@cyrusir I don't want to make generalisations about other systems (maybe people who understand the technical details of Samsung/Joule systems better than me could provide more information) but once I saw this issue being highlighted in the data I ran a simple test. 

This was to raise the thermostat for a heating zone during a DHW run and see if the zone pump and secondary pump activate. Once I had confirmed this, I then adjusted the schedule to ensure the heating zones did not run at the same time as the DHW operation times.

I have an EV rate also and one of my goals with the therm app was to see what share of the heating takes place in the low-tariff periods. The underfloor heat battery method works well for me too.

I also saw another issue previously which I didn't really investigate fully. We use most of the hot water for showers in the morning but want some in the evening for rinsing plates etc. The temperature probe which the Samsung circuit board reads is actually quite far down the tank. I was running the DHW cycle in the middle of the day to get up to a 'set temperature' that was more of an average reading throughout the tank than the temperature of the usable water at the top. I did a few quick tests measuring the temperature of water coming out of the tap vs what the Modbus data was telling me and there was a 5-8 degree difference in the values.

A Sonoff TH origin just arrived today that I am going to locate at the top of the tank, attached to the brass fittings to see if this could be a proxy for the 'usable hot water temperature' when you are only talking about a small amount of water for dishes etc. This will hopefully let me lower the hot water temperature target for the daytime DHW run or maybe eliminate it or make it conditional based on this temperature reading.

@cathoderay All the analysis is done in Python and AI is not used for this.

The logic for the 'Heating during DHW' flag is simple. 

When a DHW run is happening, the app checks if any heating zones were active at the same time. It does this two ways:

1. Zone-based check (if zone pump sensors exist): If any heating zone is active for more than a small threshold of the DHW run (15% by default), we treat that as “Heating during DHW.”

2. Power-based check (if we don’t have zone pump sensors): It looks at indoor power and if it stays above a set threshold for a meaningful portion of the DHW run (I have identified it to be >120W for the indoor unit i.e. a significant amount over the baseline value for a DHW run meaning the secondary pump and 1 or more zone pumps are working), it is flagged as “Heating during DHW (power).”

@redzer_irl — I am not sure what a 'zone pump sensor' is? Is it a HA sensor sensing on/off state, and if so how does it do the sensing? Ditto the 'indoor power', what is it the power of? The secondary (space heating) circuit pump? If the answer to both is yes, then you are detecting whether the pump is running, not whether space heating is on. You might have a variation on 'the wheel is spinning but the hamster is dead', ie the circulating pump is spinning, but the circuit is dead (no heating going that way). If that is the case, pump still spinning even though space heating is not active, I agree that is less than desirable, and should be fixed. By the way, my space heating circuit pump does go off when the DHW is on, I checked a short while ago (I do my DHW between 1300 and whenever it reaches my set, temperature, usually around 1340).

Some more details of your system will help eg is my assumption you have some form of hydraulic separation (something between the primary heat pump circuit and the space heating emitter circuit(s), a plate heat exchange or buffer) correct? 

And do some hands on tests next time a DHW cycle runs, check what is actually on, and where the heat is actually going!

I'm still intrigued to know where the wording 'Heating zones appear to be active during hot water production' comes from...      

@cathoderay

I added this as I was not able to see the pump operation from the modbus data as it is controlled by the Joule board.

Posted by: @redzer_irl

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I had added an optocoupler board previously to monitor the primary pump, secondary pump, and three zone pumps

The indoor power sensor is a Shelly CT clamp, as is the outdoor power sensor.

Posted by: @redzer_irl

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I was able then to correlate the zone pump readings with the Indoor Unit power sensor to set a threshold of 120W so that Heating during DHW can be determined without the zone pump sensors.

I have a Joule Smart Plumb Pre-plumbed cylinder that has a 200L DHW tank and an integrated 60L buffer.