The shortcoming of the regression model is its neglect of influences of other indoor environmental factors
and its lack of ability to distinguish between the three adaptive mechanisms.
5.2 Model development
The regression-based adaptive models are commonly based on data collected from field studies. There are
two main methods to obtain the regression-based adaptive model.
First, a linear regression according to Formula 1 in which mean t of a group of subjects (or t of each
o n o n
[9]
individual subject) is plotted versus an outdoor reference temperature. This method relies on the
[10]
statistical significance of the regression model, requiring a large number of data in each subset.
[11]
Second, the Griffiths method is used to derive t from small sample sizes containing less thermal
o n
variability. Here, t is defined as the temperature corresponding to neutrality and can be calculated for
o n
each vote.
The neutral operative temperature can be inferred by Formula (2):
t = T – TSV/G (2)
o n o
−1
where G is the Griffiths constant, °C .
The value for constant G varies according to the literature and whether it is a constant or a variable is still
[12]
debated.
Different variations for the outdoor reference temperature exist: exponentially weighted mean outdoor
temperature called the “running mean outdoor temperature”, t , the mean monthly outdoor air
rm
temperature, t , derived from a typical meteorological year (TMY) data file or based on mean daily
a (out)
outdoor air temperature, t , the prevailing mean outdoor air temperature, t , or actual measurements.
mda pma
No study is available, which confirms potential differences in the choice of coefficients depending on the
chosen variation of outdoor reference temperature.
5.3 Values for model coefficients
Adaptive models have been developed for different building types and in different climate zones around
[13] [14]
the world. In addition to common building types, such as residential buildings, office buildings,
[15] [16] [17]
commercial buildings, hospital buildings and school buildings.
5.4 Model application in national and international standards
Regression based adaptive comfort models have been introduced into national and international standards
since 2004. Examples for the chosen outdoor reference temperature and coefficients are shown in Table 1.

Table 1 — Conditions for the regression-based adaptive comfort models in naturally ventilated
buildings
Standard Outdoor Category T upper limit, °C T lower limit, °C Outdoor tempera-
op op
reference ture range, °C
t
pma(out)
ASHRAE 90 % ac-
10-33,5
03,*12t + 03, 03,*11t + 53,
55 ceptability
pmaout pmaout
() ()
80 % ac-
10-33,5
03,*12t + 13, 03,*11t + 43,
ceptability
pmao()ut pmao()ut
ISO 17772- t 10-30 upper, 15-30
rm
I 0,33 * t + 20,8 0,33 * t + 16,8
rm rm
1 lower
10-30 upper, 15-30
II 0,33 * t + 21,8 0,33 * t + 15,8
rm rm
lower
10-30 upper, 15-30
III 0,33 * t + 22,8 0,33 * t + 14,8
rm rm
lower
6 Adaptive PMV (aPMV) model
6.1 General
The aPMV model adjusts the existing PMV index to account for thermal adaptation by means of correction
[6]
factors based on occupants’ feedback loop.
6.2 Background and model formulation
The index of aPMV assumes occupants’ behavioural and psychological adaption as “adaptive feedback”, K ,
δ
to their thermal sensation, as is shown in Figure 1.
Key
G calculation process of original PMV
δ inputs of PMV
K adaptive feedback
δ
aPMV adaptive PMV
[6]
Figure 1 — Model diagram of aPMV
In Figure 1, the PMV model can be represented by Formula (3):
PMV = G × δ (3)
where
G is the calculation process of original PMV;
δ represents the inputs of PMV.

After introducing “adaptive feedback”, the calculation process in Figure 1 is transformed as shown in
Formula (4):
PMV
aPMV = (4)
1+×λ PMV
Where λ
...

