ISO 21978:2021

INTERNATIONAL ISO
STANDARD 21978
First edition
2021-02
Heat pump water heater — Testing
and rating at part load conditions and
calculation of seasonal coefficient of
performance for space heating
Chauffe-eau à pompe à chaleur — Essais et classification à charge
partielle et calcul du coefficient de performance saisonnier
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 8
5 Installation requirements. 9
5.1 Test apparatus and uncertainties of measurement . 9
5.2 Test room for the airside and remote condenser .10
5.3 Installation and connection of the heat pump .10
5.4 Installation of heat pumps consisting of several parts .10
5.5 Environment conditions for indoor unit installation and electrical power supply
requirements .10
6 Setting and part load test conditions .11
6.1 General .11
6.2 Setting for capacity ratio .11
6.3 Setting the external static pressure difference for ducted units .11
6.4 Setting of units with integral pumps .11
6.5 Part load test conditions .12
7 Space heating test .16
7.1 Heating capacity test .16
7.2 Heating capacity correction .17
7.2.1 General.17
7.2.2 Capacity correction of fans for units without duct connection .17
7.2.3 Capacity correction due to indoor fan for ducted units .17
7.2.4 Capacity correction due to indoor liquid pump .17
7.2.5 Effective power input .19
7.3 Test procedure .20
7.3.1 General.20
7.3.2 Preconditioning period .21
7.3.3 Equilibrium period . . .21
7.3.4 Data collection period .21
7.4 Heating capacity calculation .21
7.4.1 Steady state capacity test .21
7.4.2 Transient capacity test .21
7.5 Effective power input calculation .21
7.5.1 Steady state test .21
7.5.2 Transient capacity test .21
7.6 Determination of degradation coefficient Cd .22
7.7 Test methods for electric power input during thermostat-off mode, standby mode,
crankcase heater mode and off mode .22
7.7.1 Uncertainties of measurement .22
7.7.2 Measurement of electric power input during thermostat-off mode .23
7.7.3 Measurement of electric power input during standby mode .23
7.7.4 Measurement of electric power input during crankcase heater mode .23
7.7.5 Measurement of electric power input during off mode .23
8 Calculation methods for seasonal coefficient of performance (SCOP) .24
8.1 General formula for calculation of SCOP .24
8.2 Calculation of the reference annual heating demand, Q .24
H
8.3 Calculation of the annual electricity consumption, Q .24
HE
8.4 Calculation of SCOP and SCOP .25
on net
8.5 Calculation procedure for determination of COP values at part load conditions A to G 26
bin
8.5.1 General.26
8.5.2 Calculation procedure for fixed capacity units .27
8.5.3 Calculation procedure for staged and variable capacity units .27
9 Test results and test report .27
9.1 Data .27
9.2 Test report .28
10 Marking .29
Annex A (normative) Heating capacity test procedures given in 7.3 .30
Annex B (normative) Determination of the liquid pump efficiency .34
Annex C (informative) Examples of set of bin hours and hours for active mode, thermostat-
off mode, standby mode, off mode and crankcase heater mode .38
Annex D (informative) SCOP calculation for fixed capacity for low temperature
application — Example .40
Annex E (informative) SCOP calculation for variable capacity unit for low temperature
application —Example .44
iv © ISO 2021 – All rights reserved

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.
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.
Introduction
Heat pumps water heaters are, at present, selected and compared at a rated condition. This condition
does not represent the usual operating conditions of the equipment over a season. This operating
condition can be better assessed by comparing equipment at representative reduced capacities and
determining the Seasonal Coefficient of Performance.
This standard provides part load conditions and calculation methods for calculating the Seasonal
Coefficient of Performance (SCOP and SCOP ) of such units when they are used to fulfil the heating
on net
demands.
Other energy consumptions can occur when the unit is not used to fulfil the heating demands such as
those from a crankcase heater or when the unit is on standby. These consumptions are considered in
the calculation methods for reference SCOP.
