Something else... that works for some people...

LG has "Quiet/silent mode" that is normally intended where noise is an issue (say at night or proximity to neighbours etc). When using that mode the compressors operate at lower rate than normally called by WC. 

Some people use very effectively for oversized heat pumps to reduce cycling etc. It means operating at less than optimal efficiency for size of pump but if oversized that may suit.

I guess many other heat pumps have a similar option. Maybe called something else.

I think most heat pumps have this mode but I cant see how it can reduce cycling, unless there is something weird in the control logic (which is possible of course)

For NR mode to reduce cycling it would have to reduce the output of the heat pump.  But if it can reduce the output of the heat pump, why doesn't the controller do this when it needs to.

Something funny here, it would be good to see some plots/data to unravel this

@jamespa 

Samsung has it 'Quiet mode' and I use it a lot and it helps reduce cycling, It essentially limits the output power on mine to just under 1kw.

I think of it like this when the heatpump starts up it starts hard and aims to get flow temp up to target quickly and as it gets near it starts to throttle its output, but when the weather is mild or the house is already warm it often then can't throttle down quick enough before reaching temp and cycling.

Quiet mode with its power limit stops the hard out the gate approach and gives the unit more time to throttle down till the output is sustainable or if it isn't it cycles again but runs for a longer time before cycling.

Does that make sense?

EDIT

I've just looked back at my monitoring to before I started using quiet mode and can't really find any good evidence to backup my above statement but I'm still sure it does help maybe not as much as I initially thought.  

As to your options I'm in option 2 (But ideally I would like a combination of 2 and 3)

If I have the weather curve set to maintain IAT then my unit cycles when its above 6-8deg so I have the temps higher and so the IAT increases and then I have off periods to control the temp. I also don't want to run 24/7 as there is no need to maintain IAT when no one is in for large periods of time or over night and so windows makes it cheaper.

Currently I'm running from 4am to 8am then 12pm till 4pm (DHW runs in this window as well) then back on 5pm to 9pm and with the recent warm weather it been getting a bit warm for me but as we return to more average March temps this schedule works well.

Ideally if I could I would like thermostatic control within these windows as well, but the thermostat I use to control the on off periods does have programable hysteresis

I would probably set off @ 21.0 on @ 18.5 this would deal with solar gain as well as short weather fluctuations rather than me knocking an hour or two off or on to cope, if anyone knows of a thermostat with programable hysteresis like this I'm all ears.

Posted by: @irmartini

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Samsung has it 'Quiet mode' and I use it a lot and it helps reduce cycling, It essentially limits the output power on mine to just under 1kw.

I think of it like this when the heatpump starts up it starts hard and aims to get flow temp up to target quickly and as it gets near it starts to throttle its output, but when the weather is mild or the house is already warm it often then can't throttle down quick enough before reaching temp and cycling.

Quiet mode with its power limit stops the hard out the gate approach and gives the unit more time to throttle down till the output is sustainable or if it isn't it cycles again but runs for a longer time before cycling.

Does that make sense?

It makes sense, although shows a complete lack of thought on the part of the designers (which is disappointing) about the things that they could do, without changing the hardware, to reduce the minimum possible output (which we know is a key question - but sadly not one of the specs mandated by the various regulations which maybe why they dont care!)

As a matter of interest do you know if Samsung does an integral calculation of 'target FT - actual FT'*time and uses it at all.  Vaillant does (it calculates degree minutes and you can display the value which it calls 'energy integral') but I have yet to find out if it uses it to control cycling so that the average output is what would be expected from the target flow temperature.

@jamespa 

I'm afraid that's over my head but if anyone will know that it will be:

SarahH HERE

Also note my edit that I can't really find any good evidence for my statement although I'm convinced it helps.

In milder weather, I know my radiators can only dissipate the heat being produced at a flow temp of 32-33C, so I set the WC to around this temperature and just allow the room stat to call for heat ON/OFF as required. It may run for an hour and then off for a few hours. We then try to manually manage the call for heat further, to coincide with cheap rate slots on our ToU tariff (Cosy)

We achieve good COP's (fours and fives) in the milder weather, so no complaints.

I don't use Quiet Mode as @irmartini describes (I find it does weird things when used for space heating), but I will turn the WC (WL) flow temperature right down when bringing the system up from a cold start and then gradually increase it, to minimise the power draw in the first 30-60mins and keep it running as much as possible within our current solar generation. At present, in the current milder weather, we are turning off all night, and turning the heating back on at 9-10am when we get up. The house soon gets back up to a reasonable temp at 32-33C flow temps as it's putting out way more heat than the current heat loss.

