Can oversized Ecodan be swapped for a smaller unit?

Hardware Heatpump
21

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.

2 Likes
22

This doesn’t tell the whole picture.

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

1 Like
23

Trying to get some contextual comparison:

  • Filtering by Ecodan’s
  • adding flow temp mean when running and outside temp mean when running
  • 90 days of data

image
image1539×731 179 KB

Plotting this and highlighting our three systems:

image
image745×410 19.1 KB

An interesting question is what causes the range in performance that we see for the same flow temp and outside temperature?

2 Likes
24

Removed the system that did not have outside temperature data

1 Like
25

Certainly looks like anything I can do to get the flow temp down should start to move me into a better place.

Then I can see more clearly if I am more like your systems or that clump of ones at lower temperatures that seem to still have similar COPs to me.

1 Like
26

Perhaps this is a better way of looking at the potential at your current temperatures?

image
image851×467 44.7 KB

1 Like
27

mm, yea but that feels like a harder one to explain.

1 Like
28

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?

29

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.

1 Like
30

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?

31

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?

Kevin

32

→ https://dev.heatpumpmonitor.org/daily?id=36

33

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)

image
image1044×705 134 KB

So, for any given ‘Outside temperature’, COP is less good:

image
image1044×705 147 KB

1 Like
34

Yes they are in the sensor pockets.

Pipes are equal length (more of less) with the same level of insulation so as you say @Timbones that shouldn’t effect the measured heat.

35

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.

36

Im sure someone must have already asked but are your emmitters large enough to dissipate the heat also your flow rate

As if you can emit more heat it will heat up to your stat set point and then shut off so wouldnt be any need to swap for smaller unit

37

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.

38

Just to give you some idea how i run mine

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

Im sure someone will soon put me right on that!

John

39

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.

40

Hi Andrew

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

John

1 Like