OK, the test is ready to start.
I drained the hot water tank until the temperature from the hot tap matched that from the cold tap so I know the tank is completely full of cold water.
The starting temperature is 12.4c and the Daikin app shows the tank at 12.0c.
The tank is a Joule Cyclone CY205L Indirect Hi Gain.
The tank capacity is 205 litres and the heat exchanger rated volume is 11.8 litres.
We will see what is reported as being used to heat from 12.4c to 50.0c
It should take about 9kW of heat to raise the temperature of 205kg of water by 37.6c if my calculations are correct?