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Optimising ecodan ASHP

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(@hotheat)
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@sunandair yes I was perhaps ambitious there, maybe optimising my house would’ve been more accurate! But I may get there in time as I learn more


   
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(@kenneth)
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@hotheat I’m the same- I’ve contacted Mitsubishi and will let you know what they say. The ftc6 should have energy monitoring


   
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(@hotheat)
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@sunandair

IMG 4397

Do you know what’s happening with these short drops in flow temp - is that just adjustment as outside temp changes? You can’t see them in the 24 hour view, only the hourly view.

 

@Kenneth thank you, yes please let me know. I haven’t got round to ringing them yet but it’s on my to do list for this week!


   
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 Rod
(@rod)
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@hotheat I've seen in several forums that the Ecodan will have short pauses of around 4 minutes as a form of cycling. Mine does this at temps down to about 2c, after which it will run continuously. It seems (to me) related to a slow rise in the flow temp over the period when it's running, then it reaches a point where it just stops and restarts again 4 minutes later. If the outside air temp is constant, then the flow temp at which the cut out occurs is also constant. As temperature outside rises, these drop-outs will start to extend in length.

Typically I'll get one or two per hour max, and I did contact Mitsubishi about what is an acceptable amount of cycling - their view was that a couple of times an hour isn't an issue. It's irritating because there's a spike in power usage during the recovery, but there's a compensating saving during the drop-out. My Ecodan controls the main circulation pump, which will normally stop for 4 mins then restart for a couple of mins after which the circulation pump comes back on - this can be seen because the power consumption drops to zero then rises to about 50W. Somethimes the doesn't pump doesn't stop, just to confuse.

However what you're seeing is normal in my system, it appears to be part of the pump's management strategy. You see it a lot more clearly if you have energy consumption logging, and I use Shelly devices to monitor the temp second-by-second and with more accuracy, which also helps visualise what's going on.

 


   
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 Rod
(@rod)
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Bit more detail: this is mine today with 4-min dropouts. Definitely not defrosts: the flow temp never drops below return and I've watched it happen, there's no frost.

image

   
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 Gary
(@gary)
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@rod what is the difference between your flow and return before the drop outs?

 

I find mine will run continuously if the dT is no closer than 2C to 3C (2 hours from yesterday afternoon below with no cycling) once you get to <2C then it wants to cycle, that's will all my UHF circuits open and rads upstairs open if I restrict any of those then it will start to cycle.  If I try and run it any cooler than 32C then it will also cycle.

 

image
image

   
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 Gary
(@gary)
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@rod what is the difference between your flow and return before the drop outs?

 

I find mine will run continuously if the dT is no closer than 2C to 3C (2 hours from yesterday afternoon below with no cycling) once you get to <2C then it wants to cycle, that's will all my UHF circuits open and rads upstairs open if I restrict any of those then it will start to cycle.  If I try and run it any cooler than 32C then it will also cycle.

 

image
image

   
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 Rod
(@rod)
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@gary DeltaT at the point of the drop out is about 4.3C, and there is no obvious reduction of the dT after it settles post-drop-out to the next one.

The flow and return both climb very slowly over the period: the pump doesn't seem to modulate itself down to a point where it's stable, it just allows the increase then stops. It is also the case that the flow temp will have marginally exceeded the weather compensation set point, so it's right to stop. It's possibly related to the fact that our pump is slightly oversized for the installation, although in the diagram shown it is not modulating down to its lowest levels: it could run lower power without stopping but seems to choose not to. I'm really not clear on why it does this, but John Cantor of heatpumps.co.uk mentioned it in a posting (he has an Ecodan which does it) and he doesn't know why either, so nobody has a clue! It doesn't seem to negatively impact COP and the effect is that average flow tems are pretty much where you want them.


   
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(@hotheat)
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@rod @gary

Rod - yes that looks the same as mine, happens 1-2 times per hour as you say. Good to know they say it’s not an issue at least, I wouldn’t even know it was happening if I didn’t look for it. I agree it is something to do with rising flow temp as it didn’t happen in the first hour it was on this morning but then at fairly regular intervals since. 

gary - my dt is around 2.5c, so similar but not quite the same. But my min flow temp is also set to 32 and don’t think I’ll go lower than this as imagine I’d get even more cycling like you say 


   
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 Gary
(@gary)
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@rod Thanks for the detail, I definitely haven't seen that behaviour on mine, but mine is a bit too small.  I don't believe the Ecodan can modulate the pump speed, only the compressor, so we are stuck with fixed pump speeds of 1-5 on the controller.  Again, if pump speed is too slow I will also get cycling, mine is set at 4 which gives 20L/min flow.


   
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 Rod
(@rod)
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@hotheat I've dropped my min flow temp to 23, it has been a major efficiency boost once outside temps rise to around 12-15c. The pump can't modulate that low, but it does exactly what happens now: once the flow exceeds the set point it just stops and the UFH manifold pumps keep running if there's still a call for heat so the ecodan sees the flow and return water temps slowly drop as the existing heat from water in the pipes is delivered around the house and restarts again after a while, can take up to 10-20 minutes so cycling is very gentle and acceptable, runtime is once or twice an hour for 15-20 mins. As it has to do little work - air temp is >12 it's only taking the water from maybe 20 to 24, the COP is high 5's or 6+.


   
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(@hotheat)
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@rod I don’t have UFH so I think if this would be too low for me? Either way I only started tweaking my WC curve last week and haven’t seen any double digit temps yet to trial! But should do later this week so will give that a go then. Much nicer to be tweaking at 10-12c than negative temps too 🤣


   
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