Water-source heat pumps — Testing and rating for performance — Part 2: Water-to-water and brine-to-water heat pumps

1.1 This document establishes performance testing and rating criteria for factory-made residential, commercial and industrial, electrically-driven, mechanical- compression type, water-to-water and brine-to-water heat pumps. The requirements for testing and rating contained in this document are based on the use of matched assemblies. 1.2 Equipment may be designed for rating at one or several source and load side temperature conditions described in this document. 1.3 This document does not apply to the testing and rating of individual assemblies for separate use, nor to the testing and rating of heat pumps covered in ISO 5151, ISO 13253 or ISO 13256-1.

Pompes à chaleur à eau — Essais et détermination des caractéristiques de performance — Partie 2: Pompes à chaleur eau-eau et eau glycolée-eau

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Published
Publication Date
06-May-2021
Current Stage
6060 - International Standard published
Start Date
07-May-2021
Completion Date
07-May-2021
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INTERNATIONAL ISO
STANDARD 13256-2
Second edition
2021-05
Water-source heat pumps — Testing
and rating for performance —
Part 2:
Water-to-water and brine-to-water
heat pumps
Pompes à chaleur à eau — Essais et détermination des
caractéristiques de performance —
Partie 2: Pompes à chaleur eau-eau et eau glycolée-eau
Reference number
ISO 13256-2:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 13256-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13256-2:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ..............................................................................................................................................................................................................................vii

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 4

5 Rating and test conditions .......................................................................................................................................................................... 5

5.1 Rating conditions for the determination of net capacities ................................................................................ 5

5.1.1 Ratings ...................................................................................................................................................................................... 5

5.1.2 Load side liquid pump adjustment .................................................................................................................. 5

5.1.3 Source side liquid pump adjustment .............................................................................................................. 6

5.1.4 Liquid flow rates .............................................................................................................................................................. 7

5.1.5 Installation and connection of the unit ........................................................................................................ 7

5.1.6 Test liquids ............................................................................................................................................................................ 8

5.2 Rating test conditions for cooling and heating capacities ................................................................................. 8

6 Performance Requirements...................................................................................................................................................................... 9

6.1 General ........................................................................................................................................................................................................... 9

6.2 Maximum operating conditions test .................................................................................................................................10

6.2.1 Test conditions................................................................................................................................................................10

6.2.2 Test procedures..............................................................................................................................................................10

6.2.3 Test requirements ........................................................................................................................................................10

6.3 Minimum operating conditions test ..................................................................................................................................12

6.3.1 Test conditions................................................................................................................................................................12

6.3.2 Test procedures..............................................................................................................................................................12

6.3.3 Test requirements ........................................................................................................................................................12

6.4 Enclosure sweat and condensate test ..............................................................................................................................13

6.4.1 General...................................................................................................................................................................................13

6.4.2 Test conditions................................................................................................................................................................13

6.4.3 Test procedures..............................................................................................................................................................14

6.4.4 Test requirements ........................................................................................................................................................14

7 Test methods ..........................................................................................................................................................................................................14

7.1 General ........................................................................................................................................................................................................14

7.2 General test requirements .........................................................................................................................................................14

7.3 Equipment installation .................................................................................................................................................................14

7.4 Cooling and heating capacity tests procedure ..........................................................................................................15

7.4.1 Reconditioning period .............................................................................................................................................15

7.4.2 Data collection period ..............................................................................................................................................15

7.4.3 Net cooling capacity ...................................................................................................................................................15

7.4.4 Net heating capacity ..................................................................................................................................................16

7.5 Uncertainties of measurement ...............................................................................................................................................16

7.6 Data to be recorded ..........................................................................................................................................................................16

7.7 Uncertainties of measurements and permissible deviations for steady-state

cooling and heating capacity tests ......................................................................................................................................17

7.8 Test results...............................................................................................................................................................................................18

8 Marking provisions .........................................................................................................................................................................................18

8.1 Nameplate requirements ............................................................................................................................................................18

8.2 Nameplate information ................................................................................................................................................................18

8.3 Designation of standard rating capacities ....................................................................................................................19

8.4 Refrigerant Designation ...............................................................................................................................................................19

9 Publication of ratings ...................................................................................................................................................................................19