© ISO #### – All rights reserved
ISO/TC 159/SC 5
Secretariat: BSI
Date: 2025-11-17
Ergonomics of the thermal environment: Adaptive methods for
achieving thermal comfort
Titre manquant
ISO #####-#:####(X/DTR 23672:(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
© ISO #### 2025 – All rights reserved
ii
ISO #####-#:####(X/DTR 23672:(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Approaches to adaptive thermal comfort models . 4
5 Regression based adaptive comfort models . 5
5.1 Background and model formulation . 5
5.2 Model development . 5
5.3 Values for model coefficients . 6
5.4 Model application in national and international standards . 6
6 Adaptive PMV (aPMV) model . 7
6.1 General . 7
6.2 Background and model formulation . 7
6.3 Model development . 10
6.4 Values for model coefficients . 11
6.5 Model application in national and international standards . 11
7 The adaptive thermal heat balance (ATHB) model . 12
7.1 General . 12
7.2 Background and model formulation . 12
7.3 Model development . 12
7.4 Values for model coefficients . 12
7.5 Model application in national and international standards . 13
Annex A (informative) Derivation and recommendations of adaptive coefficients for aPMV . 14
Annex B (informative) Derivation of equations and coefficients for ATHB . 16
PMV
Bibliography . 20

© ISO #### 2025 – All rights reserved
iii
ISO #####-#:####(X/DTR 23672:(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, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documentsdocument 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).
Field Code Changed
Attention is drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which may be
obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for
identifying any or all such patent rights. Details of any patent rights identified during the development of the
document will be in the Introduction and/or on the ISO list of patent declarations received (see ).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
Field Code Changed
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 5,
Ergonomics of the physical environment.
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.
© ISO #### 2025 – All rights reserved
iv
ISO #####-#:####(X/DTR 23672:(en)
Introduction
This document is one of a series of standards, specifying methods of measuring and evaluating moderate and
extreme thermal environments to which people are exposed at working practices.
In this series of standards, there already exist several documents related to moderate thermal environments
at working practices:.
— EN ISO 7726, Ergonomics of the thermal environment –— Instruments for measuring physical quantities;
— EN ISO 7730, 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;
— EN ISO 8996, Ergonomics of the thermal environment — Determination of a metabolic rate;
— ISO 9920, Ergonomics of the thermal environment –— Estimation of thermal insulation and water vapour
resistance of a clothing ensemble;
- EN ISO 8996, Ergonomics of the thermal environment – Determination of a metabolic rate;
— ISO 13731, Ergonomics of the thermal environment— — Vocabulary and symbols
— ISO/TS 13732-2, Ergonomics of the thermal environment –— Methods for the assessment of human
responses to contact with surfaces –— Part 2: Human contact with surfacesurfaces at moderate temperature;
- TS 14415,ISO 14505 (series), Ergonomics of the thermal environment – Application of international standards
to people with special requirements;
— EN ISO 14505 series, Ergonomics of the thermal environment –— Evaluation of thermal environments in
vehicles – Determination of equivalent temperature.;
— ISO 17772-1, Energy performance of buildings— — Indoor environmental quality — Part 1: Indoor
environmental input parameters for the design and assessment of energy performance of buildings;
— ISO 17772-2, Energy performance of buildings— — Overall energy performance assessment procedures —
Part 2: Guideline for using indoor environmental input parameters for the design and assessment of energy
performance of buildings.
These standards give methods for evaluation of the thermal environment. This document covers the
evaluation of thermal sensation and comfort considering seasonal adaptive mechanisms to moderate thermal
environments.
A human being’s thermal sensation is mainly related to the thermal balance of their body as a whole. This
balance is influenced by physical activity and clothing, as well as the environmental parameters: air
temperature, mean radiant temperature, air velocity and air humidity. At the same time, thermal sensation
and comfort are additionally affected among others by seasonal differences in the human being’s state of
thermal adaptation. The mechanisms leading to thermal adaptation are grouped into physiological,
behavioural, and psychological. These effects are only partially considered in other methods for determining
thermal sensation. Adaptive thermal comfort models consider all known adaptive mechanisms in the
prediction of thermal sensation votes or comfort ranges. Therefore, in this document, first, an overview of
existing approaches is presented. Second, three examples of adaptive thermal comfort models are featured in
this document. For each example, the background and model formulation, steps towards model development
and implementation and the application in national and international standards are described.
