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You write "A good heat-pump water heater (HPWH) would reduce your hot-water bill by two-thirds" .
I assume this is compared to other electric water heating.
What is the running cost compared to gas?
Annual running cost of HPWH is cheaper according to the Energywise website, check the "ongoing running costs" Graph:http://www.energywise.govt.nz/how-to-be-energy-efficient/your-house/hot-water/choosing-the-right-water-heating-system
most comparisons of Electric/Gas/HWHP don't take into count the gas connection line charge $1 per day in auckland 0.70c Hamilton eliminating gas connection from the house can save $365 per yearcontrolled rate electric is often best for low hot water users HPHW is best for high users of hot water
Because gas water heating units are only around 85% to 90 % efficient, plus the supply charge, I don't understand why people go for this option.
Is there any more news about the Japanese CO2 pumps? This could be an amazing breakthrough for NZ. The article may also need updating, as there are two new HWHPs listed for sale on trademe in my region, one for $3,500, the other for only $3,000. At these prices, it seems like a really good option for heavy users like me.
As for the minimum safe temperature for hot water, I thought that that was well established. A breakthrough (and very simple) technology to save more energy would be to set the hot water to lower temperatures than the currently recommended 60 degrees, but with a timer causing the water to be super-heated periodically to kill any legionaires bacteria.
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...there is at least a 10dB difference between some heat pumps, and this makes a big difference with these things running at night. No buying decision should ignore noise as it is an expensive problem to manage.
I cannot find anywhere in this article about whether the Ecoenergy can be connected to a Mains pressure hot water cylinder. I am assuming it can, but can you confirm this?
Also, as per Thomas Schneider's request, can you pls provide websites for the suppliers of each product.
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Refrigerators, freezers, (& heat pumps in cooling mode) produce heat, can that heat be used to heat the hot water cylinder?
Why not a fridge freezer linked to a hot water supply?
Should external heat pump units be south facing in the summer (when cooling) and northfacing in winter (when heating)?
Provided a suitably sized hot water cylinder and Hot Water heat pump are used a considerable efficiency gain could be made by only running the heat pump at the warmest time of the day. Are the heat pumps tested fitted with such timers?
This is an interesting item. However, it would be so much more useful if the data from which your conclusions/ results were drawn made available. e.g. what output is available from each unit at a range of temperatures ant he efficiency at that point. I realise that this is more information than is required by many, but the web site could have a page to provide more technical information.
A great article. I presume this could, with suitable tempering valves for the cylinder output, be used for home radiator-based heating, which seems a missed opportunity so far by both water heatpump and solar panel suppliers? I recognise radiators are an added cost but they are far less intrusive than the usual split sytem heat pump solution. Are you aware of anyone supplying such? cheers Doug