Reference SCOP/SCOP /SCOP calculations may be based on calculated or tested values. For the
on net
purpose of SCOP/SCOP /SCOP , three design conditions average (A), Colder (C) and warmer (W) are
on net
considered as well as three temperature applications. In case of tested values, this standard gives the
methods for testing heat pumps water heater at part load conditions.
vi © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 21978:2021(E)
Heat pump water heater — Testing and rating at part
load conditions and calculation of seasonal coefficient of
performance for space heating
1 Scope
The document specifies test conditions for determining the seasonal performance characteristics of air
source heat pump water heaters for space heating with electrically driven compressors with or without
supplementary heater. The purpose of this document is to rate performance of the heat pump water
heaters for space heating with no operation of any supplementary heater. In the case of heat pump
water heaters for space heating consisting of several parts with refrigerant or water connections, this
document applies only to those designed and supplied as a complete package.
The seasonal coefficient of performance depends, inter alia, on the climate conditions and temperature
regime of the space heating distribution network.
This document defines:
— three design conditions, each of them being characterized by a design temperature which represents
the lowest temperature that can occur in that design condition;
— three water temperature distribution regimes, namely “temperature application” in the text.
The user of this document is free to determine the seasonal coefficient of performance for one or more
of the defined design conditions and for one or more of the defined temperature applications.
This document also provides a full description of three heating seasons that can be used with the
associated design conditions.
2 Normative references
There are no normative references in this document.
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
active mode
mode corresponding to the hours with a heating load of the building and whereby the heating function
of the unit is activated
Note 1 to entry: This condition can involve on/off-cycling of the unit in order to reach or maintain a required
indoor air temperature.
3.2
active mode seasonal coefficient of performance
SCOP
on
average coefficient of performance of the unit in active mode (3.1) for the designated design condition,
determined from the part load, supplementary heating capacity (where required) and bin-specific
coefficients of performance (3.7) and weighted by the bin hours (3.6) where the bin condition occurs
Note 1 to entry: For calculation of SCOP , the energy consumption during thermostat-off mode (3.45), standby
on
mode (3.42), off mode (3.34) and crankcase heater mode (3.17) are excluded. The energy consumption of a
supplementary heater is added for the part load conditions where the declared capacity of the unit is lower than
the heating load, regardless whether this supplementary heater is included in the unit or not included in the unit.
Note 2 to entry: Expressed in kWh/kWh.
3.3
annual energy consumption for heating
Q
HE
energy consumption required to meet the reference annual heating demand for a designated design
condition and set of bin hours and calculated as the reference annual heating demand divided by
the active mode seasonal coefficient of performance (3.2) and the energy consumption of the unit for
thermostat-off-, standby-, off- and crankcase heater-mode during the heating season
Note 1 to entry: Expressed in kWh/kWh.
3.4
annual heating demand
Q
H
heating demand for a designated design condition and set of bin hours, to be used as basis for calculation
of seasonal coefficient of performance (3.41) and calculated as the product of the design load (3.21) for
heating and the equivalent active mode hours for heating (3.27)
Note 1 to entry: Expressed in kWh
3.5
bin
outdoor temperature interval of 1 K
3.6
bin hours
h
j
hours per heating season for which an outdoor temperature occurs for each bin (3.5) j
3.7
bin-specific coefficient of performance
COP (T )
bin j
coefficient of performance specific for every bin (3.5) j with outdoor temperature T in a heating season
j
3.8
bin temperature
T
j
outdoor air dry bulb temperature
Note 1 to entry: Expressed in °C.
Note 2 to entry: The relative humidity can be indicated by a corresponding wet bulb temperature.
2 © ISO 2021 – All rights reserved

3.9
bivalent temperature
T
biv
lowest outdoor temperature point at which the unit is declared to have a capacity able to meet 100 % of
the heating load without supplementary heater, whether it is integrated in the unit or not
Note 1 to entry: Below this point, the unit can still provide capacity, but additional supplementary heating is
necessary to fulfil the heating load.
