ISO 916:2020

INTERNATIONAL ISO
STANDARD 916
First edition
2020-02
Testing of refrigerating systems
Essais des machines frigorifiques
Reference number
ISO 916:2020(E)
©
ISO 2020

---------------------- Page: 1 ----------------------
ISO 916:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 916:2020(E)

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 2
5 Performance warranty . 3
5.1 General . 3
5.2 Subject of technical warranties . 3
5.2.1 General. 3
5.2.2 Refrigerating capacity . 3
5.2.3 Compressor absorbed power . 3
5.2.4 Absorbed power of ancillaries . 4
5.2.5 Absorbed power of the entire system . 4
5.2.6 Cooling water demand . 4
5.2.7 Coefficient of performance . 4
5.3 Operating conditions for technical warranties . 4
5.3.1 General. 4
5.3.2 Overall refrigerating capacity . 4
5.3.3 Net or useful refrigerating capacity. 4
5.3.4 Conversion to warranty conditions . 4
5.4 Tolerance . 5
5.5 Acceptance limit. 5
6 Test preparation and procedure . 5
7 Measuring instruments . 6
7.1 General . 6
7.2 Temperature measuring instruments . 6
7.3 Pressure gauges. 6
7.4 Measuring instruments for electric power . 6
7.5 Flow meters . 6
7.6 Speed measuring devices . 6
7.7 Torque measuring devices . 7
7.8 Time measuring devices . 7
7.9 Mass measuring devices . 7
8 Determination of the refrigerating capacity . 7
8.1 Direct methods . 7
8.1.1 Overall refrigerating capacity . 7
8.1.2 Net refrigerating capacity for a liquid cooled medium .11
8.1.3 Useful refrigerating capacity .12
8.2 Indirect methods .12
8.2.1 General.12
8.2.2 Determination of the overall refrigerating capacity by means of a
calibrated compressor .12
8.2.3 Determination of the net refrigerating capacity .13
8.2.4 Determination of the useful refrigerating capacity .13
8.2.5 Determination of the overall refrigerating capacity from the overall
energy balance .13
9 Determination of the drive power .14
9.1 Power absorbed by the compressor .14
10 Measurement uncertainties .14
11 Results, conversion to guaranteed values .15
© ISO 2020 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 916:2020(E)

12 Material properties .15
Bibliography .17
iv © ISO 2020 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 916:2020(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 (see 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 (see 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 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.
This first edition of ISO 916 cancels and replaces ISO/R 916:1968, which has been technically revised.
The main changes compared to ISO/R 916:1968 are as follows:
— clarification in the Scope that this document is applicable to measurements on site;
— complete revision of the structure of the Terms and definitions clause;
— inclusion of transcritical refrigerant systems;
— new wording to the clauses “Tolerance” and “Measuring instruments”;
— deletion of “5.1.2.2, secondary cooling medium (gaseous)”;
— editorial changes;
— structured according to the current version of ISO/IEC Directives Part 2.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2020 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 916:2020(E)
Testing of refrigerating systems
1 Scope
This document applies to the performance testing of compressor driven refrigerating systems (hereafter
referred to as refrigerating systems) that operate according to the principle of vapour compression and
consist of the circuit parts for compression, condensation, and evaporation as well as the connecting
pipes and any necessary associated ancillaries required for a complete refrigeration circuit.
This document does not apply to the testing of other refrigeration systems such as absorption or steam
jet refrigerating systems.
Testing of the suitability of a refrigerating system for a specific use, such as household refrigerators,
refrigerated commercial and display cabinets, air conditioners, is not covered by this document.
This document includes testing outside laboratories or where specific laboratory testing standards for
systems do not exist and which is performed according to agreed operating conditions.
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 5167 (all parts), Measurement of fluid flow by means of pressure differential devices inserted in circular
cross-section conduits running full
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
overall refrigerating capacity
Q
og
rate at which heat is extracted from the ambient by the refrigerant
Note 1 to entry: As a rule, for single-stage refrigerating systems, the overall refrigerating capacity corresponds
to the product of the mass flow and the difference between the respective enthalpies of the refrigerant at the
inlet of the compressor and at the outlet of the condenser or aftercooler, if provided (see also 8.1.1).
3.2
net refrigerating capacity
Q
on
rate at which heat is extracted from the cooled medium in the evaporator by the refrigerant
Note 1 to entry: See also 8.1.2.
© ISO 2020 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 916:2020(E)

