SIST EN ISO 7726:2026

SLOVENSKI STANDARD
oSIST prEN ISO 7726:2023
01-julij-2023
Nadomešča:
SIST EN ISO 7726:2002
Ergonomija toplotnega okolja - Instrumenti za merjenje in spremljanje fizikalnih
veličin (ISO/DIS 7726:2023)
Ergonomics of the thermal environment - Instruments for measuring and monitoring
physical quantities (ISO/DIS 7726:2023)
Ergonomie der thermischen Umgebung - Instrumente zur Messung physikalischer
Größen (ISO/DIS 7726:2023)
Ergonomie des ambiances thermiques - Appareils de mesure des grandeurs physiques
(ISO/DIS 7726:2023)
Ta slovenski standard je istoveten z: prEN ISO 7726
ICS:
13.180 Ergonomija Ergonomics
17.020 Meroslovje in merjenje na Metrology and measurement
splošno in general
oSIST prEN ISO 7726:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 7726:2023
oSIST prEN ISO 7726:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 7726
ISO/TC 159/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:
2023-05-25 2023-08-17
Ergonomics of the thermal environment — Instruments for
measuring and monitoring physical quantities
ICS: 13.180
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
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NATIONAL REGULATIONS.
ISO/DIS 7726:2023(E)
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. © ISO 2023

oSIST prEN ISO 7726:2023
DRAFT INTERNATIONAL STANDARD
ISO/DIS 7726
ISO/TC 159/SC 5 Secretariat: BSI
Voting begins on: Voting terminates on:

Ergonomics of the thermal environment — Instruments for
measuring and monitoring physical quantities
ICS: 13.180
This document is circulated as received from the committee secretariat.
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
© ISO 2023
ISO/CEN PARALLEL PROCESSING
THEREFORE SUBJECT TO CHANGE AND MAY
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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NATIONAL REGULATIONS.
Website: www.iso.org ISO/DIS 7726:2023(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
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TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
ii
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2023

oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Symbols and abbreviation . 2
4 General . 3
4.1 Specifications and methods . 3
4.2 The heat exchanges between human body system and its environment . 3
5 The physical quantities characterizing heat exchanges between a system and its
environment . 4
5.1 The basic physical quantities . 4
5.1.1 Air temperature . 4
5.1.2 Radiation directional. 4
5.1.3 Plane radiant temperature . 5
5.1.4 Dew point temperature . 5
5.1.5 Relative humidity . 5
5.1.6 Surface temperature . 5
5.1.7 Air velocity . . . 5
5.1.8 Globe temperature . 5
5.1.9 Wet bulb temperature . 5
5.1.10 Natural wet bulb temperature . 5
5.2 Derived physical quantities . 5
5.2.1 Mean radiant temperature . 6
5.2.2 Radiant temperature asymmetry . 6
5.2.3 Operative temperature . 6
5.2.4 Partial vapour pressure . 7
5.2.5 Humidity ratio . 7
5.2.6 Turbulence intensity . 7
6 The characteristics of physical quantities measuring instruments .7
6.1 Characteristics of instruments for measuring the basic quantities . 7
6.2 Characteristics of integrating types of measuring instruments . 10
7 Specifications relating to measuring methods .10
7.1 General . 10
7.2 Specifications relating to variations in the physical quantities within the space
surrounding the subject . 10
7.3 Specifications relating to the variations in the physical quantities with time . 11
8 Specifications relating to monitoring methods .11
9 Measurement uncertainty .12
10 Specifications related to the processing of measurement results .12
10.1 Spatial maps of measured data .13
11 Clause title .13
Annex A (informative) Measurement of air temperature .14
Annex B (informative) Measurement and calculation of the mean radiant temperature .16
Annex C  Measurement of plane radiant temperature .28
Annex D  Measurement of the absolute humidity of the air .34
Annex E  Measurement of air velocity .40
iii
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Annex F  Measurement of surface temperature .43
Annex G  Measurement of operative temperature .45
Annex H  Measurement of the natural wet bulb temperature .47
Bibliography .49
iv
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
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. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. 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. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO's adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC XXX.
v
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Introduction
This document is one of a series of International Standards intended for use in the study of thermal
environments.