9.1 Published ratings ...............................................................................................................................................................................19

© ISO 2021 – All rights reserved iii
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ISO 13256-2:2021(E)

9.2 Additional ratings ..............................................................................................................................................................................19

Annex A (informative) Refrigerant enthalpy test method...........................................................................................................20

Annex B (normative) Liquid enthalpy test method ............................................................................................................................22

Annex C (informative) Additional ratings based upon previous standard version

ISO 13256-2:1998.............................................................................................................................................................................................24

Bibliography .............................................................................................................................................................................................................................26

iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 13256-2:2021(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 on 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 the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 86, Refrigeration and air-conditioning,

Subcommittee SC 6, Testing and rating of air-conditioners and heat pumps.

This second edition cancels and replaces the first edition (ISO 13256-2:1998), which has been

technically revised.
The main changes compared to the previous edition are as follows:

— Significant updates to the formatting, symbols, and terms and definitions, have been included to

more closely align with other pertinent ISO standards and the latest ISO requirements.

— The original water loop heat pump (WLHP), ground water heat pump (GWHP) and ground loop

heat pump (GLHP) application rating designations, specifying entering liquid source rating test

conditions, have been replaced with High, Medium, and Low source temperature range conditions to

represent a wider operating map at both standard and partially loaded application rating conditions.

It is now possible, when all three (High, Medium and Low) temperature ranges are specified by the

manufacturer for energy modelling programs to interpolate performance at other entering water

temperatures than those used in the standard.

— Specific antifreeze solution composition requirements have been removed to eliminate prescriptive

language and promote industry innovation of novel and improved antifreeze solutions.

— The standard has been expanded to allow multiple heating capacity ratings at differing load

temperature conditions (Very High, High, Medium, and Low). Medium was retained as the original

load condition.

— Testing tolerances and uncertainties have been harmonized with other pertinent ISO standards.

— Annexes have been significantly updated and harmonized with other pertinent ISO standards.

A list of all parts in the ISO 13256 series can be found on the ISO website.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 13256-2:2021(E)

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.
vi © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 13256-2:2021(E)
Introduction

This document covers heating and cooling systems which are generally referred to as “water-source

heat pumps.” These systems generally include an indoor heat exchanger with means to move the liquid,

a compressor, and a refrigerant-to-water or refrigerant-to-brine heat exchanger. A system may provide

both heating and cooling, cooling-only, or heating-only functions.
© ISO 2021 – All rights reserved vii
---------------------- Page: 7 ----------------------
INTERNATIONAL STANDARD ISO 13256-2:2021(E)
Water-source heat pumps — Testing and rating for
performance —
Part 2:
Water-to-water and brine-to-water heat pumps
1 Scope

1.1 This document establishes performance testing and rating criteria for factory-made residential,

commercial and industrial, electrically-driven, mechanical- compression type, water-to-water and brine-

to-water heat pumps. The requirements for testing and rating contained in this document are based on

the use of matched assemblies.

1.2 Equipment may be designed for rating at one or several source and load side temperature

conditions described in this document.

1.3 This document does not apply to the testing and rating of individual assemblies for separate use,

nor to the testing and rating of heat pumps covered in ISO 5151, ISO 13253 or ISO 13256-1.

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 817, Refrigerants — Designation and safety classification
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
water-to-water heat pump
brine-to-water heat pump

heat pump which consists of one or more factory-made assemblies which normally include an indoor

side refrigerant to water heat exchanger (load side), compressor(s), and outdoor-side refrigerant-to-

water or refrigerant-to-brine heat exchanger(s) (source side), including means to provide both cooling

and heating, cooling-only, or heating-only functions

Note 1 to entry: When such equipment is provided in more than one assembly, the separated assemblies should

be designed to be used together.

Note 2 to entry: Such equipment may also provide functions of sanitary water heating.

© ISO 2021 – All rights reserved 1
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ISO 13256-2:2021(E)
3.2
water-loop heat pump

water-to-water heat pump using, on the source side, a liquid circulating in a common piping loop

Note 1 to entry: The temperature of the liquid loop is usually within a range of 10 °C to 30 °C.

