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Crunching numbers on my home energy use

During an attempt to bring order to our household files, my husband and I discovered that we saved enough utility bills to reconstruct a nearly complete record of our household energy and water use since we moved in in 2000. Unable to let such a treasure trove sit idle, I ordered the pile and input everything into a spreadsheet.

I hoped, indeed expected, the resulting data to show clear if subtle downward trends across all three resource types (electricity, natural gas, and water). Our household size has not changed over this time, and we have replaced several major energy-using appurtenances and made numerous small changes over time.

Unfortunately, the data is not so clear. After viewing the first graph:


…I found myself spinning up several kinds of analysis trying to find one which told the story I was looking for. I know that isn’t an objective way to study data but I was not ready to conclude that all our diligence was for naught.

First, I compiled wintertime data, as our natural gas use is dominated by our house’s radiant boiler:


If I let Excel generate trend lines over these graphs, they do point ever so slightly downward. But I don’t think it’s compelling. I don’t know if what I’m looking at is all weather-related. We replaced our boiler before the 2008 winter so I would have expected gas use to drop there, and it does a tiny bit. But it doesn’t take us down to our 2003 levels. Meanwhile, electricity use has dropped more markedly and I don’t know why that is, either. We did use some space heaters before we replaced our boiler; would that account for the large drop?

Then, I examined summer data:


Notice that I’ve used a multiplier on the natural gas use to make it visible. There’s a nice drop in 2009 which derives, I am fairly sure, from installation of our solar water heating system last year. I wish its magnitude in actual energy were greater. But look at the electricity — what’s going on here? I can’t think of anything that can account for peaks in 2004 and again this year. We don’t have air conditioning. Indeed I’m not sure why the electricity use shows the strong seasonality that it does (winter is about 1.5 x summer).

So I’m puzzling over this. I’m feeling empathetic toward real scientists trying to isolate causes and effects in the complex system of climate. I have a much smaller system but it’s affected by many of the same variables and my data isn’t quite up to the task. But I’m not going to let that stop me from taking some meaningful action. Something is going on with our electricity use and I’m going to find out what.

In the meantime, I am comforting myself with the one graph I can be proud of:


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