Interesting…while i use pure modulation and no wd curve the result is effectively the same as yours as my temps are constrained between 33 and 39c. As you say the unit seems happiest at these temps with cop of over 5 usually. With just rads and 4 x 2.5kw fancoils I run normally at dt of 6. I raise this dt to 8 in December to February as i need to allow it to put out its maximum without having a high flow…which causes a lot of noise in my 22mm and 15mm piping.
My reason for modulation only is that it adapts better for the variable fancoil output. It might run at 38 at morning start up even with highish outside temps but it quickly modulates back to 33. On the other hand, on colder days with the sun shining it can still modulate down to 33 whereas a pure wd system would keep it higher. Swings and roundabouts but i still think that good wd setting on its own is too dependent on the user getting the curve right.
I feel that pure wd might be better for well set up underfloor systems.
I set up my sons new vaillant 7kw system last week and that runs with easy to use standard wd curves and the option for modulation that is preset. After start up its quite easy to reduce the vaillant curve from say a standard 0.9 to 0.8, 0.7 …until the hp fails to keep the house warm. The numbers relate to the steepness of the curve…which is a curve and not a straight line. It seems easier than Daikin with less chance of messing it up.
