Power usage estimates for non-electric entities

[hilburn]

I'm currently managing this with some external templates but it could be nice to include in the integration

The power consumption of a radiator can be found by: P = KM x ΔT^N - where KM and N are coefficients given by the manufacturer, and ΔT is the difference between the radiator's Mean Water Temperature (MWT) and the Room temperature.

e.g. from Stelrad

KM is calculated from the W/m value in row 2 multiplied by the length of the radiator in meters, N is given in row 3 - this is a requirement in the UK and EU

The MWT is tricky to calculate directly

• I have been using a 5 degree drop over the radiator based on some measurements I made with the FLIR I borrowed from work - so from the boiler setpoint of 60C that's a MWT of 57.5 (when the TRV is fully open - i.e. over_climate or over_switch setup)
• In an over_valve configuration it is more complicated, as the MWT will increase as the flow rate drops. In my test I just measured the temperature drop for the valve at various settings (every 5% down to 5%) and implemented a lookup table to convert between valve % and Temperature Drop, from which MWT can be calculated based on the boiler setpoint

Once the MWT is calculated, ΔT is trivial by subtracting the room temperature (though of course if relying on TRV temperature rather than an external sensor this tends to be wrong as the TRV sensor is heavily affected by the heat of the radiator) - I do the MWT and ΔT calculations in one template (using some macros) for each radiator

All of this gets to the final value of power useage for the radiator which can be given to the VT entity (I tell it the "current house consumption" is an input_number set to 0 and "max allowed" 1 billion so the load shedding doesn't ooccur) and allows me to track the energy used (at the end of the day, the major reason I was doing this was to work out how much of my hot water was being used for heating vs hot water for showers/baths) - but this could also easily be used for other things, e.g:

• Calculation of what boiler setpoint to use with OpenTherm (e.g. radiators are requesting 10kW of heating, boiler needs to be at 32C for that)
• Load shedding of radiators - if my boiler can produce 35kW at 60C water temperature and my radiators are asking for 40kW, either they all need to be turned down a bit, or some need to be turned off according to some prioritisation list