@editor the size matches the heat loss calc they did. But, they assumed there was some insulation in one floor where there was none. They installed the UFH and told me not to bother insulating it so how that happened is beyond me. That was a 1Kw error.  But, there should be enough fat in calculation to still be ok. But it’s not

Posted by: @davidnolan22

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@editor the size matches the heat loss calc they did. But, they assumed there was some insulation in one floor where there was none. They installed the UFH and told me not to bother insulating it so how that happened is beyond me. That was a 1Kw error.  But, there should be enough fat in calculation to still be ok. But it’s not

@davidnolan22

Perhaps you could post some more info about your setup, house and system and WC parameters - you never know it may be possible to diagnose.

Please confirm that are running your heat pump 24*7, the weather compensation curve has been adjusted, and all Thermostats/TRVs are set to max so they have no effect and if there is a mixer on the UFH that has also been set to max?

@jamespa 

I've done this last winter somewhere. I got some good advice then. 

Nub of it is, I think, poor design between UFH and rads. UFH gets most of the flow and power, rads has to make do with slightly bended flow (small LLH) temp that can only satisfy the UFH.  But, and its a big but, its not like the UFH is overheating. it struggles (and does not) get to design temp at 0 degrees, the only way I can get the flow temp up to give a flow the rads might actually produce heat is to cut the UFH flow so much, then they struggle/can't keep their area warm.   They have been out loads, made 2 attempts to improve it, but its made no difference at all.  I think, and have always though, the heat loss for whatever reason is wrong. the house needs a bigger heat pump. Its a 260m2 retro fit, that I did a reasonable job insulating, but its by no means amazing. 11.2kw heat pump.  120m2 of 150m2 of the UFH is uninsulated concrete slab that they said was fine as it will be factored in.

But, the next mitshi is a 14kw, that fails the sound assessment.  They initially messed up the first design and positioned a heat pump position that failed the sound assessment so we had a last minute change of position that means we have a stupid and hard to get to primary pipe run. That pipe run with 2 pumps on can't get the flow rate for a bigger heat pump.  the electrics are not in place for a bigger heat pump. The would need to rip apart my brand new house that we've poured our life saving and mental health into because the installers I used could not do their job properly. 

NAPIT I've not used yet, but I imagine will be a waste of time.

MCS I imagine too be be a waste of 5 years of my life. 

I've got a beautiful house in a lovely area that I can't heat up to what I was promised on an averagely cold day in Sheffield. If I ever had to sell this house, how would I sell it: "here is the heating system, good luck, it works great March to mid November". 

The mains gas has been taken out from my house back to the street now, I can't go back to a heating system that although has faults: worked, i'm no eco warrior, i did not do this to save any planets. I'd love to have a nice 20-25Kw system boiler in my house so I never had to look at the weather forecast 5 days in advice and get stressed about.  Humid and cold days..... that's when I actually start to lose sleep. 

rant over. 

Posted by: @davidnolan22

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Nub of it is, I think, poor design between UFH and rads....   120m2 of 150m2 of the UFH is uninsulated concrete slab

The last bit of that is bad.  Thats just badly (well appallingly) designed UFH and most likely the fundamental problem here - half your energy is going into heating the ground!  This of course would also be true with a larger ASHP or boiler!

Posted by: @davidnolan22

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NAPIT I've not used yet, but I imagine will be a waste of time.

MCS I imagine too be be a waste of 5 years of my life. 

Judging by what we hear here, yes to both.

Posted by: @davidnolan22

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I've got a beautiful house in a lovely area that I can't heat up to what I was promised on an averagely cold day in Sheffield.

You are very lucky, I wish I lived in or near Sheffield, sadly I'm in the South East which is convenient for London and has little else going for it.

Posted by: @davidnolan22

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(small LLH) 

Do you know what the temp drop is across the LLH (between flow and flow).  Removing it may well help.

What about adding a 3kW backup electric heater.  You would only need to use it for a small number of days per year.  Maybe you could get away with using it only during cheap tarrif periods (in which case Id be tempted to get a 6kW one - so you can max out).

Another trick is to heat DHW on the immersion in coldest weather so the heating doesnt have to go off for a couple of hours.

Any scope for a bit more insulation - draught exclusioin etc?

It sounds like its marginal so maybe with some tweaking you could get it to the point where it works except on very extreme days

You may already have thought of these however.

@jamespa 

The LLH is above, which typical max flow and return the system gets too. 

Taking it out sounds like a plan, but a) I'm no plumber and b) the installer has to think its the right thing to do and want to take it out. 

