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That said, operating a heat pump on pure (well adjusted) weather compensation with reasonably well balanced radiators without TRVs works very well for many, including me! The problem with this approach is that it takes some tweaking, which cant readily be done in the time between when installers finish the plumbing and when many want to go home.
Indeed, I can well imagine that a heat-pump based system for our 1930ies semi with about 90m^2 should work well with some simple control, including weather compensation; most internal doors stay always open due to the cats wanting to walk around freely in the house without scratching doors. To arrive at this state, it would need some preparation in advance to get most bits right, like radiator sizes and power rating, then monitor and tweak after installation. This is were external software solutions can help, Havenwise or others such as Adia which comes with its own hardware.
Ideally I would like Adia's control software and controlled radiator valves (but not their unit) in tandem with a Viessmann VitoCal 151-A (or equivalent self-contained pre-plumbed 600mm x 600m unit). This would allow controlling temperature profiles for different rooms separately, because "well-balanced" radiators and a single control loop means there is only one common profile moving in unison, even if some rooms might be cooler than others; but their temperatures are correlated. Alternatively, I might get started with Home Assistant and compatible devices for sensors and actuators.
Might this be explained by the lower OAT end of the WCC being a bit too high? With no setback, the heat pump more than keeps up, but with the setback, it has to do the recovery, and the lower the OAT. the more recovery it has to do, and so the lower the IAT at 0700.
Yes, also the higher OAT end is possibly a smidge high too.
This fits with what I have just said, the WCC, which was the same for both 2025 and 2026, although the lower IATs in 2025 will have triggered more auto-adaption, needs to be lower at the lower OAT end with no setback running. But if the same WCC is used with setback running, then the low OAT 0700 IATs will almost certainly go lower. Another example of how tricky the 'natural' experiments can be!
Also that experiments often need repetition to incorporate discoveries.
I noticed them as well, they are clearly outliers, and I meant to look into them, suspecting they may be from a few days at the very end of April 2026 when the heating was off but I forgot to delete the relevant rows. I have now done that, and the outliers have disappeared, see below.
I also did a double take on the subplot titles, 0700 and 0900 on the same one above the other plot???? Then I realised you had very neatly copied and pasted together the two morning plots...
