Posted by: @andy1618

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My questions are:

1. • Should the volumizer be on the flow side?
2. • Should there be a pressure relief valve as a bypass, just in case?
3. • Should the circulation pumps on the main loops be removed?
4. • Should the two main loops be modified into one (I’m never going to use high-temperature heating)?
5. • Can I keep the two loops but remove the pumps?
6. o If yes: should I have some way to control how much flow goes to each loop?
7. • What else should I pay attention to?

Thank you in advance for all the help!

Here are my comments, others may have something to add or even dispute what Im suggesting.

1 - Yes ideally, but it doesnt matter that much so not something to argue over

2 - Assuming you keep one circuit always open (which you should), then no.  But it wont do any harm assuming its set high enough so again not something to argue over.

3 - Yes (or bypassed) assuming that the primary pump can do the job alone. Do you know why the heat pump side is much lower than on the house side?

4 - I dont see any harm in their being in parallel, its no different to an upstairs and a downstairs radiator loop, but you may need to 'balance' the flow between them

5 - Yes but see (4)

6 - Yes, so you can balance them appropriately

7 - With a few valves it is possible to do the plumbing so that the change is reversible if that is attractive to you.  Also note any warranty implication

Posted by: @jamespa

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3 - Yes (or bypassed) assuming that the primary pump can do the job alone. Do you know why the heat pump side is much lower than on the house side?

I'm not sure about the Heat Pump side, but very often it settles around 0.8 m3/h and on the emitters branches I've set it to get around 4-5°C delta and have all the parts of the floor warm.

Regarding the warranty implications. Do you think that not using 4-port buffer will void the warranty? Is that a think that is being practiced? I will check with the installator.

Posted by: @andy1618

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Regarding the warranty implications. Do you think that not using 4-port buffer will void the warranty? Is that a think that is being practiced? I will check with the installator.

The requirement for a buffer tank to maintain a manufacturer's warranty is often used as a scaremongering tactic by installers. The best course of action is to contact the manufacturer directly for clarification on their specific technical requirements... I'd initially sidestep the installer here. 

I will note that Midea can be one of the least responsive major manufacturers in the UK to deal with, so persistence may be needed.

For a deeper dive into this common issue, you can read more here:  https://renewableheatinghub.co.uk/buffer-tanks-heat-pump-warranty/

@andy1618 see the very sage advice from @editor above.  I took would bypass the installer initially and/or check the installation manual.

Thank you so much for your help. After New Years I'll get to it.

One thing that crossed my mind: I can see very often that the HP circulation pump is starting at 2.5m³/h (after turning on or after defrosting) and then it settles down at around 0.8m³/h. Is it possible that the HP circurlation pump is going to be delivering too low flow for my system?

@andy1618 If this is of any interest / help, my Daikin EDLA08 8 kW monobloc will start a run with a flow rate of ~28 lpm. Within a minute or two, this reduces to ~14 lpm and then, after a few more minutes, it further drops to ~7 lpm. Regards, Toodles.

@toodles I'm not concerned that the behaviour is not normal. I'm concerned if pushing 0.8m³/h is going to be sufficient for 10 UFH loops + 5 radiators in open loop setup without secondaey pumps.