3.10
capacity control
ability of the unit to change its capacity by changing the volumetric flow rate of the refrigerant
Note 1 to entry: Units are indicated as ‘fixed’ if the unit cannot change its volumetric flow rate, 'two-staged' if
the volumetric flow rate is changed or varied in series of not more than two steps, 'multi-stage’ if the volumetric
flow rate is changed or varied in series of three or four steps or ‘variable' if the volumetric flow rate is changed or
varied in series of five or more steps to represent continuously variable capacity.
Note 2 to entry: Multi-stage capacity units are considered as variable capacity units in this document.
3.11
capacity ratio
CR
heating part load or full load divided by the declared heating capacity of the unit at the same
temperature conditions
3.12
coefficient of performance at declared capacity
COP
d
declared heating capacity of the unit divided by the effective power input of the unit at specific
temperature conditions, A, B, C, D, E, F and G, where applicable
Note 1 to entry: Expressed in kW/kW.
3.13
coefficient of performance at part load
COP
bin
coefficient of performance at the declared capacity, corrected with the degradation coefficient, where
applicable
Note 1 to entry: When the declared capacity of the unit is higher than the heating load, the COP includes
degradation losses. When the declared capacity of the unit is lower than the heating load (i.e. below the bivalent
temperature (3.9) condition), the COP of the declared capacity is used.
Note 2 to entry: Expressed in kW/kW.
3.14
compressor-off state
condition where the compressor is not running while the unit is operating in active mode (3.1)
Note 1 to entry: This is the “off” phase in on/off cycling.
3.15
crankcase heater mode operating hours
H
CK
annual number of hours the unit is considered to be in crankcase heater mode, the value of which
depends on the designated design condition and set of bin hours
Note 1 to entry: Three examples of crankcase heater mode hours are given in Annex C.
Note 2 to entry: Expressed in h.
3.16
crankcase heater mode power input
P
CK
power input of the unit due to crankcase heater operation mode
Note 1 to entry: Expressed in W.
3.17
crankcase heater (operation) mode
condition where the unit has activated a heating device to avoid the refrigerant migrating to the
compressor in order to limit the refrigerant concentration in oil at compressor start
3.18
declared capacity in heating
Pdh
heating capacity a unit can provide at any temperature condition A, B, C, D, E, F or G, as declared by the
manufacturer
Note 1 to entry: This is the capacity provided by the refrigerant cycle of the unit without supplementary heaters,
even if those are integrated in the unit.
3.19
degradation coefficient
Cd
measure of efficiency loss due to the cycling
Note 1 to entry: If the Cd is not determined by measurement, the default degradation coefficient is 0,9.
3.20
design condition
condition characterized by a design temperature condition and that is to be associated with a set of
bin hours
Note 1 to entry: Three design conditions are defined in this document.
3.21
design load
P
designh
space heating load declared by the manufacturer at design temperature (3.22)
Note 1 to entry: It is possible to calculate the SCOP/SCOP /SCOP of a unit for more than one P value.
on net designh
Note 2 to entry: Expressed in kW.
3.22
design temperature
T
designh
lowest outdoor air temperature considered for each design condition
3.23
effective power input during compressor-off state
Pc
off
total power input of the unit when the compressor is switched off in active mode (3.1), used for the
determination of the degradation coefficient (3.19)
Note 1 to entry: Expressed in kW.
4 © ISO 2021 – All rights reserved

3.24
effective power input with declared capacity
Pc
on
total power input when the unit is operating at part load condition, used for the determination of the
degradation coefficient (3.19)
Note 1 to entry: Expressed in kW.
3.25
electric supplementary heater
real or assumed electric supplementary heater, with a COP of 1, considered in the calculation of SCOP
(3.41) and SCOPon (3.2)
3.26
electric supplementary heater capacity
elbu(T )
j
heating capacity of a real or assumed electric supplementary heater supplementing the declared
capacity for heating when the capacity of the unit is lower than the heat load for a specific bin
temperature (3.8) T
j
Note 1 to entry: Expressed in kW.