3.3
ground-water heat pump

water-to-water heat pump using, on source side, water pumped from a well, lake, or stream

Note 1 to entry: The temperature of the water is related to the climatic conditions and is generally constant

within the range from 5 °C to 25 °C for deep wells.
3.4
ground-loop heat pump

brine-to-water heat pump using, on the source side, a brine solution circulating through a subsurface

piping loop

Note 1 to entry: The heat exchange loop may be placed in horizontal trenches or vertical bores, or be submerged

in a body of surface water.

Note 2 to entry: The temperature of the brine is related to the heat exchange load and climatic conditions and is

generally within a range from –5 °C to 40 °C.
3.5
cooling capacity

amount of heat that the equipment can remove from the water used to condition the indoor space in a

defined interval of time
Note 1 to entry: Expressed in units of watts.
3.6
net cooling capacity
cooling capacity with load side liquid pump power adjustment
Note 1 to entry: Expressed in units of watts.
3.7
heating capacity

amount of heat that the equipment can add to the water used to condition the indoor space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.8
net heating capacity
heating capacity with load side liquid pump power adjustment
Note 1 to entry: Expressed in units of watts.
3.9
rated voltage
voltage shown on the nameplate of the equipment
Note 1 to entry: Expressed in units of volts.
3.10
rated frequency
frequency shown on the nameplate of the equipment
Note 1 to entry: Expressed in units of Hz.
2 © ISO 2021 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 13256-2:2021(E)
3.11
energy efficiency ratio
EER

ratio of the net cooling capacity to the effective power input at any given set of rating conditions

Note 1 to entry: Expressed in units of watt per watt.
3.12
coefficient of performance
COP

ratio of the net heating capacity to the effective power input of the equipment at any given set of rating

conditions
Note 1 to entry: Expressed in units of watt per watt.
3.13
effective power input

average electrical power input to the equipment within a defined interval of time; i.e., the sum of:

— the power input for operation of the compressor excluding additional electrical heating devices,

— the power input of all control and safety devices of the equipment, and

— the proportional power input of the conveying devices for the transport of the heat transfer media

through the heat pump only (e.g., source and load sides liquid pumps, whether internal or external,

whether provided with the equipment or not)
Note 1 to entry: Expressed in units of watts.
3.14
brine

heat transfer liquid that has a freezing point lower than the freezing point of water

3.15
external static pressure difference
∆pe

pressure difference measured between the water (or brine) outlet section and the water (or brine) inlet

section of the unit, which is available for overcoming the pressure drop of any additional water (or

brine) circuit
Note 1 to entry: Expressed in units of pascals.
3.16
internal static pressure difference
∆pi

pressure difference measured between the water (or brine) outlet section and the water(or brine) inlet

section of the unit, which corresponds to the total pressure drop of all components on the water (or

brine) side of the unit
Note 1 to entry: Expressed in units of pascals.
3.17
fixed capacity heat pump
equipment which does not have possibility to change its capacity

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.18
two-stage capacity heat pump
equipment where the capacity is varied by two steps

Note 1 to entry: This definition applies to each cooling and heating operation individually.

© ISO 2021 – All rights reserved 3
---------------------- Page: 10 ----------------------
ISO 13256-2:2021(E)
3.19
multi-stage capacity heat pump
equipment where the capacity is varied by three or four steps

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.20
variable capacity heat pump

equipment where the capacity is varied by five or more steps to represent continuously variable

capacity

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.21
source side

source side is referring to outdoor side heat exchanger and the liquid, water or brine, circulating in it

3.22
load side

load side is referring to indoor side heat exchanger and the liquid, water, circulating in it

3.23
standard rating conditions

operating conditions while establishing the standard rating net cooling and/or heating capacities

Note 1 to entry: These conditions correspond to an operation of the heat pump at full capacity, in relation to the

source side.
3.24
application rating conditions

operating conditions while establishing additional cooling and/or heating capacities

