@davidnolan22 Thanks. It looks like this is some kind of Mitsubishi "collab" so I think arguing that this is wrong be tough. 

We'd never have known any better if we'd have specced this ourselves so I think it's something we might need to just live with.

So should this help to minimise short cycling too? I'm just trying to anticipate the installers response.

The flow rate still needs addressing by them.

@jamespa Thanks for the information. I will ask for the justification but I'm guessing it's a kind of "easy" package along with the heat pump. Saves them having to spec too much for each individual install.

@sandman1600 

yeah, they'll just turn the pump speed up. might not help you as much as you think. you need someone to measure what's happening across both manifolds to see what's happening ton the secondary side. and you might get it working OK.  But, you'll keep running up against the fact is probably oversized by some way and them swapping units will cost 4-5k.  so I imagine this may be a sticking point. I've never heard of 14kw pump in a 130m2 house before. but I'm no expert. 

Posted by: @sandman1600

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So should this help to minimise short cycling too? I'm just trying to anticipate the installers response

Not necessarily, wrongly set up it will make cycling worse (sorry, comment refers to buffer not turning up pump speed)

The solution is to replumb as a 2 port volumiser and delete the secondary pumps.  I doubt they will do that but it's worth a try. 

Heating industry has form when it comes to setting up heating sub-optimally.  Almost all condensing boilers installed since they became mandatory in 2005 are installed so they don't condense, negating the benefits of condensing boilers and costing us all 10% on our gas bills.  Why?-to reduce call outs.

I reckon that if the buffer and size were fixed, you have a very good chance of achieving the performance quoted in the proposal.  Unless they do that you won't.  The buffer is probably the more important, it's labour only no parts to change this so no material cost to the installers.  With a handful of shut off valves it's even possible to do it reversibly so it can be reverted in a few minutes.

Posted by: @sandman1600

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I will ask for the justification but I'm guessing it's a kind of "easy" package along with the heat pump. Saves them having to spec too much for each individual install.

Yes, it means they can ignore what's already there.  Although really this doesn't provide much advantage in most real cases.

So, an update... one of the team leaders from the installers visited today and checked out how we'd been set up.

There's a water pipe outside that's going into the heat pump and he suspected that the very fine filter in there may be blocked... I honestly rolled my eyes when he said this but I watched him unscrew it and indeed he cleaned out some debris.

Back to the Mitsubishi panel and the flow rate was up to between 25 and 28l. So an improvement.

The DT is still around 3 though. He thinks the increased flow is going to help with the DT, the cycling and the COP. He says they have the option of cutting the filter out completely to increase flow further as there's another filter fitted to the tank so it wasn't a big deal. 🤷🏻‍♂️

He'd discussed the sizing of the heat pump with the owner of the company and his response was "the heat loss is the heat loss" and we've been given the appropriate pump for that heatloss report. Apparently they've already taken the insulation improvements etc into consideration on the heatloss report.

So at present we're on hold and seeing what happens before we go back to them.

More like “the heat loss report is the heat loss report”

The actual heat loss, well, you’ll have live evidence. 

if increasing primary flow without having somewhere for it to go helps the DT, and I assume he means widen it, not sure about that reasoning. But good luck. 

@davidnolan22 Precisely. The heat loss report is gospel and that’s all they’ll work to.

One thing he said which sort of makes sense is that the next model down is (as you know) 11.2 and if their heat loss figures are anything close to being correct and we have a real cold spell in the winter then we could find that a smaller heat pump might struggle when we need it most.

If they’re adamant that the heat loss report is correct, I don’t see how I can convince them otherwise. 

it could be coincidental due to OAT changes but since he left, it appears like the cycling has got loads worse. 

One other thing I noticed while thumbing through the settings is that the heat pump speed for heating and DHW is set to max. 

Is that normal?

Posted by: @sandman1600

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One other thing I noticed while thumbing through the settings is that the heat pump speed for heating and DHW is set to max. 

Is that normal?

Its not abnormal, as long as there isnt excess pipe noise its OK.

Posted by: @davidnolan22

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More like “the heat loss report is the heat loss report”

The actual heat loss, well, you’ll have live evidence. 

Spot on!

Posted by: @sandman1600

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The DT is still around 3 though. He thinks the increased flow is going to help with the DT, the cycling and the COP. He says they have the option of cutting the filter out completely to increase flow further as there's another filter fitted to the tank so it wasn't a big deal.

Not sure what 'helps' means in this context!  Nothing wrong with a DT of 3.

Posted by: @davidnolan22

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if increasing primary flow without having somewhere for it to go helps the DT, and I assume he means widen it, not sure about that reasoning. But good luck. 

Spot on!

