The quick answer to your question is that the Daikin's own circulation pump probably won't be powerful enough. So in instances like this, if the installer has calculated that it's insufficient, they can repipe your 4-port buffer into a volumiser and then utilise your Grundfos post volumiser to help flow. 

Iam also looking at this route from 4 pot to maybe a volumiser thaks to Jamespa. Can I ask how does the volumiser help ,or not, if you are putting the return to the top of the old buffer then back to the HP at the bottom of the buffer. Is it not simpler to straight connect through returns.

@editor

I understand how important feedback to a question can be, so here is mine.

With no disrespect intended to Mars, I decided to chance it and go ahead with the removal of the 20ltr. 4 port buffer and secondary water circulator to further simplify my system, retaining the redundant components with the proviso that they could be re-instated if needed, .

By using only the Daikin's integral circulator the flow rates appear to be sufficient with no increase in cycling frequency. 

I'm very pleased with the results so far, with a COP (using Daikin's on-board energy meter figures!!) of just above 400%- with a happy wife to boot!

@ubert767, I'm really pleased to hear that your pump is strong enough. That’ll definitely be interesting reading for those with Daikins. I’ve been in private contact with a homeowner who’s had issues with Daikin’s defrost cycling and distribution pumps, so it’s great to hear yours is working well.

For the benefit of others, did you remove or bypass the buffer tank yourself, or did you have someone do it for you?

This is a great example for anyone still doubting whether buffer tanks actually improve system efficiency!

And, just to clarify, my doubts about the Daikin pump weren’t unfounded – most installers I’ve spoken to say that because buffer tanks are so commonly used, many manufacturers cut corners on the power of the internal pumps, leaving them with insufficient head.

@editor

Hello  Mars,

  I had the original installers  remove the buffer and pump, purely to maintain any warranties that I enjoyed.

@ubert767 

the removal of the 20ltr. 4 port buffer

out of interest,is that 20l or 200l ?

 I am planning bypassing my buffer , still waiting for someone to  do it ! 

@alfapat 

That is a 20 litre buffer

@ubert767 Thanks , no wonder I get too much of a temp drop , mine is 200L , too much mixing .

Posted by: @alfapat

↑

@ubert767 Thanks , no wonder I get too much of a temp drop , mine is 200L , too much mixing .

Ours is 100 litre and it's been piped for maximum distortion/mixing with an X shape between the pipes. Ridiculous. We're planning to get ours repiped in late spring.

@alfapat 

In order to answer my doubts about my buffer vessel I built a cheapish temperature logging system from a Raspberry Pi and five DS18B20 temperature sensors(one sensor on each buffer port and one measuring O.A.T.) This allowed me to see the differentials across the flow and return ports, to check the distortion in the buffer vessel and record the system cycling intervals.

Posted by: @alfapat

↑

Iam also looking at this route from 4 pot to maybe a volumiser thaks to Jamespa. Can I ask how does the volumiser help ,or not, if you are putting the return to the top of the old buffer then back to the HP at the bottom of the buffer. Is it not simpler to straight connect through returns.

It provides extra system volume which is useful for defrost but may well not be necessary.  Have you any idea what volume of water you have in your secondary circuit.

One of the ports at top and the other at bottom to ensure it's actually both heated by the water passing through and engaged in the flow.  Otherwise you could end up with most of the water in the volumiser just being 'bypassed'