This series of International Standards deals in particular with
— the finalization of definitions for the terms to be used in the methods of measurement, testing
or interpre-tation, taking into account standards already in existence or in the process of being
drafted;
— the laying down of specifications relating to the methods for measuring the physical quantities
which char-acterize thermal environments;
— the selection of one or more methods for interpreting the parameters;
— the specification of recommended values or limits of exposure for the thermal environments coming
within the comfort range and for extreme environments (both hot and cold);
— the specification of methods for measuring the efficiency of devices or processes for personal or
collective protection from heat or cold.
Any measuring instrument which achieves the accuracy indicated in this International Standard, or
even bet-ter improves on, may be used.
The description or listing of certain instruments in the annexes can only signify that they are
"recommended", since characteristics of these instruments may vary according to the measuring
principle, their construction and the way in which they are used. It is up to users to compare the quality
of the instruments available on the market at any given moment and to check that they conform to the
specifications contained in this Inter-national Standard.
vi
oSIST prEN ISO 7726:2023
DRAFT INTERNATIONAL STANDARD ISO/DIS 7726:2023(E)
Ergonomics of the thermal environment — Instruments for
measuring and monitoring physical quantities
1 Scope
This International Standard specifies the minimum characteristics of instruments for measuring
physical quantities characterizing an environment as well as the methods for measuring the physical
quantities of this environment.
Its aim is simply to standardize the process of recording information leading to the determination of
values of physical quantities. Other International Standards give details of the methods making use of
the information obtained in accordance with this standard.
This International Standard is used as a reference when establishing
a) specifications for manufacturers and users of instruments for measuring the physical quantities of
the environment;
b) a written contract between two parties for the measurement of these quantities.
It applies to the influence of hot, moderate, comfortable or cold environments on people. This Standard
is applied in the cases in which comfort or human strain are the main concern and may be supersedes
by other Standards.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
The following standard contains provisions which, through reference in this text, constitute provisions
of this International Standard. At the time of publication, the edition indicated was valid. All standards
are subject to revision, and parties to agreements based on this International Standard are encouraged
to investigate the
possibility of applying the most recent edition of the standard indicated below. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 7243, Ergonomics of the thermal environment — Assessment of heat stress using the WBGT (wet bulb
globe temperature) index
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 7933, Ergonomics of the thermal environment – Analytical determination and interpretation of heat
stress using calculation of the predicted heat strain
ISO 8996, Ergonomics of the thermal environment — Determination of metabolic rate
ISO 9920, Ergonomics of the thermal environment — Estimation of thermal insulation and water vapour
resistance of a clothing ensemble
ISO 11079, Ergonomics of the thermal environment — Determination and interpretation of cold stress
when using required clothing insulation (IREQ) and local cooling effects
ISO 13731, Ergonomics of the thermal environment — Vocabulary and symbols
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
ISO 14505-2, Ergonomics of the thermal environment - Evaluation of thermal environment
in vehicles. Part 2: Determination of Equivalent Temperature.
ISO 15265, Ergonomics of the thermal environment — Risk assessment strategy for the prevention of stress
or discomfort in thermal working conditions
ISO 15743, Ergonomics of the thermal environment — Cold workplaces — Risk assessment and management
3 Terms and definitions
3.1 Symbols and abbreviation
For the purposes of this Standard the definitions given in ISO 13731 and the following apply.
