Revisiting hot water heat pumps

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#2919351 27-May-2022 09:40

We heat the hot water 4am - 7am, which includes our 5am - 6am free hour and off-peak half price power on Electric Kiwi MoveMaster. Some days we end up using a fair bit of hot water during the day, like if we get out of bed after 7am on the weekends, so especially in winter we have a top-up heating mid to late afternoon, which is shoulder power rates for EK. Each day there is at least one bath and 2-4 showers. We don't run out of hot water.

AklBen

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#2919362 27-May-2022 10:25

timmmay:

We heat the hot water 4am - 7am, which includes our 5am - 6am free hour and off-peak half price power on Electric Kiwi MoveMaster. Some days we end up using a fair bit of hot water during the day, like if we get out of bed after 7am on the weekends, so especially in winter we have a top-up heating mid to late afternoon, which is shoulder power rates for EK. Each day there is at least one bath and 2-4 showers. We don't run out of hot water.

Sounds excellent.

I am sure you've figured it out, but how much heating is typically required between 4-7am? I'm curious around the savings vs. just having the HW cylinder do it's own thing all day...

timmmay

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#2919368 27-May-2022 10:44

AklBen:

Sounds excellent.

I am sure you've figured it out, but how much heating is typically required between 4-7am? I'm curious around the savings vs. just having the HW cylinder do it's own thing all day...

I don't know for sure because in our free hour we turn on hot water heating, two heat pumps, dishwasher, clothes drier if required, office fan heating, etc. I can show you summer and winter power usage, but in summer the water heating was configured I think from 5am - 9am rather than 4am - 7am from memory. The change was because once we moved to MoveMaster as well as free hour 5-6am there's also half price power 11pm - 7am.

Assuming we need about 3 hours of water heating, and we had the free hour previously, we reduce our water heating cost by 50% over just having the free hour, and by maybe 75% over a standard power plan.

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#2919372 27-May-2022 10:57

i would use perhaps 1 to 1.5h of water heating per day on a typical day and if the wife or kids decide to have a bath its another 1-1.5h. So thats 3-4.5kw of power and 3-4.5kw extra on those bath days.

Peak time thats 30c/kwh (values are guesstimates), so $.9 to $1.35 to heat, off peak its 11c/kwh, so $.33 to $.495 to heat. so a typical day it could be $.85 different and on a bath day, $1.7. It can make a difference but you need to install a timer and at $300 odd its got a bit of a payback, especially if you are on cheaper power.

AklBen

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#2919373 27-May-2022 10:59

^ Right so you truly do need to have off-peak or free power and/or alternative source of energy to make that work out...

timmmay

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#2919375 27-May-2022 11:02

Yes, there's not much point if your power is a constant price. I had my timer installed something like 2016, it cost about $400 from memory. I reckon I've probably saved at least $1-$2 per day since then, so I'm $1400 or more up.

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#2919387 27-May-2022 11:34

AklBen:

^ Right so you truly do need to have off-peak or free power and/or alternative source of energy to make that work out...

yes, im on fixed 19c/kwh so it doesn't really help me at all.

dahc

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#2919471 27-May-2022 15:39

Any concerns about turning off hot water cylinders and creating breeding grounds for legionella bacteria or is that not really a risk?

Delphinus

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#2919472 27-May-2022 15:43

My HWC is only on for an hour a day (Free hour). Supplemented by solar in summer and wetback in winter.

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#2919475 27-May-2022 16:02

dahc:
Any concerns about turning off hot water cylinders and creating breeding grounds for legionella bacteria or is that not really a risk?

This was discussed in a thread a few years ago. From memory, so long as the cylinder is fully heated at least once every day it's fine.

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#2919482 27-May-2022 16:11

timmmay:
dahc:

Any concerns about turning off hot water cylinders and creating breeding grounds for legionella bacteria or is that not really a risk?

This was discussed in a thread a few years ago. From memory, so long as the cylinder is fully heated at least once every day it's fine.

60 degrees once per day

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#2919486 27-May-2022 16:39

Volt:

I've installed a Reclaim Energy Co2 HWHP, with a 300L Rheem internal tank (recommended alternative to their own tank) in my new build.

Why didn't you go with their own tank? Can you also comment on noise and how often the unit kicks in?

I'm considering getting one of these units too. Intent is to use the PV preset so it only runs during peak generation.

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#2919624 27-May-2022 23:58

dahc:

Any concerns about turning off hot water cylinders and creating breeding grounds for legionella bacteria or is that not really a risk?

As long as it gets above 60 degrees regularly its fine. In our case its getting up there once a day.

I have turned the temperature up a few degrees to offset the loss however have noticed around 9.30pm some nights an annoying dripping sound on the roof due to the water expansion as it heats up.

We find by 6pm the following day its still really warm.

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#2920099 29-May-2022 20:02

Newtown:

Volt:

I've installed a Reclaim Energy Co2 HWHP, with a 300L Rheem internal tank (recommended alternative to their own tank) in my new build.

Why didn't you go with their own tank? Can you also comment on noise and how often the unit kicks in?

I'm considering getting one of these units too. Intent is to use the PV preset so it only runs during peak generation.

I didn't use their tank because it is wider than my cupboard.

Unit is about as loud as similarly sized air conditioner.

It runs about twice a day, usually for 30-90 minutes depending on demand. Heating starts at 39c and stops at 59c (default settings), hot water is delivered to the tank at 63c.

I don't have PV or an off peak tariff, so it runs when it wants to.

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#2920147 29-May-2022 20:36

I have been looking into this exact topic over the past month as part of a rewire (Phase 1 is done, phase 2 is new hot water, fast EV charger, etc.). Currently I am looking at the EcoSpring ES190, which will replace a 130l (VERY small!!!) old low pressure system which needs replacing / upgraded. These are $3200 at Plumbing World Plumbing World | Hot Water Products - EcoSpring ES190 190L Hot Water Heat Pump. I am on the Move Master plan with EK, in Auckland, so see this as the best option.

There is also the Midea equivalent (I cannot work out if it's from the same factory, or just a rebadged Ecospring. Slightly cheaper at $2800 Buy MIDEA Heat Pump Water Heater 170L (tradedepot.co.nz). The Midea unit is reviewed here (from an AU user) - notes the low power consumption. OFF GRID Heat Pump Hot Water System update - YouTube

There was also a split unit from Daiken but is was $7500 and I couldn't see what benefit that offers. Hot Water Heat Pump Price Guide (hpac.co.nz)

I also read somewhere that with a small house its most efficient to heat water with a Heat Pump, then continuous gas. I am also after an outdoor unit to gain inside space.

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