@sandman1600 

What I mean is, your UFH power is 79wm2 I think, at mean water temp 50, so in your house that is 9. something kw of power.

they designed it to 42.5 mean water temp, not 50, so at the temp they designed to, you cannot emit more than 8ish kw into your house. 

they might have a bit of paper saying it’s 14, but common sense and other data would suggest it’s  nothing like that.  If they truly do think it’s 14, then a sensible question maybe why they designed to to 45 degrees then and show then the emitter power.  At 45 degree flow, you cannot put 14 kw of heat in, not even that close to it. I know they did not do the UFH, but they must have had a look at it. 

but I appreciate this is tricky. 

Thanks again @jamespa  @davidnolan22 

Now we’ve raised it with them I’m just trying to see what it does over the next few days before I refer back to them.

There was a lot of cycling in the early hours this morning but it’s been fairly settled today.

The delta t drops to anything from 1 to 2 at times, particularly when cycling. I’m assuming I’m going to have to accept that as a side effect of the buffer tank..?

As for replumbing the tank to bypass the buffer, I’d honestly rather get somebody else in that I trust to do that. I’m not sure these guys skill set would allow them to stray from their regular methods. For now I’m trying to demonstrate the oversizing of the pump so we can at least get that resolved if possible.

The cycling looks bad on the 24 hour report but the hourly graphs on MELCloud show a max of three dips per hour. 

Does that look normal? I don’t want to go back to them with evidence if it’s not proving anything.

@sandman1600 

it’s tricky. 

Looking at the graphs: it’s not ideal. It’s on/ off all the time as it can’t modulate lower. Personally, I’d not be happy with that. And it’s not been settled today, it’s been turned off.

post a graph on compressor output. 

but, it’s been warm today in Sheffield, I’ve not had my heating turned on for over 30 hours.

Your installer increased the flow into your buffer, but did not touch the secondary side of the system, which to me would not help you at all. All this would do is narrow DT and lead to more cycling.

the problem you have is that you warranty and contract is with your installer. If anyone else touches it, they may walk away from you. 

Posted by: @davidnolan22

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it’s tricky. 

Thanks. I figured it didn’t look great.

I can’t see a graph that includes compressor data  I’ve attached the most detail graph it produces. Not sure that’s any help though.

I’ve not switched the heating off here yet because it looks like next week will be cooler again and the lower level takes ages to heat up so at the minute, I don’t want to meddle.

The DT definitely worsened a little after the flow increased so that’s definitely something I can go back with.

I get what you’re saying about the warranty. We’ve had insurance policies sent through today from a third party company which serves as a guarantee.

I’m not going to make any changes right now. For the foreseeable future I want to get my head around how it works and then I’ll consider tweaking it.

I just don’t trust the installers to come back and start fiddling with it… even if they would. I think it’s just going to potentially complicate things (at best!).

I’ve circle your compressor output. It’s just going from low to minimum output to off. And then as we thought, off all day. But it’s warm today, but must be a better control strategy that that. Whats your COP yesterday? 

Posted by: @davidnolan22

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@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. 

It sounds not much different in area from ours, I can't remember how big it is, but we have a 12kW pump because we are in Scotland and it can reach -15 in the winter.  This winter we had 3 nights in a row with -8 and a lot of days with -5 to +5, so if the OP is in Sheffield I don't see how they can justify such a big pump unless the house is uninsulated or really old cavity wall.

Yeah, big balance isn’t it. Big enough to heat commonly cold days, but not so big ruins more typical temps. 

im not sure where in the country the unit this thread is about. But the shoulder months can be tricky with the mitshubishi controls.

when it does not drop at night below 9-10 and 14 in the day, I just turn it off and light wood burner if we ever need it. 

the unit above seems to have minimum compressor output at high 30s Hz. For comparison my 11.2 minimum is 26-30hz. 

If your Cop is ok, and warm, might be fine. If your cop in this weather is still below 3, that would be a concern. 

Posted by: @sandman1600

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The delta t drops to anything from 1 to 2 at times, particularly when cycling. I’m assuming I’m going to have to accept that as a side effect of the buffer tank..?

Dont worry about this.  Long story and discussion but dont worry about it.

Posted by: @sandman1600

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As for replumbing the tank to bypass the buffer, I’d honestly rather get somebody else in that I trust to do that. I’m not sure these guys skill set would allow them to stray from their regular methods. For now I’m trying to demonstrate the oversizing of the pump so we can at least get that resolved if possible.

Understood however you may find it difficult to persuade anyone to do it because they feel they would be taking responsibility for someone else's system! 

Posted by: @sandman1600

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The cycling looks bad on the 24 hour report but the hourly graphs on MELCloud show a max of three dips per hour. 

 

Three dips per hour is normal.  Looking at the graph it was cycling all day.  There were periods when the OAT was low enough that you wouldn't expect cycling BUT, it started off pretty warm and Im guessing there was some solar gain pushing it more into cycling zone, so these could possibly be 'explained away'.  Cycling is a design feature both of heat pumps and boilers and, bearing in mind that a correctly sized heat pump is bound to cycle if the OAT is above about 10 and certainly 12, I don't see you have a case based on cycling alone. 

Posted by: @sandman1600

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The DT definitely worsened a little after the flow increased

If you mean by this that the DT dropped, of course it did.  If you increase the flow and the load remains the same, DT will drop and vice versa, because DT is essentially determined by the emitters and the flow rate NOT the heat pump.  Dont worry about it, its not a problem and it is expected!

I think you are probably getting a bit distracted.  In the end the key measure is COP.  And in the end if you want the installers to do something you are going to have to prove that COP is persistently too low or prove that the heat pump is substantially oversized.  Cycling, whilst indicative of the latter, isn't going to prove much now we are in the shoulder season when cycling is bound to happen even with a right-sized heat pump.  Had it been the dead of winter maybe, but its now probably too late in the season. 

