NBN ISO 21978:2021

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.