I can't give you graphs but....

ASHP Daikin Altherma 3-6kw

Heat loss? Dunno design temp by me 39º @ -3º 

Control mode: pure weather compensation

Volumiser yes -  size? (I'll have to look) 

No Zoning totally open with radiators throughout. 

Defrosting approx every 2 hours - for about 15 minutes - no noticeable heat loss just a slightly noisy high speed water flow around the system which is how I know it's defrosting and a sudden brief drop off in electrical consumption in the Octopus app (it's when the valve does a reverse ferret apparently 😁).

If I look at the MMI data while it's happening the flow temp between flow & return rapidly equalises - in front of my eyes - like 7º in a few seconds. It moves to defrost, the flow speeds up and stays that way throughout. Outside, it's almost silent as small black dots appear then become spaces of thawing and expand across the vents. It's quite fast and efficient.

But a bit disappointing drama-wise - no steam. 🙈

ASHP Daikin Altherma 3-8kw

House loss?  5431 @ -3.4 

Control mode: pure weather compensation

Volumiser yes - don't know size 

No Zoning open with radiators throughout. 

Defrosting approx every 1.5/2 hours - for about 6 mins 

Big spike in power on restart, yesterday trundling along using 900w, defrost for 6 mins,  restart, and didn't get back down to the 900w level for 53 mins, 40 mins of that was over 2200w peaking at 3350w.

In that whole time the room temperature didn't change from before defrost so no idea why it went to those extremes.

Last night I turned off modulation (temperature the heat pump can modulate from the curve, was initially set to 5) and switched to quiet mode (slightly lowers the heat pump output).

So far so good, restarts after defrost today only went over 1400w for 18 mins and peaked briefly at 2000w getting back down in 40 mins 

No noticible difference in performance .

Got to be down to -4 over the next 3 to 4 days so will see how that goes.

Here is my heat pump's behaviour (Midea 14kW running in weather compensation mode) over the last week, including cold outdoor air temperature periods when the heat pump ran regular defrost cycles. The set LWT is about where it should be, but, because of the defrost cycles, the effective (mean) LWT is far less than it should (and needs) to be. The unwanted fall in indoor air temperatures during these cold spells can also be clearly seen (ie it is an MCS fail), as can the slow recovery when the it warms up outside. Weather compensation is the problem here, the weather compensation logic says it is warmer outside, the house needs less heat, when in fact it needs more, because it is still colder than it should be because of the preceding cold snap. My auto-adapt script (boosts the LWT a bit when the room temp is below what it should be) does help a bit, but not enough, I still have the slow recovery, as seen during 5th Jan. 

Thats a brilliant plot with a full range of temperatures.  Your 'no cycle' window is clearly shown as about 8C-5C.  The cycles even only just above 8C look quite short and frequent, whereas you might hope that they would be long and infrequent at just a small delta above the max 'no-cycle' temp.  I do realise we have already discussed this but the plot really nicely brings it all together.

Here is mine (showing FT only - I haven't yet worked out how to superimpose graphs in HA) over the same time.  Actually a very similar pattern but with longer 'on' periods.

@jamespa - I agree, it is a useful plot. Sometimes nature does oblige, and provide a convenient operating range which we can observe. I do however wish the steady state (no cycling) window wasn't so small. There is also a question of whether I can tweak the around zero and below behaviour ie when defrost cycles dominate the picture. I have addressed this in the other Is my heat Pump Defective thread. 

Posted by: @jamespa

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I haven't yet worked out how to superimpose graphs in HA

I don't think you can. You can use the 'History Explorer Card' add-on if it is still available to get multiple plots on the same page (and the plots are far easier on the eye than HA's native plotting). However, HA stores all its data in a sqlite database, and if you export the data in csv format, then you can chart it any way you want. You can use the SQLite Web add-on to get at the data, and use Query Tab (you have to run a query) > Export CSV to get the data. Don't be tempted to work on the database from outside HA when HA is running, it will corrupt and destroy it (you might however be able to copy the database file, and work on that copy, the point is don't work on a live database).  

Posted by: @cathoderay

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@jamespa I do however wish the steady state (no cycling) window wasn't so small. There is also a question of whether I can tweak the around zero and below behaviour ie when defrost cycles dominate the picture.

I think we commented on this briefly earlier and I agree. 

I also think it might be more or less inherent with our climate and the 3:1 (or in reality poorer) modulation ratio of current heat pumps. 

Defrost is more or less bound to occur between 0 and 4C, when its both cold and damp. 

For much of the UK we design for around -2C OAT/20C IAT, but stop heating at 16C because the 'waste' heat is sufficient to cover the difference.  So deltaT at design OAT is 16--2 =18C)  Even with a 3:1 modulation depth and perfectly matched sizing, this means that it will start cycling at deltaT=6, which is 10C, leaving a steady state window of 4C-10C only!  Fortunately that is where our climate sits for much of the time, but of course by no means all the time.

@cathoderay i like those graphs. how do you generate them

i hsve sn Adlar systen

Thanks

David Seed

Posted by: @david

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i like those graphs. how do you generate them

Thank you!

I use plotly in python, with the data coming from csv files. If you are already familiar with python, you will find it a doddle, if you aren't familiar with python but are fairly computer literate you should be able to get to grips with it in hours rather than days. If you a computing novice then it will be more of a diddle than a doddle, but still achievable.  

ASHP Model: Daikin Altherma 3M 4KW

House loss: Calculated 3.3 at -3C, definitely overestimated though.

Control mode: Weather Comp + Thermostat with room modulation +/- 4C adjustment to WDC

Volumiser/buffer tank & size: 40L

Zoning?: 5 rads all fully open

So far I've only noticed 3 defrosts in one 24 hr period when the temp was consistently 1C

Performance Graphs: N/A

Flow Temp ~33C, OAT 1C, IAT 19C

I heard two of the three defrost cycles is because it's now the only time my HP will run the flow rate above 60%. Otherwise it's locked down in the installer menu. I also enable the quiet mode between 20:00 to 07:00

Both the fan and pump ramp to 100% for 15 mins and draws about 1.6kw I think. Very obvious due to the sudden switch in operation though not particularly annoying. I can mostly hear the water noise above my head as the DWH tank is in the loft.

Defrosts were at 4AM, 6AM and then midnight.

Slight correct to the above defrost behaviour as the fan only ramps at the beginning and end of the cycle. The bit in the middle is when both the water and heat pumps run at 100% to melt the ice. Caught sight of one as a big plume of mist drifted over the garden. 

ASHP Model: Daikin Altherma 3M 4KW

House loss: Calculated 4.1kw at -3C. 

Control mode: Weather Comp (system installed in August so I am still playing with offsets (usually at -2))

Volumiser 26 litres

Zoning?: No, all radiators and UFH fully open

Overnight unit defrosts every 45 mins. Not sure if this is something normal as system is new. It is keeping us comfortable (even with -2 offset), however consumption during defrost cycles is quite high. 

Any recommendation to reduce the frequency of defrosts? I understand that these temps favour a lot defrosting (high humidity and temps 0-3C)

Performance Graphs: 

Flow Temp ~39C-40C, OAT 0-3C, IAT 21.5C