Note 1 to entry: These conditions correspond to an operation of the heat pump at reduced capacity, in relation to

the source side.
3.25
standard rating capacity
net cooling and/or heating capacity measured at standard rating conditions
4 Symbols
Symbol Description and Units
c specific heat of liquid, J/kgK
Δ measured internal static pressure difference, Pa
Δ measured external static pressure difference, Pa
h specific enthalpy of refrigerant entering indoor side, J/kg
h specific enthalpy of refrigerant leaving indoor side, J/kg
η representative efficiency
P power input to indoor-side compartment, W
ϕ total power input
ϕ net cooling capacity, W
ϕ net heating capacity, W
ϕ load side pump power adjustment for non integrated pump, W
pai
ϕ load side pump power adjustment for integrated pump, W
pae
ϕ source side pump power adjustment for non integrated pump, W
paoi
4 © ISO 2021 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 13256-2:2021(E)
ϕ source side pump power adjustment for integrated pump, W
paoe
ϕ cooling capacity, (load-side data), W
ϕ cooling capacity, (source-side data), W
ϕ heating capacity, (load-side data), W
ϕ heating capacity, (source side data), W
q measured volumetric flow rate, l/s
q refrigerant and oil mixture flow rate, m /s
t temperature, liquid entering equipment, °C
t temperature, liquid leaving equipment, °C
W mass of cylinder and bleeder assembly, empty, g
W mass of cylinder and bleeder assembly, with sample, g
W mass of cylinder and bleeder assembly, with oil from sample, g
w liquid mass flow rate, kg/s
X concentration of oil to refrigerant-oil mixture
X mass ratio, refrigerant to refrigerant-oil mixture
5 Rating and test conditions
5.1 Rating conditions for the determination of net capacities
5.1.1 Ratings

Rating shall be established at the test conditions specified in 5.2, using the test procedures described

in Clause 7. Ratings relating to cooling and heating capacities shall be net values (see 7.4.3 and 7.4.4),

including the effects of liquid pump heat (see 7.4.3 and 7.4.4), but not including supplementary heat.

Energy efficiency ratios shall be based on the effective power input as defined in 3.10.

5.1.2 Load side liquid pump adjustment
5.1.2.1 Heat pump with non-integrated load side liquid pump

If no load side liquid pump is provided with the heat pump, a pump power adjustment is to be included

in the effective power input to the heat pump, using the following formula:
q× Δ
φ = (1)
pai
where
ϕ is the pump power adjustment, in W;
pai
η = 0,3 by convention;

∆ is the absolute value of the measured indoor-side internal static pressure difference, in Pa;

q is the measured volumetric fluid flow rate, in cubic meter per second.
5.1.2.2 Heat pump with integrated load side liquid pump

If a load side liquid pump is an integral part of a heat pump, only the portion of the pump power required

to overcome the internal resistance shall be included in the effective power input to the heat pump. The

© ISO 2021 – All rights reserved 5
---------------------- Page: 12 ----------------------
ISO 13256-2:2021(E)

fraction which is to be excluded from the total power consumed by the pump shall be calculated using

Formula (1):
q×Δ
φ = (2)
pae
where
ϕ is the pump power adjustment, in W;
pae
η = 0,3 by convention;
∆ is the measured indoor-side external static pressure difference, in Pa;
q is the measured volumetric fluid flow rate, in m /s.
5.1.3 Source side liquid pump adjustment
5.1.3.1 Heat pump with non-integrated source side liquid pump

If no source side liquid pump is provided with the heat pump, a pump power adjustment is to be included

in the effective power consumed by the heat pump, using Formula (3):
q× Δ
φ = (3)
paoi
where
ϕ is the pump power adjustment, in W;
paoi
η = 0,3 by convention;

∆ is the absolute value of the measured internal static pressure difference, in Pa;

q is the measured volumetric fluid flow rate, in m /s.
5.1.3.2 Heat pump with integrated source side liquid pump

If a source side liquid pump is an integral part of the heat pump, only the portion of the pump power

required to overcome the internal resistance shall be included in the effective power input to the

heat pump. The fraction which is to be excluded from the total power consumed by the pump shall be

calculated using Formula (4):
q×Δ
φ = (4)
paoe
where
ϕ is the pump power adjustment, in W;
paoe
η = 0,3 by convention;
Δ is the measured external static pressure difference, in Pa;
q is the measured volumetric fluid flow rate, in m /s.
6 © ISO 2021 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 13256-2:2021(E)
5.1.4 Liquid flow rates
5.1.4.1 General

All ratings shall be determined at liquid flow rates described below, expressed as cubic meter per second.

