Monitoring Immersion via Myenergi Eddi

I am looking to implement monitoring of my immersion heater to make the figures for my heat pump monitoring a bit more reflective of all power usage (not just the ASHP unit).

I have a solar diversion setup with the Myenergy Eddi and am currently trying to decide would it be better to have the electric meter (SDM120M) on the output side of the Eddi (variable voltage / current based on the available solar and can be off for long periods (This does not seem ideal…) or on the Input side, where it will also account for the background usage of the Eddi.

The setup is wired that the disinfection cycle will trigger the Eddi (via the relay board voltage sensing) and any export over 1.5kw triggers the heat pump to run (again via the relay board). The power for the immersion heater all comes via the Eddi regardless with the heat pump power source only being used as a voltage trigger and not for any actual power draw.

In think having the meter before the Eddi and monitoring all input and then disregarding the background draw would be the most sensible way to install but I am looking for any other opinions or Ideas that I may not have considered.

Neither the data sheet nor instruction manual give the self-consumption of the meter, so it is probably insignificant, in the order of a few watts, so you can ignore it. If you put the SDM on the input side, I’d expect it to be more accurate as it’s only dealing with a probably distorted current rather than both current and voltage, and you can use it to get a value for the self-consumption of the Eddi - the website says 3 W on standby. You almost certainly have a greater loss from voltage drops when the immersion heater is powered.

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My plan was to disregard the standby power of the Eddi unit to allow for a better reflection of energy use but as you say at 3w will it make a significant impact over Kw used for DHW.

From a practical standpoint due to the space confines it would also realistically be easier to go pre Eddi power input.

Now just to find a way of having a separate feed in the heat pump app for the immersion power. (as this is a known COP, while I want it visible there is no point in tanking the COP of the pump for this).