I have an oversized (for my property) Samsung unit. I can only run constantly when the temp drops below 5C, and even then it gets too warm in the bedroom overnight so I tend to turn off between midnight and 4am, and reheat in the cheap 4-7am slot on my Cosy tariff. I'd need ambient temps close to zero to be able to run constantly. I also turn off between the 4-7pm peak.

I run my system such that the room thermostat controls the heat pump through call for heat, and as long as the room stat is calling for heat, the heat pump will stay on. If it can't dissipate all of the heat it's producing due to the radiators being too small/LWT is set too low, the flow temps just rise until the system reaches equilibrium. Flow temps of ~32C is about as low as I can reasonably go, but I can reduce to 30C overnight if it's really cold.

Our digital room stat has adjustable hysteresis of 0.2-1.0C, and I find a setting of 0.5C is a good compromise between comfort and achieving reasonably long heating runs. the heating may stay on for 45-60mins and then be off for 60mins as the room stat goes between 19.5-20.0C, or whatever I care to set it at.

The trick is to try to ensure reasonably long runs to achieve good efficiency. Cycling 4 times an hour probably isn't great. Reduce the flow temps as low as possible, and try to maximise run times within what is comfortable (obviously you don't want large temperature swings making things too uncomfortable).

Make observations / take measurements to see what works well for your system. Some systems are happier than others when cycling.

See I’m hoping to keep my flow temps lower. It’s 7c outside and I’m on 29c flow. 

im similar in that everything is open. We tend to like around 19c but stats set to 21c. House it’s around 19-20 currently. 

so it’s working it’s just cycling too much really. 

If you are concerned about cycling all you can do is run it a few degrees warmer till you either get no cycling or reduce it to a level you are happy with.  I find 32C and I get no cycling, at some point the thermostat will hit its limit and HP will turn off till house drops 0.5C and thermostat turns it on again that can be several hours.

Posted by: @benseb

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See I’m hoping to keep my flow temps lower. It’s 7c outside and I’m on 29c flow. 

im similar in that everything is open. We tend to like around 19c but stats set to 21c. House it’s around 19-20 currently. 

so it’s working it’s just cycling too much really. 

Are your emitters capable of emitting the heat being produced at a flow temp of 29C? If they are not, then the return temp will rise and narrow the dT as the heat being produced cannot be dissipated into the room, and the heat pump will cycle. If that is the issue, the solution is larger emitters or higher flow temps (the heat has to go somewhere).

For any given ambient temperature, you can find your minimum flow temp by running the heat pump constantly and with room stats set high, and see where the flow temps settle (you will need to set the ASHP to always on though so it cannot cycle). For my system (rads only, no UFH), in milder weather (above 10C), the minimum flow temp I can achieve is around 32-33C, and as the outside temp falls (along with the COP), my minimum flow temp reduces to around 30C as less heat is being produced due to the lower COP.

You likely have two choices - run with a lower flow temp (29C) and the unit cycles, or run with a higher flow temp without cycling and allow the room stat to turn off for periods when the house is at temperature. The former is more efficient due to lower flow temps but excessive cycling reduces the efficiency, whereas the latter benefits from potentially longer runs without cycling but efficiency is reduced due to the higher flow temps. You may want to run some comparisons to determine which works better for you (for your definition of better). You will likely find there is a sweet spot for flow temps, below which it is not worth venturing.

Posted by: @benseb

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We had a 14kW twin fan Ecodan fitted about 6 years ago. At the time the house was rather cold and lots of stone walls

 

we’ve just finished completely stripping back 3 of the coldest rooms. So about 1/3 -1/2 of the house. These rooms are now very high insulation. Almost to passivhaus standards. 

weve also replaced 3 big of radiators which were plumbed in microbore with a big 5 loop UFH circuit  

If your UFH is a high mass construction you may be able to store quite a bit of heat so you can run the heating above the cycling temperature or to a less extreme cycling count and live with long off times. So is your UFH a screed construction? What other emitters do you have? Are you thinking of screeding the other half of your floor area?

And as @old_scientist said there might be issues if your return temps aren’t keeping low. 
The 14kw  ecodan will have a minimum output of somewhere around 4.5kw which will challenge your emitter setup to lose enough heat at low flow temps. 

Our ecodan is an 8.5 in a 180 sqM old house and we can’t quite get down to 32c flow temps (rads only) but we are fine at 34c with one cycle sometimes two cycles per hour. Our return temps are pretty much horizontal on the MELCloud graphs at that flow temp. 

Hmm lots to think about. 

the house is about 250 m²  roughly half of that is UFH. Ie most of downstairs.  but only one large room (lounge) is proper UfH with screed the rest is retro fit so doesn’t have the same thermal mass.   so still good output but we can’t charge it up the way we can with screed  

we’re also on Octopus cozy I did experiment with over running the heating during the cheaper periods and let it cool down a bit on the peak periods but it wasn’t running very efficiently and as our battery tends to keep everything off peak anyway it wasn’t making much sense

I’ll have to keep an eye on the cost of running either with a lower temperature and more cycles versus slightly high temperature less cycles

one thing I need to consider is due to the shape of the house We have quite a few pumps. There’s two on the primaries for the Heatpump and then another three for the internal distribution so I think we have about 400 W of pumps when the system is running that can be about 50% of the heat pump usage. 

Posted by: @benseb

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 we’re also on Octopus cozy I did experiment with over running the heating during the cheaper periods and let it cool down a bit on the peak periods but it wasn’t running very efficiently and as our battery tends to keep everything off peak anyway it wasn’t making much sense

Yes, if you have battery storage and can flatten the import price, then ramping up in cheap slots and set back or switching off at more expensive times makes little sense - it will be more efficient to just run constantly (or as constantly as you can) at as low a flow temp as reasonable. Without battery storage, it absolutely makes sense to leverage the price differential between cheap, day rate and peak rate times, even when it means giving up a little efficiency to do so (half price electricity for 8 hours a day gives substantial usage if you can shift half or more of your usage into that 1/3rd of the day) by 'charging up' your DHW and UFH screed.

There are advantages to an oversized heat pump too, which rarely get discussed, so it's not all doom and gloom. As you are not working it flat out in the coldest weather, it's likely to frost up less and you are operating it within it's most efficient range (generally between 30-70%), outside of which efficiency rolls off. After a winter holiday (or extended power cut) where the heating has been turned off or down to minimum, you have the extra capacity to reheat the home quicker rather than merely being able to maintain an exiting comfortable temperature.

I've been experimenting with flow temperature, now the house doesn't have windows open for builders, etc.

Managed to push our WC curve down -7c from where it was. This is great except if the heating goes off for any period, then it's slow to recover, but fine for maintenance.

Settled on about -5, so means currently at 6c outside, we're on 29c flow temp. Using about 20kwH of power a day. Not bad for a 200+ year old, 250sqm house eh!

Will start to look at cycling next week now I have a starting point for what flow temp it 'needs'

@benseb that sounds a good point from which to start. Since our battery is just a third of your size I would be heating in just the low cosy period and then mostly off and take the efficiency hit. But you don’t need to do that. Happy fiddling to get the cycling better!