© ISO #### 2025 – All rights reserved
v
ISO #####-#:####(X/DTR 23672:(en)
This document is intended to be used with reference to ISO 28803:2012, when considering persons with
special requirements, such as those with physical disabilities. Ethnic, national or geographical differences
needmust also to be taken into account.
© ISO #### 2025 – All rights reserved
vi
Ergonomics of the thermal environment —: Adaptive Thermal
Comfort approaches methods for achieving thermal comfort
1 Scope
This document defines adaptive thermal comfort and its mechanisms, and describes current approaches to
predict adaptive thermal comfort.
This document applies to human thermal comfort in indoor built environments and seasonal adaptive
processes. It is applicable to healthy humans exposed to indoor environments where thermal comfort is
desirable, but where moderate deviations from thermal comfort occur, in the design of new environments or
the assessment of existing ones.
2 Normative references
There are no normative references in this document.
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
—
3.1
accommodation/ thermoregulation
accommodation
acute response to a (thermal) stimuli supporting homeostatic regulation
3.13.2
3.2
adaptation
changes that reduce the [(physiological or psychological]) strain produced by stressful components of the total
environment.
Note 1 to entry: This change maycan occur within the lifetime of an organism (phenotypic) or be the result of genetic
selection in a species or subspecies (genotypic) ).
[SOURCE: Glossary of terms for thermal physiology]
© ISO #### 2025 – All rights reserved
3.1.13.2.1
3.2.1
adaptation
behavioural changes like changing posture or activity, clothing level adjustments or
adjustments to the indoor thermal environment (e.g. window opening or using a fan) that affect the human
body’s heat balance
3.1.23.2.2
3.2.2
adaptation
altered response of the thermoregulation system through adjustments in physiological
parameters, such as the onset of sweating as a consequence of repeated warm or cold stimuli that reduces
thermal stress on the human body
3.1.33.2.3
3.2.3
adaptation
changes in perception of, and reaction to, sensory information from thermoreceptors due to
habituation, changed expectations, or perceived control influenced by a person’s longer history of experiences
with indoor and outdoor climate
3.23.3
3.3
adaptive thermal comfort
all known adaptive mechanisms in the prediction of thermal sensation votes or comfort ranges
3.33.4
3.4
mean daily outdoor air temperature
𝑡𝑡
𝑚𝑚𝑚𝑚𝑚𝑚
¯
𝒕𝒕
𝒎𝒎𝒎𝒎𝒎𝒎
arithmetic mean of outdoor air temperature for a 24-hour period used to calculate prevailing mean outdoor
¯
air temperature (𝑡𝑡 𝑡𝑡 )
𝑝𝑝𝑚𝑚𝑚𝑚 𝑝𝑝𝑚𝑚𝑚𝑚
3.4
3.5 3.5
mean monthly outdoor air temperature
ta(out)
arithmetic average of the mean daily minimum and mean daily maximum outdoor (dry-bulb) temperatures
for the month in question when used as an input variable for the adaptive model
3.6
3.6
neutral operative temperature
to n
the operative temperature at which the average person will be thermally neutral
3.7
3.7
prevailing mean outdoor air temperature
𝑡𝑡
𝑝𝑝𝑚𝑚𝑚𝑚
¯
𝒕𝒕
𝒑𝒑𝒎𝒎𝒎𝒎
arithmetic average of the mean daily outdoor temperatures over some period of days, which are no fewer than
seven and no more than 30 sequential days prior to the day in question in the adaptive model
© ISO #### 2025 – All rights reserved
3.8
3.93.8 3.8
running mean outdoor temperature
t
rm
𝒕𝒕
𝒓𝒓𝒎𝒎
exponentially weighted running mean of the daily mean outdoor air temperature in the adaptive model
3.10
3.9
Predictive Mean Vote
3.9
predictive mean vote
PMV
standard index that predicts the mean value of the votes of a large group of persons on the 7 point thermal
sensation scale based on the heat balance of the human body
3.113.10
[SOURCE: ISO 7730]
3.12
3.10
Predicted Percentage of Dissatisfied
predicted percentage of dissatisfied
PPD
standard index that establishes a quantitative index related to the percentage of thermally dissatisfied people
who feel too cool or too warm
[SOURCE: ISO 7730]
© ISO #### 2025 – All rights reserved
4 Approaches to adaptive thermal comfort models
Approaches to model human thermal comfort include:
a) a) the heat balance (e.g. PMV) or thermophysiological (e.g. Gagge’s 2-node) approach,
b) b) adaptive models based on regression-analysis, and
[ ]
c) c) a combination of heat balance/ and thermophysiological models with the adaptive approach. 1 .
