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Heat-pump water heaters Updated: 12 May 2009

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water heating refrigerators Posted by: Harping Bowker 23 Jul 2009 8:33pm

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)?

Timers Posted by: Stetsun 17 Jul 2009 9:08pm

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?

More detailed results would be useful Posted by: Eric 11 Jun 2009 6:40pm

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.

Other uses Posted by: rayda 09 Jun 2009 12:02am

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

Comparison with Gas Hot water heating Posted by: Gregory & Karen Scott 08 Jun 2009 8:45pm

How does the energy savings of Heat Pump hot water heating compare with instant Gas Hot water heating.

With Gas, you do not require a hot water cylinder.

Reply 1: Posted by: pominnz 01 Jul 2010 1:49pm

I'm with Genesis energy and my gas per kw is close to 3.1 times less than the cost of electricity per kw.

Gas - 6.75 c/unit
Daily fixed charge - 90 c/day
Electric - 21.39 c/unit
Daily fixed charge - 33.33 c/day

So over 30 days, using 2000kw (during the winter)

power type |kw |fixed daily |Total
------------------------------------------
Gas |$135 |$27 |$162
Electric |$427.80 |$9.99 |$437.79

A difference of $275.79 or ratio 1:2.7 gas:electric

The cost and advantages also depending on your usage.

For example
Over 30 days, using 200kw

power type |kw |fixed daily |Total
------------------------------------------
Gas |$13.5 |$27 |$40.50
Electric |$66.66 |$9.99 |$77.65

This time a difference of $37.15 or 1:1.9 gas:electric

Taking the above into account, and the fact that heatpumps can vary in efficiency depending on their type and outside temperature, it might be worth choosing gas, over electric.

Reply 2: Posted by: Nicholas Wilson 05 Aug 2010 3:53pm

Sorry but doesn't the analysis you've just outlined there refer to standard electric hot water heating? Econergy on their website claim independent research shows their heat pump reduces annual electricity bills by 69.4% which means that in your example above the electric hot water heating bill would be $153 and therefore slightly cheaper than gas. This seems to stack up with the levels of savings people are reporting in the testimonials on the Econergy website. Actual electricity bills would be higher of course as you use electricity for other purposes than just heating, but as the Consumer analysis shows this is a substantial proportion of a household's energy costs.

Also connection costs if you are not already hooked up to gas should be factored in. I've been quoted around $4k by Vector to hook up to the gas mains, and that's not even including any gas water heater. I should note I live down an steep shared right of way which I imagine is technically challenging so costs could be much lower for others. Even so, for that sort of money I could easily install a hot water heat pump and potentially even use it for central heating (likely need a new cylinder though). All up its something I'm giving serious consideration to.

Reply 3: Posted by: ADL Raymond D 29 Sep 2010 10:24pm

http://www.energywise.govt.nz/how-to-be-energy-efficient/your-house/hot-water/choosing-the-right-water-heating-system

Who supplies Econergy HP4000 LT? Posted by: Thomas S 08 Jun 2009 3:28pm

You would probably be impartial enough if you had links to manufacturer/suppliers since e.g. there is no result for Econergy HP4000 LT when searching on line. Cheers Tom