In terms of the original question, I think I am leaning towards not swapping the unit.
I think currently it would be a bit close to our heat loss and added to that all the practicalities of getting the unit installed and dealing with the old one and potentially losing my warranty it isn’t really worth it at this stage.
I think the priorities are to:
Get more of the heat energy produced by the heat pump into the house lowering flow temperature needed by:
Improving the pipe insulation in the cellar, making sure it is continuous
simplifying some of the old cellar pipework that is just adding extra length (and heat loss) because of where the old boiler used to be
Keep more of that energy in the house reducing flow temperature required even more
Insulate under the suspended floor (this is throughout our ground floor and draughty too)
Continue insulation of internal walls
Once all that is done I an certain I will have an even more oversized system but it should be able to run at a lower flow temperature so use less energy.
The one thing I don’t really now is a plan for is increasing the size of emitters so a lower flow temp can be maintained and this will actually effectively get worse without the heat loss to the cellar from pipes.
Maybe by then there will be more people swapping around over and undersized units on eBay so I can swap for a smaller one then.
We have much more emitter output than this (1x medium type 22, 2x fairly large type 11 and 1 huge single panel) as it is likely that very little (if any) of the heat was being delivered from the 4 radiators in the bedrooms.
Because our bedrooms are all well insulated and have TRVs set to a lower temperature they spend nearly all of the time taken out of the system.
If I improve the insulation in the rest of the house hopefully the temperature will even out a bit meaning these rads can be (more) open
Just another random thought…
Could the position of the flow temperature sensor play a part?
If there is a lot of pipe (depending on how well insulated it is) between the heat pump and the sensor that would make the COP for a given flow temperature worse?
It’s the dT that really matters, so as long as both the flow and return pipes are the same length and have equal insulation, I don’t think it will affect the measured heat.
How well the sensors are fitted to the pipework matters more, plus the insulation around them.
It looks like your DT between flow and return goes to zero when the compressor is off which suggests the temperature sensors are good. I assume they are the wet sensor pockets as we supply them?
Really interested in this thread as grappling with cycling on my 11.2 ecodan (Sheffield) - I don’t have 90 days of data - lots of changes on the system I’m the last month.
But would be interesting to see where my unit sat on this graph. Can it be added / highlighted at all in the future?
Using the Compare feature, we can see both systems fit the same profile given ‘Flow - Outside temperature’, but yours (red) runs hotter. (Hourly data over 90 days)
In which case I still need to work out what it is that is pulling my system down as all the things I have come up with so far to improve COP are to reduce the flow temp (which I should definitely still do) but not things that might be reducing my COP at a given temperature difference between flow and out door.
Yea my emitters are probably undersized (especially due to the bedrooms being the most insulated so TRVs on those rads are normally closed, effectively reducing our emitter output at any given time).
In theory a smaller unit that can modulate down to lower its output for more continuous running / longer cycles should be more efficient than one that spends a lot of time cycling on and off.
our house is a 220 year old stone property with solid 500mm thick walls
we originally sized it for a 16kw which as its turned out like you it is slightly oversized, i carried out a heat loss calc and its closer to 12kw
what i found when it was warmer outside the flow temp would increase above the set point as i have it so that the compressor does not switch off, which obviously then overheated the house so what i do now is have the xternal stat switch it off and on .2 degrees either side of the set point temp
Being a stone house it stores a lot of heat so when it does go off its usually a good hour or so before it comes back on depending on outside temp and if it is cold out then the weather compensation flow temp is correct and it doesnt overheat
This seems to work for us ok. Our EPC says we should use 25000 kwh for heat and hot water per year and we have a check meter on the heat pump and it uses between 4000 and 4500kwh a year so i guess that isnt bad considering the property
Is that in WC mode, Auto Adapt (room temp) mode or fixed temperature?
There is something to be said for forcing a larger gap between cycles when it is warm enough to do so and especially if you have lots of thermal mass as it means the start of your next cycle can be quite efficient.
Mine is a Samsung and i run in weather comp all the time but on/off it via an external stat as last resort. not sure on Ecodan but my unit is set to only turn off both water pump and compressor from the stat signal
I did ask Samsung on running time of the compressor and they said it can run continously. better that than on off frequently