3.27
equivalent active mode hours for heating
H
HE
assumed annual number of hours while the unit is assumed to operate at the design load for heating
(P ) in order to satisfy the reference annual heating demand
designh
Note 1 to entry: Expressed in h.
3.28
fixed outlet
water(brine) outlet temperature that is used when the control of the unit has no means to automatically
vary the water(brine) outlet temperature with the outdoor temperature
3.29
heat pump water heater for space heating
air source heat pump water heater with electrically driven compressor(s) with or without supplementary
heater for space heating purpose
Note 1 to entry: This is also referred to as heat pump in this document.
3.30
high temperature application
temperature application where the indoor heat exchanger water(brine) outlet temperature of 55 °C is
met at design temperature
3.31
low temperature application
temperature application where the indoor heat exchanger water(brine) outlet temperature of 35 °C is
met at design temperature
3.32
medium temperature application
temperature application where the indoor heat exchanger water(brine) outlet temperature of 45 °C is
met at design temperature
3.33
net seasonal coefficient of performance
SCOP
net
seasonal efficiency of a unit in active heating mode without supplementary heaters which is determined
from selected conditions
Note 1 to entry: For calculation of SCOP , the energy consumption during active mode (3.1) is used. This excludes
net
the energy consumption during thermostat-off mode (3.45), standby mode (3.42), off mode (3.34) or that of the
crankcase heater. For the part load conditions where the declared capacity of the unit is lower than the heating
load, the energy consumption of a supplementary heater is not included.
Note 2 to entry: Expressed in kWh/kWh.
3.34
off mode
mode wherein the unit is completely switched off and cannot be reactivated by control device, external
signal or by a timer
Note 1 to entry: Off mode means a condition in which the equipment is connected to the mains and is not providing
any function. The following will also be considered as off mode: conditions providing only an indication of off
mode condition; conditions providing only functionalities intended to ensure electromagnetic compatibility.
3.35
off mode operating hours
H
OFF
annual number of hours the unit is considered to be in off mode (3.34), the value of which depends on
the designated design condition and set of bin hours
Note 1 to entry: Three examples of off mode operating hours are given in Annex C.
Note 2 to entry: Expressed in h.
3.36
off mode power input
P
OFF
power input of the unit while in off mode (3.34)
Note 1 to entry: Expressed in W.
3.37
operation limit temperature
TOL
outdoor temperature below which the declared capacity is equal to zero
Note 1 to entry: Expressed in °C.
3.38
part load for heating
P (T )
h j
heating load at a specific bin temperature (3.8) T , calculated as the design load multiplied by the part
j
load ratio
Note 1 to entry: Expressed in kW.
3.39
part load ratio
pl(T )
j
bin temperature (3.8) minus 16 °C divided by the design temperature minus 16 °C
6 © ISO 2021 – All rights reserved

3.40
reactivation function
function facilitating the activation of other modes, including active mode (3.1), by remote switch
including remote control, internal sensor, timer to a condition providing additional functions, including
the main function, but excluding thermostats
3.41
seasonal coefficient of performance
SCOP
overall coefficient of performance of the unit, representative for the designated design condition and
set of bin hours
Note 1 to entry: SCOP is calculated as the annual heating demand (3.4) divided by the annual energy consumption
for heating (3.3).
Note 2 to entry: Expressed in kWh/kWh.
3.42
standby mode
mode wherein the unit is switched off partially and can be reactivated by a control device (such as a
remote control), an external signal or a timer
Note 1 to entry: The unit is connected to the mains, depends on signal input to work as intended and provides
only the following functions, which may persist for an indefinite time: reactivation function (3.40), or reactivation
function and only an indication of enabled reactivation function, and/or information or status display.
3.43
standby mode operating hours
H
SB
annual number of hours the unit is considered to be in standby mode (3.42), the value of which depends
on the designated design condition and set of bin hours
Note 1 to entry: Three examples of standby hours are given in Annex C.
Note 2 to entry: Expressed in h.
3.44
standby mode power input
P
SB
power input of the unit due to standby mode (3.42) operation
Note 1 to entry: Expressed in W.