If this is today it actually doesnt look too bad.  At 12C+ you expect cycling

Here is mine today, several overnight defrosts, then a period of stability, then into cycling due to demand too low, with a spike to heat the DHW

Nothing they told you gives me any confidence that the person who visited has grasped the problems causing poor COP (poorly selected/ poorly set up buffer tank and oversizing, with the former almost certainly being the principal contributor.)  Heat pumps arent magic nor are they mysterious.  To get them working at optimum efficiency  you basically have to do one thing and one thing only namely get the flow temperature down as low as possible (which is achieved by having as little cycling as possible and a direct connection from heat pump to emitters).

At this stage I think you may have to make a decision whether to accept what you have or escalate seriously and fight it out.  Assuming you now are running at roughly the right flow temperature your COP will go down from current when it gets colder, and might go up a bit as it gets more consistently warm.   It may be possible to improve a bit by balancing flows either side of the buffer, but with a 50l buffer avoiding mixing is essentially impossible.

@sandman1600 

If your heat loss is really 14, and your UFH capacity at mean water temp 50 is 9kw, if they are right, the the pump won’t be your problem…. Your need to run your water over 55 and the R32 wont do that. 

With the DT, I think we're seeing drops below 3 occasionally but I think that's mainly while its cycling which I guess makes sense?

Posted by: @jamespa

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If this is today it actually doesnt look too bad.  At 12C+ you expect cycling

Ah okay. I'm obviously getting confused. So there's no way of avoiding this level of cycling? 

Posted by: @jamespa

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Nothing they told you gives me any confidence that the person who visited has grasped the problems causing poor COP (poorly selected/ poorly set up buffer tank and oversizing, with the former almost certainly being the principal contributor.) 

No, I'd agree with that. In fact, I'd say at every step of the way on this journey, including when speccing our UFH and oil boiler before this, I think installer knowledge has been limited. Many seem to have a wide overview of their trade but a very narrow view of the finer points. And we went through SO many different quotes.

In this situation, we have to accept that there's no way they're going to swap the tank. It's the only variety they install and it's probably a nice easy solution that "just works" on some basic level. As far as they're concerned, it's doing the job.

The heat pump I am concerned about and I feel there is some room for movement there.  I'm just not sure how to tackle the oversized argument when they're clutching to the heat loss report like religious text.

The guy that visited today was amazed at how "switched on" I was compared to their usual customer... me... who's entire flaky knowledge base has been developed in a week, predominantly by the help of this forum.

Says a lot.

Posted by: @davidnolan22

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@sandman1600 

If your heat loss is really 14, and your UFH capacity at mean water temp 50 is 9kw, if they are right, the the pump won’t be your problem…. Your need to run your water over 55 and the R32 wont do that. 

I kind of see what you're saying but with my really basic understanding I'm just struggling to communicate the evidence of the heatloss to them. They keep using the "yeah but when it gets really cold" argument.

Posted by: @sandman1600

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Ah okay. I'm obviously getting confused. So there's no way of avoiding this level of cycling? 

Nope.  The problem is this:  Most heat pumps have a modulation range of ~3:1.  So if the heat pump is correctly sized at -2, with a house heat loss proportional to 16-(-2) = 18C, then it will cycle when the temperature is greater than 16-18/3=10C. (I base it on 16 because many houses are in equilibrium at ~16, due to the heat from occupants and waste heat from electrical devices).

The only one I know with a materially greater modulation range is the Mitsubishi R290 8kW, due to having two compressors (there may be some others but they aren't common - yet)

Posted by: @sandman1600

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The heat pump I am concerned about and I feel there is some room for movement there.  I'm just not sure how to tackle the oversized argument when they're clutching to the heat loss report like religious text.

Unless you can get the details of the heat loss calculations they used/the data they entered into the tool (which doubtless they will initially refuse - but you could argue are yours because you paid for them) the only way you can do this is through data.  Daily Energy consumption and (more importantly) energy delivered vs average outside air temperature.  The problem is you have very little time for the data to have accumulated but it may be enough.

Its best to plot the data.  Attached is an example (my gas consumption over 2 years) which is basically how I sized my own heat pump.

Posted by: @sandman1600

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In this situation, we have to accept that there's no way they're going to swap the tank. It's the only variety they install and it's probably a nice easy solution that "just works" on some basic level. As far as they're concerned, it's doing the job.

Noted.  They dont have to swap it just replumb it (reversibly if they insist), but I expect the same conclusion applies.

I think you may either have to accept as is or go nuclear with a refusal to sign anything left to sign and the 'unfit for purpose' statement based on COP  - leave them to work out what the reason is, after all they are 'experts', you merely need to show its not good enough not why its not good enough.

Posted by: @sandman1600

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The guy that visited today was amazed at how "switched on" I was compared to their usual customer... me... who's entire flaky knowledge base has been developed in a week, predominantly by the help of this forum.

Says a lot.

Its clear from your posts that, in a couple of weeks, you have understood more than some installers will understand in their lifetime, sadly.