5.1.4.2 Source side flowrate

The manufacturer shall specify a flow rate, for the source side for all of the tests performed unless

automatic adjustment of the liquid flow rate is provided by the equipment. A separate control signal

output for each step of liquid flow rate will be considered as an automatic adjustment.

5.1.4.3 Load side flowrate
5.1.4.3.1 Ratings where the leaving temperature on the load side is fixed

For units with integral liquid pump, the external static pressure shall be set at the same time as the

temperature difference. When the liquid pump has one or several fixed speeds, the speed of the pump

shall be set in order to provide the minimum external static pressure. In case of variable speed liquid

pump, the manufacturer shall provide information to set the pump in order to reach a maximal external

static pressure of 10 kPa.
5.1.4.3.2 Rating where the leaving te
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 13256-2
ISO/TC 86/SC 6
Water-source heat pumps — Testing
Secretariat: JISC
and rating for performance —
Voting begins on:
2021-01-27
Part 2:
Voting terminates on:
Water-to-water and brine-to-water
2021-03-24
heat pumps
Pompes à chaleur à eau — Essais et détermination des
caractéristiques de performance —
Partie 2: Pompes à chaleur eau-eau et eau glycolée-eau
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 13256-2:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 13256-2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 13256-2:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ..............................................................................................................................................................................................................................vii

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 4

5 Rating and test conditions .......................................................................................................................................................................... 5

5.1 Rating conditions for the determination of net capacities ................................................................................ 5

5.1.1 Ratings ...................................................................................................................................................................................... 5

5.1.2 Load side liquid pump adjustment .................................................................................................................. 5

5.1.3 Source side liquid pump adjustment .............................................................................................................. 6

5.1.4 Liquid flow rates .............................................................................................................................................................. 7

5.1.5 Installation and connection of the unit ........................................................................................................ 7

5.1.6 Test liquids ............................................................................................................................................................................ 8

5.2 Rating test conditions for cooling and heating capacities ................................................................................. 8

6 Performance Requirements...................................................................................................................................................................... 9

6.1 General ........................................................................................................................................................................................................... 9

6.2 Maximum operating conditions test .................................................................................................................................10

6.2.1 Test conditions................................................................................................................................................................10

6.2.2 Test procedures..............................................................................................................................................................10

6.2.3 Test requirements ........................................................................................................................................................10

6.3 Minimum operating conditions test ..................................................................................................................................12

6.3.1 Test conditions................................................................................................................................................................12

6.3.2 Test procedures..............................................................................................................................................................12

6.3.3 Test requirements ........................................................................................................................................................12

6.4 Enclosure sweat and condensate test ..............................................................................................................................13

6.4.1 General...................................................................................................................................................................................13

6.4.2 Test conditions................................................................................................................................................................13

6.4.3 Test procedures..............................................................................................................................................................14

6.4.4 Test requirements ........................................................................................................................................................14

7 Test methods ..........................................................................................................................................................................................................14

7.1 General ........................................................................................................................................................................................................14

7.2 General test requirements .........................................................................................................................................................14

7.3 Equipment installation .................................................................................................................................................................14

7.4 Cooling and heating capacity tests procedure ..........................................................................................................15

7.4.1 Reconditioning period .............................................................................................................................................15

7.4.2 Data collection period ..............................................................................................................................................15

7.4.3 Net cooling capacity ...................................................................................................................................................15

7.4.4 Net heating capacity ..................................................................................................................................................16

7.5 Uncertainties of measurement ...............................................................................................................................................16

7.6 Data to be recorded ..........................................................................................................................................................................16

7.7 Uncertainties of measurements and permissible deviations for steady-state

cooling and heating capacity tests ......................................................................................................................................17

7.8 Test results...............................................................................................................................................................................................18

8 Marking provisions .........................................................................................................................................................................................18

8.1 Nameplate requirements ............................................................................................................................................................18

8.2 Nameplate information ................................................................................................................................................................18

8.3 Designation of standard rating capacities ....................................................................................................................19

8.4 Refrigerant Designation ...............................................................................................................................................................19

9 Publication of ratings ...................................................................................................................................................................................19