3.45
thermostat-off mode
mode corresponding to the hours with no heating demand of the building, whereby the heating function
of the unit is switched on, but is not operational, as there is no heating demand
Note 1 to entry: Cycling on/off in active mode (3.1) is not considered as thermostat-off.
3.46
thermostat-off mode operating hours
H
TO
annual number of hours the unit is considered to be in thermostat-off mode (3.45), the value of which
depends on the designated design condition and set of bin hours
Note 1 to entry: Three examples of standby hours are given in Annex C.
Note 2 to entry: Expressed in h.
3.47
thermostat-off mode power input
P
TO
power input of the unit due to thermostat-off mode (3.45) operation
Note 1 to entry: Expressed in W.
3.52
variable outlet
water(brine) outlet temperature that is used when the control of the unit has means to automatically
vary the water(brine) outlet temperature with the outdoor temperature
4 Symbols
Symbol Definition Units
Cd Degradation coefficient —
COP Coefficient of performance kW/kW
COP Coefficient of performance at part load kW/kW
bin
COP (T ) Bin-specific coefficient of performance kW/kW
bin j
COP Coefficient of performance at the declared capacity kW/kW
d
CR Capacity ratio kW/kW
EEI Energy efficiency index of liquid pump —
h Bin hours h
j
H Equivalent active mode hours for heating h
HE
H Crankcase heater mode operating hours h
CK
H Off mode operating hours h
OFF
H Standby mode operating hours h
SB
H Thermostat-off mode operating hours h
TO
j Bin number —
n Total number of bin —
P Crankcase heater mode power input W
CK
Pc Effective power input during compressor-off state kW
off
Pc Effective power input with declared capacity kW
on
Pdh Declared capacity in heating kW
P Design load heating kW
designh
P (T ) Part load for heating kW
h j
P Off mode power input W
OFF
P Standby mode power input W
SB
P Thermostat-off mode power input W
TO
pl(T ) Part load ratio for bin temperature T —
j j
Q Annual heating demand kWh
H
Q Annual energy consumption for heating kWh
HE
SCOP Seasonal coefficient of performance kW/kW
SCOP Net seasonal coefficient of performance kW/kW
net
SCOP Active mode seasonal coefficient of performance kW/kW
on
T Bivalent temperature °C
biv
T Design temperature conditions for heating °C
designh
T Bin temperature (outdoor temperature) °C
j
T Operation limit temperature °C
ol
8 © ISO 2021 – All rights reserved

Symbol Definition Units
elbu(T ) electric supplementary heater capacity kW
j
5 Installation requirements
5.1 Test apparatus and uncertainties of measurement
The test apparatus shall be designed in such a way that all requirements for adjustment of set values,
stability criteria and uncertainties of measurement according to this document can be fulfilled.
Water systems or other heat transfer liquid systems shall be sufficiently free of entrained gas as to
ensure that the measured results are not significantly influenced.
The inlet and outlet water temperatures of the heat pump shall be measured in the center of the flow
and as close as possible to the unit. The response time of the temperature sensor and the sampling
interval shall be chosen to maintain the uncertainties in Table 1.
Ducted air systems shall be sufficiently airtight to ensure that the measured results are not significantly
influenced by exchange of air with the surroundings.
When performing measurements, set the highest room temperature on the unit/system control device.
If, in the instructions, the manufacturer indicates a value for the temperature set on the control device
for a given part load conditions, this value shall be used.
Temperature and pressure measuring points shall be arranged in order to obtain mean significant values.
For free air intake temperature measurements, it is required either:
— to have at least one sensor per square meter, with not less than four measuring points and by
restricting to 20 the number of sensors equally distributed on the free air surface; or
— to use a sampling device that shall be completed by four sensors for checking uniformity if the
surface area is greater than 1 m .
Air temperature sensors shall be placed at a maximum distance of 0,25 m from the free air surface.
For water and brine, the density and specific heat in Formulae (2), (3) and (4) shall be determined in the
temperature conditions measured near the volume flow measuring device.
