kSIST FprEN ISO 14505-3:2026
(Main)Ergonomics of the thermal environment - Evaluation of thermal environments in vehicles - Part 3: Evaluation of thermal comfort using human subjects (ISO/FDIS 14505-3:2026)
- Abstract
This document specifies and gives guidelines for a standard test method for the assessment, using human participants, of thermal comfort in vehicles. It is not restricted to any particular vehicle but provides the general principles that allow assessment and evaluation. The method can be used to determine a measure of the performance of a vehicle for conditions of interest, in terms of whether it provides thermal comfort to people or not. This can be used in vehicle development and evaluation.
This document is applicable to all types of vehicles, including cars, buses, trucks, off-road vehicles, trains, aircraft, ships, submarines, and to the cabins of cranes and similar spaces. It applies where people are enclosed in a vehicle and when they are exposed to outside conditions. For those exposed to outside conditions, such as riders of bicycles or motorcycles, drivers of open sports cars and operators of fork lift trucks without cabins, vehicle speed and weather conditions can dominate responses. The principles of assessment, however, still apply.
This document applies to both passengers and operators of vehicles where its application does not interfere with the safe operation of the vehicle.
It describes the principles of the assessment and evaluation of thermal comfort, including the use of test methods and trials. It also describes subjective methods that can be used in assessment.
- Status
- Not Published
- Public Enquiry End Date
- 30-Jul-2025
- Technical Committee
- VSN - Safety of machinery
- Current Stage
- 5020 - Formal vote (FV) (Adopted Project)
- Start Date
- 03-Jul-2026
- Due Date
- 21-Aug-2026
- Completion Date
- 26-Aug-2026
kSIST FprEN ISO 14505-3:2026 is a SIST standard for ergonomics of the thermal environment in vehicles, aligned with ISO/FDIS 14505-3. It specifies a standard test method and guidance for assessing thermal comfort with human participants in vehicles, cabins, and similar spaces. It is intended for vehicle development, evaluation, and comparison of thermal comfort performance.
What does kSIST FprEN ISO 14505-3:2026 specify?
kSIST FprEN ISO 14505-3:2026 specifies how to assess thermal comfort in vehicles using human participants. It gives general principles and a standard test method that can be applied across vehicle types and operating conditions.
The scope covers cars, buses, trucks, off-road vehicles, trains, aircraft, ships, submarines, and cabins of cranes and similar spaces. It applies both when occupants are enclosed and when they are exposed to outside conditions, while noting that speed and weather can dominate responses in open vehicles such as bicycles, motorcycles, open sports cars, and fork lift trucks without cabins.
The document is organized into:
- Clause 4 - assessment of vehicle environments using human participants
- Clause 5 - principles of assessment
- Clause 6 - design of human participant trials
- Clause 7 - test method for assessing thermal comfort in vehicle
- Annex A - normative test method
- Annexes B to E - informative questionnaire and practical examples
| Annex | What it covers |
|---|---|
| Annex A | Normative test method for vehicle thermal comfort |
| Annex B | Example of a single-sheet subjective questionnaire |
| Annex C | Practical example using the test method |
| Annex D | Practical example for vehicle glazing |
| Annex E | Practical example for vehicle seats |
What are the key requirements of kSIST FprEN ISO 14505-3:2026?
kSIST FprEN ISO 14505-3:2026 is built around subjective testing with human participants, supported where useful by objective and behavioural measures. The document turns that idea into practical rules for participant selection, trial design, data collection, and interpretation.
Human participant testing must be justified and ethical
Clause 4 says human participant methods are used where direct measurement of thermal comfort is needed, where a standardized test is being set up, where predictions are being compared with actual responses, or where objective and subjective measures are being related. Such methods are to be used only when ethical considerations and accepted practices for human participants, as provided in ISO 12894, have been followed.
In practice, this means a test plan needs a clear purpose and proper participant handling before any comfort ratings are taken.
Subjective methods are the main assessment tool
Clause 5.1 says subjective methods use scales to quantify how people feel in the environment. The document points to scales for thermal sensation, comfort, stickiness, preference, acceptance, and satisfaction, and it notes that the thermal comfort methods here do not consider tolerance.
In practice, the questionnaire wording and scale structure matter because the participant’s rating is the primary comfort result.
