@heacol I'd agree if turning the pump down had made any difference at all to the consumption and comfort... but it hasn't.

@webcmg Our house is a recent self build, timber frame with block, K-rend rendering, and part wood cladding. We're fairly well insulated and had to do an airtightness test to get our RHI. We've got UFH downstairs and larger radiators upstairs. I also bought a Flir last year to track down gaps our builder had missed.

I've attached some screenshot of the consumption and yield for heating plus a Total usage for the house from HA. It's been -9ºC at nights last week so I've seen the highest consumption since moving in.

You don't have a hidden Hot Tub that your wife's been hiding from you? 😉 

November:-

December so far.

Total December house usage.

@webcmg Then I am sorry to say, you have an exceptionally badly designed system. I would complain to the installers competent persons scheme and MCS.

@colin - I'm interested to know where those charts came from, because I am not sure they make sense for December. They show a notable decline in consumption for the period 10-12th Dec, which was right in the middle of the recent cold snap. Perhaps you went away over that period, and turned the heating down? The charts are also not very clearly labelled: is 'Environmental yield' (a rather odd phrase at the best of times) so called 'yield' over and above input, or total 'yield'. If the latter your COP for December doesn't look so hot (at about 2).

Here's my kWh in (consumption, energy used) and kWh out (total heat output generated) for the last three weeks, data taken manually from the Midea app and then charted. The COP on the left hand side hovers between around 3.5 and 4.0, on the right hand side it is nearer 2.5, with an average over the whole period of 3.18. 

@colin thanks, please can you send the same graphs for DHW consumption and yield?

@webcmg Here you go.

November

December

@cathoderay Those stats came from SensoApp and Home Assistant. I'm not sure how accurate the SensoApp stats are but I'm sure there's room for my setup to be optimised. It's been nearly -10 for nearly a week last week so I'd expect my COP to suffer. We may have been out or put the log burner on for those days so a slight dip. The COP on the Vaillant is calculated as (Consumed Units+Yield)/Consumed United. When I checked a wee while ago I thought I wasn't doing too badly but I'll be checking in more detail when my heating engineer next visits. 

Posted by: @colin

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The COP on the Vaillant is calculated as (Consumed Units+Yield)/Consumed Units.

This has come up before, different jargon (yield? environmental yield????) and formulas, adding to the general obfuscation. The industry really needs bashing about the ears to bring it to some sort of order, eg total input (should really include all input ie not just the compressor) and total output (both in kWh so energy used), no need to bother with the yield nonsense, and COP is simply output/input, a COP of three means you put one unit in, and got three units out. Not having a go at you, of course, just a lament against the way the industry uses smoke and mirrors. On the Valliant formula,your COP isn't so bad, using eyeballed averages, about 25kWh in, 50kWh yield so COP is around (25+50)/25 = 3, which may be pretty much where I'm at, and perhaps many people are at, given the recent cold spell.

The other potential problem is the apps not measuring or recording accurately, one of the reasons for asking about where the charts came from. The Midea app uses variable rounding, which just creates more smoke and mirrors, and it is rarely clear whether cumulative figures are based on summed rounded figures, or sums of figures with decimal places (perhaps the former, as the cumulative figures are always rounded too). Luckily my heat pump has an external supply meter which means I can check the app readings, and invariably they are not the same as those from the external meter. Usually the external meter shows a larger figure, by about 5% (maybe that is the non-compressor use) but over the last week it was the other way round - the app reported a larger input than the meter.           

@cathoderay This looks more like my usage profile. What's your setup/house size etc? DO you have heat exchanger and buffer tank?

@colin thanks, do you have an intermediate heat exchanger (VMZ MWT 150) and buffer tank? I am also interested in your settings for your VMZ AI:

• Comp. hyster.CH = 3k
• Max. re. feed head = 900 mbar
• DHW mode (Normal) - options are normal, balanced or eco
• Max, anti-cycl. time = 5h
• Conf. heat. build. pump = Auto
• Conf. DHW. build. pump = Auto
• Compr. current limit = 25
• Compr. noise. reduct. = 40%
• Intermed heat exchange = Yes

@heacol yes, worried that's the case. Need someone to take a look at it, but need remaining insulation issues and rad changes to be addressed first. Not sure where we stand r.e the competent person scheme because Vaillant commissioned the design, a plumber installed the pipework and rads and another company did the UFH. We didn't contract anyone we just bought a new build house. Any ideas?

@webcmg Our setup doesn't have anything like that, our Arotherm+ is connected to a Vaillant uniSTOR 300Ltr Unvented Cylinder with two or three other buffer/expansion tanks.