ISO 18501

Performance rating of positive displacement refrigerant compressor

This proposed document specifies the terms and definitions, classification basic parameters, technical requirements, marking, packaging and storage of positive displacement refrigerant compressor. The document is applicable to positive displacement refrigerant compressors for air-conditioning, heat pump, refrigerant purposes.

Détermination des performances des compresseurs frigorifiques à déplacement positif

General Information

• Status: Not Published
• ICS: 27.200 - Refrigerating technology
• Technical Committee: ISO/TC 86/SC 4 - Testing and rating of refrigerant compressors
• Drafting Committee: ISO/TC 86/SC 4 - Testing and rating of refrigerant compressors
• Current Stage: 6000 - International Standard under publication
• Due Date: 24-Feb-2025
• Completion Date: 24-Feb-2025

Standards Content (Sample)

International
Standard
First edition
Performance rating of positive
displacement refrigerant
compressor
Détermination des performances des compresseurs frigorifiques à
déplacement positif
PROOF/ÉPREUVE
Reference number
© ISO 2025
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Rating requirements . 4
4.1 General requirements .4
4.2 Rating conditions .4
5 Published rating . 5
5.1 General requirements .5
5.2 Individual published rating .6
5.3 Number of individual published ratings requirement .6
5.4 Polynomial equations .6
5.4.1 Ten-coefficient polynomial equation .6
5.5 Published data.7
5.6 Application envelope .8
6 Tolerance . . 9
7 Marking provisions .10
Annex A (informative) Method to handle zeotropic mixtures .11
Annex B (informative) Superheat correction .13
Bibliography . 14
PROOF/ÉPREUVE
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 86, Refrigeration and air-conditioning,
Subcommittee SC 4, Testing and rating of refrigerant compressors.
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.
PROOF/ÉPREUVE
iv
International Standard ISO 18501:2025(en)
Performance rating of positive displacement refrigerant
compressor
1 Scope
This document specifies normative references, terms and definitions, rating requirements, published
rating, tolerance and marking provisions of positive displacement refrigerant compressors. This document
applies to positive displacement refrigerant compressors and their performance in air-conditioning,
heating, refrigeration and dehumidification applications. Single stage, two-stage and refrigerant-injected
compressors without intermediate temperature load (only one evaporator) are included in this document.
Subcritical operation and transcritical operation are also included in this document.
Compressors for other applications, compression types and operations can also refer to this document.
The manufacturer is solely responsible for the determination of values to be used in the published product
information.
This document is intended as guidance for the industry, including manufacturers, engineers, installers
and service contractors. It defines the minimum amount of information in a standard form to enable the
evaluation and comparison of different compressors for use in an application.
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 18976, Testing of refrigerant compressors
ISO 817, Refrigerants — Designation and safety classification
IEC 60038, IEC standard voltages
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18976 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
positive displacement refrigerant compressor
machine that increases the pressure of a refrigerant vapour by reducing the compression chamber volume
3.2
fixed displacement compressor
compressor with only one displacement capacity
3.3
modulating compressor
compressor with more than one displacement capacity, either continuous or discrete modulating capacities
PROOF/ÉPREUVE
3.3.1
continuous modulating compressor
compressor with more than four displacement capacities or infinitely variable displacement capacities
Note 1 to entry: This includes but is not limited to variable speed, continuously variable mechanical unloading or
cyclic modulation of discrete.
3.3.2
discrete modulating compressor
compressor with two to four discrete displacement capacities
3.4
subcooling
difference between the bubble point temperature of the refrigerant corresponding to its pressure and the
temperature of the liquid refrigerant
3.5
superheat
difference between the temperature of the vapour refrigerant and its dew-point temperature corresponding
to its pressure
3.6
refrigerating capacity
product of the refrigerant mass flow at the compressor inlet port and the difference between the specific
refrigerant enthalpy at the compressor inlet port and the specific enthalpy of fluid entering the evaporator
expansion device
3.7
heating capacity
product of the refrigerant mass flow leaving the compressor discharge port and the difference of the specific
refrigerant enthalpy at the discharge port and the outlet of the condenser or gas cooler
3.8
power input
time rate of energy usage of the compressor plus any accessories required to sustain operation of the
compressor at the rating condition
3.9
refrigerating coefficient of performance
ratio of the refrigerating capacity to the power input
3.10
heating coefficient of performance
ratio of heating thermal capacity to the power input
3.11
intermediate port
inlet port for vapour or liquid within a compression chamber at a pressure between suction and discharge
pressure
3.12
interstage port
inlet port for vapour or liquid between two stages of compression
3.13
economizer
heat exchanger or flash tank that is used to lower the liquid specific enthalpy of the refrigerant entering the
evaporator while producing vapour that is reintroduced to the compression process
PROOF/ÉPREUVE
3.14
economized operation
system operation mode which reduces the specific enthalpy of the refrigerant entering the evaporator and
produces vapour which is injected into the compression process
Note 1 to entry: For economized operation with heat exchanger economizer, partial high-pressure liquid refrigerant is
throttled to intermediate pressure to subcool the remaining refrigerant. The vapourized refrigerant can be piped to
the intermediate port or interstage port of the compressor.
Note 2 to entry: For economized operation with flash tank economizer, all refrigerant at outlet condenser is throttled
to intermediate pressure in the flash tank. The saturated liquid goes to evaporator loop and saturated vapour can be
piped to the intermediate port or interstage port of the compressor.
3.15
variable frequency drive
VFD
power electronic device supplying an electric motor with a variable frequency and voltage
3.16
subcritical operation
operating condition with discharge pressure below the critical pressure of the refrigerant
3.17
transcritical operation
operating condition with discharge pressure above and the suction pressure below the critical pressure
3.18
liquid injection
injection of high-pressure side liquid refrigerant into the compressor
3.19
step
level of modulation achieved by changing the displacement capacity
EXAMPLE Compressor operating frequency, compressor rotation speed, frequency of variable frequency drive
and mechanical unloading setting.
3.19.1
maximum step
step producing the highest displacement capacity of the modulating compressor defined by the manufacturer
3.19.2
minimum step
step producing the lowest displacement capacity of the modulating compressor defined by the manufacturer
3.19.3
reduced step
step producing less displacement capacity than the maximum step of the modulating compressor
3.20
fluid
liquid, gas or vapour including the state of appearance close to and above the critical pressure
3.21
publish
transfer information to any entity decided by the manufacturer
PROOF/ÉPREUVE
4 Rating requirements
4.1 General requirements
All published ratings shall be based on tests conducted in accordance with ISO 18976.
...

