Posted by: @derek-m

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At the moment your setback isn't actually a 'setback', but more a 'switch off', which takes no account of the prevailing weather conditions and IAT. It may be preferable to lower your room thermostat to a more appropriate value rather than 12C, thereby limiting how low the IAT can fall.

An alternative would be to add additional Python code, to monitor both OAT and IAT and decide to reduce the setback period and increase the recovery period if the weather conditions are more severe.

I agree, the setback is used to effect an on/off switch (and have said as much more than once!). Limiting the drop in IAT as you suggest is certainly an option. However, recall that one of my key 'principles' was that the desired vs actual IAT difference can act as a proxy for all the other variables. For example, if the normal difference at the end of the setback is 2 degrees, then if it becomes 4 degrees, then something, whatever it is, is cooling the house at a faster rate; and, as a consequence, more heat needs to be added at a greater rate.

It is still very early days. I think I need to observe the way the actual vs desired IAT varies with different OATs and conditions, and tweak the auto-adapt code based on those observations. For example, if the actual IAT is less than two degrees below the desired IAT then it is 'situation normal', and only a minor recovery boost is needed, however once the difference is more than two degrees, then a bit more oomph and then some is needed. 

Very happy to let you have a copy of my csv data. Let me know what variables you would like, and at what intervals (minutes or hours), alternatively I can send you the whole lot, but note that not all variables have been collected since the beginning, eg the MD02 sensor for room temp (IAT) was only added in late September, in readiness for the start of the heating season.   

@cathoderay

If you can provide all the variables covering the past week at 1 minute intervals that should be more than adequate.

@derek-m - no problem, here they are (posted publicly in the interests of open data etc etc; the relevant column heads should be self explanatory eg ambient is the OAT, if not, ask and I will explain; energy in and energy out are lifetime, you get Midea's day/hour/whatever figures by making a relevant subtraction, MD02 is the room temp/humidity sensor; all this is the raw data collected over modbus from the wired controller, no calculations have been done on it):

@cathoderay

Many thanks Ray.

The latest 48 hours data, comparing last night's data with the night before: 

Note that yesterday (1700) I increased the default right hand end of the weather compensation curve LWT from 32 to 34 degrees. I have also added another line, the Set LWT, ie the combined result of the built in weather compensation curve as modified by my auto-adaption script, and being the set, or target, LWT. Apologies for the somewhat unsettling colour scheme, I will sort that out in due course. Some observations:

(a) overall, the heat pump does a reasonable job of matching the actual LWT/RWT combination/average to the set LWT

(b) comparing last night's setback and recovery with the preceding night's setback and recovery provides, I think, some useful information. On both nights, the setback periods were very similar: similar OAT around 7 degrees, similar drop in IAT (nadirs 16.7 previous night, and 16.9 last night). But the recoveries are different: yesterday's recovery was slow, taking over 12 hours, while this mornings recovery was much faster, about four hours. The key difference appears to be the OAT, which rose sharply yesterday morning, unlike this morning, when it hardly rose at all. Somewhat paradoxically, the higher OAT appears to have slowed the recovery because it sets, based on the WCC, a lower LWT in the immediate post setback period, around 40 degrees yesterday compared around 45 degrees this morning. Some of that increase this morning will come from the higher right hand end of the WCC, but most of it comes, I think, from the lower OAT, via the WCC. This suggests I might need to tweak my auto-adaption depending on the OAT, eg when the OAT is higher, the auto-adaption adjustment, somewhat counter-intuitively, needs to be a bit larger. This is inevitably an iterative trial and error process, but that's fine by me, because I am tuning my actual system to the real world, nary a model in sight 😉

(c) overall, the recovery boost extra energy use continues to be considerably less than that saved during the setback, meaning an overall net saving in energy use.    

part of the reason why im using fixed flow temp, with wcc sometimes it takes alot longer to heat after setting back overnight.

Posted by: @newhouse87

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part of the reason why im using fixed flow temp

Standard weather compensation doesn't work well with setbacks, the logic uses only the OAT and doesn't know the IAT is below what it should be.

I did try a fixed flow temp a while back, but it dramatically increased my energy use. The data I collected back then was much cruder than I collect now, and the charting less sophisticated, but this one does show a clear increase in heat pump energy use when changed from weather compensation to fixed flow temps. Note the heat pump was fitted in Feb 2022, most of the data on that chart is pre-heat pump, and there are clearly some anomalies!

@cathoderay Did you try running fixed flow temp for say 12 hours and off until morning then and see if house still warm and usage reasonable compared to your current wcc and off for few hours at night? I have no doubt a fixed flow running the same amount of hours as a wcc curve would be higher usage.

@newhouse87 that's exactly what I do, heat up the UFH overnight at a fixed flow of 40C so the house is a degree warmer than required first thing.  This is at a off peak electricity rate that is 25% of the cost at peak so COP really doesn't matter from a financial perspective.  Then it automatically changes back to Weather Comp for the peak period.  At current temps the heating may come back on in the evening when the temp drops sufficiently but depending on outside temp it may not come on at all.

@gary Yeah id like to do that at night rate but fan outside too loud for light sleeper like me.

@gary @newhouse87 - I don't have UFH or an off peak tariff, so my current strategy is a bit different. I do have a house with a high thermal mass for is size, but that cuts both ways, holds the heat well when it has it, but equally is slow to heat up when it is cooler than it should be. I'm still inclined to the idea that the lowest energy use will come from not heating the house above what it needs to be at any one time, because, for any given OAT, the higher the IAT, the greater the loss. Indeed, one way of looking at a setback is that it incorporates this principle: why keep the house at daytime temps overnight, when it doesn't need to be at daytime temps? 

At the moment my pressing concern is that I have now confirmed by various tests that the erratic DHW heating I mentioned elsewhere is almost certainly caused by the auto-adaption script. Or more accurately, the modbus register writes the script uses to set the WCC end points. It appears these have the same effect as going into the 'For Serviceman' menu, exiting it somehow resets things and even more bizarrely turns off some aspect of the DHW heating controls. Given the way you set the end points manually is by going into the 'For Serviceman' menu, perhaps this isn't that surprising, but sure is a nuisance. If anyone has any ideas about how to deal with this, please say what they are!

Interesting to see your findings, @cathoderay.  From what I can see in my own n=1 study (this house (which is large and fairly well insulated, but without a huge thermal mass), these particular settings on this particular day) is that setting back doesn't seem to show much in the way of difference.  

Here's the hourly consumption across one day (fairly typical out of a run of 5 days or so on the same settings), with the average of 0.7kWh/h shown.  You can see it ticking over at a setback of 17°C before working hard to recover to 20°C at 7ish, then levelling off for most of the day.  In my case that average of 0.7kWh/h actually looks fairly plausible as a kind of constant ticking-over kind of level once the house is warmed up.  My guess is that running constantly without a setback would therefore smooth out to a pretty similar value.  Very unscientific I know, but about the best I can do with the limited info Vaillant's sensoAPP provides; will see what happens with some different settings on different days...

Since our installer came back and factory reset the system to get rid of the time schedule gremlins, we've had one night at constant temperature, which we actually found less comfortable; we didn't need it that warm overnight, and in the morning the rads were just ticking over as compared to tangibly warming the place as it does during setback recovery - perceived warmth/comfort is a funny thing.  I think there's also something about the stats being in the hallways in the middle of the house, so at night when the doors are closed they are sitting in the warmest parts of the house, with the peripheral rooms sitting cooler.  By making it recover from a setback, all the rooms warm up nicely in the morning.  I've changed it back to a 18°C setback now, so will see how that feels...