The uncertainties of measurement shall not exceed the values specified in Table 1.
Table 1 — Uncertainties of measurement
Measured quantity Unit Uncertainty
Liquid
Temperature °C ±0,15 K
Temperature difference K ±0,15 K
Volume flow m /s ±1 %
±1 kPa (≤20 kPa)
Static pressure difference kPa
±5 % (>20 kPa)
Concentration (for brine) % 2 %
Air
Dry bulb temperature °C ±0,2 K
Wet bulb temperature °C ±0,4 K
Volume flow m /s ±5 %
Table 1 (continued)
Measured quantity Unit Uncertainty
±5 Pa (∆P ≤ 100 Pa)
Static pressure difference Pa
±5 % (∆P ≥ 100 Pa)
Electrical quantities
Electric power W ±1 %
Electrical energy kWh ±1 %
Voltage V ±0,5 %
current A ±0,5 %
Additionally, the heating capacity measured on the liquid side shall be determined within a maximum
uncertainty calculated according to Formula (1) independently of the individual uncertainties of
measurements including the uncertainties on the properties of the fluid.
maximum uncertainty=+2 ×100 (%) (1)
Partloadratio
5.2 Test room for the airside and remote condenser
The size of the test room shall be selected to avoid any resistance to air flow at the air inlet and air
outlet orifices of the test object. The air flow through the room shall not be capable of initiating any
short circuit between the two orifices, and therefore the velocity of air flow at these two locations shall
not exceed 1,5 m/s when the test object is switched off.
Unless otherwise stated by the manufacturer, the air inlet and air outlet orifices shall not be less than
1 m from the surfaces of the test room.
Any direct heat radiation (e.g. solar radiation) onto heating units in the test room onto the heat pump or
onto the temperature measuring points shall be avoided.
5.3 Installation and connection of the heat pump
The heat pump shall be installed and connected for the test as recommended by the manufacturer in
the installation and operation manual. If a back-up heater is provided (as an option or not), it shall be
switched off or disconnected to be excluded from the testing.
5.4 Installation of heat pumps consisting of several parts
In the case of heat pumps consisting of several refrigeration parts (split heat pumps), the following
installation conditions shall be met for the tests:
a) each refrigerant line shall be installed in accordance with the manufacturer's instructions; the
length of each line shall be between 5 m and 7,5 m;
b) the lines shall be installed so that the difference in elevation does not exceed 2,5 m;
c) thermal insulation shall be applied to the lines in accordance with the manufacturer's instructions;
d) unless constrained by the design, at least half of the interconnecting lines shall be exposed to the
outdoor conditions with the rest of the lines exposed to the indoor conditions.
5.5 Environment conditions for indoor unit installation and electrical power supply
requirements
Temperature conditions of parts of the unit located in the indoor side shall be between 15 °C to 30 °C.
The dry bulb temperature shall be measured.
10 © ISO 2021 – All rights reserved

For all units, electrical power voltage and frequency shall be given by the manufacturer.
6 Setting and part load test conditions
6.1 General
Set points for internal control equipment of the unit, i.e. thermostats, pressure switches or mixing
valves, shall be set to the values as stated in the installation and operating instructions.
If several set points or a range are stated, the manufacturer shall indicate the one to be used for the tests.
6.2 Setting for capacity ratio
The capacity ratio to be tested shall be set according to the instructions of the manufacturer. The
manufacturer shall provide laboratories with the necessary information on the setting of the unit for
operating at the required capacity conditions upon request. The unit shall operate continuously during
the part load test. The only discontinuity allowed is the defrost cycle of a unit.
For staged or variable capacity units, the setting of the compressor (stage, frequency) shall be done
for each part load condition. The manufacturer shall provide in the documentation information
instructions on how to obtain the necessary data to set the required frequencies. To set up a system
with staged or variable capacity control, skilled personnel with knowledge of control software may
be required. The manufacturer or his nominated agent is allowed to attend when the system is being
installed and prepared for tests.