Yeah, the back up heater..... thats a funny one. As may sound like the simplest solution.... but, I didn't sign up for that. I don't really want a 3Kw 1:1 heater.  and you say the coldest days, yesterday in Sheffield was 0.6 ave temp, and I would have needed the heater for much of the day. Is that really that cold?? I don't think so. They have already installed me 6 circulation pumps that I have to pay for, I'm not keen to add 60kw to the daily heating bill for any day that is close to zero. 

There is no more insulation I can add.  I have been so anal about draughts.  had the window company come back so many times to readjust just anything if I felt I could feel a draught to check, I've been round with silicone gun, you name it I've done it.  I changed all the bathroom vents to expensive ones that stopped back draughts that cost me £500.  After seeing what I went through the builder and Plummers said there reluctant  working on another house with a heat pump. They warned me and I should have listened. 

Posted by: @davidnolan22

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The LLH is above, which typical max flow and return the system gets too. 

Taking it out sounds like a plan, but a) I'm no plumber and b) the installer has to think its the right thing to do and want to take it out. 

Yeah, the back up heater..... thats a funny one. As may sound like the simplest solution.... but, I didn't sign up for that. I don't really want a 3Kw 1:1 heater.  and you say the coldest days, yesterday in Sheffield was 0.6 ave temp, and I would have needed the heater for much of the day. Is that really that cold?? I don't think so. They have already installed me 6 circulation pumps that I have to pay for, I'm not keen to add 60kw to the daily heating bill for any day that is close to zero. 

OK so feed to rads colder than feed to UFH and colder than flow temp from heat pump.  Not good, losing efficiency and thus oomph to building.  Taking it out will make a small difference, but maybe not enough to cover the problem.

Your ASHP isnt the problem so far as I can see, the problem is the UFH.  Without insulation it was always going to be an expensive madness to push probably 4kW straight into the ground, whatever heating you put on the back end.  If your installer was responsible for this then I would tell him to fix it, which involves digging it all up and doing the job properly (or something else, eg compensating you for the stupid build or at least putting in a backup heater FOC.

I presume that turning up the flow temp doesnt work - because the heat pump is already running at max power 24x7.

Posted by: @davidnolan22

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.  and you say the coldest days, yesterday in Sheffield was 0.6 ave temp, and I would have needed the heater for much of the day. Is that really that cold?? I don't think so.

I just checked degreedays for East Midlands.  There were only 11 periods of 24hrs in the last 386days when the average temperature was <1C.  Not sure how Sheffield compares to the East Midlands weather station, but I really wouldn't rule out a backup run eg overnight on cheap rate to charge the slab.

@jamespa 

we did have this discussion during the build. I was quoted 10-15k to dig up all the floors and insulate them, and some were in an old cottage and couldn't really be done.  I had the designer from Ambient come to my house and say not to worry that actually laying on a concrete slap on the ground is better than people imagine and only 6% loss downwards.  I watched a video from Urban Plummer which said something similar. 

Digging the floors up now is never going to happen.

I can't turn up the flow, its maxed out at 35-36. I can only get flow up but shutting off parts of the UFH. I might play with this some more. run the floors patchy but hotter. This wont create energy though. Just allow some to get to the rads. 

Lets see what happens after their next visit. It apparently just needs setting up better.

Posted by: @davidnolan22

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Digging the floors up now is never going to happen.

fair enough!

Posted by: @davidnolan22

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After seeing what I went through the builder and Plummers said there reluctant  working on another house with a heat pump.

Better advice IMHO would be don't work on a house with uninsulated UFH, or if you do fit radiators instead!

Posted by: @davidnolan22

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Lets see what happens after their next visit. It apparently just needs setting up better.

Well thats an admission by the installer then that he is responsible for getting it working!  Hold onto that.

I have heard those arguments about UFH heat loss but cant see how the physics supports them (and nobody has yet explained how it would).  Perhaps if the UFH pipes are close to the surface and any surface covering is highly conductive then yes.  Heat will escape the easiest way it can, and if you put anything faintly insulating on top then the heat is going down not up.  Convection doesn't exist in solids so 'heat rises' is not true in this case, it will spread any way it can.

I take it you have solid flooring not carpet, directly bonded to the slab, not sitting on top of an insulating layer.

@jamespa

yeah, LVT direct to it, very thin profile. maybe 10-15mm on top of pipe 

@briansprankle, please share more specifics about your issue(s) to see if we can point you in the right direction.

Posted by: @davidnolan22

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yeah, LVT direct to it, very thin profile. maybe 10-15mm on top of pipe 

Thats good at least.  Is your soil locally damp or dry?  Im presuming the floor is something like 100mm slab on hardcore on soil with a DPC somewhere.  If the soil is damp it will be damp (and therefore even more heat conductive) up to the DPC

Thank you for your input. We are now in dialog with Global, hopefully things can be sorted? We'll keep you updated.