3.3
useful refrigerating capacity
Q
oe
rate at which heat is usefully extracted by the refrigerant or cooled medium
Note 1 to entry: The useful refrigerating capacity corresponds to the product of the flow of the refrigerant or
cooled medium and its difference in enthalpy between the two points specified by agreement between which the
cooling effect is made useful (see also 8.1.3).
4 Symbols and units
Parameter Symbol Unit
2
Heat-transfer area A m
Specific heat capacity c J/(kg⋅K)
Coefficient of performance COP —
Specific enthalpy h J/kg
Mass flow m kg/s
Absolute pressure p bar
Power P W
Heat flow Q W
Refrigerating capacity Q W
o
Temperature t °C
Absolute temperature T K
2
Overall coefficient of heat transfer u W/(m ⋅K)
2
Surface coefficient of heat transfer α W/(m ⋅K)
Insulation thickness δ m
Isentropic efficiency η —
i
Thermal conductivity λ W/(m⋅K)
2
Kinematic viscosity ν m /s
3
Density ρ kg/m
Indices:
Index Parameter
amb Ambient
cor Corrected
e Useful
g Overall
K Cooled medium, liquid
L Heat-transfer medium
m Mechanical
n Net
R Refrigerant
W Coolant, liquid (cooling water)

Index Location
Reference point: 1 Measuring point: compressor inlet (suction port)
Reference point: 2 Measuring point: compressor outlet (discharge port)
2 © ISO 2020 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 916:2020(E)

Index Location
Reference point: 3 Measuring point: condenser/gas cooler refrigerant inlet
Measuring point: condenser/gas cooler refrigerant outlet
Reference point: 4
or upstream of internal heat exchanger, if installed
Measuring point: upstream of the expansion valve for the
Reference point: 5
evaporator
Reference point: 6 Measuring point: evaporator refrigerant inlet
Reference point: 7 Measuring point: evaporator refrigerant outlet
Reference point: 8 Measuring point: aftercooler refrigerant inlet
Reference point: 9 Measuring point: aftercooler refrigerant outlet
5 Performance warranty
5.1 General
5.1.1 Only the characteristics essential to the economic efficiency and the operation of refrigerating
systems and verifiable by usual measurement methods shall be the subject of performance warranty. This
requires allowances for the variations of operating conditions which are hardly avoidable in practice.
5.1.2 For the data according to 5.2.1 to 5.2.7, it is recommended to indicate several values near the
operating conditions according to 5.3, particularly for the temperature values. To avoid interpolation,
these values may be presented graphically within the variation limits for each pair of values. Permissible
deviations shall be subject to agreement.
5.1.3 The influence of temporary variations on other operating conditions shall be subject to
agreement.
5.2 Subject of technical warranties
5.2.1 General
Subject of the technical warranties are the refrigerating capacity and the power absorbed at operating
conditions which need to be agreed.
5.2.2 Refrigerating capacity
The refrigerating capacity shall be agreed as:
— overall refrigerating capacity (see 3.1);
— net refrigerating capacity (see 3.2); or
— useful refrigerating capacity (see 3.3).
5.2.3 Compressor absorbed power
The following shall be subject to agreement:
a) the power absorbed at the compressor shaft;
b) the power output at the driver shaft;
c) the power absorbed by the motor, e.g. electrical power input at the motor terminals; or
d) the fuel consumption of the engine.
© ISO 2020 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 916:2020(E)

