ISO 13256-1:2021

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

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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
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Published in Switzerland
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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
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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
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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.
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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.
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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.
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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.
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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.
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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
3
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
∆
pe
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 13256-1:2021(E)

3.19
internal static pressure difference
∆
pi
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
2
A nozzle area, m
n
α pressure ratio
C nozzle discharge coefficient
d
c specific heat of dry air entering indoor side, J/kg·K
pa1
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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
pf
D nozzle throat diameter, mm
n
Δ measured internal static pressure difference, Pa
pi
Δ measured external static pressure difference, Pa
pe
h specific enthalpy of air entering indoor air-side, J/kg of dry air
a1
h specific enthalpy of air leaving indoor air-side, J/kg of dry air
a2
h specific enthalpy of refrigerant entering indoor side, J/kg
r1
h specific enthalpy of refrigerant leaving indoor side, J/kg
r2
6
K latent heat of vaporization of water, J/kg (2,47 x 10 , J/kg at 15 °C)
1
η representative efficiency
P power input to indoor-side compartment, W
i
p pressure, at nozzle throat, kPa absolute
n
p velocity pressure at nozzle throat or static pressure difference across nozzle, Pa
v
ϕ total power input
c
ϕ fan power adjustment, W
fa
ϕ latent cooling capacity, (indoor air-side data), W
lci
ϕ net cooling capacity, W
nc
ϕ net heating capacity, W
nh
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
3
q measured airflow rate at standard air conditions, m /s
a
q air mass flow rate, kg/s
m
3
q refrigerant and oil mixture flow rate, m /s
ro
3
q air volume flow rate, standard air, m /s
s
3
q air-volume flow rate, calculated, m /s
V
3
q air volume flow rate, measured, m /s
Vi
q flow rate, liquid condensate (steam), kg/s
wc
Re Reynolds number
t temperature, air entering indoor side, dry bulb, °C
a1
t temperature, air leaving indoor side, dry bulb, °C
a2
t temperature, liquid entering equipment, °C
f3
t temperature, liquid leaving equipment, °C
f4
v kinematic viscosity of air
3
v specific volume of dry air at conditions existing at nozzle at standard barometric pressure, m /kg
n
3
specific volume of air at nozzle, m /kg of air-water vapour mixture
v
n
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
w specific humidity, air entering indoor side, kg/kg of dry air
i1
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ISO 13256-1:2021(E)

Symbol Description and Units
w specific humidity, air leaving indoor side, kg/kg of dry air
i2
W specific humidity at nozzle inlet, kg/kg of dry air
n
X concentration of oil to refrigerant-oil mixture
0
X mass ratio, refrigerant to refrigerant-oil mixture
r
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
...