Tuesday, April 28, 2009

Degrees of Heat and Consumption

Let no one, least of all me, be surprised by the relationship between average monthly temperature and a domestic household's monthly therm (natural gas) consumption. Thanks to archived utility bill data, I can plot the January-December gas consumption onward from January 2005:

Two things jump out at me in this picture. First, before 2006, I was not in the habit of turning off the power supply to the boiler each May 1. It ran on standby all summer long. Hence, with the boiler running in 2005, my total natural gas consumption during the summer months was effectively DOUBLE what it should have been for that period. The second point is the normal summer months give me an idea of how much gas is devoted to water heating and cooking combined, since those are the only other gas appliances in use.

The take-away here is that the year-on-year data trends are a way of detecting anomalies in consumption. Note however that this is not "real time" error detection; in effect, such information becomes evident when you get your utility bill, usually a couple weeks after the meter reading date. It's better than nothing, but certainly not as useful as having sub-meters for each appliance. And while electricity submetering is fairly easy to do for domestic appliances, even I am not inclined to pursue that... not yet, at least.

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