Objective and behavioural methods can support the subjective results
Clause 5.2 describes objective methods as measurements made with instrumentation or performance outputs, such as skin temperature or skin wetness. Clause 5.3 describes behavioural methods such as posture changes, movement patterns, and seat choice.
In practice, these methods can help explain the subjective ratings, but they need careful interpretation because they do not map perfectly to thermal comfort.
Trial design must match the purpose of the test
Clause 6 says the trial design depends on the aim of the study. It points to repeated measures designs, balanced order of exposure, and practical use of Latin square arrangements when multiple vehicles, seats, or glazing types are compared.
In practice, the design has to prevent bias and make sure each condition is compared fairly.
Participants should represent the user population
Clause 6.2 says participants should be a representative sample, with attention to factors such as age, gender, driving experience, and anthropometry. It also stresses avoiding bias.
In practice, the participant group should reflect the intended users of the vehicle, not just a convenient group.
Operating conditions must be controlled or recorded
Clause 6.4 says the conditions under which the vehicle is tested determine the environment being assessed. HVAC-system settings, starting conditions, time of day, solar direction, clothing, road or weather conditions, and other influencing factors should be controlled where possible or at least recorded.
In practice, the thermal result is only meaningful if the test conditions are documented well enough to repeat or compare them.
Results need careful analysis and interpretation
Clause 6.5 says results should be shown in graphs and tables and analyzed against the question being asked. The document also notes that subjective scales are not automatically ratio data, so rank-based or other non-parametric methods may be more appropriate in many cases.
In practice, a rating of 4 is not automatically “twice” a rating of 2, so the statistics have to match the scale type.
Annex A gives the standard test method
Annex A is the core procedural requirement. It calls for representative test conditions, at least eight participants, test duration of no less than 30 min, and ratings taken every 10 min, including at the beginning and end of the test. It also requires integration of the final two ratings over the participants and use of the median and range to judge the outcome.
In practice, the vehicle environment is not considered comfortable if the criteria in Table A.1 are met, so the test is set up to identify unacceptable thermal conditions as well as acceptable ones.
What terms does kSIST FprEN ISO 14505-3:2026 define?
kSIST FprEN ISO 14505-3:2026 defines a small set of terms that are central to thermal comfort evaluation in vehicles.
- Cold stress - climatic conditions where body heat exchange is just sufficient or too high to maintain heat balance only at the cost of significant physiological strain.
- Heat stress - climatic conditions where body heat exchange is just sufficient or too low to maintain heat balance only at the cost of significant physiological strain.
- Equivalent temperature - the temperature of a uniform room with equal air and mean radiant temperature and no air movement, where heat loss matches the actual condition.
- Local equivalent temperature - the same idea as equivalent temperature, but applied to a defined zone of the body.
- Thermal asymmetry - the degree to which opposite parts of the body are exposed to different climatic conditions.
- Thermoneutral zone - the temperature range in which the body maintains heat balance by vasomotor reactions alone.
- HVAC-system - the heating, ventilation and air-conditioning system of the vehicle or cabin.
Who uses kSIST FprEN ISO 14505-3:2026?
kSIST FprEN ISO 14505-3:2026 is used by vehicle designers, test engineers, ergonomists, and quality teams who need to measure thermal comfort in a repeatable way. It is also relevant to manufacturers and suppliers of vehicles, seats, glazing, and HVAC-system components.
In practice, it supports vehicle development, comparative testing, comfort validation, and interpretation of passenger or operator responses across road, rail, air, and marine applications.
What changed in kSIST FprEN ISO 14505-3:2026 from the previous edition?
kSIST FprEN ISO 14505-3:2026 is identified as a second edition that cancels and replaces the first edition, ISO 14505 part 3:2006. The foreword states that it has been technically revised.
Which standards are used with kSIST FprEN ISO 14505-3:2026?
kSIST FprEN ISO 14505-3:2026 cites these standards as references or supporting documents:
| Standard | What it contributes |
|---|---|
| ISO 7726 | Instruments for measuring physical quantities in the thermal environment |
| ISO 9886:2004 | Methods for evaluating thermal strain by physiological measurements |
| ISO 10551:2019 | Guidance on subjective judgement scales for assessing physical environments |
| ISO 13731 | Vocabulary and symbols for the thermal environment |
| ISO 12894 | Ethical considerations and accepted practices for human participant work |
ISO 10551 is especially important because the subjective scales in this document are based on its guidance. ISO 9886 supports the use of physiological measures when objective data are added to subjective comfort ratings.