The heat balance approach focuses on the heat balance between the human body and the surrounding
[ ]
environment, 2 , while thermophysiological approaches include the physiological responses of the human
[ ]
body such as vasoconstriction, vasodilation, sweat secretion, skin wettedness, and blood flow rate. 3 . The
latter two modelling approaches b) and c) including the adaptive views on human thermal perception consider
the human being as an active player in the relationship between environmental conditions and individual
perception. Thermal adaptation in contrast to accommodation is considering long-term adjustments and
[ ]
includes three mechanisms: physiological, behavioural and psychological adaptations. 4 . Physiological
adaptation includes a variety of processes that altered the response of the thermoregulation system to thermal
stimuli. These processes include adjustments in physiological parameters, such as the onset of sweating or
altered body core temperatures. Behavioural adaptation consists of changes in behavioural reactions like
changing posture or activity, clothing level adjustments or adjustments to the indoor thermal environment
(e.g. window opening or using a fan) that affect the human body’s heat balance. Psychological adaptation is
used to describe changes in perception of, and reaction to, sensory information from thermoreceptors due to
habituation, changed expectations, or perceived control influenced by a person’s longer history of experiences
with indoor and outdoor climate.
[ ]
A large variety of adaptive thermal comfort models exists. 1 . The adaptive thermal comfort models based on
regression analysis (Clause 5(Clause 5)) establish the indoor thermal comfort temperature or neutral
operative temperature as a function of outdoor air temperatures and are mainly based on data from field
[ ]
studies. 5 . Combinations of heat balance or thermophysiological models with the adaptive approach are
[ ]
based on combinations of field and laboratory work (Clauses 6 and 7). 1(Clauses 6 & 7) . These approaches
can differ in the underlying heat balance and thermoregulation model, and in the way the adaptive processes
are modelled.
This document presents three examples focusing on adaptive approaches:
[ ]
— the regression based adaptive comfort models, 4 , which do not explicitly consider the human heat balance
nor thermoregulation (Clause 5(Clause 5), ),
[ ]
— the adaptive PMV (aPMV) model, 6 , which is based on the heat balance equations of the PMV index and
quantifies occupants’ feedback loop of thermal adaptations with coefficient lambda (Clause 6(Clause 6),),
[ ],[ ]
— the adaptive thermal heat balance model (ATHB), 7 8) , which is a framework for models based on the
heat balance equations of the PMV index, and considers each adaptive mechanisms individually
(Clause 7(Clause 7). ).
© ISO #### 2025 – All rights reserved
5 Regression based adaptive comfort models
5.1 5.1 Background and model formulation
Regression models consider that all three adaptive mechanisms are driven by seasonal changes, which maycan
be represented by the outdoor environmental conditions. Hence, the neutral operative temperature for
occupants who have the opportunity to interact with the building and its devices relates primarily to the
outdoor environmental conditions.
This relationship is commonly expressed as shown in Formula (1)Formula (1)::
t = a *·T + b, (1)
o n o
where
to n is the neutral operative temperature;
To is the outdoor reference temperature;
[
a is the slope of the function, proportional to the degree of adaption to the regional climatic conditions 4
t is the neutral operative temperature;
o n
To is the outdoor reference temperature;
a is the slope of the function, proportional to the degree of adaption to the regional climatic
conditions [4];
b is the y-intercept.
]
;
b is the y-intercept.