5.2.4 Absorbed power of ancillaries
The power absorbed by fans, pumps, agitators, heaters, and other associated ancillaries shall be subject
to agreement.
5.2.5 Absorbed power of the entire system
The drive power of the entire system shall be subject to agreement.
5.2.6 Cooling water demand
The cooling water demand may be a subject of the technical warranties.
5.2.7 Coefficient of performance
The coefficient of performance, COP, may be subject to agreement instead of the power absorbed
according to 5.2.3 to 5.2.5.
5.3 Operating conditions for technical warranties
5.3.1 General
The following shall be subject to agreement:
a) refrigerant designation;
b) condition of the heat-transfer medium when entering, e.g. the condenser, aftercooler, oil cooler (if
provided).
5.3.2 Overall refrigerating capacity
The following shall be subject to agreement:
a) Pressure and temperature of the refrigerant
1) at the suction port of the compressor; and
2) at the outlet of the condenser or of the receiver or aftercooler, respectively.
5.3.3 Net or useful refrigerating capacity
The following shall be subject to agreement:
a) the condition of the cooled medium at the inlet and outlet of the evaporator or at two defined points
of the cooled medium circuit; or
b) the condition of the cooled medium at the inlet or outlet of the evaporator or at a defined point of
the cooled medium circuit as well as the corresponding mass flow.
The condition of the cooled medium does not only include its temperature but also its physical data.
5.3.4 Conversion to warranty conditions
The conversion to warranty conditions requires the indication of the compressor speed or the power
supply frequency (for motor compressors), respectively, the refrigerant pressures in the evaporator and
the condenser or the evaporation and condensing temperature, respectively, as well as the intermediate
pressures in case of multiple-stage systems.
For this purpose, the permissible deviations of the operating conditions for testing shall be specified.
4 © ISO 2020 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 916:2020(E)

Methods for correction to measured performance to indicate performance at warranty conditions shall
be agreed. See also 11.5.
5.4 Tolerance
The tolerance refers to deviations from the assured property (e.g. refrigerating capacity, power
absorbed, and COP) which are caused by the manufacturing process and shall be agreed separately.
5.5 Acceptance limit
The permissible deviation of measured values from the assured property is the sum of the tolerance
and the overall measurement uncertainty of the applied measurement method.
In cases where zero negative tolerance has been specified in relation to manufacturing tolerances in
5.4, allowance for measurement uncertainty shall still apply.
6 Test preparation and procedure
6.1 The test shall be carried out with all values in steady-state condition and in addition particularly
with the compressor and the motor at operating temperature.
6.2 Prior to any measurement, it shall be ensured that heat exchanger surfaces not in contact with the
refrigerant are clean. This applies, for example, to the cooling water side of condensers and the secondary
refrigerant side of the evaporator.
6.3 Readjustment of the system prior to measurements is permitted. During the actual test, only
mutually agreed interventions are permitted.
6.4 The test shall be carried out at operating conditions complying as precisely as possible to those
agreed in accordance with 5.3.
6.5 The steady-state condition must be proven over a sufficiently long time period, while the initial
and the final values of all quantities relevant to the test shall be within previously agreed limits.
6.6 Values deviating strongly from the arithmetic mean of the readings are not taken into account.
6.7 Readings are acceptable as long as the steady-state condition can be maintained.
6.8 All measurements shall be carried out in accordance with applicable standards, e.g.
ISO 5167 (all parts). The measuring instruments shall be chosen in accordance with Clause 7.
6.9 The refrigerating system under test shall be provided with the required connections for pressure
and temperature measurements. These connections shall not impair the intended function of the system.
6.10 For measuring the overall refrigerating capacity, it shall be ensured that the liquid refrigerant is
free from bubbles downstream of the condenser or the aftercooler, respectively. Proper purging of the
refrigerating system is additionally required.
6.11 Two consecutive measurement series shall be conducted.
© ISO 2020 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO 916:2020(E)