What does the kSIST FprEN ISO 14505-3:2026 document contain?
kSIST FprEN ISO 14505-3:2026 contains a full structure for planning and running thermal comfort assessments in vehicles. It includes the scope, normative references, terms and definitions, assessment principles, trial design guidance, and a formal test method.
Annex A provides the normative method, including participant selection, exposure time, rating schedule, and interpretation criteria. Annex B gives an example of a single-sheet questionnaire, which helps users build practical rating forms without redesigning the scales from scratch.
Annexes C, D, and E provide worked examples. These show how the method can be used for a passenger car, for comparing vehicle glazing, and for comparing vehicle seats. The examples help users see how the ratings, tables, and simple statistical interpretation fit together in a real test.
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- Effective Date
- 03-May-2023
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Frequently Asked Questions
kSIST FprEN ISO 14505-3:2026 is a draft published by the Slovenian Institute for Standardization (SIST). Its full title is "Ergonomics of the thermal environment - Evaluation of thermal environments in vehicles - Part 3: Evaluation of thermal comfort using human subjects (ISO/FDIS 14505-3:2026)". This standard covers: This document specifies and gives guidelines for a standard test method for the assessment, using human participants, of thermal comfort in vehicles. It is not restricted to any particular vehicle but provides the general principles that allow assessment and evaluation. The method can be used to determine a measure of the performance of a vehicle for conditions of interest, in terms of whether it provides thermal comfort to people or not. This can be used in vehicle development and evaluation. This document is applicable to all types of vehicles, including cars, buses, trucks, off-road vehicles, trains, aircraft, ships, submarines, and to the cabins of cranes and similar spaces. It applies where people are enclosed in a vehicle and when they are exposed to outside conditions. For those exposed to outside conditions, such as riders of bicycles or motorcycles, drivers of open sports cars and operators of fork lift trucks without cabins, vehicle speed and weather conditions can dominate responses. The principles of assessment, however, still apply. This document applies to both passengers and operators of vehicles where its application does not interfere with the safe operation of the vehicle. It describes the principles of the assessment and evaluation of thermal comfort, including the use of test methods and trials. It also describes subjective methods that can be used in assessment.
This document specifies and gives guidelines for a standard test method for the assessment, using human participants, of thermal comfort in vehicles. It is not restricted to any particular vehicle but provides the general principles that allow assessment and evaluation. The method can be used to determine a measure of the performance of a vehicle for conditions of interest, in terms of whether it provides thermal comfort to people or not. This can be used in vehicle development and evaluation. This document is applicable to all types of vehicles, including cars, buses, trucks, off-road vehicles, trains, aircraft, ships, submarines, and to the cabins of cranes and similar spaces. It applies where people are enclosed in a vehicle and when they are exposed to outside conditions. For those exposed to outside conditions, such as riders of bicycles or motorcycles, drivers of open sports cars and operators of fork lift trucks without cabins, vehicle speed and weather conditions can dominate responses. The principles of assessment, however, still apply. This document applies to both passengers and operators of vehicles where its application does not interfere with the safe operation of the vehicle. It describes the principles of the assessment and evaluation of thermal comfort, including the use of test methods and trials. It also describes subjective methods that can be used in assessment.
kSIST FprEN ISO 14505-3:2026 is classified under the following ICS (International Classification for Standards) categories: 13.180 - Ergonomics; 43.020 - Road vehicles in general. The ICS classification helps identify the subject area and facilitates finding related standards.
