Tuesday 11 January 2011

Household energy consumption without major consumers

I've already noted that the tumble dryer, washing machine and dishwasher account for a quarter of Alex's energy consumption. However, now that we have the data for each of these appliances through sub-metering, we can subtract these appliances from the overall demand. This produces a graph of the appliances which account for the remaining 75% of the total energy consumption.

Also as noted earlier, it's not feasible to subtract individual appliance's power demand from the aggregate demand. However, we should get reasonable results by using the energy consumption. Below is a graph of Alex's overall energy consumption over one day, with the tumble dryer, washing machine and dishwasher removed.

As before, we can see the repeating patterns overnight and peaks during the day. Interestingly, without three of the major consumers, it's easier to identify some other major consumers.

For example, a kettle draws the maximum amount of power, which is approximately:
230 V * 13 A = 3000 W

Given that our samples are recorded over minute intervals, that's the equivalent of:
3 kW * (1/60) = 0.05 kWh each minute

Therefore, jumps of 0.05 kWh or more might correspond to the kettle. We can confidently rule out all peaks below 0.05 kWh as belonging to the kettle. Since the kettle's duration of use is only likely to be a few minutes, we expect it to be represented by a thin peak of only a few points.

In fact, close to the 840th minute, we can see the energy consumption quickly jumps from approximately 0.035 to 0.085; exactly the signature we're looking for. The fact that this signature is identifiable even during the use of another unknown appliance is encouraging.

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