ISO 13256-2:2021

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

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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
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Published in Switzerland
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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
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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
pf
Δ measured internal static pressure difference, Pa
pi
Δ measured external static pressure difference, Pa
pe
h specific enthalpy of refrigerant entering indoor side, J/kg
r1
h specific enthalpy of refrigerant leaving indoor side, J/kg
r2
η representative efficiency
P power input to indoor-side compartment, W
i
ϕ total power input
c
ϕ net cooling capacity, W
nc
ϕ net heating capacity, W
nh
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 13256-2:2021(E)

ϕ source side pump power adjustment for integrated pump, W
paoe
ϕ cooling capacity, (load-side data), W
ci
ϕ cooling capacity, (source-side data), W
co
ϕ heating capacity, (load-side data), W
hi
ϕ heating capacity, (source side data), W
ho
q measured volumetric flow rate, l/s
3
q refrigerant and oil mixture flow rate, m /s
ro
t temperature, liquid entering equipment, °C
f3
t temperature, liquid leaving equipment, °C
f4
W mass of cylinder and bleeder assembly, empty, g
1
W mass of cylinder and bleeder assembly, with sample, g
3
W mass of cylinder and bleeder assembly, with oil from sample, g
5
w liquid mass flow rate, kg/s
f
X concentration of oil to refrigerant-oil mixture
0
X mass ratio, refrigerant to refrigerant-oil mixture
r
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
()
pi
φ = (1)
pai
η
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;
pi
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 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
pe
φ = (2)
pae
η
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;
pe
3
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
()
pi
φ = (3)
paoi
η
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;
pi
3
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
pe
φ = (4)
paoe
η
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;
pe
3
q is the measured volumetric fluid flow rate, in m /s.
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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
...