Cres respiratory convective heat flow, [W·m-2]
E evaporative heat flow at the skin surface, [W·m-2]
Eres respiratory evaporative heat flow, [W·m-2]
Icl,st static clothing thermal insulation, [W·m-2·K]
K conductive heat flow, [W·m-2]
M metabolic rate, [W·m-2]
p atmospheric pressure, [Pa]
pa water vapour partial pressure at air temperature, [Pa]
R radiative heat flow, [W·m-2]
C convective heat flow, [W·m-2]-2
Re,cl static clothing water vapour resistance, [m2·kPa·W-1]
RH relative humidity, [%]
S body heat storage rate, [W·m-2]
ta air temperature, [°C] or [K]
td dew-point temperature, [°C] or [K]
tg globe temperature or black globe temperature or temperature of the sensor placed inside the
globe, [°C] or [K]
tnw natural wet bulb temperature, [°C] or [K]
to operative temperature, [°C] or [K]
tpr plane radiant temperature, [°C] or [K]
tr mean radiant temperature, [°C] or [K]
ts surface temperature, [°C] or [K]
tw wet bulb temperature, [°C] or [K]
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
va air velocity, [m·s-1]
W effective mechanical power, [W·m-2]
wa humidity ratio, [g·kg-1]
4 General
4.1 Specifications and methods
The specifications and methods contained in this International Standard have been divided into two
classes according to the extent of the thermal annoyance to be assessed. The type C specifications and
methods re-late to measurements carried out in moderate environments. The type S specifications and
methods relate to measurements carried out in severe environments.
The specifications and methods described for each of these classes have been determined bearing
in mind the practical possibilities of in situ measurements and monitoring and the performances of
measuring instruments available at present.
Instructions for monitoring (how, where, when) and for post processing recorded data are provided.
4.2 The heat exchanges between human body system and its environment
The energy balance equation on the human body is:
S = (M-W) ± R ± C ± E ± Eres± Cres ± K (1)
where
S body heat storage rate
M metabolic rate
W effective mechanical power
R radiative heat flow
C convective heat flow
E evaporative heat flow at the skin
Eres respiratory evaporative heat flow
Cres respiratory convective heat flow
K conductive heat flow
Where the sign ± indicates the direction of heat flow between the human body and its surroundings.
Each term in equation (1) requires the knowledge of some physical quantities. In tables 1 these
quantities and their connections with energy balance on a human body are shown.
In general, the quantities affecting the energy balance on a system can be divided into two categories,
basic and derived, depending to the possibility to measure them directly or indirectly.
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Table 1 — Main independent quantities involved in the analysis of the thermal balance on
human body and analysed in this Standard. Heat conduction is not considered because its
limited influence on the total balance.
Elements in thermal balance t t t v p
a r s a a
Air tempera- Mean radiant Surface tem- Air ve- Partial vapour
ture temperature perature locity pressure
Heat transfer by radiation, R X X
1)
Heat transfer by convection, C X X
Heat exchanges through evap-  X X
oration:
— evaporation from the skin,
E
— evaporation by respiration,
E
res
Convection by respiration, C X
res
Heat transfer by conduction X
1)
Heat transfer by convection is also affected by body movements. The resultant air velocity at skin level is
usually defined relative air velocity (v ).
ar
5 The physical quantities characterizing heat exchanges between a system and
its environment
5.1 The basic physical quantities
The basic physical quantities are the quantities directly measurable.
These quantities are as follows:
— air temperature;
— radiation;
— plane radiant temperature;
— dew point temperature;
— relative humidity;
— air velocity;
— surface temperature;
— globe temperature;
— wet bulb temperature;
— natural wet bulb temperature.
5.1.1 Air temperature
It is the temperature of the air around the human body. It is measured by a temperature sensor shielded
against radiation (see Annex A).
5.1.2 Radiation directional
It is the energy exchanged by radiation from system and its environment. It can be measured by a
radiometer (see Annex C).
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
5.1.3 Plane radiant temperature
It is the uniform temperature of an enclosure where the irradiance on one side of a small plane
element is the same as in the non-uniform actual environment. It can be measured from radiation with
a radiometer or calculated from the surface temperatures of the environment and the shape factors
between the surfaces and the plane element (see Annex C).
5.1.4 Dew point temperature
The dew-point temperature is defined as the temperature at which the partial vapor pressure of water
in moist air would be sufficient to saturate the air. In other words, the partial vapor pressure at the
given temperature is equal to the partial saturation vapor pressure at the dew-point temperature (see
Annex D).
5.1.5 Relative humidity
The relative humidity is the actual vapour pressure divided by vapour pressure at saturation at the
same temperature (see Annex D).
5.1.6 Surface temperature
It is the temperature of a given surface. This is used to evaluate the radiant heat exchange between the
hu-man body by means of the mean radiant and/or the plane radiant temperature. It is also used to
evaluate the effect of direct contact between the body and a given surface (see Annex F).
