@davidnolan22 I will continue to think about this. 

We could do with a comment from @bobtskutter on the pump arrangement  , he is good on the hydronics.  It feels like there is the potential for the 4 pumps on the emitter side to create a racetrack around the LLH which could exclude or inhibit energy from transferring across from the heat pump side. 

Furthermore since, at max output, you need a DT of 6 there is the likelihood of  quite a sizable penalty due to the mixing.  Given that you appear to have separate returns from the various emitter loops, I can see an easy way to get a handle on flow rates either side. 

I would also imagine that its impossible to keep this in balance with zones opening/closing, so treating the whole house as a single zone, which you are currently doing, may well be sensible.

Its good that it is at least almost working, and agree it shouldn't be this difficult.  The installer really needed to think about why it was sensible to have 5 separate pumps in the system and how they were going to work seamlessly together, but evidently he didnt.

Hi Gary,

Yes, I think I’m getting the hang of it and whats gone on this winter. And yes, during the cold snap previously there was not enough energy going into the floor constantly. But I’ve been told to set the flow to 45 and use the stats.

After I set the flow much lower, in the low 30s and ran it constant, it ran so much better. I think my system design temp is 36 at -3 not 45. Despite that not being the plan…..

Anyhow, the new header has not helped matters much, but I’ll get it back balanced as best I can and I think I will be able to get it to work.

And then the defrost. I’m if the secondary circuits are meant stay open due to the lower temps and not enough volume and the primary loop, is there a way to protect the system during heavy defrost conditions. I assume it’s total system volume. 

I’ve got 65L in the UFH that I know from the UFH design. I’ve got 6 big rads, so maybe another 60 to 80. The the pipes to and from things. 

maybe 175L total volume for 11.2kw systems. Is that optimal? I know paul Spence put a post about 25L per KW, which is 280L for me.  Or is this overkill?  Again, I’m told so many different things it’s hard to make heads or tails of it. 

@jamespa thanks again. It makes sense. Before the new bigger LLH, I had a 35mm piped distribution header. There was no blending there, only when I put the UFH flows too high, past I assume the 28l a min on the primary, and this was only on the rad circuit. As soon i turned down a flow on the UFH a bit, the rads went straight back to the primary temp sensor. That was kind of my guide of when to stop increasing flows in the UFH

Posted by: @davidnolan22

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And then the defrost. I’m if the secondary circuits are meant stay open due to the lower temps and not enough volume and the primary loop, is there a way to protect the system during heavy defrost conditions. I assume it’s total system volume. 

I’ve got 65L in the UFH that I know from the UFH design. I’ve got 6 big rads, so maybe another 60 to 80. The the pipes to and from things. 

maybe 175L total volume for 11.2kw systems. Is that optimal? I know paul Spence put a post about 25L per KW, which is 280L for me.  Or is this overkill?  Again, I’m told so many different things it’s hard to make heads or tails of it. 

The spec for your model calls for a total of 39l for 'cooler climates'.  I think we are in the 'warmer climate' region according to the relevant EU directive, but since we are also very damp I would be wanting 39l plus.  There is absolutely no harm in 'additional' volume; 175l should be fine. 

I dont know about 25l/kW, this might be a figure to reduce cycling but you haven't yet posted a problem with cycling and, since your heat pump appears to be well matched size wise to your house you most likely wont!

There should be no need to 'protect' the system, if it needs so much heat for defrost that it is going to materially cool the house then something radical needs to be done (like a very large volumiser which can somehow be separated) but again no evidence you need this nor have I heard of a case where it is needed.  The amount of energy required for defrost is pretty predictable so it shouldn't be a problem.

For now Id balance the system as best you can, adjust the WC curve if needed to get the house at the right temperature with everything running constantly and all the stats set above the desired temperature, and see how it goes.  We may not get another deep frost until next season, so you may not know for a while!  

Posted by: @davidnolan22

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 Again, I’m told so many different things it’s hard to make heads or tails of it. 

Heating systems, not just those with heat pumps, can be quite complex, because there are so many variations and variables.  That said, the underlying physics, and it is physics, is actually very simple, so a little genuine understanding goes a long way.  However only a proportion of 'professionals' actually seem to understand it, many go 'by experience' and some spout pure BS.  That's just how it is.  The simple test is to ask for an explanation and, if one isn't forthcoming, or it doesn't make sense, or its 'because we have been doing it like that for 40 years, then doubt the advice!

Not content with that problem, we make heating systems more complex by trying to impose control that, in reality, we dont have because of the thermal mass of the house and the fact that rooms within the house aren't thermally separated to any material extent.  This is counter-productive to cost in many, perhaps most, cases with a heat pump (and even in at least some cases with a boiler).  However the manufacturers of 'smart' controls would go out of business if they told us that!

Time and time again we find on this forum that KISS applies (Keep it simple, stupid).  Most houses, including, Im fairly certain, yours, would be best (cheapest and most comfortable) run on a single zone (with perhaps TRVs on a small minority of emitters, eg in some bedrooms), 24*7 on pure weather compensation and without system separation.  Unfortunately only some installers currently do this!

@jamespa I think many installers feel that they have not completed an installation if they haven’t fitted an LLH, TRV’s on every radiator (without leaving instructions to leave them wide open as they are only really to tidy up the look of the emitter in most rooms!😉) a secondary pump plus an on/off thermostat to knacker the heat pump when it has a hysteresis of 0.1 degree C and has no pity at all on that heat pump’s life; extra satisfaction may be gained by these same installers if they can include a third pump and a buffer tank too! 😉 Ruefully, Toodles.