I mentioned yesterday that I've ordered two water flow meters. Despite measuring water flow, their main use will be to help me attribute our gas consumption.
First, the water flow meters will be cut into both the heating circuit and the domestic hot water output. Pairs of temperature sensors will go onto the incoming and outgoing pipes of both circuits. By measuring flow and temperature difference, I can work out exactly how much power the boiler is actually putting out. At the same time, I will measure the overall gas consumption at the house gas meter (luckily mine has an impulse at the lowest gear).
Most of the time (during winter) the gas will be used to heat the house - with brief periods for hot water, and for cooking in the evening. I know when we're using gas for hot water, because the flow in the heating circuit stops, and starts in the hot water circuit. But what about cooking?
That took some thinking (I considered a camera above the hob, or sensors on the cooker controls), but then I realized that I can learn a model of the efficiency of the boiler, probably dependent on outside temperature, maybe also return flow temperature. That model can be calibrated with data from times when I know I am not cooking (i.e. most of the day). Knowing the power output at any time, I can compare the gas consumption predicted by the model with that measured at the meter point - any additional gas used will have gone into cooking.
That way I can use inexpensive water meters to create virtual gas meters. And know exactly how much of our gas consumption went onto heating, hot water, and cooking.
(Virtual sensors and data driven modelling is my research area).
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