Best practise for heat <-> dhw cutover

[gvzdus]

Hi, with my LT cascade installation I am heating up once per day the ~500l DHW buffer (operationMode 3 ; forceDHW 1).
I notice that each change on the Three-Way-Valve seems to trigger a compressor stop by the built in control SW of Panasonic. Probably they do so because of worries that during change of the Three-Way-Valve there might be some seconds of complete blockage. However, my Orkli 40713200 valve seems to be designed like "always non-blocking".
So I am thinking of

• managing the valve directly by one of the Heishamon Large relays
• do the DHW heating in heating mode (max. 55° possible due to SW limit)
  Goal 1: Avoid 2 compressor starts per day during heating time.
  Goal 2: Optimize the target temperature during heating: Initially: Start with current DHW buffer temp + 1K, then increase to target temp +2/3 K. (Idea: Do never cool down the upper hot layer in the buffer).

Any thoughts / experiences? Or even confirmation of my observation "switch over always causes a compressor stop"?

P.S. Here a graph about a DHW cycle, started at 12:02:

• WP1 (heatpump 1) turns off for a few minutes
• WP2 is set by my smarthome system to 55°
• WP2 goes into defreeze
• 12:25: DHW heating done, WP1 turns off again, while I gradually decrease the target temp for WP2 to keep it from shutting down.

From the logfile:
2025.01.07 12:25:13 1: Cooling down: wp2out=52.50 wp2target=55 wptarget=39 newtarget=51
2025.01.07 12:26:13 1: Cooling down: wp2out=46.25 wp2target=51 wptarget=39 newtarget=45
2025.01.07 12:27:13 1: Cooling down: wp2out=41 wp2target=45 wptarget=39 newtarget=40
2025.01.07 12:28:13 1: Cooling down: wp2out=40.50 wp2target=40 wptarget=39 newtarget=39

[geduxas]

No, stop is to prevent overheating.
Also did you tried dhw smart mode? I haven't time to proper test it as how it works in total..

[gvzdus]

I don't get how it should be helpful:
"During SMART DHW start time 20:00 (Default Setting) to SMART DHW stop time 05:00 (Default setting) Heat pump re-heat the tank water only when tank temperature drop below 20°C (Default setting)
Time between 05:00 to 20:00
Heat pump reheat the tank water when tank temperature as below condition
Reheat when tank temperature below tank set temperature + R/C (Tank re-heat Temperature) - 3°C"

I might try to decrease the max. temp. of my DHW buffer a bit, but afraid to risk my marriage.
It never goes to < 20°. Also in "Haustechnik Dialog", they speculate this is only supported by Panasonic "all in one" devices.

[geduxas]

I think i misunderstood that smart function.. thout it is smarter :D

So yes last effort to go without stop is somehow adjust temperatures.. i think there was some discussion about it. You could search for it.

[stumbaumr]

The compressor turns off because after switching from DHW to heating the target temperature drops so much that the difference between target and outlet is bigger than 2K.
With my rules I modify the heating curve and re-adjust it as soon as the outlet temperature fits again the previous target temperature...

[MiG-41]

Is it also checking , if i.e. external thermostat is on ? ( if both are off it will turn off anyway , no need to do this magic. with changing curves)

[stumbaumr]

I only use a heating curve with watertemperature. The separate room thermostats (https://www.mi.com/de/product/mi-temperature-and-humidity-monitor-2 ) display the temperature in by the missus required rooms for reaffirmation that it is not to cold.
Goal is to have her complain that it is to warm and then tell her to bring fresh air in by opening the garden door and the roof windows for a short period of time.
I have a screenshot of a timeperiod without defrosting where you can see that the compressor never halts even after DHW-production. My average compressor runtime - including the two starts when defrosting - is 2 1/2 hours...