I prefer this method over (1) as I'm in control of what the heat pump does, and when (the heat pump has no understanding of my ToU tariff or our current solar production). I have no idea if (1) would result in a superior COP, but any variations are likely swamped by the financial benefits of the ToU. Similarly, I know the heat pump will be more efficient in an hour because the weather will be warmer in an hour, so if I can hold off turning the heating on, when I do turn it on I'll be running at a warmer OAT. If I leave the heat pump to just get on with it (method 1), it may be cycling off just at the time when it's cheapest and/or most efficient, or cycling on just when it's most expensive.

Posted by: @jamespa

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[As a matter of interest do you know if Samsung does an integral calculation of 'target FT - actual FT'*time and uses it at all.  Vaillant does (it calculates degree minutes and you can display the value which it calls 'energy integral') but I have yet to find out if it uses it to control cycling so that the average output is what would be expected from the target flow temperature.

I don't know how the Samsung does it, but what I can tell you is the power draw reduces as the flow temps approach the desired set point. It seems to be related as much to the return flow temperature (or narrowing dT) as the flow temp. I don't have charts, but from observations on a cold start, I see a power draw of maybe 2.5-2.8kW which gradually reduces (modulates) down to around 1kW as the flow temp reaches the set point and the dT with return temp narrows to 5C or below. The gradual backing off is effective at preventing any overshoot.

Posted by: @old_scientist

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I have no idea if (1) would result in a superior COP, but any variations are likely swamped by the financial benefits of the ToU.

I have to agree that in many cases ToU tarrifs will dominate.  I guess I should've framed the question as 'in the absence of ToU tarrifs!

Posted by: @jamespa

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Posted by: @old_scientist

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I have no idea if (1) would result in a superior COP, but any variations are likely swamped by the financial benefits of the ToU.

I have to agree that in many cases ToU tarrifs will dominate.  I guess I should've framed the question as 'in the absence of ToU tarrifs!

I think you are right to frame the question as you did, as ToU tariffs are very relevant to any heat pump strategy (at least for those who are on them).

Obviously if someone is on a fixed rate tariff (such as the OVO 15p fixed rate heat pump tariff), then that may change things for them.

This whole discussion highlights just how much of a mess oversized heat pumps can create (but I’d still take an oversized unit over an undersized one).

Focusing on the subject at hand, the problem isn’t just the cycling itself. It’s that the entire control strategy is broken when a heat pump is too large for the house. Modern heat pumps are designed to run continuously at the lowest possible flow temperature, and the moment they start cycling aggressively, you’re losing efficiency, increasing wear on the compressor and making the system more expensive to run. The fact that so many people have to experiment with batch heating, thermostat tweaks and quiet modes just to get their system working properly is a clear sign that something has gone wrong at the design stage.

One of the big takeaways from installer training materials is that the industry still hasn’t shaken the habit of oversizing heating systems. Boilers could get away with it because they had raw power and quick recovery times, but heat pumps don’t work like that. They need to be sized correctly from the start, otherwise you get exactly what we’re seeing here: cycling in mild weather, inefficient operation and homeowners scrambling for ways to stop their system from constantly switching on and off.

What’s also interesting is that some of the traditional “fixes” for cycling, like buffer tanks, make things worse. If they aren’t designed properly, they introduce temperature distortions that actually increase running costs rather than stabilising the system. The only real fix for an oversized heat pump would be to swap it for a properly sized unit, but since that’s not an option for most people, the next best thing is damage control in the form of trying to stretch out run times as much as possible while keeping cycling to a minimum.

Weather compensation alone won’t save an oversized system if the minimum modulation is still too high. Batch heating can help if the house has enough thermal mass, but it can also lead to uncomfortable temperature swings. Thermostatic control with a wide hysteresis could reduce overall cycles, but it’s still just managing the symptoms rather than fixing the root cause. Some people are using quiet modes or power-limiting features as a workaround, which is proof that manufacturers could offer better modulation at the lower end if they really wanted to, yet they don’t, likely because industry regulations don’t force them to.

So what’s the best strategy? There isn’t a perfect one as far I know. It’s about finding the least bad option based on the specific system. If I were dealing with this, I’d experiment with batch heating but with carefully controlled flow temperatures to avoid massive swings, and I’d look into whether the heat pump has any settings that can artificially cap output without tanking efficiency.

But really, this whole conversation shouldn’t even be happening. The fact that so many people are having to come up with workarounds to make their oversized heat pumps behave just proves that installers are still getting the basics wrong.

You could use Home Assistant with a cheap wifi or Zigbee switch and essentially make whatever rules or conditions for the target temperature you want (This is how I control an oversized Samsung).

Posted by: @irmartini

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Ideally if I could I would like thermostatic control within these windows as well, but the thermostat I use to control the on off periods does have programable hysteresis

I would probably set off @ 21.0 on @ 18.5 this would deal with solar gain as well as short weather fluctuations rather than me knocking an hour or two off or on to cope, if anyone knows of a thermostat with programable hysteresis like this I'm all ears.