Hot Water System. Gas v Heatpump

Forums › Home Workshop DIY › Hot Water System. Gas v Heatpump

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#3157728 9-Nov-2023 17:31

davidgo2:

if I were doing it again, and if it were an option, I'd see if I could couple it with an even bigger tank - the 200 litre tank is more then adequate as long as its on at least 4 hours during the day and 4 hours overnight, but if we had a bigger tank we could go for longer periods without heating and have even more ability to use it as storage/buffer with respect of use of excess solar.

Caution: You are advised to heat your water to at least 55°C, preferably 60°C, at least once every 24 hours to ensure you kill any of the bacteria that cause Legionnaires' Disease that might be in your water supply. This is less likely to be a problem if you are on a properly protected mains water supply, but those are surprisingly less common in NZ than you might expect.

If water is maintained at 50°C for two hours, 90% of the bacteria will be killed off. If water reaches 60°C, the same percentage of bacteria will be killed off in two minutes. If the water reaches 70°C, all the Legionella bacteria will die instantly.

https://www.urisk.co.uk/what-temperature-kills-legionella/

Handle9

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#3157729 9-Nov-2023 17:40

PolicyGuy:
My advice: go for it, your conscience will be easier and your carbon footprints will come down from Giant Size to positively dainty 😀

If the gas appliances are working well then it’s usually more environmentally friendly to run them to end of life than replace them. A planned transition as they reach EOL usually has the best net effect.

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#3157844 10-Nov-2023 07:41

Caution: You are advised to heat your water to at least 55°C, preferably 60°C, at least once every 24 hours to ensure you kill any of the bacteria that cause Legionnaires' Disease that might be in your water supply. This is less likely to be a problem if you are on a properly protected mains water supply, but those are surprisingly less common in NZ than you might expect.

If water is maintained at 50°C for two hours, 90% of the bacteria will be killed off. If water reaches 60°C, the same percentage of bacteria will be killed off in two minutes. If the water reaches 70°C, all the Legionella bacteria will die instantly.

https://www.urisk.co.uk/what-temperature-kills-legionella/

Yeah. These tanks get the water up to 65 degrees and then mix the output down to 55 to feed them in the house - which I am fairly sure is required by NZ law for exactly this reason. Legionella builds up over time so periodically heating the tank above 60c deals to the problem.

raytaylor

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#3158268 11-Nov-2023 13:22

Back to OPs question for a moment,
The payback of a heat pump is very difficult to justify now that contact energy is doing their good nights plan - effectively we have free hot water for our electric cylinder because I added a wifi timer which paid for itself in a month.

While still enjoying our discount for ripple control, the wifi timer switch delays reheating until 9pm so its free.

If you plan on using solar in the future, an electric cylinder also makes a suitable dump load before exporting to the grid.

Has anyone here done the calcs on a heat pump cylinder vs resistance heated water for solar installations? I can imagine it would work for underfloor or radiator heating, but if only for a hot water supply i dont think the extra expense could be justified.

A plumber friend of mine explained that the earlier Rheem ones on the market in NZ did most of their heating via heat pump but to top them off, the last 15 degrees was still resistance. But the other problem was that they would fail after 6-8 years and any payback was lost in having to replace it.

I am all for heat pumps which save water in our dams, but I wonder if electric is really a better solution - especially with solar. Unless there is a 10 year manufacturers warranty on the heat pump.

Ray Taylor

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Spreadsheet for Comparing Electricity Plans Here

morrisk

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#3158761 13-Nov-2023 06:50

Another approach to the switch from gas to electricity that I have found in researching this topic is the use of a ceramic PTC element that runs on DC from PV panels.

Described here:

https://www.greenheat.co.nz/advantages

Has anyone any experience of this approach? I can find little written on the use of the technology for hot water heating and in particular the reliability and life span of these elements.

BlargHonk

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#3158766 13-Nov-2023 07:45

raytaylor:

Back to OPs question for a moment,
The payback of a heat pump is very difficult to justify now that contact energy is doing their good nights plan - effectively we have free hot water for our electric cylinder because I added a wifi timer which paid for itself in a month.

While still enjoying our discount for ripple control, the wifi timer switch delays reheating until 9pm so its free.

If you plan on using solar in the future, an electric cylinder also makes a suitable dump load before exporting to the grid.

Has anyone here done the calcs on a heat pump cylinder vs resistance heated water for solar installations? I can imagine it would work for underfloor or radiator heating, but if only for a hot water supply i dont think the extra expense could be justified.

A plumber friend of mine explained that the earlier Rheem ones on the market in NZ did most of their heating via heat pump but to top them off, the last 15 degrees was still resistance. But the other problem was that they would fail after 6-8 years and any payback was lost in having to replace it.

I am all for heat pumps which save water in our dams, but I wonder if electric is really a better solution - especially with solar. Unless there is a 10 year manufacturers warranty on the heat pump.

How much did it cost to get the wifi timer added? Does it just go on the switchboard HWC circuit?

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davidgo2

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#3158982 13-Nov-2023 12:25

BlargHonk:

How much did it cost to get the wifi timer added? Does it just go on the switchboard HWC circuit?

