Split systems have the compressor unit outside and the hot water tank generally inside although the tank can also be located outside the house separate from the compressor. In some cases you can use your existing tank.
All-in-one units have the compressor and tank together and the whole system usually sits outside (although an indoor unit is being developed, which is ducted to the outside).
Optimal conditions for heat pumps
Generally, the hotter the outside air, the better the heat pump runs. Heat pump water heaters tend to work best in areas with average air temperatures above 7°C. But the better systems (Class A) will still run more efficiently than a traditional electric or gas water heater in below-zero temperatures.
If you live in a colder part of the country, ask your manufacturer if their system is designed to work at low temperatures. Ask to see performance results at different temperatures for the model you are thinking of buying. Ensure that the system is “Class A Rated – suitable for cold climates” when installing south of Auckland. This means it has an active defrost cycle.
Select a model that achieves an energy saving of at least 60% for your climate zone; ensure that the system is compliant to AS/NZS2712:2007 and that the tank is NZ MEPS rated.
Consumer NZ report
In April 2009 Consumer NZ (with the support of EECA) carried out tests on the performance of six heat pump water heaters suitable for household use.
The complete report can be accessed free of charge from the Consumer NZ website www.consumer.org.nz/reports/heat-pump-waterheaters.
In 2009, EECA introduced a Heat Pump Water Heating (HPWH) Pilot scheme designed to collect data on the energy and economic performance of a range of residential HPWH technologies installed in different regions of New Zealand. The report details the finding of that pilot scheme and can be found at www.eeca.govt.nz/node/11863.
This is general advice. We recommend you get more specific advice from your local EDA, where available. Call 0508 326-337 (0508 ECO DESIGN) or visit www.ecodesignadvisor.org.nz – free, independent, informed advice on creating homes that are healthier for you and the planet.
Original information from EECA Energywise website (accessed August 2012) and BRANZ Build 116 (Feb/Mar 2010) article Water Heating Options, by Albrecht Stoecklein. Updated with additional commentary and costs by EDAs and reviewed by Adrian Kerr, Project Solar, October 2012.