@jamespa 

Thanks again for all that. It makes sense. I do want to get as much data as possible but also concerned that at the end of next week they'll be finishing the entire job (solar panels) and wanting it signed off. I also would rather tackle it before we've had the pump for too long but I can also see that we need to give it some time to gather evidence.

I wonder if Mitsubishi support would offer an opinion on the graphs? If they were willing to state that it looks oversized, it might be ammunition.

We did tell the installers about the upgrades to the EPC but sadly, as with most key information we told them about the house, it seems to have been ignored. 

I will keep working on lowering the WC flow temperature daily now... but it does look like since lowering it again this morning, the flow temperature is bouncing all over the place again. I've attached a few more graphs below. There's also a pie chart of the operation mode for the last 24 hours and it looks like 17% of the time, it's been off. So does that suggest cycling?

I can't see anyway in Melcloud to view anything other than hourly graphs. I've checked the Octopus app this afternoon and I'm amazed to see that the first full day of weather compensation has seen a drop in energy usage despite having the pump running 24/7 and having a really warm house. I mean, there's a long way to go before we get it to the right flow temperature but even so, I'm amazed.

I'll uploaded photos of the water tank in a separate post. Excuse the state of the place. It will be all boxed in one day.

@jamespa The tank...

I think you’ve got a piped header , not a buffer.

The called for temps are now low and you are cycling the machine. The fact that it’s cycling at temps of 5 OAT and below means, im pretty sure, you are well over sized. 

the flow rate is very low for the 14kw pump, the installer set that flow rate, so they seem to know you don’t need much heat.

Post more data over the coming days, but I think you need the 6 or maybe 8.5kw machine

but please don’t quote me! 

@davidnolan22 Thanks David. It's so frustrating because I can finally see the potential of heat pumps but I feel like being lumbered with an oversized unit is such a cause for concern.

It was a pretty cold day here yesterday. Frost overnight. So I'm impressed that the house was kept so warm. I mean, to wake up to a comfortable house is fantastic. But yes, it's definitely not optimum performance.

I've got the WC set to -3/43 now... so if I moved it back to a fixed temperature of 45, isn't that going to just use loads more energy? Oh but you're saying run it for only 10 to 12 hours instead of 24/7? 

My worry there is that we're going to be giving up the constant warmth for peaks and troughs throughout the day.

Thanks for the heads up about the cycling. I've seen a couple of rules of thumb online and most seems to point to 8.5 being a good option for our size... certainly not 14. Gutted. Fingers crossed I can get them to see sense.

Thanks again. The advice from you and James is just brilliant. I wish I could send a virtual pint your way.

Posted by: @sandman1600

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We did tell the installers about the upgrades to the EPC but sadly, as with most key information we told them about the house, it seems to have been ignored. 

That's important.  Hold onto it, gather any evidence.

If somehow that can be combined with operational evidence then you may have a chance.

Does melcloud display oat somehow?  Ideally on the same plot.  Oat plus a cycling system might prove it's oversized.  Does it cycle at say 6, 7 C?

I didn't realise installation is still ongoing: that puts you in a much better position.  Very likely they don't get paid until you sign.  They will therefore attempt to bully you into signing, if possible don't be bullied.  Have they done a handover of the ashp and given you proper instructions, if not then that alone is sufficient 

@sandman1600 

It’s tricky, if you run it in the 30s, it will cycle a lot. If you run it in the 40s, it will cost a bit more to run and you will have to run it more on/off which is not ideal for a heat pump, but I think your actual heat loss is a lot lot lower than you think and youre going to have to compromise. 

the one thing you 100% cannot do is run zones. With your heat pump, you have to run it as open as you can, everything open always.

if it was mine, I think I would run it fixed flow and more on/off, initially to get more data and a feel for heating and cooling. For instance, if you run 45 fixed flow for certain hours, how does this heat the house at what outdoor temp and how long does it hold that temp for.  You’ve going to need to really get a feel for this. 

But if you can get the UFH plan from when you had that laid it will help with outputs.

it took me ages to actually get control of my unit, run tests and then sort it out myself. But, I honestly think youre going to come up against the limits of a 14kw heat pump in a house that might only be 5kw heat loss (educated guess!!!) 

A few comments that might be helpful. 

As James mentioned, usually the biggest source of over estimating heat loss is the ventilation rate (air changes per hour) and with high ceilings that over estimation will be magnified. 

The specs of the 14kW Mitsubishi give a minimum output at 7C OAT of 4.2kW with a 35C flow temp, 3.7kW with a 40C flow temp, and 3.2kW with 45C flow. At higher OATs it's even worse, for example 6.2kW minimum at 12C OAT and 35C flow temp. 

MELCloud can't AFAIK do flow temps and OAT on the same graph, closest thing is the "Internal Temperatures" and "Temperature History" for the last 24 hours to give flow and OAT to the same scale.

@sandman1600   Whilst I agree with hat you may end up batch heating at a higher ft, at this stage I would continue to get to the ft that just heats the house on a 24*7 basis a so you know what the baseline is and b to assist with your argument with the installer.  You are in the unusual position that you have posted before the installer has left and you have signed it off, you should exploit that.