The shortcoming of the regression model is its neglect of influences of other indoor environmental factors and
its lack of ability to distinguish between the three adaptive mechanisms.
5.2 5.2 Model development
The regression-based adaptive models are commonly based on data collected from field studies. There are
two main methods to obtain the regression-based adaptive model.
First, a linear regression according to Formula 1Formula 1 in which mean t of a group of subjects (or t of
o n o n
[ ]
each individual subject) is plotted versus an outdoor reference temperature. 9. This method relies on the
[ ]
statistical significance of the regression model, requiring a large number of data in each subset. 10 .
[ ]
Second, the Griffiths method 11 is used to derive t from small sample sizes containing less thermal
o n
variability. Here, t is defined as the temperature corresponding to neutrality and maycan be calculated for
o n
each vote.
The neutral operative temperature maycan be inferred by Formula (2)Formula (2)::
t = T – TSV/G  (2)
o n o
−1
where G is the Griffiths constant, °C .
−1
G is the Griffiths constant, °C .
The value for constant G varies according to the literature and whether it is a constant or a variable is still
[ ]
debated. 12 .
© ISO #### 2025 – All rights reserved
Different variations for the outdoor reference temperature exist: exponentially weighted mean outdoor
temperature called the “running mean outdoor temperature”, t , the mean monthly outdoor air temperature,
rm
t , derived from a Typical Meteorological Yeartypical meteorological year (TMY) data file or based on mean
a (out)
daily outdoor air temperature, 𝑡𝑡 ,𝑡𝑡 ¯ , the prevailing mean outdoor air temperature, 𝑡𝑡 𝑡𝑡 ¯ , or actual
𝑚𝑚𝑚𝑚𝑚𝑚 𝑚𝑚𝑚𝑚𝑚𝑚 𝑝𝑝𝑚𝑚𝑚𝑚 𝑝𝑝𝑚𝑚𝑚𝑚
measurements. No study is available, which confirms potential differences in the choice of coefficients
depending on the chosen variation of outdoor reference temperature.
5.3 5.3 Values for model coefficients
Adaptive models have been developed for different building types and in different climate zones around the
[ ] [ ]
world. In addition to common building types, such as residential buildings, 13 , office buildings, 14 ,
[ ] [ ] [ ]
commercial buildings, 15 , hospital buildings 16 and school buildings. 17 .
5.4 5.4 Model application in national and international standards
Regression based adaptive comfort models have been introduced into national and international standards
since 2004. Examples for the chosen outdoor reference temperature and coefficients are shown in
Table 1Table 1.
Table 1 — Conditions for the regression-based adaptive comfort models in naturally ventilated
buildings
Standard Outdoor Category Top upper limit, ℃°C Top lower limit, ℃°C Outdoor
reference temperature
range, ℃°C
tpma(out) 90 %
0. ,31∗𝑡𝑡 +   0. ,31∗𝑡𝑡 +
ASHRAE ( ) ( )
𝑝𝑝𝑝𝑝𝑝𝑝𝑜𝑜𝑜𝑜𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑜𝑜𝑜𝑜𝑡𝑡
acceptabilit 10-33.,5
¯ ¯
55 𝑡𝑡 + 20. ,3 𝑡𝑡 + 15. ,3
𝑝𝑝𝑚𝑚𝑚𝑚(𝑜𝑜𝑜𝑜𝑜𝑜) 𝑝𝑝𝑚𝑚𝑚𝑚(𝑜𝑜𝑜𝑜𝑜𝑜)
y
80 %
0. ,31∗𝑡𝑡 +   0. ,31∗𝑡𝑡 +
𝑝𝑝𝑝𝑝𝑝𝑝(𝑜𝑜𝑜𝑜𝑡𝑡) 𝑝𝑝𝑝𝑝𝑝𝑝(𝑜𝑜𝑜𝑜𝑡𝑡)
acceptabilit 10-33.,5
¯ ¯
𝑡𝑡 + 21. ,3 𝑡𝑡 + 14. ,3
𝑝𝑝𝑚𝑚𝑚𝑚(𝑜𝑜𝑜𝑜𝑜𝑜) 𝑝𝑝𝑚𝑚𝑚𝑚(𝑜𝑜𝑜𝑜𝑜𝑜)
y
ISO t 10-30 upper, 15-
rm
I 0.,33 * trm + 20.,8 0.,33 * trm + 16.,8
17772-1 30 lower
10-30 upper, 15-
II 0.,33 * t + 21.,8 0.,33 * t + 15.,8
rm rm
30 lower
10-30 upper, 15-
III 0.,33 * trm + 22.,8 0.,33 * trm + 14.,8
30 lower
© ISO #### 2025 – All rights reserved
6 Adaptive PMV (aPMV) model
6.1 6.1 General
The aPMV model adjusts the existing PMV index to account for thermal adaptation by means of correction
[ ]
factors based on occupants’ feedback loop. 6 .