9.1 Published ratings ...............................................................................................................................................................................19

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 13256-2:2021(E)

9.2 Additional ratings ..............................................................................................................................................................................19

Annex A (informative) Refrigerant enthalpy test method...........................................................................................................20

Annex B (normative) Liquid enthalpy test method ............................................................................................................................22

Annex C (informative) Additional ratings based upon previous standard version

ISO 13256-2:1998.............................................................................................................................................................................................24

Bibliography .............................................................................................................................................................................................................................26

iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 13256-2:2021(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 on 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 the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 86, Refrigeration and air-conditioning,

Subcommittee SC 6, Testing and rating of air-conditioners and heat pumps.

This second edition cancels and replaces the first edition (ISO 13256-2:1998), which has been

technically revised.
The main changes compared to the previous edition are as follows:

— Significant updates to the formatting, symbols, and terms and definitions, have been included to

more closely align with other pertinent ISO standards and the latest ISO requirements.

— The original water loop heat pump (WLHP), ground water heat pump (GWHP) and ground loop

heat pump (GLHP) application rating designations, specifying entering liquid source rating test

conditions, have been replaced with High, Medium, and Low source temperature range conditions to

represent a wider operating map at both standard and partially loaded application rating conditions.

It is now possible, when all three (High, Medium and Low) temperature ranges are specified by the

manufacturer for energy modelling programs to interpolate performance at other entering water

temperatures than those used in the standard.

— Specific antifreeze solution composition requirements have been removed to eliminate prescriptive

language and promote industry innovation of novel and improved antifreeze solutions.

— The standard has been expanded to allow multiple heating capacity ratings at differing load

temperature conditions (Very High, High, Medium, and Low). Medium was retained as the original

load condition.

— Testing tolerances and uncertainties have been harmonized with other pertinent ISO standards.

— Annexes have been significantly updated and harmonized with other pertinent ISO standards.

A list of all parts in the ISO 13256 series can be found on the ISO website.
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ISO/FDIS 13256-2:2021(E)

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.
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ISO/FDIS 13256-2:2021(E)
Introduction

This document covers heating and cooling systems which are generally referred to as “water-source

heat pumps.” These systems generally include an indoor heat exchanger with means to move the liquid,

a compressor, and a refrigerant-to-water or refrigerant-to-brine heat exchanger. A system may provide

both heating and cooling, cooling-only, or heating-only functions.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 13256-2:2021(E)
Water-source heat pumps — Testing and rating for
performance —
Part 2:
Water-to-water and brine-to-water heat pumps
1 Scope

1.1 This document establishes performance testing and rating criteria for factory-made residential,

commercial and industrial, electrically-driven, mechanical- compression type, water-to-water and brine-

to-water heat pumps. The requirements for testing and rating contained in this document are based on

the use of matched assemblies.

1.2 Equipment may be designed for rating at one or several source and load side temperature

conditions described in this document.

1.3 This document does not apply to the testing and rating of individual assemblies for separate use,

nor to the testing and rating of heat pumps covered in ISO 5151, ISO 13253 or ISO 13256-1.

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 817, Refrigerants — Designation and safety classification
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
water-to-water heat pump
brine-to-water heat pump

heat pump which consists of one or more factory-made assemblies which normally include an indoor

side refrigerant to water heat exchanger (load side), compressor(s), and outdoor-side refrigerant-to-

water or refrigerant-to-brine heat exchanger(s) (source side), including means to provide both cooling

and heating, cooling-only, or heating-only functions

Note 1 to entry: When such equipment is provided in more than one assembly, the separated assemblies should

be designed to be used together.

Note 2 to entry: Such equipment may also provide functions of sanitary water heating.

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ISO/FDIS 13256-2:2021(E)
3.2
water-loop heat pump

water-to-water heat pump using, on the source side, a liquid circulating in a common piping loop

Note 1 to entry: The temperature of the liquid loop is usually within a range of 10 °C to 30 °C.

3.3
ground-water heat pump

water-to-water heat pump using, on source side, water pumped from a well, lake, or stream

Note 1 to entry: The temperature of the water is related to the climatic conditions and is generally constant

within the range from 5 °C to 25 °C for deep wells.
3.4
ground-loop heat pump

brine-to-water heat pump using, on the source side, a brine solution circulating through a subsurface

piping loop

Note 1 to entry: The heat exchange loop may be placed in horizontal trenches or vertical bores, or be submerged

in a body of surface water.