Can't speak too much for the general case - but in the case of the Rheem unit its a soft start, so only requires only about 5 amps, single phase (notwithstanding the 20 amps mentioned on the brochure, which Rheem confirmed). This is well within the realm of a standard Shelly IOT device [which include timers if thats how you want to do it] which you can just wire onto the circuit - and if you have a switch for it, behind the switch. (and this is how I do it on mine) As I recall, the Rheem units also have a limited ability to turn themselves off during a peek time - but don't handle daylight savings and did not have the amount of flexibility I was after. I don't imagine a competent sparky would need to charge much more then the initial callout fee. The variant of Shelly I am using is the Shelly Plus1PM - which I believe has NZ certification and cost me about $60 for the hardware.

I was reading online that for units with greater draw you can use a Shelly type device to feed a larger relay, or sometimes get away with a "snubber", which I understand to be some kind of Capacitor that helps with the initial startup load.

raytaylor

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#3159151 13-Nov-2023 17:25

I supplied the wifi timer, cousin is an electrician and owed me a favor.

I got a DIN mountable one which was about $90 and we installed it in one of these

https://hager.com/nz/products/product-information/vd103nt-smdistrvd-icsurface3m-w-o-door

About $20 from ideal electrical.

Its wired in between the switch inside the hot water cupboard (not on the fuse board) and the cylinder itself

Board RippleDecoder=HWBreaker==============WallSwitch=WifiTimer==Cylinder

I'd say it might be $90 for half an hour of electricians time and travel depending upon your local rates so all up maybe $230-$250 including parts.

Our hot water cylinder element is 3kw and heats for about 1.5hours so daily it would be costing about $1.05 a day - so by delaying the heating until after 9pm when electricity is free, it will pay for itself in about 3 months - more with electricians labour.

I did the same with an old night store heater in the hallway which charges up in winter between 9pm and midnight then releases about 1.3kw of heat per hour until morning so the house is a few degrees warmer when we wake up. However that timer is on the fuse board itself and we ran a dedicated tps cable to it.

Ray Taylor

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Spreadsheet for Comparing Electricity Plans Here

andysh

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#3160101 16-Nov-2023 11:13

Ended up going with ECOPLUS heatpump: https://regencyplumbing.co.nz/heat-pump-hot-water-cylinders/

Getting it installed in a couple of weeks, but all accounts, should be quiet and efficient! At the moment, I have got no PV and my On/off peak are the same rate so no need for timers or the like.

Referrals:

Tesla: https://ts.la/andrew897313

Sharesies: https://sharesies.com/r/XRGS77

davidgo2

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#3160106 16-Nov-2023 11:38

andysh:

Ended up going with ECOPLUS heatpump: https://regencyplumbing.co.nz/heat-pump-hot-water-cylinders/

Getting it installed in a couple of weeks, but all accounts, should be quiet and efficient! At the moment, I have got no PV and my On/off peak are the same rate so no need for timers or the like.

Good on you. That's the same model I got and I'm super happy with it - so the things I said about installing a timer etc are an option for you if things do change for you later on.

I used the same installers as well (not a surprise - I think they are the only ones who Rheem sell it through in Auckland) - It may be an idea to double-check exactly how/where they plan on installing the unit before they commence work. (In my case I overlooked something and the install made it difficult to reach the main outdoor tap, and made the only outdoor drain pretty much inaccessible and I only became aware of this once the job was complete. Its not a major, and I've worked around it, but something I'd have handled differently had I known. That said, the workmanship was otherwise fine)

gzt

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#3160116 16-Nov-2023 12:03

What did the whole setup end up costing? if you don't mind me asking. Related, is there a govt energy subsidy thing on h/w heatpumps?

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JayADee

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#3160230 16-Nov-2023 17:36

I wish there was a subsidy on HW heat pumps since after this lpg one dies that's what I want to switch to. LPG is getting too expensive.

I also want to swap out the gas cook top for induction. I only got lpg in the first place because the cook of the family insisted but now he's had a chance to try out induction he's willing to swap.

andysh

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#3161797 21-Nov-2023 00:18

gzt: What did the whole setup end up costing? if you don't mind me asking. Related, is there a govt energy subsidy thing on h/w heatpumps?

I'll let you know once its all done, but there is a price on that website.

Referrals:

Tesla: https://ts.la/andrew897313

Sharesies: https://sharesies.com/r/XRGS77

mattwnz

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#3161799 21-Nov-2023 00:30

I find it interesting how in recent years how people have turned against gas for instant hot water heating, even as a transition energy. IMO for many homes , and most homes only have 2 or so people , it is likely a lot cheaper and energy efficient to use instant gas water heating, than using an electric hot water cylinder. There doesn't seem to be an electric equivalent in NZ. Even heat pump water heaters must store water, and thus loses a lot of that energy through the tank over time. These gas systems have probably also meant that we haven't needed to spend as much on our electricity network to increase it's capacity. There also maybe bio-gases in the future that can be used on the same system.

andysh

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#3161800 21-Nov-2023 00:32

Instant gas wasn't an (easy) option for us unfortunately. Current location to far away from the meter and gas pipes to thin. Would have either been massive gas pipe work, or plumping work.

Referrals:

Tesla: https://ts.la/andrew897313

Sharesies: https://sharesies.com/r/XRGS77

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