5.1.7 Air velocity
It is a quantity defined by its magnitude and direction. The quantity to be considered in the case
of thermal environments is the magnitude of the velocity vector of the flow at the measuring point
considered (see Annex E).
5.1.8 Globe temperature
is the temperature measured from a black-globe thermometer consisting of a black globe in the centre
of which is placed a temperature sensor such as a thermocouple or a resistance probe (see Annex B).
5.1.9 Wet bulb temperature
The wet-bulb temperature is the reading registered by a temperature sensor, shielded against radiation,
placed in a moist gas stream and covered with a wetted cloth or wick. This temperature is lower than
that of the gas stream itself and is the dynamic equilibrium value attained when the convective heat
transfer to the sensor effectively equals the evaporative heat load associated with the moisture loss
from the wetted sur-face. If small corrections are applied to a wet bulb thermometer (e.g. a gas stream
velocity greater than 3 m·s-1), it returns with a good approximation the thermodynamic wet-bulb
temperature. This is the limiting temperature reached as a gas cools on adiabatic saturation and is
more properly termed the adiabatic-saturation temperature to avoid confusion (see Annex D).
5.1.10 Natural wet bulb temperature
The natural wet bulb temperature is the temperature value read by a sensor covered with a wetted
wick that is ventilated naturally (i.e. placed in the environment under consideration without additional
forced ventilation). Since the sensor is unshielded, this quantity is affected also by radiation and cannot
be confused with the psychrometric wet bulb temperature (see Annex H).
5.2 Derived physical quantities
The derived physical quantities are calculated from basic ones or represent or characterize a group of
factors of the environment, weighted according to the characteristics of the sensors used. The second
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
ones are often used to define an empirical index of comfort or thermal stress without having recourse
to a rational method based on estimates of the various forms of heat exchanges between the human
body and the thermal environments, and of the resulting thermal balance and physiological strain.
Some derived quantities are de-scribed in the specific standards as they apply and where measuring
requirements are included.
— mean radiant temperature;
— radiant temperature asymmetry;;
— operative temperature;
— partial vapour pressure;
— humidity ratio.
5.2.1 Mean radiant temperature
It is the uniform temperature of an imaginary enclosure in which radiant heat transfer from the human
body is equal to the radiant heat transfer in the actual non-uniform enclosure.
The mean radiant temperature can be calculated from quantities measured by instruments which
allow the generally heterogeneous radiation from the walls of an actual enclosure to be "integrated"
into a mean value (see annex B).
The mean radiant temperature can also be calculated from measured values of the temperature of the
sur-rounding walls and the size of these walls and their position in relation to a person. (See annex B.)
The mean radiant temperature may also be calculated from the plane radiant temperature in six
opposite directions weighted according to the projected area factors for a person. Similarly, it can be
estimated from the measurement of the radiant flux from different directions. (See annex B).
NOTE The concept of mean radiant temperature allows the study of radiative exchanges between man and his
environment. It presupposes that the effects on man of the actual environment which is generally heterogeneous
and the virtual environment which is defined as homogeneous are identical. When this hypothesis is not valid, in
particular in the case of asymmetric radiation, the radiation exchanges arising from thermally different regions
and the extent of their effect on man should also be assessed using the concept of plane radiant temperature.
5.2.2 Radiant temperature asymmetry
The radiant temperature asymmetry is the difference between the plane radiant temperature of the
two oppo-site sides of a small plane element (see 5.1.3).
The concept of radiant temperature asymmetry is used when the mean radiant temperature does not
completely describe the radiative environment, for instance when the radiation is coming from opposite
parts of the space with appreciable thermal heterogeneities (see Annex B).
The asymmetric radiant field is defined in relation to the position of the plane element used as a
reference. It is, however, necessary to specify exactly the position of the latter by means of the direction
of the normal to this element.
The radiant temperature asymmetry is measured or calculated from the measured value of the plane
radiant
temperature in the two opposing directions (see Annex C).
5.2.3 Operative temperature
The operative temperature is the uniform temperature of an imaginary black enclosure in which an
occupant would exchange the same amount of heat by radiation plus convection as in the actual non-
uniform environment (see Annex G).
