The Shortest Days

With Winter Solstice right around the corner, the sun hangs low on the horizon and disappears to the west shortly before 4 in the afternoon. Yesterday was a good day (sunny, cold and short) to check the performance of a well insulated passive solar house. During the day, obviously, there's no need for supplemental heat from the woodstove. At noon in mid-December sunlight penetrates deeply into the house, lighting up the back wall of the first floor. The temperature inside is just below 70F. A couple days ago I made an adjustment to a setting on the solar hot water system allowing more solar heat to be pumped through the slab, and yesterday was the first day to give it a try. Around mid-day I turned up the thermostat and pumped heat through the floor for a couple hours. Our domestic hot water usage is predominantly later in the day so a little loss of heat to the floor in the middle of the day leaves enough time for the tank to recover temperature before the sun goes down. At 10pm with the temperature outside approaching the single digits, inside it was still a pleasant 66F. I could have lighted a fire in the woodstove before retiring for the night, but I thought it would be a good night to see just how cold it would get inside without the benefit of extra heat. The heat for the night would come from what was stored in the concrete floor. A 4:30am it was a little on the chilly side at 54F so I started up the woodstove to give us a little boost before the sun starts working again. Not bad though. When your average house would have been burning something all day and night to keep from freezing, I used nothing but solar gain. It will take some time to tweak the system to achieve maximum efficiency, but we're off to a good start.