Posted by: @cathoderay

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Posted by: @derek-m

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I think that you will find that many of the ASHP's actually contain a speed controlled water pump within the unit, which varies the flow rate to control the DeltaT at the heat pump.

I get the impression this is what is supposed to happen, but looking at the Midea Operational Parameters, the flow rate seems to favour around 1.4 m^3/h, it's almost always around that value when I have a look. It doesn't seem to vary very much. If I manage to get the modbus monitoring to work, we'll get a much more detailed picture, may even be able to see what causes to change if/when it does.  

Have a look at page 80 of the manual below, since it would appear that there is a fixed speed pump option.

@iancalderbank Hi Ian I would not follow my route unless you also want to also add a PWM to 0-10v converter since I was not aware of the PWM option during install [because the simplified docs from a number of wholesalers did not mention it] and I thus did not fit a PWM capable pump (I am now much better informed on this).  If you do want to go down that  [CIM500] route then there seem to be many on ebay.  I bought mine from a someone selling 20 or so as they had been incorrectly specified in a job all installed and then removed to be replaced with the correct module.  They are £75 right now.

[edit] I will point out that my heat pump [Samsung gen6] does not have a pump in it, hence this approach, as Derek pointed out, if your heat pump has an integrated pump then it is already part of the "equation".

William

@derek-m - if I read the table on that page correctly, the default setting for S2 positions 3 and 3 is 11 ie on/on which equals variable speed Wilo (pump brand) with 9.0m head (quite punchy, more than enough to make your ears pop). The m^3/h seen in the wired controller does vary, I think I have seen it as low as around 1m^3/h, but only very rarely, most of the time it is around the 1.4 mark. I think it can vary, but isn't being varied very much.

Posted by: @cathoderay

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@derek-m - if I read the table on that page correctly, the default setting for S2 positions 3 and 3 is 11 ie on/on which equals variable speed Wilo (pump brand) with 9.0m head (quite punchy, more than enough to make your ears pop). The m^3/h seen in the wired controller does vary, I think I have seen it as low as around 1m^3/h, but only very rarely, most of the time it is around the 1.4 mark. I think it can vary, but isn't being varied very much.

     

To know for certain which water pump is installed and the correct settings for DIP Switch S2, you would need to look inside the heat pump unit.

It may be possible to carry out a quick check by requesting more heat energy, either by increasing the LWT setting in fixed LWT mode, or increasing the offset in weather compensation mode. Dependent upon how the heat pump is programmed to respond it should increase the flow rate for a period of time.

If this method does change the flow rate then carry out the reverse to see if the flow rate falls.

To transfer more heat energy whilst maintaining the specified DeltaT requires a greater flow rate.

Posted by: @derek-m

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It may be possible to carry out a quick check by requesting more heat energy, either by increasing the LWT setting in fixed LWT mode, or increasing the offset in weather compensation mode. Dependent upon how the heat pump is programmed to respond it should increase the flow rate for a period of time.

I've just tried temporarily increasing the warm end of the weather comp curve by ten degrees. Flow rate effectively remained unchanged, at 1.41 to 1.42m^3/h. It was also 1.4 something just before I did the test, when the compressor wasn't running. I looks like it's a fixed flow rate, but as I said before, I do recall seeing it at a lower figure once or twice. Next time I open the outside unit, I'll have a look at those dip switches, also what the actual pump in there is.

I ordered a Samsung gen6 8kw ashp and a pre-plumbed cylinder online. The seller included "Freedom heat pumps" installer instructions which had incomplete instructions and didn't quite match with the plumbing arrangement of the pre plumbed cylinder. This resulted in six months of immersion heated water!

The instructions also led to the burning out of the pump relay on the samsung circuit board as it omitted to mention the need for an auxilliary relay between the board and the pump (Samsung book mentions this though) so I ended up hacking in a SSR direct to the circuit board in the middle of winter, goodbye warranty 🙂

The pre-plumbed cylinder has a plate exchanger separating the heat pump from the pre-plumbed cylinder. The exchanger was mounted on its side which doesn't help it to be air free and the direction of flows were the same, resulting in a poorer heat exchange (I re-piped and re-orientated it). Other than saving a wee bit of antifreeze I don't really see much point in the plate exchanger at all.

The set up instructions used external room thermostats and excessive water temperatures for my house.

The Samsung manual assumes a PWM pump and the pre-plumbed cylinder came with a normal pump (one on each side of the plate exchanger). I am currently agonising over whether I should get a PWM pump and whether to ditch the plate exchanger alltogether. 

D

@derekdeleon

Posted by: @derekdeleon

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I am currently agonising over whether I should get a PWM pump and whether to ditch the plate exchanger alltogether. 

I have the 16kW Samsung Gen6.  As I was going to reuse my vented indirect solar thermal store, so I put in a heat exchanger for the hot water, with some modifications simerlar to the mixergy layout.  (required a wireless camera in the cylinder - which was challenging given the cylinder is  Faraday cage)

To cut a long story short, seems to be working ok, at least on heating the cylinder - an additional coil between the cylinder and the shower, means I need a couple degrees hotter than with a direct cylinder .  A cylinder recharge cycle looks as below. (30 mins, approx)

@william1066

That's an interesting way to do the hot water, sounds like you like a challenge 🙂 I just went with an unvented 250l cylinder with a 3m2 coil. Reckon I'm going to take out the plate exchanger as it isn't big enough to do the duty anyway. I looked it up on the manufacturers website and they even make it clear that it probably won't be good enough for heat pumps! Wrongly specced by the supplier 🙁

https://nordictec-store.com/gb/62-ba-16-serie-0016mplate-1-thread     Mine is the 24 plate version.

I'm not really sure where to add this in the forums, but this seems like a suitable thread. My latest post about our installation this time last year is about after sales support - and in the main I've been very happy. The post, and others, is available here: https://world.hey.com/alastair.graham

Hope that it's of use to some of you thinking about getting more home energy tech installed.

@william1066 ever since installing a Mixergy, i went home and with bits i had laying around converted my own cylinder to a heat pump plate loaded. which it has now been for nearly 3 years.

@derekdeleon It looks like they got the connections right, but you probably don't have enough surface area.

The BA-16-24 has a Heat Exchange Area: 0.384m² - which seems a bit small - as you found out.

Mine is the Ba-23-70, which seems to do the job (Heat Exchange Area - 1.610 m² about 4x the BA-16-24). [not comparable with finned tube surface area, of course - if anyone has a ratio to calculate equivalent plate vs finned tube surface area, please share as I am interested in that figure] 

At the time I chose this plate heat exchanger, I basically "guessed" the size by looking at pictures of the mixergy plate heat exchanger, counting the plates and estimating approx size.  Mine seems to work pretty well.

At the moment I can get 12kW of heat transfer rate through this setup to the cylinder.

I would be very interested in hearing more about your conversations with the trade about ASHP installations. We have had the original installers back at least 6 times and the Daikin engineers out 3 times since installation last October.  I am beginning to wonder if the unit (Altherma 3H HT)  is still faulty. The most recent engineer (from Daikin) told us that he had replaced the broken booster heaters and checked that the software was up to date. He did wonder if we had a big enough unit for the size of house. The unit can still only manage to heat the circulating water to about 35-40C when the spec claims that 65C can be achieved.