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
5.2.4 Partial vapour pressure
The partial vapour pressure of a sample of moist air is the pressure which the water vapour would
exert if it alone occupied the whole volume occupied by the mixture at the same temperature. It is
proportional to the absolute humidity, which represents to the actual amount of water vapour contained
in the air as opposed to quantities such as the relative humidity or the saturation level.
The partial vapour pressure can be determined directly or indirectly by the measurement of several
quantities simultaneously (see Annex D).
5.2.5 Humidity ratio
The humidity ratio of a given moist air sample is defined as the ratio of the mass of water vapor to the
mass of dry air in the sample (see Annex D).
5.2.6 Turbulence intensity
Turbulence Intensity is a scale characterizing turbulence expressed as a percent.
6 The characteristics of physical quantities measuring instruments
The characteristics depend on the class (C and S).
6.1 Characteristics of instruments for measuring the basic quantities
When a measurement is carried out, it is necessary to make difference between the accuracy of the
physical quantity that is affected by the variables involved in the measuring operations (e.g. the
position of the sensors) and the accuracy of the sensor. To obtain reliable results the former is the most
important.
The measuring ranges, the measuring accuracy of the sensors for measuring the basic quantities are
summarized in table 3. These characteristics shall be considered to be minimum requirements for
each class (C and S). That means that according to needs and technical manufacturing possibilities, it is
always possible to specify more exact characteristics or more prescriptive values. For certain quantities,
very precise thermal stress measurements may require the use of appliances with measuring ranges in
class S and accuracy of class C.
Class C (comfort) Class S (stress) Comments
Quantity Symbol Measur- Accuracy Response Measur- Accuracy Response
ing range time ing range time
Air tempera- t 10 °C ÷ Required: ≤1 min -60 °C ÷ Required: ≤1 min Response
a
ture 35 °C 150 °C time takes
±(0,3 °C + ±(0,6 °C +
into account
0,005∙|t |°C) 0,01∙|t |°C)
a a
that the
measure-
Desiderable: Desiderable:
ment is
±(0,1 °C + ±(0,15 °C +
carried out
0,001 7∙|t |°C) 0,002∙|t |°C)
a a in air.
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Class C (comfort) Class S (stress) Comments
Quantity Symbol Measur- Accuracy Response Measur- Accuracy Response
ing range time ing range time
2 2
Radiation r -35 W∙m Required: ≤1 min -300 W∙m Required: ≤1 min Accuracy
d
2 2
directional ÷ 35 W∙m ±5 W∙m ÷ -100 values
10 %
W∙m have been
spectral Desiderable:
chosen as a
±5 W∙m
2 2
range: ±5 W∙m -100 W∙m
function of
÷ +100
10 %
the different
0,3 µm ÷
W∙m
measuring
50 µm
Desiderable:
ranges and
> +100
5 %
proportional
W∙m
to the read
±5 W∙m
spectral
value in
range:
the ranges
5 %
300 W∙m ÷
0,3 µm ÷
-100 W∙m
50 µm
and >
+100 W∙m .