6.2 6.2 Background and model formulation
The index of aPMV assumes occupants’ behavioural and psychological adaption as “Adaptive
Feedbackadaptive feedback”, Kδ, to their thermal sensation, as is shown in Figure 1Figure 1. .

Key
G calculation process of original PMV
δ inputs of PMV
K adaptive feedback
δ
aPMV adaptive Predicted Mean Vote

G calculation process of original PMV
δ inputs of PMV
Kδ adaptive feedback
aPMV adaptive PMV
[6 ]
Figure 1 — Model diagram of aPMV .

In Figure 1Figure 1,, the PMV model maycan be represented by Formula (3)Formula (3)::
PMV = G × δ
(3)
Where
G is the calculation process of original PMV;
© ISO #### 2025 – All rights reserved
δ represents the inputs of PMV.
where
G is the calculation process of original PMV;
δ represents the inputs of PMV.
After introducing “Adaptive Feedbackadaptive feedback”, the calculation process in Figure 1Figure 1 is
transformed as shown in Formula (4)Formula (4)::
𝑃𝑃𝑃𝑃𝑃𝑃 𝑃𝑃𝑃𝑃𝑃𝑃
𝑝𝑝𝑎𝑎𝑎𝑎𝑎𝑎 =    (4)
1+λ×𝑃𝑃𝑃𝑃𝑃𝑃 1+𝜆𝜆×𝑃𝑃𝑃𝑃𝑃𝑃
Where λ is an adaptive coefficient.
For λ is an adaptive coefficient.
mul
a 4
Formula 4 is the “adaptive Predicted Mean Votepredicted mean vote model (aPMV model (aPMV model)”. )”.
The aPMV model incorporates the theory of PMV index and the mechanism of adaptive thermal comfort using
different adaptive coefficient λ values, as illustrated in Figure 2Figure 2. When λ is equal to zero,
Formula 4Formula 4 is the same as PMV index (straight solid line), meaning that the PMV index can accurately
predict thermal sensations. In warm conditions (PMV>0), when occupants’ hot feelings are lower than PMV
predicts, the aPMV will be less than the PMV (like λ = +0.,66 dashed line); when occupants’ hot feelings are
higher than PMV predicts, the aPMV will be greater than the PMV (like λ = -0.,66 dashed line). In cool
conditions (PMV<0), when occupants’ cold feelings are lower than PMV predicts, the aPMV will be greater
than the PMV (like λ = -0.,66 dash-dot line); when occupants’ cold feelings are higher than PMV predicts, the
aPMV will be less than the PMV (like λ = +0.,66 dash-dot line). In addition, the higher the absolute value of λ,
[ ]
the more occupants adapt themselves. 6 .
The aPMV theory aims to reduce the deviation between PMV prediction and actual thermal sensation on the
7-voting scale from -3 to +3, representing “cold”, “cool”, “slightly cool”, “neutral”, “slightly warm”, “warm”, and
“hot”. The smaller absolute λ value indicates lower capacity of adaptation and the aPMV model is equal to the
PMV index when λ is zero. On the hot side, the lowest available vote for occupants is +1 (slightly warm).
Assuming that the PMV index
...