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Thinking this through a bit more,

  1. You want a COP of around 5.0 with outside temp of 10c and know this is achievable with the Daikin unit (when it is running in equilibrium at a flow temp of 37c.)
  2. Your unit has a minimum compressor power of 920 w so that means you have to put 920 x 5 = 4.6kW out from your radiators as a minimum.
  3. Your house needs, say half of this - around 2.3kW to equilibrate at 21c internally when it is 10c outside. (it would equilibrate to 32c with the full 4.6kW)
  4. So you need to a) cycle 50% on and 50% off with the on and off periods as long as possible and bearable and b) get the radiator output to 4.6kW when the room temp is 21c.

Lengthening the cycle might be achieved by increasing the on-off hysteresis using the largest overshoot/hysteresis settings for both room temp and for Leaving water temp.

Increasing the rad output can be done by either increasing the rad sizes or increasing the Flow temp above 37c. With the latter solution there will be a trade off with COP but I suspect your optimum is above your current 37c setting. I would try it at say 45c to see what the COP looks like then, if it is no better than now then drop that to 40c.

I do hope this helps. One final check/question - is your unit set for RT control or Ext RT control? Field code C-07 = 2 or 1. It should be 2 as that uses the Madoka properly.
All the best.

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