Note 2 to entry: The temperature of the brine is related to the heat exchange load and climatic conditions and is

generally within a range from –5 °C to 40 °C.
3.5
cooling capacity

amount of heat that the equipment can remove from the water used to condition the indoor space in a

defined interval of time
Note 1 to entry: Expressed in units of watts.
3.6
net cooling capacity
cooling capacity with load side liquid pump power adjustment
Note 1 to entry: Expressed in units of watts.
3.7
heating capacity

amount of heat that the equipment can add to the water used to condition the indoor space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.8
net heating capacity
heating capacity with load side liquid pump power adjustment
Note 1 to entry: Expressed in units of watts.
3.9
rated voltage
voltage shown on the nameplate of the equipment
Note 1 to entry: Expressed in units of volts.
3.10
rated frequency
frequency shown on the nameplate of the equipment
Note 1 to entry: Expressed in units of Hz.
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ISO/FDIS 13256-2:2021(E)
3.11
energy efficiency ratio
EER

ratio of the net cooling capacity to the effective power input at any given set of rating conditions

Note 1 to entry: Expressed in units of watt per watt.
3.12
coefficient of performance
COP

ratio of the net heating capacity to the effective power input of the equipment at any given set of rating

conditions
Note 1 to entry: Expressed in units of watt per watt.
3.13
effective power input

average electrical power input to the equipment within a defined interval of time; i.e., the sum of:

— the power input for operation of the compressor excluding additional electrical heating devices,

— the power input of all control and safety devices of the equipment, and

— the proportional power input of the conveying devices for the transport of the heat transfer media

through the heat pump only (e.g., source and load sides liquid pumps, whether internal or external,

whether provided with the equipment or not)
Note 1 to entry: Expressed in units of watts.
3.14
brine

heat transfer liquid that has a freezing point lower than the freezing point of water

3.15
external static pressure difference
∆pe

pressure difference measured between the water (or brine) outlet section and the water (or brine) inlet

section of the unit, which is available for overcoming the pressure drop of any additional water (or

brine) circuit
Note 1 to entry: Expressed in units of pascals.
3.16
internal static pressure difference
∆pi

pressure difference measured between the water (or brine) outlet section and the water(or brine) inlet

section of the unit, which corresponds to the total pressure drop of all components on the water (or

brine) side of the unit
Note 1 to entry: Expressed in units of pascals.
3.17
fixed capacity heat pump
equipment which does not have possibility to change its capacity

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.18
two-stage capacity heat pump
equipment where the capacity is varied by two steps

Note 1 to entry: This definition applies to each cooling and heating operation individually.

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ISO/FDIS 13256-2:2021(E)
3.19
multi-stage capacity heat pump
equipment where the capacity is varied by three or four steps

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.20
variable capacity heat pump

equipment where the capacity is varied by five or more steps to represent continuously variable

capacity

Note 1 to entry: This definition applies to each cooling and heating operation individually.

3.21
source side

source side is referring to outdoor side heat exchanger and the liquid, water or brine, circulating in it

3.22
load side

load side is referring to indoor side heat exchanger and the liquid, water, circulating in it

3.23
standard rating conditions

operating conditions while establishing the standard rating net cooling and/or heating capacities

Note 1 to entry: These conditions correspond to an operation of the heat pump at full capacity, in relation to the

source side.
3.24
application rating conditions

operating conditions while establishing additional cooling and/or heating capacities