kSIST FprEN ISO 14505-3:2026 has the following relationships with other standards: It is inter standard links to SIST EN ISO 14505-3:2006. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
kSIST FprEN ISO 14505-3:2026 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN ISO 14505-3:2025
01-julij-2025
Ergonomija toplotnega okolja – Vrednotenje toplotnega okolja v vozilih – 3. del:
Vrednotenje toplotnega ugodja s pomočjo preskusnih oseb (ISO/DIS 14505-3:2025)
Ergonomics of the thermal environment - Evaluation of thermal environments in vehicles
- Part 3: Evaluation of thermal comfort using human subjects (ISO/DIS 14505-3:2025)
Ergonomie der thermischen Umgebung - Bewertung der thermischen Umgebungen in
Fahrzeugen - Teil 3: Bewertung der thermischen Behaglichkeit durch Versuchspersonen
(ISO/DIS 14505-3:2025)
Ergonomie des ambiances thermiques - Évaluation des ambiances thermiques dans les
véhicules - Partie 3: Évaluation du confort thermique en ayant recours à des sujets
humains (ISO/DIS 14505-3:2025)
Ta slovenski standard je istoveten z: prEN ISO 14505-3
ICS:
13.180 Ergonomija Ergonomics
43.020 Cestna vozila na splošno Road vehicles in general
oSIST prEN ISO 14505-3:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
oSIST prEN ISO 14505-3:2025
oSIST prEN ISO 14505-3:2025
DRAFT
International
Standard
ISO/DIS 14505-3
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment — Evaluation of the
Voting begins on:
thermal environment in vehicles —
2025-05-28
Part 3:
Voting terminates on:
2025-08-20
Evaluation of thermal comfort using
human participants
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,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
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POTENTIAL TO BECOME STANDARDS TO
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RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 14505-3:2025(en)
oSIST prEN ISO 14505-3:2025
DRAFT
ISO/DIS 14505-3:2025(en)
International
Standard
ISO/DIS 14505-3
ISO/TC 159/SC 5
Ergonomics of the thermal
Secretariat: BSI
environment — Evaluation of the
Voting begins on:
thermal environment in vehicles —
Part 3:
Voting terminates on:
Evaluation of thermal comfort using
human participants
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
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
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TO SUBMIT, WITH THEIR COMMENTS,
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NOTIFICATION OF ANY RELEVANT PATENT
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PROVIDE SUPPORTING DOCUMENTATION.
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 14505-3:2025(en)
ii
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Assessment of vehicle environments using human participants . 2
5 Principles of assessment . 3
5.1 Subjective methods .3
5.2 Objective methods .3
5.3 Behavioural methods . .3
5.4 Assessment of thermal comfort .3
6 Design of human participant trials . 4
6.1 Aim of trial .4
6.2 Selection of human participants .4
6.3 Measurement of participant responses .4
6.3.1 General .4
6.3.2 Subjective scales .5
6.4 Selection of operating conditions .7
6.5 Analysis and interpretation of results .7
7 Test method for assessing thermal comfort in vehicle . 7
Annex A (normative) Test method for assessment of vehicle thermal comfort . 8
Annex B (informative) Example of single-sheet subjective questionnaire .10
Annex C (informative) Practical example of vehicle thermal comfort assessment using test
method .11
Annex D (informative) Practical example of assessment of thermal comfort properties of
vehicle glazing .13
Annex E (informative) Practical example of assessment of thermal comfort properties of
vehicle seats .15
iii
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(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,
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 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
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, Subcommittee SC5.
This second edition cancels and replaces the first edition (ISO 14505 part 3 (2006)), which has been
technically revised.
The main changes are as follows:
— xxx xxxxxxx xxx xxxx
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
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(en)
Introduction
Direct methods for the assessment of thermal environments (hot, moderate, cold) in vehicles involve
measurements of the responses of human participants. There are three types: subjective methods, objective
methods, and behavioural methods. Subjective methods quantify the responses of people to an environment
using subjective scales. Objective methods are those which quantify the physical, physiological or mental
condition of a person by the use of instrumentation or measures of an output such as performance measures.
Behavioural methods quantify or represent human behaviour in response to an environment. Each of these
methods has been developed according to basic principles and the most appropriate form of the method and
combination of methods used in concert for the assessment of thermal environments in vehicles will depend
upon the context and vehicle environment of interest. This part of ISO 14505 provides both principles
and application of methods for the assessment of thermal comfort in vehicle environments using human
participants. The most appropriate methods for evaluating thermal comfort in vehicles are subjective. The
principles for the construction of subjective assessment scales are given in ISO 10551 and are used in the
development of the test method specified in this part of ISO 14505. Physiological measurements on human
participants are described in ISO 9886 and are beyond the scope of this part of ISO 14505.
