I don't know what the spec sheet says but the lowest I've seen my 8kW Samsung R290 Gen 7 go is approx. 2.8kW of heat for 460W elec

@irmartini at 15 outside?? That’s pretty damn impressive! The Samsung was on shortlist. Thanks for sharing that!

@tomasmcguinness 

Yes 15deg outside that was from the past hour.

Edit I should say that's Met office 15deg, I don't know the actual outside temp as measured by the heatpump but it can vary by nearly 2 deg but its generally not too far off.

Posted by: @tomasmcguinness

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As I'm getting closer to my own ASHP installation, I've started looking at particular models, which I think will be the most suitable.

My heat loss is around 312W/k or 7.5kW at -3. Outside temp did hit -5 this winter, so a little head room would be nice, but nothing we couldn't weather (pardon the pun).

Heating needs to go on when it's 12 or less outside. My gas boiler can keep the house warm with a 30 ish flow when it's that temp outside. Might work with an even lower flow temp, but due to the boiler being stupidly oversized, it would just cycle like crazy.

That means I'm looking for a modulation range of around 2.8kW to 7.5kW. 

I'm really struggling to find a source for that information. Plenty about *max* outputs, but not a whole lot about minimum outputs.

Mick Wall shared some Polish documents on the Vaillant aroTHERM: https://community.openenergymonitor.org/t/vaillant-arotherm-owners-thread/21891 It shows that a 35/30 flow would result in a min output of 3.5 when it's 12 outside. As the flow temp increases the min output lowers and at 55/47 it's 2.6. The COP drops a lot of course.

I can't seem to find anything about minimum outputs for the Samsung Gen 7 for example. 

Would anyone have an experience with that kind of modulation range, willing to recommend a particular heat pump?

 

You will need to go hunting for the performance tables (like the Vaillant one) for the models under consideration, as min output is rarely published other than buried in these.  Remember you need the min output at the max OAT not at the min OAT.

In general terms modulation depth appears (where it is published) to be about 2.5:1 - 3:1.  The gotcha to look out for is badge engineered models where more than one 'variant' is sold with the max o/p limited in firmware.  Daikin, Midea do this big time.  The Vaillant 5 and 3.5kW models are said also to be the same.  You can tell by looking at physical dimensions, weight and refrigerant charge in the spec table.  If they are the same between two different models, its a pretty sure bet that the lower power one is simply the higher power one with a firmware cap.  The minimum output will be the same for both, so the modulation depth of the lower output variant rather less.  

You need the performance tables anyway because sticker capacities are nothing like actual capacities in many cases, and anyway vary (in most cases and thermodynamically) with OAT and FT.  The Vaillant '7kW' machine is good for about 8.6kW at -3, a typical design temp in the South East of England, whereas the Daikin machines appear to be 'tweaked' in various ways so it depends on the details.  Samsung do cap their outputs at the sticker number and Mitsubishi do likewise, so as long as the design OAT is sufficiently high you get what it says on the tin.  Midea, in many cases, have lower actual capacities than the stickers would indicate.  

@jamespa In case it is of any help and enlightenment, I am attaching charts just taken from my Daikin EDLA08 8kW ASHP from Homely dashboard for the last 7 days. The chart with both consumption and output tends to drown the consumption line so I have produced the comparison as well. This has been to heat the whole house to 22.5 degrees C and I frequently see that the total house consumption may be 500 to 600 Watts and of that, 200 to 300 is the normal house load; from this I conclude our heat pump can modulate down to ~400 Watts. Hope that may help.

Regards, Toodles.

A snapshot of our 7kW Vaillant was at an OAT of 18C producing 1.1kW with 40% of the time on & 60% of time off. 
The lowest in continuous production was 3.2kW (again heat) at 14C. The cop for the day’s heating was6.6 using Vaillant figures (believed to be overoptimistic in general), which is great.

@tomasmcguinness

Mitsubishi's figures are in https://library.mitsubishielectric.co.uk/pdf/book/Ecodan_ATW_Databook_Vol.6_.0_.pdf#page-1 (I'd suggest downloading it and reading it offline as it's a 400+ page PDF). For their new R290 ASHPs see the tables on pages 88 and 89. 

TL;DR the 8kW unit can modulate down to 2.0 kW at 12C OAT and 25C flow temp. And 1.9 kW at 12C OAT and 35C flow temp.

It's able to modulate so low because the 8 kW unit contains two compressors, 6 kW inverter (modulating) and 2 kW fixed (for additional output when it needs it). 

Posted by: @robs

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It's able to modulate so low because the 8 kW unit contains two compressors, 6 kW inverter (modulating) and 2 kW fixed (for additional output when it needs it). 

That's an interesting development, are mitsubishi the first to do this?

I would be careful you don't fall down a rabbit hole. Modulation seems to vary massively with different heating systems, flow temp etc. irrespective of what the paperwork says in an ideal world. Example mine can modulate on paper to just under 50% name plate capacity, but for that to occur many stars need to align, they don't very often, but that doesn't matter that much. A heat pump will cycle to manage min outputs below min modulation and there is very little impact on CoP. 

I wouldn't get to trapped in the discussion of how far a heat pump may be able to modulate, but the better discussion is how well it manages to operate below min modulation. And what strategies it allows you to get meaningful cycling and not short cycling.

The difference being, short cycling adds little or no useful heat energy to the house, meaningful cycling adds heat, my heat pump needs to run more than 10 mins to get meaningful heat into the house.

If after reaching its minimum level continuous operation it cycles cleaning 80% on 20% off in an hour  gradually reducing its on period to just ~15minute on rest off as the external temperature increases then it is smooth control. The result was a COP of 7.3. Not to be complained about!

So the end of the compressor range is not the end of the story.

My Midea r32 6kw(5.7kw rounded up) supposedly runs as low as 25⁰c and regularly seems to pull just 500/600w but that includes the base load of the house as well ie fridge freezer and anything on standby. 

Hard to tell as Midea app is naff and only going off octopus mini live data

It's a big old ugly beast though