Heat pump water heater — Testing and rating at part load conditions and calculation of seasonal coefficient of performance for space heating

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.

Chauffe-eau à pompe à chaleur — Essais et classification à charge partielle et calcul du coefficient de performance saisonnier

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Publication Date
02-Feb-2021
Current Stage
9092 - International Standard to be revised
Start Date
26-Aug-2021
Completion Date
26-Aug-2021
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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 21978:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 21978:2021(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 21978:2021(E)
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

8.3 Calculation of the annual electricity consumption, Q ..................................................................................24

8.4 Calculation of SCOP and SCOP ...................................................................................................................................25

on net
© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 21978:2021(E)

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
---------------------- Page: 4 ----------------------
ISO 21978:2021(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.

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.
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 21978:2021(E)
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
---------------------- Page: 6 ----------------------
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.
© ISO 2021 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 21978:2021(E)
3.2
active mode seasonal coefficient of performance
SCOP

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

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

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

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

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

3.8
bin temperature
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
---------------------- Page: 8 ----------------------
ISO 21978:2021(E)
3.9
bivalent temperature
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

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

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

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.
© ISO 2021 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 21978:2021(E)
3.16
crankcase heater mode power input
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
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
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
designh
lowest outdoor air temperature considered for each design condition
3.23
effective power input during compressor-off state
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
---------------------- Page: 10 ----------------------
ISO 21978:2021(E)
3.24
effective power input with declared capacity

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 )

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
Note 1 to entry: Expressed in kW.
3.27
equivalent active mode hours for heating

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
© ISO 2021 – All rights reserved 5
---------------------- Page: 11 ----------------------
ISO 21978:2021(E)
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
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
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

load ratio
Note 1 to entry: Expressed in kW.
3.39
part load ratio
pl(T )
bin temperature (3.8) minus 16 °C divided by the design temperature minus 16 °C
6 © ISO 2021 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 21978:2021(E)
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
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 21978
ISO/TC 86/SC 6
Heat pump water heater — Testing
Secretariat: JISC
and rating at part load conditions and
Voting begins on:
2020­10­30 calculation of seasonal coefficient of
performance for space heating
Voting terminates on:
2020­12­25
Chauffe-eau à pompe à chaleur — Essais et classification à charge
partielle et calcul du coefficient de performance saisonnier
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 21978:2020(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 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 21978:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 21978:2020(E)
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 .............................................................................................................................................................................................15

7.1 Heating capacity test .......................................................................................................................................................................15

7.2 Heating capacity correction ......................................................................................................................................................16

7.2.1 General...................................................................................................................................................................................16

7.2.2 Capacity correction of fans for units without duct connection ............................................16

7.2.3 Capacity correction due to indoor fan for ducted units ..............................................................16

7.2.4 Capacity correction due to indoor liquid pump .................................................................................16

7.2.5 Effective power input ................................................................................................................................................17

7.3 Test procedure ......................................................................................................................................................................................19

7.3.1 General...................................................................................................................................................................................19

7.3.2 Preconditioning period ...........................................................................................................................................19

7.3.3 Equilibrium period .................. ......................................................................................................................... ...........19

7.3.4 Data collection period ..............................................................................................................................................19

7.4 Heating capacity calculation ....................................................................................................................................................20

7.4.1 Steady state capacity test ......................................................................................................................................20

7.4.2 Transient capacity test .............................................................................................................................................20

7.5 Effective power input calculation ........................................................................................................................................20

7.5.1 Steady state test .............................................................................................................................................................20

7.5.2 Transient capacity test .............................................................................................................................................20

7.6 Determination of degradation coefficient Cd ...........................................................................................................20

7.7 Test methods for electric power input during thermostat-off mode, standby mode

and crankcase heater mode and off mode ....................................................................................................................21

7.7.1 Uncertainties of measurement .........................................................................................................................21

7.7.2 Measurement of electric power input during thermostat­off mode ................................21

7.7.3 Measurement of electric power input during standby mode .................................................22

7.7.4 Measurement of electric power input during crankcase heater mode ..........................22

7.7.5 Measurement of electric power input during off mode ..............................................................22

8 Calculation methods for seasonal coefficient of performance (SCOP) ......................................................22

8.1 General equation for calculation of SCOP ....................................................................................................................22

8.2 Calculation of the reference annual heating demand, Q ..............................................................................23

8.3 Calculation of the annual electricity consumption, Q ..................................................................................23

8.4 Calculation of SCOP and SCOP ...................................................................................................................................23

on net
© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 21978:2020(E)

8.5 Calculation procedure for determination of COP values at part load conditions A to G 24

bin

8.5.1 General...................................................................................................................................................................................24

8.5.2 Calculation procedure for fixed capacity units ...................................................................................25

8.5.3 Calculation procedure for staged and variable capacity units ..............................................25

9 Test results and test report ....................................................................................................................................................................26

9.1 Data ................................................................................................................................................................................................................26

9.2 Test report ................................................................................................................................................................................................27

10 Marking .......................................................................................................................................................................................................................27

Annex A (normative) Heating capacity test procedures given in 7.3 ...............................................................................28

Annex B (normative) Determination of the liquid pump efficiency .................................................................................32

Annex C (informative) Examples of set of bin hours and hours for active mode, thermosta-

off mode, standby mode, off mode and crankcase heater mode ......................................................................36

Annex D (informative) SCOP calculation for fixed capacity for low temparature

application — Example ...............................................................................................................................................................................38

Annex E (informative) SCOP calculation for variable capacity unit for low temparature

application —Example ................................................................................................................................................................................42

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ISO/FDIS 21978:2020(E)
Foreword

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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.

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ISO/FDIS 21978:2020(E)
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 2020 – All rights reserved
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 21978:2020(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 standard 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 the standard 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 standard also provides a full description of three heating seasons that may 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.
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ISO/FDIS 21978:2020(E)
3.2
active mode seasonal coefficient of performance
SCOP

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

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

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

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

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

3.8
bin temperature
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.

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ISO/FDIS 21978:2020(E)
3.9
bivalent temperature
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

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

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

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.
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ISO/FDIS 21978:2020(E)
3.16
crankcase heater mode power input
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
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
designh
space heating (P ) load declared by the manufacturer at T condition
designh designh

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
designh
lowest outdoor air temperature considered for each design condition
3.23
effective power input during compressor-off state
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.
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ISO/FDIS 21978:2020(E)
3.24
effective power input with declared capacity

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

and SCOP
3.26
electric supplementary heater capacity
elbu(T )

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
Note 1 to entry: Expressed in kW.
3.27
equivalent active mode hours for heating

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
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ISO/FDIS 21978:2020(E)
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
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
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

load ratio
Note 1 to entry: Expressed in kW.
3.39
part load ratio
pl(T )
bin temperature (3.8) minus 16 °C divided by the design temperature minus 16 °C
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ISO/FDIS 21978:2020(E)
3.40
reactivation function
function facilitating the
...

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