This part of ISO 14505 complements standards concerned with the ergonomics of thermal environments
and in particular can be used together with thermal indices that are valid for use in vehicle environments.
v
oSIST prEN ISO 14505-3:2025
oSIST prEN ISO 14505-3:2025
DRAFT International Standard ISO/DIS 14505-3:2025(en)
Ergonomics of the thermal environment — Evaluation of the
thermal environment in vehicles —
Part 3:
Evaluation of thermal comfort using human participants
1 Scope
This part of ISO 14505 gives guidelines and specifies a standard test method for the assessment, using human
participants, of thermal comfort in vehicles. It is not restricted to any particular vehicle but provides the
general principles that allow assessment and evaluation. The method can be used to determine a measure
of the performance of a vehicle for conditions of interest, in terms of whether it provides thermal comfort to
people or not. This can be used in vehicle development and evaluation.
This part of ISO 14505 is applicable to all types of vehicles, including cars, buses, trucks, off-road vehicles,
trains, aircraft, ships, submarines, and to the cabins of cranes and similar spaces. It applies where people
are enclosed in a vehicle and when they are exposed to outside conditions. For those exposed to outside
conditions, such as riders of bicycles or motorcycles, drivers of open sports cars and operators of fork lift
trucks without cabins, vehicle speed and weather conditions can dominate responses. The principles of
assessment, however, will still apply.
This part of ISO 14505 applies to both passengers and operators of vehicles where its application does not
interfere with the safe operation of the vehicle.
It presents the principles of the assessment and evaluation of thermal comfort, including the use of test
methods and trials. It also presents subjective methods that can be used in assessment.
This part of ISO 14505 is a basic ergonomics standard which can contribute to the development of standards
concerned with specific vehicles and products.
2 Normative references
Two options of text (remove the inappropriate option).
1) The normative references shall be introduced by the following wording.
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 7726, xxx, Ergonomics of the thermal environment — Instruments for measuring physical quantities
ISO 9886:2004, Ergonomics — Evaluation of thermal strain by physiological measurements
ISO 10551:2019, Ergonomics of the physical environment — Subjective judgement scales for assessing physical
environments
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.
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(en)
3.1
cold stress
climatic conditions under which the body heat exchange is just equal to, or too large for, heat balance at the
expense of significant physiological strain that sometimes cannot be compensated
3.2
equivalent temperature
temperature of a homogenous “room”, 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
3.3
heat stress
climatic conditions under which the body heat exchange is just equal to, or too small for, heat balance at the
expense of significant physiological strain that sometimes cannot be compensated
3.4
HVAC-system
heating, ventilation and air-conditioning system of the vehicle/cabin
3.5
local equivalent temperature
temperature of a homogenous “room”, with mean radiant temperature equal to air temperature and zero air
velocity, in which a defined zone of the human body surface exchanges the same heat loss by convection and
radiation as in the actual conditions
3.6
thermal asymmetry
degree to which opposite parts of the human body are exposed to different climatic conditions
3.7
thermoneutral zone
temperature interval within which the body maintains heat balance exclusively by vasomotor reactions
4 Assessment of vehicle environments using human participants
Although mathematical and physical models and thermal indices can provide repeatable, reliable methods
of assessment, vehicle environments are often complex, dynamic and influenced by many factors. Models
and indices are therefore often limited in validity. Human participants are required to provide a direct
means of measuring thermal comfort and to validate other techniques. It is important, therefore, to
develop assessment methods involving human participants. Such methods shall only be used where ethical
considerations and accepted practices involving human participants, as provided in ISO 12894, have been
carried out. They are used for one of four main reasons:
1 to evaluate thermal comfort in vehicle environments;
2 to set up or carry out standardized test methods of thermal comfort in vehicles;
3 to compare measures of thermal comfort in vehicles with prediction methods (models, indices) based
upon measures of the thermal environment in vehicles;
4 to determine the relationship between objective measures, such as skin temperatures, and subjective
measures of thermal comfort.
