Water-source heat pumps — Testing and rating for performance — Part 1: Water-to-air and brine-to-air 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-air and brine-to-air heat pumps. The requirements for testing and rating contained in this document are based on the use of matched assemblies. 1.2 Equipment designed for rating at one liquid temperature range under this document may not be suitable at all liquid temperature ranges covered 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 13256‑2.

Pompes à chaleur à eau — Essais et détermination des caractéristiques de performance — Partie 1: Pompes à chaleur eau-air et eau glycolée-air

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Status
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 13256-1
Second edition
2021-05
Water-source heat pumps — Testing
and rating for performance —
Part 1:
Water-to-air and brine-to-air heat
pumps
Pompes à chaleur à eau — Essais et détermination des
caractéristiques de performance —
Partie 1: Pompes à chaleur eau-air et eau glycolée-air
Reference number
ISO 13256-1:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 13256-1:2021(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 13256-1:2021(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 .......................................................................................................................................................................... 6

5.1 Rating conditions for the determination of net capacities ................................................................................ 6

5.1.1 Ratings ...................................................................................................................................................................................... 6

5.1.2 Power input of fans for heat pumps without duct connection ................................................. 6

5.1.3 Power input of fans for heat pumps with duct connection ......................................................... 6

5.1.4 Power input of liquid pumps ................................................................................................................................. 7

5.1.5 Airflow rates ........................................................................................................................................................................ 7

5.1.6 Liquid flow rates .............................................................................................................................................................. 8

5.1.7 Test liquids ............................................................................................................................................................................ 9

5.2 Rating test conditions for cooling and heating capacities ................................................................................. 9

6 Performance Requirements...................................................................................................................................................................10

6.1 General ........................................................................................................................................................................................................10

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

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

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

6.2.3 Test requirements ........................................................................................................................................................11

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 General...................................................................................................................................................................................15

7.4.2 Reconditioning period .............................................................................................................................................15

7.4.3 Data collection period ..............................................................................................................................................15

7.4.4 Net total cooling capacity ......................................................................................................................................15

7.4.5 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...............................................................................................................................................................................................19

8 Marking provisions .........................................................................................................................................................................................19

8.1 Nameplate requirements ............................................................................................................................................................19

8.2 Nameplate information ................................................................................................................................................................19

8.3 Designation of standard ratings capacity......................................................................................................................19

8.4 Refrigerant designation ................................................................................................................................................................20

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 13256-1:2021(E)

9 Publication of ratings ...................................................................................................................................................................................20

9.1 Published ratings ...............................................................................................................................................................................20

9.2 Additional ratings ..............................................................................................................................................................................20

Annex A (normative) Test requirements ......................................................................................................................................................21

Annex B (informative) Airflow measurement ..........................................................................................................................................28

Annex C (normative) Indoor air enthalpy test method ..................................................................................................................35

Annex D (informative) Refrigerant enthalpy test method ..........................................................................................................38

Annex E (normative) Liquid enthalpy test method ............................................................................................................................40

Annex F (informative) Correction of fan or pump power input for external static pressures

other than zero ....................................................................................................................................................................................................42

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

ISO 13256-1:1998.............................................................................................................................................................................................43

Annex H (informative) Cooling condensate measurements ......................................................................................................44

Bibliography .............................................................................................................................................................................................................................45

iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 13256-1:2021(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 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 6, Testing and rating of air-conditioners and heat pumps.

This second edition cancels and replaces the first edition (ISO 13256-1:1998), 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.

— Airflow testing requirements have been updated to align with the complexities of testing more

sophisticated constant airflow electronically commutated fan motors.

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

— Annexes have been added and/or significantly updated that harmonize 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 13256-1:2021(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 13256-1:2021(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 coil with air-moving means, 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 13256-1:2021(E)
Water-source heat pumps — Testing and rating for
performance —
Part 1:
Water-to-air and brine-to-air 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-air and brine-to-

air heat pumps. The requirements for testing and rating contained in this document are based on the use

of matched assemblies.

1.2 Equipment designed for rating at one liquid temperature range under this document may not be

suitable at all liquid temperature ranges covered 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 13256-2.

