@heacol I recall a considerable amount of discussion (relating to LLH’s mainly rather than buffer tanks as such though) some while back and one of the threads is:

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/low-loss-header-is-losing-1-5c-from-flow-temperature/paged/2

There were other threads along similar lines and this is where I felt a ‘consensus’ was evident. If I am wrong, my apologies to all for leading you astray!

In my own case, I have a Daikin heat pump and I THINK that the primary pump adjusts automatically to maintain a set Delta T. Having an LLH in circuit, I have attempted to adjust the speed of the Wilo Pico pump (secondary pump) to minimise temperature difference between flow to LLH and flow out of LLH to the Wilo pump. Similarly, I have attempted a similar arrangement for the return to the LLH in and the out returning to the heat pump. I find that at times, the balance is within 0.3 degrees C but at other times, this may be as much as a degree of difference!! I think both pumps have a degree of dynamic control and that this is the reason for the apparent variation. Regards, Toodles.

@toodles I am totally against any form of system separation in a domestic environment and most commercial environments. I have installations with over 400 Kw in capacity and 9 heat pumps, all connected to a single flow and return, the separation/buffer arguments just do not stack up. Any form of separation makes things complicated and can cause significant performance losses. In my opinion, simplicity is always best.

Posted by: @heacol

↑

@toodles I am totally against any form of system separation in a domestic environment and most commercial environments. I have installations with over 400 Kw in capacity and 9 heat pumps, all connected to a single flow and return, the separation/buffer arguments just do not stack up. Any form of separation makes things complicated and can cause significant performance losses. In my opinion, simplicity is always best.

If only others took the same approach we would see far, far fewer posts on this forum (and others) complaining about poor performance, and indeed far fewer posts complaining about other problems, the origin of which it is difficult to diagnose due to the presence of system separation.  

We would probably see an increase in posts about low flow errors which otherwise are masked by the buffer.  But the underlying causes in many cases need to be fixed, so in many ways that's a good thing.

There is probably a business to be made from removing buffer tanks!

Maybe mine as well !As in Buffer remove.

New sensor in place and so to correct the flow indications between from HP to buffer /Tank there is a difference of 2.6 c. That is to say HP to tank and tank to emitters . Emitters return is 33.7 and Buffer/Tank to HP 36c

Too much or ?

Posted by: @alfapat

↑

Maybe mine as well !As in Buffer remove.

New sensor in place and so to correct the flow indications between from HP to buffer /Tank there is a difference of 2.6 c. That is to say HP to tank and tank to emitters . Emitters return is 33.7 and Buffer/Tank to HP 36c

Too much or ?

Sorry if Ihave written this somewhere , but it didnt save .

I have visited the sensors this morning and after previously turning the secondary pump down to reduce the turbulance , I have also turned down the circulation pump one notch and results are this :

 

 Flow from HP:41.4c,  flow out of LLH :35.3c , return to LLH:31.5c and return from LLH to HP: 36.0c

Still too much of a drop I guess

 

Not great, 5C = 10-15% efficiency loss (much more according to @heacol).  TBH I cant understand whats going on in the buffer, its like there is no stratification at all and you have essentially a vessel sitting there at ~36C, with both outputs therefore at this temperature.  Im beginning to wonder if its correctly plumbed but cant remember if we have already discussed this.  Is it worth posting (or reminding us of) some pictures indicating flow/return to/from HP/rads.  Also please can you remind me how the pumps either side are controlled and in particular can you get to a situation where one is on and the other off for a reasonable period of time (thus, inevitably, 'stirring' the tank)?

Here is the layout as much as I can.

Above left Ch pipes

 Above zone valves.

Above right flow from HP.
Above showing Ch pump on white pipes. 
If there is anything more specific I will take more.

no diagram!

Posted by: @jamespa

↑

no diagram!

Ha should I have , sadly not, Only the one I have drawn.

What would you like to see , and I can give you some information

Sorry I didn't spot the pictures above.

Buffer tank looks very squat (which would explain lots).  How high is it and what is the vertical distance between the ports.

Also what capacity is your heat pump and what diameter the pipes to the buffer tank.  

@jamespa Will check James

Tank Capacity is 200l Pipes are 28mm Copper , not sure if you want the size of CH pipes I can check but definitely smaller of course either 24 or 21mm . Tank vertical distance is 65cm for HP pipes  and 67 cm roughly for CH.

Thanks

Sadly with a 60cm high tank I think the chances of maintaining stratification (IE a temperature gradient from top to bottom, which is what you want) is negligible, which accounts for the almost complete mixing you observe with the temp sensors.  Whilst the tank remains you are stuck with the 5C drop across it.   I suspect that adjusting flow rates will make a marginal difference at best to this.

@jamespa Thanks , looks like I should remove it then . Question I have , if the HP pipes are 28mm and they are directly connected to the smaller CH pipes , does that not cause a problem , except if you had control of the pump speeds ?