Plane radiant t 0 °C ÷ Required: -60 °C ÷ Required:
pr
temperature 50 °C +200 °C
±(0,6 °C + ±(1,2 °C +
0,05∙|t |°C) 0,02∙|t |°C)
pr pr
Desiderable: Desiderable:
±(0,2 °C + ±(0,6 °C +
0,04∙|t |°C) 0,02∙|t |°C)
pr pr
These levels These levels shall
shall be be guaranteed
guaranteed at least for a
at least for deviation |t -t |
pr a
a deviation < 50 °C
|t -t | <
pr a
10 °C
Dew point t -5 °C ÷ Required: -5 °C ÷ Required: 0,5
dew
temperature 28 °C 0,2 +50 °C
Desiderable: 0,2
Desiderable:
0,1
Relative hu- RH 20 % ÷ Required: ≤3 min 5 % ÷ Required: 3 % ≤3 min The range
midity 80 % 3 % 95 % proposed
Desiderable: 2 %
for class S
10 °C ÷ Desiderable:
intruments
35 °C 2 %
is consistent
with the
limits of
the current
measure-
ment tech-
nology
Air velocity v 0,05 ÷ 1 Required: Required: 0,1 ÷ Required: Required: (*) the
a
-1 -1
m∙s 20 m∙s turbulence
±(0,1 + ≤ 2 sec ±(0,1 + 0,05∙v ) ≤ 2 sec
a
intensity can
-1 -1
0,05∙v ) m∙s m∙s
a
be calculat-
Desidera- Desidera-
ed only with
Desiderable: ble: Desiderable: ble:
a suitable
±(0,05 + ≤ 1 sec ±(0,1 + 0,03∙v ) ≤ 1 sec
a frequency
-1 -1
0,05∙v ) m∙s m∙s
a of the meas-
Per misure Per misure
urement
These levels di turbo- di turbo-
shall be lenza lenza
The ranges
guaranteed
are made
≤ 0,2 sec ≤ 0,2 sec
whaetever
consistent
the direction
(*) (*)
with the
of air flow
accuracies
within a
specified
solid angle ω
= 3π sr
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
Class C (comfort) Class S (stress) Comments
Quantity Symbol Measur- Accuracy Response Measur- Accuracy Response
ing range time ing range time
Surface tem- t 0 °C ÷ Required: ≤1 min -50 °C ÷ Required: ≤1min The accu-
s
perature 50 °C +200 °C racy of the
±(0,6 °C + ±(0,6 °C +
measure-
0,01∙|t |°C) 0,01∙|t |°C)
s s
ment is
affected by
Desiderable: Desiderable:
the contact
±(0,15 °C + ±(0,15 °C +
pressure
0,002∙|t |°C) 0,002∙|t |°C)
s s
Globe temper- t 0 °C ÷ Required: ≤30min -50 °C ÷ Required: ≤30min (**) for
g
ature(**) 50 °C +200 °C a globe
±(0,6 °C + ±(0,6 °C +
150 mm in
0,01∙|t |°C) 0,01∙|t |°C)
g g
diameter.
Desiderable: Desiderable:
±(0,15 °C + ±(0,15 °C +
0,002∙|t |°C) 0,002∙|t |°C)
g g
Psychrometric t 5 °C ÷ Required: ≤1 min - - - Response
w
wet bulb tem- 40 °C time takes
±(0,6 °C +
perature into account
0,01∙|t |°C)
w
that the
measure-
Desiderable:
ment is
±(0,15 °C +
carried out
0,002∙|t |°C)
w in air.
Natural wet t - - 5 °C ÷ Required: ≤1min Response
nw
bulb temper- 40 °C time takes
±(0,6 °C +
ature into account
0,01∙|t |°C)
nw
that the
measure-
Desiderable:
ment is
±(0,15 °C +
carried out
0,002∙|t |°C)
nw
in air.
For the purposes of this International Standard, the time constant of a sensor is considered to be
numerically equal to the time taken for the output of the sensor, in response to a step change in the
environmental quantity being measured, to reach 63 % of its final change in steady-state value without
overshoot. The response time, which is in practice the time after which the quantity being measured
(for example: temperature of the thermometer) can be considered to be sufficiently close to the exact
figure for the quantity to be measured (for example: temperature of the air), can be calculated from the
time constant. A 90 % response time is achieved after a period equal to 2,3 times the time constant. It
is necessary to wait, as a minimum, for a time equivalent to the response time before a measurement
is taken. In table 4 the Standard environmental conditions for the determination of time constants of
sensors are reported.
Table 4 — Standard environmental conditions for the determination of time constants of
sensors
t t p v
a r a a
Air temperature = t any < 0,15 m·s-1
a
Mean radiant temperature = t = t any < 0,15 m·s-1
r a
Plane radiant temperature = 20 °C = t any < 0,15 m·s-1
a
To be specified according
Partial vapour pressure = 20 °C = t
a
to the measuring method
Air velocity = 20 °C = t any -
a
Surface temperature = 20 °C = t any < 0,15 m·s-1
a
As the time constant of a sensor does not depend solely on the sensor (mass, surface area, presence
of a protective shield) but also on the environment, and hence on factors connected with a given
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
measurement (air velocity, radiation, etc.), it is necessary to indicate the conditions under which these
values were obtained. The characteristics of measuring instruments for basic physical quantities are
specified in table 4 (classes C and S). They shall be used as a reference except where this contradicts
the principle for measuring the quantities under consideration. In any case it is important to consider
instrumental measurement uncertainty and measuring chain uncertainty (see 8).
