Joe (bostonsteamer) wrote,

Energy consumption nerdgasm

When I got our first power bill for the new house, I had what one would consider a sticker shock. The bill was almost an order of magnitude larger than our old bill! How could this happen to Northwest Profile #12, the 60F thermostat guy? This triggered a fact-finding nerdgasm freakout where I learned some interesting stuff (one should always learn something new during a nerdgasm).

Follow along with me on my nerdy energy journey:

Part 1: The revelation of total energy consumption
Our old house used primarily natural gas. Electricity was only used for the fridge, light bulbs, etc. In the new house, our gas bill went down since more things are powered by electricity. I'd need to look at my total energy consumption to see if our energy use has changed.

Part 2: The mathing
Natural gas is measured in therms and electricity is measured in kilowatt hours (kWh), so let's use kWh for both forms. 1 therm is about 29.3 kWh. Here's my daily energy consumption of electricity and gas in the old and new houses:

New HouseOld House
45.116.4kWh of Electricity per day
5.8629.3kWh of gas per day
50.9735.7total daily energy consumption (kWh)

Part 3: The equalizing
It looks bad at first, until I realized that our new house is more than 2x larger than our old. So let's control for square footage:

New House (2400)Old House (910)(sq ft)
50.9735.7total daily energy consumption (kWh)
2.123.92Energy consumption per 100 sq ft

Part 4: The cash money
Wow, I'm actually using less energy per area of house. Time to break out the Dom Pérignon, right? Well, not so fast. Even though we can compare the amount of electricity and gas consumed by converting gas to kWh, that doesn't change the fact that each type of energy has a different cost. The cost of gas can be found by adding the line items on the bill (delivery charge and cost of gas are the two main ones). It's $0.037 per kWh for PSE customers. The cost of electricity is a bit more tricky in Seattle, because we pay a blended rate to encourage conservation (one rate for the first X kWh, and a higher rate for everything beyond that). So everyone's going to pay a different rate. Mine happens to be $0.079 per kWh. Electricity happens to be 2.1 times costlier than gas for me. Suck on that, salmon unable to spawn!

Let's see what happens when we take the different costs of energy into account:

New House (2400)Old House (910)(sq ft)
$3.56$0.51Electricity cost per day
$0.22$1.08Gas cost per day
$3.78$1.59Total energy cost per day
$0.16$0.17Daily energy cost per 100 sq ft

Part 5: Conclusion
Every good lab report should have a conclusion.

The new house is more than 2x as big, and I'm paying more than 2x more per day in energy costs, but controlled for the relative sizes of the two houses, it's about the same. The extra energy expense is just one of the hidden costs of living in a larger home. Some energy isn't dependent on the size of the house (washing dishes and laundry), and some is (lighting and heating). Thus it would make sense that the larger the house, the less energy you consume per sq ft. The old house was built in 2008 and had hydronic heating. The "new" house was built in 1911 and has those shitty rectangular wall heaters. So that probably cancels out the economy of scale.

Lastly, I could look at the costs the other way and claim I'm "saving" a penny a day, so hold onto that bottle of Dom Pérignon, because at this rate I'll be able to afford it in about 41 years!

Nerdgasm Complete.
Tags: house, math, money

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