Note 1 to entry: These conditions correspond to an operation of the heat pump at reduced capacity, in relation to

the source side.
3.25
standard rating capacity
net cooling and/or heating capacity measured at standard rating conditions
4 Symbols
Symbol Description and Units
c Specific heat of liquid, J/kgK
Δ Measured internal static pressure difference, Pa
Δ Measured external static pressure difference, Pa
h specific enthalpy of refrigerant entering indoor side, J/kg
h specific enthalpy of refrigerant leaving indoor side, J/kg
η representative efficiency
P power input to indoor-side compartment, W
ϕ Total power input
ϕ Net cooling capacity, W
ϕ Net heating capacity, W
ϕ Load side pump power adjustment for non integrated pump, W
pai
ϕ Load side pump power adjustment for integrated pump, W
pae
ϕ Source side pump power adjustment for non integrated pump, W
paoi
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ISO/FDIS 13256-2:2021(E)
ϕ Source side pump power adjustment for integrated pump, W
paoe
ϕ cooling capacity, (load-side data), W
ϕ cooling capacity, (source-side data), W
ϕ heating capacity, (load-side data), W
ϕ heating capacity, (source side data), W
q measured volumetric flow rate, l/s
q Refrigerant and oil mixture flow rate, m /s
t temperature, liquid entering equipment, °C
t temperature, liquid leaving equipment, °C
W mass of cylinder and bleeder assembly, empty, g
W mass of cylinder and bleeder assembly, with sample, g
W mass of cylinder and bleeder assembly, with oil from sample, g
w Liquid mass flow rate, kg/s
X concentration of oil to refrigerant-oil mixture
X mass ratio, refrigerant to refrigerant-oil mixture
5 Rating and test conditions
5.1 Rating conditions for the determination of net capacities
5.1.1 Ratings

Rating shall be established at the test conditions specified in 5.2, using the test procedures described

in Clause 7. Ratings relating to cooling and heating capacities shall be net values (see 7.4.3 and 7.4.4),

including the effects of liquid pump heat (see 7.4.3 and 7.4.4), but not including supplementary heat.

Energy efficiency ratios shall be based on the effective power input as defined in 3.10.

5.1.2 Load side liquid pump adjustment
5.1.2.1 Heat pump with non-integrated load side liquid pump

If no load side liquid pump is provided with the heat pump, a pump power adjustment is to be included

in the effective power input to the heat pump, using the following formula:
q× Δ
φ = (1)
pai
where
ϕ is the pump power adjustment, in W;
pai
η = 0,3 by convention;

∆ is the absolute value of the measured indoor-side internal static pressure difference, in pascals;

q is the measured volumetric fluid flow rate, in cubic meter per second.
5.1.2.2 Heat pump with integrated load side liquid pump

If a load side liquid pump is an integral part of a heat pump, only the portion of the pump power required

to overcome the internal resistance shall be included in the effective power input to the heat pump. The

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ISO/FDIS 13256-2:2021(E)

fraction which is to be excluded from the total power consumed by the pump shall be calculated using

Formula (1):
q×Δ
φ = (2)
pae
where
ϕ is the pump power adjustment, in W;
pae
η = 0,3 by convention;
∆ is the measured indoor-side external static pressure difference, in pascals;
q is the measured volumetric fluid flow rate, in cubic meter per second.
5.1.3 Source side liquid pump adjustment
5.1.3.1 Heat pump with non-integrated source side liquid pump

If no source side liquid pump is provided with the heat pump, a pump power adjustment is to be included

in the effective power consumed by the heat pump, using Formula (3):
q× Δ
φ = (3)
paoi
where
ϕ is the pump power adjustment, in W;
paoi
η = 0,3 by convention;

∆ is the absolute value of the measured internal static pressure difference, in pascals;

q is the measured volumetric fluid flow rate, in cubic meter per second.
5.1.3.2 Heat pump with integrated source side liquid pump

If a source side liquid pump is an integral part of the heat pump, only the portion of the pump power

required to overcome the internal resistance shall be included in the effective power input to the

heat pump. The fraction which is to be excluded from the total power consumed by the pump shall be

calculated using Formula (4):
q×Δ
φ = (4)
paoe
where
ϕ is the pump power adjustment, in W;
paoe
η = 0,3 by convention;
Δ is the measured external static pressure difference, in pascals;
q is the measured volumetric fluid flow rate, in cubic meter per second.
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ISO/FDIS 13256-2:2021(E)
5.1.4 Liquid flow rates
5.1.4.1 General

All ratings shall be determined at liquid flow rates described below, expressed as cubic meter per second.

5.1.4.2 Source side flowrate

The manufacturer shall specify a flow rate, for the source side for all of the tests performed unless

automatic adjustment of the liquid flow rate is pr
...

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