Heat through the fall

I've been happy that we didn't need heat but for two days we were in residence at the house during Oct. I think I've zeroed in on the right ambiant temp, 53 degrees, for when we're not there. In fact, during Nov, the heat has only run 2 or 3 days and in single, light 2-3 hr cycle on those days. Overall, I know this will be significant kwh savings during this mid-Oct to mid-Dec utility billing cycle. Last year, we used 1,000 kwh during this period. To date for this period, we're actually net-positive by 100 or so kwh. That'll quickly go away this week but we certainly won't use 1,000 by mid-Dec. I'm guessing we'll be more in the 400-500kwh range. That'll leave us with about 1,000 kwh credit with the utility from summer generation. Even though we'll be up for the holidays through the end of the year, that should easily be enough to be net positive for the year. I'm guessing we'll have 300-500kwh left over depending on how meak Dec solar generation is (yes, we can sneak out 200kwh generation in Dec).

Now that we're up here for Thanksgiving week, I'm focused on learning and optimizing for in-house use. Yes, we're sized for and able to achieve net zero partially because we're only here about 25% of the time. While that does use less heat overall, its not 25%. The most expensive heating cycle is heating from 53 to 70 when we're coming up. I've made this better by only heating the bedrooms at first and using the fireplace for pick-up but it still generally uses 50kwh to warm the place when the outdoor is 35-40 degrees. Once the house is warm, it generally only cycles overnight in this temp range and thus only uses 12-16kwh per day. Our non-heat usage is generally 15-20kwh. At least one principle of Passive House design is true of solar gain and ambiant heating sources keeping the place warm during the day.

I've been using the fireplace at night and there is a benefit of saving probably one cycle from that heat (5kwh or so). However, the downside is that it allows the radiant slab to get cool and thus the geo has to work harder when it does cycle on. I'm guessing there's only a small net and, if we didn't enjoy the fire so much, I probably would forgo most nights.

The net is, being here full time doesn't increase energy usage for heat as much as one might think. I'm guessing it is double but not 200% as per our usage of the house would indicate. We'll sanity check those numbers after this week.