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
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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.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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Introduction
Heat pumps water heaters are, at present, se
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