If you do want to prove these you need the daily records of COP, OAT and energy delivered over a period of many days, ideally since you had the pump.

Obviously its up to you and I dont want to interfere, Im just observing that getting too concerned about cycling and low DT at a time of year when both are bound to happen, at least to some extent, may ultimately not help a lot.

@jamespa Thanks again. That helps clarify what we need to be looking at.

I've been monitoring it over the last few days and COP has been:

24/3: 3.17 (3.5 heating 1.13 water)
23/3: 3.71 (4.23 h 1.34 w)
22/3: 3.52 (4.16 h 1.33 w)
21/3: 3.48 (3.78 h 0.85 w)
20/3: 3.06 (3.26 h 1.38 w)
19/3: 2.95 (3.09 h 1.33 w)

So the warmer weather has been helping achieve better COP. I've attached the MELPump graphs from the last few days.

We've chatted to another engineer (an apparently trusted friend of our original oil boiler engineer) who understand the issue and he's happy to take a look when we need him... I just don't want these current installers back. Even if they agreed to it, I wouldn't trust their cookie cutter approach.

As cycling is expected in the current warmer temperatures, I'm not sure we have compelling data to be able to make a strong argument for oversizing.

I'm still going to follow up with what we do have but I don't have any high hopes that they'll be receptive.

Thats good data.  I will compare heating COP (which doesnt seem too bad) with mine later today and make some observations, but I think its worth taking a look at DHW.  Those DHW  COPs are rather lower than I would hope

I looks like the target DHW temp is 50/51, It might be worth cutting that back to 48 which is a common recommendation (or even 45 if you dont use too much DHW).  

Whats the 'coil surface area' for the DHW tank.  Its on the label but I cant read it from the photo.  DT for the tank heating seems low, but this may be just that the water pump speed is high.

Is there anything 'odd' about the DHW?  Does the Ecodan have the option to set the aggressiveness with which DHW is heated (eg 'eco', 'normal', 'fast').  You are spending a lot on DHW but I cant see much evidence of drain off (ie using it), mostly a steady decline in temp due to loss from tank which, ultimately, is a lot of wasted energy.

Edit - Ecodan appears to have 'normal' and eco mode for DHW.  Suggest you try Eco and reducing tank temp to 48, might improve the DHW COP a fair bit (or might not!)  Simple explanation here 

OK, further to the above (which please do read as its about a different and possibly equally important topic) this plot is a bit of a goldmine!

The bars at the bottom show that it comes on only for very short periods once OAT is above about 6.  This is bad because the heat pump spends a lot of time heating up the pipework and the ODU rather than the house!.

On this day you got a COP of 4.23, spec sheet says 5.2 for OAT 7, FT 30,  Not so far out, but not great, almost certainly due to the very short run time (it never stabilises)  Once OAT is 6 or less it operates stably.  

The low stable/cycle transition point (6 vs 10-12 with a correctly sized heat pump) is symptomatic of oversizing.  

The very short run time even at a temperature just above the stable/cycling transition point is symptomatic of low system volume (for the heat pump in question) combined with oversizing.  How many radiators do you have?

The start up spike on the compressor will be compromising efficiency and, in this case, is presumably unnecessary.  Not sure if that can be tweaked by any means but if it can it would be good.  Quiet mode might possibly do it, certainly worth trying!

The house temperature doesn't appear to follow the on/off of the heat pump, ie the house reacts slowly.

Things would likely improve a bit if you could increase the 'on' time (the on/off ratio wont change, so the heat pump will be off for longer also, but as your house reacts slowly it probably wont notice).  There may be a flow temperature hysteresis setting buried in the installer menu which might help.   A bigger buffer tank (but plumbed as a 2 port volumier ) would also have helped.

I think the mystery is beginning to fall away now as you (hopefully) get the settings closer to optimum.  DHW needs attention though, see post above.

Small buffer tank may yet prove to be a source of inefficiency at lower OAT, difficult to explore that until next season however its possible to make some measurements.  Im working on an article about this which i hope I might complete in the next 2-4 weeks.

@jamespa Thanks again for all the information. I've read everything and it's very helpful.

I've lowered the DHW temperature to 48 which after one day has made a bit of an impact on the COP (up to 2.06 yesterday). It was set to 50. I've found the ECO setting so I'll give that a try. I work from home mostly and I can use quite a lot of hot water on certain days. That's maybe only 3 days a week on average though and not at weekends.

The coil surface area for the tank is 3m2.

I don't think there's anything else odd about the DHW though that I can think of.

Posted by: @jamespa

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The very short run time even at a temperature just above the stable/cycling transition point is symptomatic of low system volume (for the heat pump in question) combined with oversizing.  How many radiators do you have?

We only have one... a small towel rail in the bathroom. Everything else is UFH. 

I'll have a go at switching to quiet mode and see what effect that has too. There's around 3 different levels of "quiet" so I'll start on the default one and then reduce it if I don't see any changes.

Posted by: @jamespa

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Things would likely improve a bit if you could increase the 'on' time (the on/off ratio wont change, so the heat pump will be off for longer also, but as your house reacts slowly it probably wont notice).  There may be a flow temperature hysteresis setting buried in the installer menu which might help. 

This makes real sense. I just can't see an obvious way to achieve it with any of the settings in the app or the FTC7 controller. An ECO mode here would make perfect sense to me. I'm googling now to see if I can find anyway of achieving this.

Going back to the DT, I've just watched a Mitsubishi commissioning video and it suggests a pump speed of 5 when setting up to get the system moving and pushing air out but then says you can decrease that later to adjust the DT. So maybe I'll give that a try too.