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Double heat pump for DHW?

Transparent · 2025-01-01T19:41:33Z

The Christmas break has provided the opportunity to talk into the evenings with other family members, two of whom have engineering degrees. The one most likely to buy a heat-pump in the near future asked "What arrangement should we have in order to supply five showers in a row at the start of the day?" We tossed around the problem for a while, and considered the options: size of Domestic Hot Water cylinder (too large and it can't complete an anti-legionella cycle with a 3kW immersion heater) over-sized ASHP with large-bore pipes (but then needs a volumiser, and is less efficient in warmer weather) install a storage battery to operate a (second?) immersion heater, and thus supplement output from the heat-pump (but how to prevent the HP shutting down?) There was one option we couldn't resolve between us...... in part because the device we'd require doesn't actually exist yet! Could we use the tepid water in the volumiser, pass it through a water-to-water heat pump, and send the output to heat the top half of the DHW cylinder via a second coil? I've placed Heat Pump 2 in the diagram as described in the text above. Feel free to re-plumb the pipework, remove the volumiser completely or do whatever else you wish to make the physics work. Doodle on my diagram if you want, and re-post it.I can tidy up whatever you suggest and create a posh version as required.

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Domestic Hot Water & Cylinders

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IRMartini

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28/01/2025 2:48 pm

How about this?

“Anything worth doing, is worth doing right.”

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Transparent

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Topic starter 28/01/2025 2:55 pm

Posted by: @ianmk13

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I would imagine that that the availability of 4-phase ASHPs (compared to their single-phase siblings) may be a relevant consideration

It certainly would @ianmk13
There would appear to be an excess of phases to the tune of +1 🤗

Contrary to what we in UK might imagine, 3-phase heat pumps are plentiful.
The majority of domestic heat pumps being installed in mainland Europe are now three-phase.

Here, we can expect an installer to be specifying a 3-phase ASHP for 11kW and above.

But mainstream manufacturers like Samsung will happily supply a 3-phase 8kW unit if an installer chooses one (Model No. AE080RXYDGGEU)

As for those with storage batteries, there's no reason why an existing battery couldn't have the inverter(s) changed to provide 3-phase.

Although dedicated 3-phase inverters are available,
most 1ph inverters that can operate 'in parallel' are quite capable of being divided across the phases.

My existing Growatt SPF5000ES units offer that functionality,
as do the Sunsynk 5kW ECCO inverters which I will shortly be installing.

Inverters in parallel all use the same common battery, whether they are connected to single or three-phase mains input.

This post was modified 8 months ago 2 times by Transparent

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IanMK13

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28/01/2025 6:51 pm

Posted by: @transparent

↑

Posted by: @ianmk13

↑

I would imagine that that the availability of 4-phase ASHPs (compared to their single-phase siblings) may be a relevant consideration

It certainly would @ianmk13
There would appear to be an excess of phases to the tune of +1 🤗

Sorry. Fat fingers 🤣

Posted by: @transparent

↑

As for those with storage batteries, there's no reason why an existing battery couldn't have the inverter(s) changed to provide 3-phase

Not so with my GivEnergy All-In-One, unfortunately ☹️

This post was modified 8 months ago by IanMK13

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Transparent

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Topic starter 28/01/2025 7:53 pm

Posted by: @ianmk13

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Not so with my GivEnergy All-In-One

That's a tricky issue, and one which I expect to see being raised many times this year (2025) as consumers begin to realise what GivEnergy's strategy means for them.
Have a look at what I posted as a synopsis of that strategy here on another topic.

It's a well respected company, and they've taken a hard-nosed decision to concentrate on the new iteration of their All-in-One system.

They will gain a lot of customers in the UK who 'just want a storage battery' and aren't going to spend much time researching the subject.
Most of them will be very satisfied with what they've had installed, and remain largely unaware of its constraints.

Save energy... recycle electrons!

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IanMK13

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29/01/2025 5:57 pm

Posted by: @transparent

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It's a well respected company, and they've taken a hard-nosed decision to concentrate on the new iteration of their All-in-One system.

Yes, that's another ball-ache coming so soon after my purchase of what will quickly become an obsolete system. In order to expand the storage capacity I will either have to add a further All-In-One, which includes another inverter (which will require DNO approval) or and a totally separate 'conventional' battery and inverter system (again, requiring DNO approval). That said, I will probably need additional inverter capacity for resiliance in any event once I install a heat pump - my present 6kW will be insufficient for 'whole home backup'.

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