6.3 Setting the external static pressure difference for ducted units
The volume flow and the pressure difference shall be related to standard air and with dry heat
exchanger. If the air flow rate is given by the manufacturer with no atmospheric pressure, temperature
and humidity conditions, it shall be considered as given for standard air conditions.
The air flow rate as stated in the installation and operating instructions shall be converted into
standard air conditions. The air flow rate setting shall be made when the fan only is operating.
The rated air flow rate as stated in the installation and operating instructions shall be set and the
resulting external static pressure (ESP) measured.
If the ESP is lower than 30 Pa, the air flow rate is decreased to reach this minimum value. The apparatus
used for setting the ESP shall be maintained in the same position during all the tests.
If the installation and operating instructions state that the maximum allowable duct length is for inlet
and outlet together less than 2 m, the unit shall be tested with the duct length and the ESP is considered
to be 0.
6.4 Setting of units with integral pumps
For units with integral water or brine pumps, 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.
Deviations from set values shall not exceed values indicated in Table 2. Variations from specified
conditions shall not exceed values indicated in Table 3.
Table 2 — Permissible deviations from set values
Permissible deviation of the Permissible deviations of
Measured quantity arithmetic mean values individual measured
from set values values from set values
Liquid
— inlet temperature ±0,2 K ±0,5 K
— outlet temperature ±0,3 K ±0,6 K
a
— volume flow ±1 % ±2,5 %
— static pressure difference — ±10 %
Air
— inlet temperature
— dry bulb ±0,3 K ±1 K
— wet bulb ±0,4 K ±1 K
Voltage ±4 % ±4 %
a
Frosting period excluded.
Table 3 — Variations allowed for the test conditions when the heat pump is running
Variations of arithmetical mean Variation of individual readings
values from specified test condi- from specified test conditions
tions
Readings
Interval Interval Interval Interval
a b a b
H D H D
Air
c
— dry-bulb temperature ±0,6 K ±1,5 K ±1,0 K ±5,0 K
— wet-bulb temperature ±0,4 K ±1,0 K ±0,6 K —
Liquid
— inlet temperature ±0,2 K — ±0,5 K −5 K
— outlet temperature ±0,5 K — ±1 K +2 K
a
Interval H applies when the heat pump is in the heating mode, except for the first 10 min after termination of a defrost
cycle, and the first 10 min after a restart of the heat pump.
b
Interval D applies during a defrost cycle and during the first 10 min after the termination of a defrost cycle when the
heat pump is operating in the heating mode.
c 2
For units with outdoor heat exchanger surfaces greater than 5 m , the deviation on the air inlet dry bulb temperature
is doubled.
6.5 Part load test conditions
For the part load tests, the appropriate test conditions shall be chosen from Tables 6 to 8 depending
on the selected design conditions and temperature applications. One or several design conditions and
temperature applications can be applied.
Three design conditions average (A), Colder (C) and warmer (W) are considered as well as three
temperature applications, low, medium and high, as given in Table 4 and Table 5, respectively.
12 © ISO 2021 – All rights reserved

Table 4 — Design conditions
Design conditions
Design
temperature
Average Warmer Colder
T
(A) (W) (C)
designh
— Dry bulb −10 °C 2 °C −22 °C
— Wet bulb −11 °C 1 °C —
Table 5 — Temperature applications
Temperature application
Low Medium High
Water(brine) outlet
35 °C 45 °C 55 °C
temperature
For each temperature application, the heat pump can either operate with a fixed or a variable water
outlet temperature.
For outdoor air dry bulb temperatures higher or equal to −10 °C the wet bulb temperature equals the
dry bulb temperature minus 1 K. For dry bulb temperatures below −10 °C, the wet bulb temperature is
not defined.
If the declared TOL is lower than T , then the outdoor dry bulb temperature is equal to T for
design designh
the part load condition E in Table 6, Table 7 and Table 8.
The part load ratios shall be based on the part load ratio formulae and not on the rounded values given
for each condition in Table 6 to 8.
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