Heat Pumps for Water Heating

New Zealand availability, circa 2008

Domestic types of heat pump units:

outdoors/indoors combined storage cylinder and heat pump units

Sanders Engineering, Tauranga (indoors, ductable airflows, 200litre):
http://web.mac.com/robs6/Site/Heat_Pump.html
Quantum (Australia) from Eco systems (Lower Hutt); indoors or outdoors, 340litres, no heater element:
http://www.eco.co.nz/products/quantum.php
Rheem (Australia) A551310 300litre outdoors:
http://www.rheem.co.nz/domestic_product.asp?prod_id=109&cat_id=
There are similar units eg. Dux, Solarhart, which don't seem to be promoted in NZ.

outdoors swimming-pool-type units, plumbed to indoor storage cylinder

Hot Water Heat Pumps Ltd, Auckland:
http://www.poolheating.co.nz/domestic_hot_water.aspx
Climate Zone Holdings Ltd, Christchurch;
National (plumbed hot water),
Sova (plumbed refrigerant to indoors heating-storage unit):
http://www.climatezone.co.nz/hot_water_heat_pumps.html

Sensible Safe Temperature for hot water, Legionella

Safetycrats worry that in poorly maintained systems, legionella can multiply rapidly between temperatures of 20 — 43°C.
Some solar-sourced energy systems struggle to raise the stored water much above 50°C.
Most systems have a conventional electric heating element which can be arranged to periodically bring the temperature up to 60°C to kill off any legionella, although there is debate as to whether it is desirable for burn safety to heat water above 50°C.

An early NZ practice of setting the hot water temperature to 70°C is increasingly thought of as excessive. It can still cause significant burns when tempering valves fail, and causes additional heat loss through the cylinder insulation.
The higher temperature possibly allowed for cheaper smaller storage cylinders to be used, but with the inefficiency of the tempering valve and insulation, this practice is increasingly seen as short-sighted. Storing a bigger volume of hot water at a lower temperature is safer, more practical and more economic in the long term.
A setting of 55°C has been promoted recently.

Some Australian systems do not provide an electric element.
The US considers that 50°C is the maximum safe temperature that the human body should encounter, with legionella an insignificant risk.
For more information and alternatives to higher temperatures, scroll towards the bottom of this page:
http://www.climatezone.co.nz/hot_water_heat_pumps.html

Solar water heating grants