MQTT Gas kWh

I wonder how local MQTT derives gas kWh?

The meter measures volume - it needs calorific value to calculate kWh. So presumably all kWh values returned by MQTT are estimates?


  • Further comment: so far as I can find out, the meter stores a fixed calorific value of 39.5.

    I don't think this gets updated.

  • Jane told me today that we use the calorific value from the MPRN on the Glow service and it is fixed on the meter at 40 (or maybe 39.5) - so I think you are basically correct. There should be volume in the MQTT stream too - so you could DIY the kWh.

  • From my bill:

    Usage = Units Consumed (Cubic Metres) × Volume Correction (for temperature & pressure) × Calorific Value (/m3 ) / 3.6

    From what I can see from my bill history, the volume correction seems to be fixed (1.02264) but the calorific value has varied a bit. (currently 39.2).

    Reverse engineering the local MQTT numbers suggests that glow assumes a calorific value of 39.5.

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