Now that we’re through 2012, and all the utility bills are in, I took a look at how we did in 2012 vs. the previous year. These numbers probably aren’t that interesting on their own; no big changes or revelations. But some might be interested for comparison. This is a 1931 single-family house in the Twin Cities, with 1250 square feet above ground, and maybe 400 square feet conditioned below ground. The basement has heat, but that zone is usually turned down pretty low. We have an 83% AFUE furnace (the one appliance I really wish were more efficient, but it’s not very old), and a single 1-ton mini-split AC installed this past year.
The top line numbers:
- 2011: 839 therms, 4538 kWh consumed = 99.4 million BTUs
- 2012: 687 therms, 4577 kWh consumed = 84.2 million BTUs
On the face of it, that looks like quite an improvement, but the vast majority of the decrease was in natural gas, which is influenced by the weather. We can use Heating Degree Days and Cooling Degree Days to quantify air conditioning requirements, and from degreedays.net, I find:
- 2011: 7357 heating and 1128 cooling degree days (@65F base)
- 2012: 6390 heating and 1238 cooling degree days (@65F base)
So we had about 13% fewer heating degree days, and consumed 18% fewer therms of natural gas, our primary heating fuel – fairly strong correlation, but maybe some improvement. I don’t measure cooling energy independently (yet) so I can’t correlate that at all.
On the solar production side, we had this from our 11 panel, 2.53kW array:
- 2011: 3306 kWh, or 72.8% of our consumption
- 2011: 3352 kWh, or 73.2% of our consumption
Not a big change there. So other than the weather, we didn’t have significant changes in our home other than slightly older kids, and the addition of a mini-split heat pump for AC & some heating.
I’ve mostly run out of ideas to make this old house more efficient. Every light is CFL or LED, we’ve insulated the walls & attic, replaced the windows, etc. We are considering some renovation, and that will probably change our energy use if we go through it. I’ll keep you posted!