7 Measuring instruments
7.1 General
7.1.1 The condensing and evaporating temperatures are derived from the absolute pressure readings,
where the sources according to 12.1 are used and the purging measures according to 6.10 are followed.
7.1.2 Only measuring instruments with fully verifiable indications shall be used. It is essential that the
measurement uncertainty can be determined by calibration and does not vary during testing. Measuring
instruments whose condition may vary during the test shall be verified both before and after testing. The
measurement uncertainty values indicated below refer to the extended measurement uncertainty with a
confidence interval of 95 % corresponding to twice the standard deviation.
7.1.3 Besides the types of measuring instruments indicated below, other generally accepted measuring
instruments or devices may be used provided they comply with the indicated measurement uncertainties.
7.2 Temperature measuring instruments
The measurement uncertainty of the temperature measuring instrument shall be within the following
limits while 7.1 shall be taken into account:
a) for measuring the temperatures of cooled medium in the evaporator or cooling water in the
condenser ±0,1 K;
a) for all other temperature measurements ±0,5 K.
7.3 Pressure gauges
The measuring range shall be chosen such that the measurement uncertainty does not exceed 2 % of
the indicated value.
a) if Bourdon-tube, diaphragm or bellows manometers are used, classes 0,6 to 0,1 (precision
manometers) shall be chosen;
b) if pressure transducers are used, they shall be calibrated prior to measurement;
c) if liquid filled pressure gauges are used for measuring the pressure differences, it shall be ensured
that the uncertainty of the measurement does not exceed 1 % of the indicated value. The medium
to be measured shall not be absorbed by the barrier liquid.
7.4 Measuring instruments for electric power
The measurement uncertainty shall not exceed:
a) 0,5 % of the full scale value for indicating measuring instruments;
b) 1 % of the measured value for integrating measuring instruments.
7.5 Flow meters
The measurement uncertainty of flow meters shall be within 2 % of the indicated value.
7.6 Speed measuring devices
The measurement uncertainty shall not exceed 0,75 % of the indicated value.
6 © ISO 2020 – All rights reserved

---------------------- Page: 11 ----------------------
ISO 916:2020(E)

7.7 Torque measuring devices
The measurement uncertainty shall not exceed 1 % of the rated load.
7.8 Time measuring devices
The measurement uncertainty shall not exceed 0,1 % of the measured value.
7.9 Mass measuring devices
The measurement uncertainty shall not exceed 0,2 % of the measured value.
8 Determination of the refrigerating capacity
8.1 Direct methods
8.1.1 Overall refrigerating capacity
8.1.1.1 General
The refrigerating capacity is calculated from the refrigerant mass flow and a difference of enthalpy.
If the refrigerant vapour at the compressor inlet is dry, saturated or superheated (i.e. free from
entrained liquid), the overall refrigerating capacity is given by Formula (1)
Qm=−()hh (1)
og R 15
Condition 1 corresponds to the condition at the compressor inlet, condition 5 corresponds to the
condition upstream of the expansion valve before the evaporator (see Figures 1 and 2).
The refrigerant mass flow is determined either from the heat balance in accordance with 8.1.1.2 or
from the flow measurement in accordance with 8.1.1.3. This method is suitable for various designs of
refrigerating systems. Figures 1 and 2 show representations of refrigerating system schematics and
their characteristic in the p–h diagram.
a) Single-stage refrigerating system
© ISO 2020 – All rights reserved 7

---------------------- Page: 12 ----------------------
ISO 916:2020(E)

b) Single-stage refrigerating system with aftercooler
c) Single-stage refrigerating system with economiser
d) Two-stage refrigerating system with intermediate pressure separator
Key
A compressor, A from low pressure to D evaporator
LP
intermediate pressure, A from
HP
intermediate pressure to high pressure
B condenser E economiser
C expansion valve, C to intermediate N aftercooler
MP
pressure, C to evaporator pressure
LP
S liquid separator, S at intermediate pressure
MP
Figure 1 — Schematics and log-p-h diagrams of subcritical and trans-critical refrigerating
systems
8 © ISO 2020 – All rights reserved

---------------------- Page: 13 ----------------------
ISO 916:2020(E)

a) Single-stage refrigerating system with internal heat exchanger and dry evaporation
b) Refrigerating system with internal heat exchanger and flooded evaporator
Key
A compressor D evaporator
B condenser F internal heat exchanger
C expansion valve S liquid separator at evaporation pressure
LP
Internal heat transfer, Δh ≈ Δh
4–5 8–9
Figure 2 — Schematics and log-p-h diagrams of single-stage refrigerating systems
with internal heat exchanger
8.1.1.2 Determination of the refrigerant mass flow from the heat balance
8.1.1.2.1 The refrigerant mass flow can be determined by using the heat balance at each component of
the circuit through which it passes. Any case of previously branching off partial flows shall be taken into
account.
© ISO 2020 – All rights reserved 9

---------------------- Page: 14 ----------------------
ISO 916:2020(E)

8.1.1.2.2 For single-stage systems, the condenser is the most suitable circuit component for establishing
a he
...