I hope to post later a template for a rejection that has been buzzing around in my mind.  You need to collect some more evidence and, if I get the chance to post it, the template should point you at the evidence you need to collect.  It should all be on melcloud, if you can get daily rather than hourly plots it would be much more useful.  With a cop of around 2 from what you have posted so far the installation fails the building regs, fails by a long way what is in their proposal and would fail the requirements for the bus grant if that's what you are using (what grant are you using).  That's a pretty strong argument that it's not in its current state fit for purpose and thus grounds not to sign off.

I will post again but it may not be untill tomorrow morning.

I should add that I still think you can get it working well as it is, so if you don't think it's worth trying to press the installer then let's focus on getting it optimised.

Further to the above here is a template for what you might say if you wish to decline sign off.  ? indicates info from melcloud or elsewhere, or references to legislation ( I am happy to find these tomorrow).

Let me know if this is helpful.

Thanks for the pictures, I need a bigger screen to understand them which I won't be able to do until tomorrow.

Since the heat pump was installed on ? I have been monitoring its performance using melcloud and my electricity meter.  Cop, measured on a daily basis and reported by Melcloud, has averaged ? and varied between ? and ?.  The consumption reported is consistent with my electricity meter.  I have had some success in improving the figure by reducing the maximum flow temperature in the weather compensation curve from 55 (the figure set up by the installers notwithstanding that the design temperature was 45) to ?, but recent cop figures are still approximately ?  This is clearly inconsistent with:

• Your proposal
• The requirement in paragraph ? of part L of the building regulations
• The requirement under paragraph ? of the bus regulations
• The requirement under ?  of the ? [regulations of any other grant you are using]

• The unit appears to cycle on and off at all outdoor temperatures and never reach a steady state
• The maximum daily output energy during the period monitored was ?kWh
• The flow rate has been set up as ? which, with an emitter dt of ? corresponds to an output power of ? max, well below the unit specification.  [point made by @davidnolan above  needs clarifying]
• During the survey I advised of the following fabric upgrades relative to those set out in the EPC, I am unclear whether these were taken into account.

@jamespa Thanks for the continued advice... just catching up with the forum.

We have signed off the plumbing works which I'm guessing included the heat pump. This was done as the plumbers left on their last day before we'd even been able to use the heat pump. However, I imagine for the full funding, we'd need to sign off the remainder of the work, particularly the solar install. So even if its not specifically for the heat pump, I'm happy to refuse to sign that off until they play ball... if they will play ball.

I'm not sure I've got any evidence of telling them what upgrades were carried out. We had three surveys of different levels before they started work and every time I told them what insulation has been done since we moved in (2023 - the EPC was from 2018). I also expressed my concerns that there was asbestos in the garage, we had no loft space that needed insulation and that the roof was metal sheet and all that info was ignored completely and has delayed the install... but that's by the by. They don't listen.

I should just add that the company is one of Mitsubishi's accredited installers and they're also tied to the local council that have funded the install. I'm hoping these ties will make the want to get this right.

Its being installed under the ECO4 funding due to my partner having a qualifying health condition.

It's insane that they're apparently using MCS installers that are telling us to leave it at 55 degrees. As soon as it was installed I dropped it immediately to 50 and the installers put it back up to 55 the following day.

Ideally, I'd like them to swap this with the correct sized ASHP... I'm thinking the 8.5 would be more appropriate... as I don't really want to be using workarounds to make it work for us. If we can't make that happen though, at least there's a plan B. I was reading on another thread that somebody suggested using the Mitsubishi Auto Adapt with the right weather compensation settings has helped to reduce cycling. 🤷‍♂️

I'm a little concerened with batch heating as I'm not confident our house holds onto heat that well but happy to give it a go.

MELCloud only displays OAT on the temperature history report but this report only allows 1) Room Temp, 2) The Set Room Temp, 3) Outside Temp and 4) Tank Temperature so I can sort of do a comparison but not all on the same graph.

I've been searching to see if Mitsubishi had some kind of web portal that allowed better reporting but I can't see anything.

The COP for yesterday was around 2.16 so a slight improvement... and considering that at the 55 degrees they insisted on, the COP was around 0.75, its massively better.

The template would be much appreciated. Thank you! I'm getting a better understanding of what to complain about but I want to make sure I'm fully prepared. I'm going to start snapping the graphs each hour so I don't lose the data. I've stitched what I've got together and I'll attach them at end of this post. Hopefully you can read them now I've stitched them... theres a few hours missing from yesterday I think but I'm trying to be consistent from here on.

I've made no more changes (since yesterday around 8 AM) to the WC curve to see what happens. It does still seem to be bouncing around a lot. And around 7:40 it plumetted to around 32 and then shot up to about 53 for minutes even though the temp is outisde the weather compensation. Is that normal?

Posted by: @davidnolan22

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@sandman1600 

It’s tricky, if you run it in the 30s, it will cycle a lot. If you run it in the 40s, it will cost a bit more to run and you will have to run it more on/off which is not ideal for a heat pump, but I think your actual heat loss is a lot lot lower than you think and youre going to have to compromise. 

the one thing you 100% cannot do is run zones. With your heat pump, you have to run it as open as you can, everything open always.

Thanks David. This is another option for sure. Heads a bit muddled with the various options right now but this is definitely an option. 👍🏻