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-air heat pump
brine-to-air heat pump

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

conditioning coil with air-moving means, compressor(s), and refrigerant-to-water or refrigerant-to-

brine heat exchanger(s), 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, air cleaning, dehumidifying,

and humidifying.
© ISO 2021 – All rights reserved 1
---------------------- Page: 8 ----------------------
ISO 13256-1:2021(E)
3.2
water-loop heat pump

water-to-air heat pump using liquid circulating in a common piping loop functioning as a heat source in

`heating mode and/or heat sink in cooling mode

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-air heat pump using water pumped from a well, lake, or stream functioning as a heat source in

heating mode and/or heat sink in cooling mode

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-air heat pump using a brine solution circulating through a subsurface piping loop functioning

as a heat source in heating mode and/or heat sink in cooling mode

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
total cooling capacity

amount of sensible and latent heat that the equipment can remove from the conditioned space in a

defined interval of time
Note 1 to entry: Expressed in units of watts.
3.6
net total cooling capacity
total cooling capacity with fan 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 conditioned space in a defined interval of time

Note 1 to entry: Expressed in units of watts.
3.8
net heating capacity
heating capacity with fan 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 13256-1:2021(E)
3.11
energy efficiency ratio
EER

ratio of the net total 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
standard air

dry air at 20,0 °C and at a standard barometric pressure of 101,325 kPa, having a mass density of

1,204 kg/m
3.14
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. fans, pumps, whether internal or external, whether provided with

the equipment or not)
Note 1 to entry: Expressed in units of watts.
3.15
latent cooling capacity

amount of latent heat that the equipment can remove from the conditioned space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.16
sensible cooling capacity

amount of sensible heat that the equipment can remove from the conditioned space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.17
brine

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

3.18
external static pressure difference

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

brine) inlet section of the unit, which is available for overcoming the pressure drop of any additional

ducted air (or water/brine) circuit
Note 1 to entry: Expressed in units of pascals.
© ISO 2021 – All rights reserved 3
---------------------- Page: 10 ----------------------
ISO 13256-1:2021(E)
3.19
internal static pressure difference

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

brine) inlet section of the unit, which corresponds to the total pressure drop of all components on the

air (or water/brine) side of the unit.
Note 1 to entry: Expressed in units of pascals.
3.20
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.

3.21
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.

3.22
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.

3.23
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.

3.24
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.
3.25
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.
3.26
standard rating capacity
net cooling and/or heating capacity measured at standard rating conditions
4 Symbols
Symbol Description and Units
A nozzle area, m
α pressure ratio
C nozzle discharge coefficient
c specific heat of dry air entering indoor side, J/kg·K
pa1
4 © ISO 2021 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 13256-1:2021(E)
Symbol Description and Units
c specific heat of dry air leaving indoor side, J/kg·K
pa2
c specific heat of liquid, J/kg·K
D nozzle throat diameter, mm
Δ measured internal static pressure difference, Pa
Δ measured external static pressure difference, Pa
h specific enthalpy of air entering indoor air-side, J/kg of dry air
h specific enthalpy of air leaving indoor air-side, J/kg of dry air
h specific enthalpy of refrigerant entering indoor side, J/kg
h specific enthalpy of refrigerant leaving indoor side, J/kg
K latent heat of vaporization of water, J/kg (2,47 x 10 , J/kg at 15 °C)
η representative efficiency
P power input to indoor-side compartment, W
p pressure, at nozzle throat, kPa absolute

p velocity pressure at nozzle throat or static pressure difference across nozzle, Pa

ϕ total power input
ϕ fan power adjustment, W
ϕ latent cooling capacity, (indoor air-side data), W
lci
ϕ net cooling capacity, W
ϕ net heating capacity, W
ϕ sensible cooling capacity, (air-side data), W
sci
ϕ total cooling capacity, (airside data), W
tci
ϕ total cooling capacity, (liquid side data), W
tco
ϕ total heating capacity, (air-side data), W
thi
ϕ total heating capacity, (liquid side data), W
tho
q measured volumetric flow rate, l/s
q measured airflow rate at standard air conditions, m /s
q air mass flow rate, kg/s
q refrigerant and oil mixture flow rate, m /s
q air volume flow rate, standard air, m /s
q air-volume flow rate, calculated, m /s
q air volume flow rate, measured, m /s
q flow rate, liquid condensate (steam), kg/s
Re Reynolds number
t temperature, air entering indoor side, dry bulb, °C
t temperature, air leaving indoor side, dry bulb, °C
t temperature, liquid entering equipment, °C
t temperature, liquid leaving equipment, °C
v kinematic viscosity of air

v specific volume of dry air at conditions existing at nozzle at standard barometric pressure, m /kg

specific volume of air at nozzle, m /kg of air-water vapour mixture
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
w specific humidity, air entering indoor side, kg/kg of dry air
© ISO 2021 – All rights reserved 5
---------------------- Page: 12 ----------------------
ISO 13256-1:2021(E)
Symbol Description and Units
w specific humidity, air leaving indoor side, kg/kg of dry air
W specific humidity at nozzle inlet, kg/kg of dry air
X concentration of oil to refrigerant-oil mixture
X mass ratio, refrigerant to refrigerant-oil mixture
Y expansion factor
5 Rating and test conditions
5.1 Rating conditions for the determination of net capacities
5.1.1 Ratings

Ratings 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 7.4.4 and 7.4.5),

including the effects of circulating-fan heat (see 7.4.4 and 7.4.5), but excluding any supplementary heat.