ISO/DISPRF 18501:2024(en)
ISO/TC 86/SC 4
Secretariat: SAC
Date: 2024-11-042025-01-27
Performance rating of positive displacement refrigerant
compressorscompressor
Détermination des performances des compresseurs frigorifiques à déplacement positif
PROOF
ISO/PRF 18501:2025(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.org
Published in Switzerland
© ISO #### 2025 – All rights reserved
ii
ISO/DISPRF 18501:20242025(en)
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Rating requirements . 4
4.1 General requirements . 4
4.2 Rating conditions . 5
5 Published rating . 6
5.1 General requirements . 6
5.2 Individual published rating . 6
5.3 Number of individual published ratings requirement . 6
5.4 Polynomial equations . 6
5.5 Published data . 7
5.6 Application envelope . 9
6 Tolerance . 9
7 Marking provisions . 11
Annex A (informative) Method to handle zeotropic mixtures . 12
Annex B (informative) Superheat correction . 14
Bibliography . 15

iii
ISO/PRF 18501:2025(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 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 86, Refrigeration and air-conditioning,
Subcommittee SC 4, Testing and rating of refrigerant compressors.
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.
Field Code Changed
© ISO #### 2025 – All rights reserved
iv
DRAFT International Standard ISO/DIS 18501:2024(en)