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(en)
5 Principles of assessment
5.1 Subjective methods
Subjective methods quantify the response of people to an environment using subjective scales. Such scales
are based upon psychological continua (or constructs) that are relevant to the psychological phenomenon
of interest. It is important to know the properties of the scales in order to correctly interpret the results.
Scales of thermal sensation (hot or cold), preference, comfort, and stickiness are often used in thermal
comfort assessment. Advantages of subjective methods are that they are simple to administer and are
directly related to the psychological phenomenon. Disadvantages are that they can interfere with what they
are measuring, some groups may not be able to perform the subjective task (for example, babies, children,
people with disabilities) and there is no reason given as to why such a response is provided. ISO 10551 should
be used for guidance on the construction of subjective scales. Five types of scales are identified. These are:
Perceptual (How do you feel now? e.g. hot); Affective (How do you find it? e.g. comfortable); Preference (How
would you prefer to be? e.g. cooler); Acceptance (acceptable/unacceptable); Tolerance (Is the environment
tolerable?). From these basic subjective dimensions, questionnaires of subjective scales can be developed.
The subjective assessment methods presented in this part of ISO 14505 are concerned with thermal comfort
and therefore do not consider “tolerance”.
5.2 Objective methods
Objective methods are those which quantify the physical or mental condition of a person by the use of
instrumentation or measures of an output such as performance measures. The principle of the method is
that the measure can be interpreted in terms of the human condition of interest (e.g. thermal comfort).
An example would be the measurement of mean skin temperature of the body that would vary with the
thermoregulatory response to heat and cold (providing a rationale for the method) and that has been shown
in research to correlate with subjective responses of comfort. Another example would be skin wetness.
Disadvantages of objective methods can be that they might interfere with what they are attempting to
measure, the correlation between the measure and thermal comfort is not perfect and that thermal comfort
is a psychological phenomenon, a condition of mind. An advantage of objective measures is that they are
often independent of, and can be used to complement, the results of other methods such as subjective
measures. ISO 9886 should be used to provide methods for measurement and interpretation of physiological
strain in terms of body core temperature, mean skin temperature, heart rate and body mass loss. Other
measures, such as heart rate variability, may also be relevant.
5.3 Behavioural methods
Behavioural methods quantify or represent human behaviour in response to an environment. The particular
aspect of human behaviour observed is related to the human condition of interest (for example, thermal
comfort in vehicles) and a method of interpretation is required. Examples would include changes in posture,
movement patterns (for example, away from uncomfortable environments), and popularity of sitting
positions (for example, if some seats were in a cold draught they would be occupied “last”). Advantages
of behavioural methods include minimum interference with what is being measured and a direct “active”
measure of discomfort. Disadvantages include the difficulty in establishing validity and reliability of the
method and direct interpretation of the results in terms of thermal comfort. For example, a change in
posture could be due to chair discomfort or other “non-thermal” reasons.
5.4 Assessment of thermal comfort
Thermal comfort assessment is most effectively carried out using subjective methods. This is because
comfort is a psychological phenomenon and a subjective rating provides a direct and quantifiable method.
The simple test method provided in this part of ISO 14505 therefore uses subjective methods. Both objective
and behavioural methods can be used to complement the test method provided, however, they would require
expert advice beyond the scope of this part of ISO 14505.
oSIST prEN ISO 14505-3:2025
ISO/DIS 14505-3:2025(en)
6 Design of human participant trials
6.1 Aim of trial
The design of any vehicle test or trial using human participants will depend upon the specific aims of that
test or trial. However, there are general principles and these are outlined below.
A typical thermal comfort trial involves driving vehicles over a route and measuring operating conditions
and thermal responses of passengers. For specific investigations, simulators and environmental chambers /
wind tunnels are often used.
An optimum trial design will achieve its aim with efficient use of resources. To achieve this it is important to
be clear about the specific aim or aims. For example, if the aim is to compare three types of vehicle seats for
thermal comfort then a repeated measures design, where all participants sit on all seats (in a balanced order)
in identical conditions, could provide the best comparison of the seats. Contrast this with the evaluation of
a thermal comfort index where a wide range of environmental conditions, including seats, can be optimum.
If both aims need to be met then it is essential that both types of requirement are met in the design. It is
necessary, therefore, to be specific about the aims of the trial.
6.2 Selection of human participants
A valid method of e
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