Energy efficiency ratios shall be based on the effective power input as defined in 3.11.

5.1.2 Power input of fans for heat pumps without duct connection

In the case of heat pumps which are not designed for duct connection and which are equipped with

an integral fan, all power consumed by the fans shall be included in the effective power input to the

heat pump.
5.1.3 Power input of fans for heat pumps with duct connection
5.1.3.1 If no fan is provided with the heat pump, a fan power a
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 13256-1
ISO/TC 86/SC 6
Water-source heat pumps — Testing
Secretariat: JISC
and rating for performance —
Voting begins on:
2021-01-27
Part 1:
Voting terminates on:
Water-to-air and brine-to-air heat
2021-03-24
pumps
Pompes à chaleur à eau — Essais et détermination des
caractéristiques de performance —
Partie 1: Pompes à chaleur eau-air et eau glycolée-air
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 13256-1:2021(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 13256-1:2021(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 13256-1:2021(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 .......................................................................................................................................................................... 6

5.1 Rating conditions for the determination of net capacities ................................................................................ 6

5.1.1 Ratings ...................................................................................................................................................................................... 6

5.1.2 Power input of fans for heat pumps without duct connection ................................................. 6

5.1.3 Power input of fans for heat pumps with duct connection ......................................................... 6

5.1.4 Power input of liquid pumps ................................................................................................................................. 7

5.1.5 Airflow rates ........................................................................................................................................................................ 7

5.1.6 Liquid flow rates .............................................................................................................................................................. 8

5.1.7 Test liquids ............................................................................................................................................................................ 9

5.2 Rating test conditions for cooling and heating capacities ................................................................................. 9

6 Performance Requirements...................................................................................................................................................................10

6.1 General ........................................................................................................................................................................................................10

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

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

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

6.2.3 Test requirements ........................................................................................................................................................11

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 General...................................................................................................................................................................................15

7.4.2 Reconditioning period .............................................................................................................................................15

7.4.3 Data collection period ..............................................................................................................................................15

7.4.4 Net total cooling capacity ......................................................................................................................................15

7.4.5 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...............................................................................................................................................................................................19

8 Marking provisions .........................................................................................................................................................................................19

8.1 Nameplate requirements ............................................................................................................................................................19

8.2 Nameplate information ................................................................................................................................................................19

8.3 Designation of standard ratings capacity......................................................................................................................19

8.4 Refrigerant designation ................................................................................................................................................................20

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 13256-1:2021(E)

9 Publication of ratings ...................................................................................................................................................................................20

9.1 Published ratings ...............................................................................................................................................................................20

9.2 Additional ratings ..............................................................................................................................................................................20

Annex A (normative) Test requirements ......................................................................................................................................................21

Annex B (informative) Airflow measurement ..........................................................................................................................................28

Annex C (normative) Indoor air enthalpy test method ..................................................................................................................35

Annex D (informative) Refrigerant enthalpy test method ..........................................................................................................38

Annex E (normative) Liquid enthalpy test method ............................................................................................................................40

Annex F (informative) Correction of fan or pump power input for external static pressures

other than zero ....................................................................................................................................................................................................42

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

ISO 13256-1:1998.............................................................................................................................................................................................43

Annex H (informative) Cooling condensate measurements ......................................................................................................44

Bibliography .............................................................................................................................................................................................................................45

iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 13256-1:2021(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 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 6, Testing and rating of air-conditioners and heat pumps.

This second edition cancels and replaces the first edition (ISO 13256-1:1998), 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.

— Airflow testing requirements have been updated to align with the complexities of testing more

sophisticated constant airflow electronically commutated fan motors.

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

— Annexes have been added and/or significantly updated that harmonize 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 13256-1:2021(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 13256-1:2021(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 coil with air-moving means, 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 13256-1:2021(E)
Water-source heat pumps — Testing and rating for
performance —
Part 1:
Water-to-air and brine-to-air 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-air and brine-to-

air heat pumps. The requirements for testing and rating contained in this document are based on the use

of matched assemblies.

1.2 Equipment designed for rating at one liquid temperature range under this document may not be

suitable at all liquid temperature ranges covered 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 13256-2.

