Posted by: @batalto

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The LLH has been removed for a while now (about 20 days) - I thought I would provide some initial feedback now the data is starting to come in. A picture tells a thousand words, so there you have it (below)

From what I can see (and measure) the removal of the LLH has a much larger impact in the colder weather than the warm. Below is a chart of average power usage (heating only) between having a LLH and not having it. Its still too early to be sure, but it looks like an outsized effect as the temps drop.

These results are for only weather compensation running 24hrs a day. There is zero set back for any of this data. Going forward I am testing some set back, so it'll be less reliable to compare. But for the moment there you have it. Was my LLH losing me heat, most certainly yes. Was it worth removing it, definitely. at 5 degrees ambient its about 6kw per day (or £2 in cost at 34p/kwh). Adding up it is probably hundreds (of £) a year at todays prices in savings.

That's encouraging.  To save me copying the numbers, is the energy delivered about the same before and after? The consumption is lower and the COP looks higher.     

@kev-m I haven't run the numbers, I'll have to do it later. Anecdotally I'll say the house is much much warmer than it was.

@kev-m I just pulled the numbers and the heat delivered is broadly the same (a few kw + or - here or other). To be honest it makes sense as that's the power needed to maintain 21 degrees. It wouldn't change unless I raised the target temps. If it was more efficient it would take less power, which it is doing.

@batalto 

so with the LLH,  the ASHP is using more energy but delivering the same.  Is this because energy is being emitted from the LLH like a radiator or something else?  

@kev-m at a basic level, yes. A LLH is more or less a radiator. The issue is it's placement where it allows the flow from the HP and the flow back to mix. The heat pump never sees a true return temp as the hot water parasitically flows back. Because of this you need a hotter leaving temp to ensure enough heat makes it across the LLH into the house and not back to the heat pump. Examples below.

A prospective ASHP installer stated that a low loss header would reduce SCOP by 12.5%. Perhaps this is a conservative figure as they are (notionally) accountable for the performance of the system they have specified. However they deemed it an essential part of the system were I to keep the 8mm micro-bore, in order to increase the return temperature as well as decouple the CH flow rates.

I too am having an issue with a LLH but for different reasons. I have a LLH because Daikin decided I needed two 14kW units for a 250 sqm house. I think we have way too much capacity which is causing efficiency issues and short cycling. I've turned one unit off and in terms of heating it's fine with one. But...

They used a Worcester Greenstar LLH to join the two units which has multiple ports on primary and secondary. There are no electronics to join the two units, but they are set to slightly different settings on the WD curve - lead/lag supposedly!

On the primary going top to bottom as 1,2,3 & 4 we have F1, F2, R2 and R1. Even though I've turned two off for heating (use less power for same heat like this!) as it's cold (<7 degrees) its antifreeze protection spins water at about 40 l/min through the LLH. The flow on 1 when  heating is about 10 l/min. The inlet  and outlet temp. on pump 2 are the same and in-between those of pump1 even though it's not heating. I suspect the high flow is dragging the flow down and warming the return. The Delta T on 1 is only about 3 or 4 degrees. When it gets warmer I'll turn 2 off at the main switch and see what happens, but I need it for the H/W so can't be permanently off. I don't (yet) have a pipe thermometer so the readings are from the Daikin control panels.

On the secondary side we go (top to bottom) S F1, S F2, S R1 and S R2. Secondary one and secondary 2 have separate pumps on different settings.

The other odd thing is the H/W, done by pump 2 only, goes directly to the H/W tank but the return goes through the LLH between R1 and R2. When heating H/W the flow is about 25 l/min. Goodness knows what happens in the LLH when the H/w is running on 2 and CH on1!

This install was designed by Daikin and overseen by them - it's a long story and they paid for the two ASHPs as a replacement for a single Altherma 3 H HT. Good news though is that we can have heating and hot water!

In summary I think we have two issues - massive over capacity and LLH issues. If I run both ASHPs for heating COP is <2 but on 1 alone (2 off) I'm getting about 2.3 when it's cold (say 1 degree ambient) Not sure how to resolve this...

@chrislay I just took the punt I didn't need the LLH and straight piped the connection with ball valves - that way if I ever need to put it back, I can. Yours sounds a little more complex, but ultimately that's the answer. I suspect you'll have to get in a plumber with very good heat pump knowledge. Where are you based?

To get a better cop you need a lower flow temp. 

@batalto Hi. I'm based in North Yorkshire.

@chrislay I'm not sure who is that way. Maybe @heatcol?

@batalto @chrislay A low loss header is not needed in any installation. We will use a small tank (50 litres) where we will put the 2 heat pump flows in to, and the returns together (you can use the LLH for this and disconnect the returns and tee them together) Then set both units to the same weather compensation curve, remove all under floor actuators off the manifolds in common areas (lounges, dining, kitchen, hall bathrooms, toilets etc) same as turning those spaceship controllers of yours up full. If the house is too warm, turn both units down the same and vice versa. If the units go out on low flow, you may have to put a bypass in, but try not to as it will reduce performance. This will significantly improve your SCOP, I would estimate it to go up to about 4.5.