Performance rating of positive displacement refrigerant
compressorscompressor
1 Scope
This document specifies normative references, terms and definitions, rating requirements, published rating,
tolerance and marking provisions of positive displacement refrigerant compressors. This document applies
to positive displacement refrigerant compressors and their performance in air-conditioning, heating,
refrigeration and dehumidification applications. Single stage, two-stage and refrigerant-injected compressors
without intermediate temperature load (only one evaporator) are included in this document. Subcritical
operation and transcritical operation are also included in this document.
Compressors for other applications, compression types and operations can also refer to this document. The
manufacturer is solely responsible for the determination of values to be used in the published product
information.
This document is intended as guidance for the industry, including manufacturers, engineers, installers and
service contractors. It defines the minimum amount of information in a standard form to enable the evaluation
and comparison of different compressors for use in an application.
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 18976, Testing of refrigerant compressors
IEC 60038, IEC standard voltages
ISO 817, Refrigerants — Designation and safety classification
IEC 60038, IEC standard voltages
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18976 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
positive displacement refrigerant compressor
machine that increases the pressure of a refrigerant vapour by reducing the compression chamber volume
ISO/PRF 18501:2025(en)
3.2
displacement capacity
theoretical suction volumetric flow rate through the compressor
Note 1 to entry: Expressed in m /h.
3.2 3.3
fixed displacement compressor
compressor with only one displacement capacity
3.3 3.4
modulating compressor
compressor with more than one displacement capacity, either continuous or discrete modulating capacities
3.3.1 3.4.1
continuous modulating compressor
compressor with more than four displacement capacities or infinitely variable displacement capacities
Note 1 to entry: This includes but is not limited to variable speed, continuously variable mechanical unloading or cyclic
modulation of discrete.
3.3.2 3.4.2
discrete modulating compressor
compressor with two to four discrete displacement capacities
3.4 3.5
subcooling
difference between the bubble point temperature of the refrigerant corresponding to its pressure and the
temperature of the liquid refrigerant
3.5 3.6
superheat
difference between the temperature of the vapour refrigerant and its dew-point temperature corresponding
to its pressure
3.6 3.7
refrigerating capacity
product of the refrigerant mass flow at the compressor inlet port and the difference between the specific
refrigerant enthalpy at the compressor inlet port and the specific enthalpy of fluid entering the evaporator
expansion device
3.7
3.8
heating capacity
product of the refrigerant mass flow leaving the compressor discharge port and the difference of the specific
refrigerant enthalpy at the discharge port and the outlet of the condenser or gas cooler
3.8 3.9
power input
time rate of energy usage of the compressor plus any accessories required to sustain operation of the
compressor at the rating condition
3.9 3.10
refrigerating coefficient of performance
ratio of the refrigerating capacity to the power input
© ISO #### 2025 – All rights reserved
ISO/DISPRF 18501:20242025(en)
3.10 3.11
heating coefficient of performance
ratio of heating thermal capacity to the power input
3.11 3.12
intermediate port
inlet port for vapour or liquid within a compression chamber at a pressure between suction and discharge
pressure
3.12 3.13
interstage port
inlet port for vapour or liquid between two stages of compression
3.13 3.14
economizer
heat exchanger or flash tank that is used to lower the liquid specific enthalpy of the refrigerant entering the
evaporator while producing vapour that is reintroduced to the compression process
3.14 3.15
economized operation
system operation mode which reduces the specific enthalpy of the refrigerant entering the evaporator and
produces vapour which is injected into the compression process
Note 1 to entry: For economized operation with heat exchanger economizer, partial high-pressure liquid refrigerant is
throttled to intermediate pressure to subcool the remaining refrigerant. The vapourized refrigerant can be piped to the
intermediate port or interstage port of the compressor.
Note 2 to entry: For economized operation with flash tank economizer, all refrigerant at outlet condenser is throttled to
intermediate pressure in the flash tank. The saturated liquid goes to evaporator loop and saturated vapour can be piped
to the intermediate port or interstage port of the compressor.
3.15 3.16
variable frequency drive
VFD
power electronic device supplying an electric motor with a variable frequency and voltage
3.16 3.17
subcritical operation
operating condition with discharge pressure below the critical pressure of the refrigerant
3.17 3.18
transcritical operation
operating condition with discharge pressure above and the suction pressure below the critical pressure
3.18 3.19
liquid injection
injection of high-pressure side liquid refrigerant into the compressor
3.19 3.20
step
level of modulation achieved by changing the displacement capacity
EXAMPLE Compressor operating frequency, compressor rotation speed, frequency of variable frequency drive and
mechanical unloading setting.
ISO/PRF 18501:2025(en)
3.19.1 3.20.1
maximum step
step producing the highest displacement capacity of the modulating compressor defined by the manufacturer
3.19.2 3.20.2
minimum step
step producing the lowest displacement capacity of the modulating compressor defined by the manufacturer
3.19.3 3.20.3
reduced step
step producing less displacement capacity than the maximum step of the modulating compressor
3.20 3.21
fluid
liquid, gas or vapour including the state of appearance close to and above the critical pressure
3.21 3.22
publish
transfer information to any entity decided by the manufacturer
4 Rating requirements
4.1 General requirements
All published ratings shall be based on tests conducted in accordance with ISO 18976.
Published ratings shall be established with an ambient temperature around the compressor and its
accessories of 35 °C. If rating at ambient temperatures other than 35 °C, the actual ambient temperature used
to establish the rating shall be stated by the manufacturer.
Published ratings shall be established using the nameplate rated voltage and frequency. For dual nameplate
voltage ratings, published ratings shall be established using both voltages, or using the higher of the two
voltages, if only a single rating is to be published. For compressors with a voltage range, the rated voltage
should be published.
For liquid-injected compressors, the manufacturer shall report the controlled discharge temperature.
For economized compressors, refrigerating capac
...