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-air heat pump
brine-to-air heat pump

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

conditioning coil with air-moving means, compressor(s), and refrigerant-to-water or refrigerant-to-

brine heat exchanger(s), 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, air cleaning, dehumidifying,

and humidifying.
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ISO/FDIS 13256-1:2021(E)
3.2
water-loop heat pump

water-to-air heat pump using liquid circulating in a common piping loop functioning as a heat source in

`heating mode and/or heat sink in cooling mode

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-air heat pump using water pumped from a well, lake, or stream functioning as a heat source in

heating mode and/or heat sink in cooling mode

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-air heat pump using a brine solution circulating through a subsurface piping loop functioning

as a heat source in heating mode and/or heat sink in cooling mode

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
total cooling capacity

amount of sensible and latent heat that the equipment can remove from the conditioned space in a

defined interval of time
Note 1 to entry: Expressed in units of watts.
3.6
net total cooling capacity
total cooling capacity with fan 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 conditioned space in a defined interval of time

Note 1 to entry: Expressed in units of watts.
3.8
net heating capacity
heating capacity with fan 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 13256-1:2021(E)
3.11
energy efficiency ratio
EER

ratio of the net total 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
standard air

dry air at 20,0 °C and at a standard barometric pressure of 101,325 kPa, having a mass density of

1,204 kg/m
3.14
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. fans, pumps, whether internal or external, whether provided with

the equipment or not)
Note 1 to entry: Expressed in units of watts.
3.15
latent cooling capacity

amount of latent heat that the equipment can remove from the conditioned space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.16
sensible cooling capacity

amount of sensible heat that the equipment can remove from the conditioned space in a defined

interval of time
Note 1 to entry: Expressed in units of watts.
3.17
brine

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

3.18
external static pressure difference

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

brine) inlet section of the unit, which is available for overcoming the pressure drop of any additional

ducted air (or water/brine) circuit
Note 1 to entry: Expressed in units of pascals.
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ISO/FDIS 13256-1:2021(E)
3.19
internal static pressure difference

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

brine) inlet section of the unit, which corresponds to the total pressure drop of all components on the

air (or water/brine) side of the unit.
Note 1 to entry: Expressed in units of pascals.
3.20
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.

3.21
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.

3.22
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.

3.23
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.

3.24
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.
3.25
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.
3.26
standard rating capacity
net cooling and/or heating capacity measured at standard rating conditions
4 Symbols
Symbol Description and Units
A nozzle area, m
α pressure ratio
C nozzle discharge coefficient
c specific heat of dry air entering indoor side, J/kg·K
pa1
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ISO/FDIS 13256-1:2021(E)
Symbol Description and Units
c specific heat of dry air leaving indoor side, J/kg·K
pa2
c specific heat of liquid, J/kg·K
D nozzle throat diameter, mm
Δ Measured internal static pressure difference, Pa
Δ Measured external static pressure difference, Pa
h specific enthalpy of air entering indoor air-side, J/kg of dry air
h specific enthalpy of air leaving indoor air-side, J/kg of dry air
h specific enthalpy of refrigerant entering indoor side, J/kg
h specific enthalpy of refrigerant leaving indoor side, J/kg
K latent heat of vaporization of water, J/kg (2,47 x 10 , J/kg at 15 °C)
η representative efficiency
P power input to indoor-side compartment, W
p pressure, at nozzle throat, kPa absolute

p velocity pressure at nozzle throat or static pressure difference across nozzle, Pa

ϕ Total power input
ϕ Fan power adjustment, W
ϕ latent cooling capacity, (indoor air-side data), W
lci
ϕ Net cooling capacity, W
ϕ Net heating capacity, W
ϕ sensible cooling capacity, (air-side data), W
sci
ϕ total cooling capacity, (airside data), W
tci
ϕ total cooling capacity, (liquid side data), W
tco
ϕ total heating capacity, (air-side data), W
thi
ϕ total heating capacity, (liquid side data), W
tho
q measured volumetric flow rate, l/s
q Measured airflow rate at standard air conditions, m /s
q Air mass flow rate, kg/s
q Refrigerant and oil mixture flow rate, m /s
q Air volume flow rate, standard air, m /s
q Air-volume flow rate, calculated, m /s
q Air volume flow rate, measured, m /s
q flow rate, liquid condensate (steam), kg/s
Re Reynolds number
t temperature, air entering indoor side, dry bulb, °C
t temperature, air leaving indoor side, dry bulb, °C
t temperature, liquid entering equipment, °C
t temperature, liquid leaving equipment, °C
v Kinematic viscosity of air

v specific volume of dry air at conditions existing at nozzle at standard barometric pressure, m /kg

specific volume of air at nozzle, m /kg of air-water vapour mixture
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
w specific humidity, air entering indoor side, kg/kg of dry air
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ISO/FDIS 13256-1:2021(E)
Symbol Description and Units
w specific humidity, air leaving indoor side, kg/kg of dry air
W specific humidity at nozzle inlet, kg/kg of dry air
X concentration of oil to refrigerant-oil mixture
X mass ratio, refrigerant to refrigerant-oil mixture
Y expansion factor
5 Rating and test conditions
5.1 Rating conditions for the determination of net capacities
5.1.1 Ratings

Ratings 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 capaci
...

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