All measurement instruments should be periodically calibrated to satisfy all required specifications.
6.2 Characteristics of integrating types of measuring instruments
Any measuring instrument integrating the measurement of several variables (e.g. WBGT meters) shall
have a measuring interval, and an accuracy equal to or better than those of the minimum between
corresponding individual variables.
All measurement instruments should be periodically calibrated to satisfy all required specifications.
7 Specifications relating to measuring methods
7.1 General
The methods for measuring the physical quantities characterizing the environment shall take account
of the fact that these characteristics vary in location and time. Furthermore, the methods can be
different depending on the environment use, for example for human occupation or for the collections
preservation. In this standard only environments for human occupation are considered.
The thermal environment may vary with time and the horizontal location and the vertical direction (as
shown in paragraph 5.2). Therefore, it should be taken into account how long a time a person is working
at the different locations.
7.2 Specifications relating to variations in the physical quantities within the space
surrounding the subject
An environment may be considered to be "homogeneous" from the microclimatic point of view if, at
a given moment, air temperature, mean radiant temperature, mean air velocity and partial vapour
pressure can be considered to be practically uniform around the subject, i.e. when the deviations
between each of these quantities and their mean spatial value calculated as a mean of the locations
does not exceed the values obtained by multiplying the required measuring accuracy from table 3 by
the corresponding factor X listed in table 5. This condition is frequently met in case of air temperature,
air velocity and partial vapour pressure, but more rarely in the case of mean radiant temperature.
Table 5 — Values of X factor for determining the microclimatic homogeneity of an environment
Factor X
Class C (comfort) Class S (stress)
Air temperature 4 5
Globe temperature 2 2
Air velocity 2 3
Relative humidity 2 3
When the environment is heterogeneous, the physical quantities shall be measured at several locations
at or around the subject or in a position representative of the occupation and account taken of the
partial results obtained in order to determine the mean value of the quantities to be considered in
assessing the comfort or the thermal stress. Other Standards in this series like ISO 15265 or ISO 15743
provide information about the previous analyses of the comfort or the thermal stress conditions of
the workplaces being studied or of workplaces of a similar type may and information of interest in
determining whether certain of the physical quantities are distributed in a homogeneous way. It is usual
oSIST prEN ISO 7726:2023
ISO/DIS 7726:2023(E)
in the case of poorly defined rooms or workplaces to consider only a limited zone of occupancy where
the criteria of comfort or thermal stress shall be respected. In case of dispute in the interpretation of
data, measurements carried out presuming the heterogeneous environment shall be used as a reference.
Table 6 shows the heights to be used for measuring the basic physical quantities. In class S all quantities
shall be measured at the eights required by standards which define the stress indices and which takes
precedence over this International Standard.
The different sensors shall be placed at the heights indicated in table 6 where the person normally
carries out his activity. When it is impossible to interrupt the activity in progress, it is necessary to
place the sensors in positions such as that the thermal exchanges are more or less identical to those to
which the person is exposed (this measurement detail shall be mentioned in the results).
Table 6 — Measuring heights for the physical quantities of an environment in class C
Recommended heights
Sitting Standing
Head level 1,1 m 1,7 m
Abdomen level 0,6 m 1,1 m
Ankle level 0,1 m 0,1 m
7.3 Specifications relating to the variations in the physical quantities with time
The physical quantities in the space surrounding the person can change as a function of time, for
example the following reasons:
a) the environment is naturally ventilated;
b) for a given activity, the quantities can vary as a function of external incidents such as those which
accompany a manufacturing process in the case of an industrial activity;
c) the quantities vary as a result of the movements of the person in different environments (for
example, a warm environment close to a machine and a comfortable rest environment).
d) Changes in external irradiation
An environment is said to be stationary in relation to the subject when the physical quantities used
to describe the level of exposure are practically independent of the time, i.e. for instance whe
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