Winter solstice efficiency

[J.P.M.]

Well my point was that I am not particularly interested in any data point. I don't care if PVWattts is high, low or in between. Same for the SAM system.

I am not too interested in how the points on the line are calculated as long as they are calculated in a consistent manner and not subject to arbitrary adjustments as time goes on.

What I am interested in...... is the slope of the line. I want to compare the slope of the predicted production (even if it is over or under) to the slope of my actual production over a long period of time.

Understood.

[Mike90250]

Mike: A question/comment or several:

Does it take 2 days to heat the dwelling or 2 days for the assembly to heat up ? If the assembly, I bet it takes about as long to cool down, +/- some.
Any heat exchange surface inside the masonry/flue ?
Any allowance for outside combustion air ? Not trying to preach to the choir here but combine that with a tighter building envelope and interior R.H. will probably go up.

The inner core is pre-cast refractory material. Shell is brick, flue is common flue tile.
When burning normally, the inside walls are pale white, the soot burns off, and off the door glass too,
From a cold start, it's recommended 5 or so, "seasoning" fires, to slowly drive out any accumulated summer moisture, and to not shock the thermal mass, and slowly heat the mass up. And yes, several days to cool down. Spring and fall are tricky, we have to watch the weather forecast and fire according to the forecast, not what we feel. The thermal flywheel also is forgiving of not having to fire every 12:00 hours, generally, evening fire at 5pm, morning fire at 8am and the mass evens it all out to a delicious warmth.
We do have 3 feed vents for outside air, but since Calif has some odd rule that dampers can only be closed 70%, we have 30% thermal siphon going up the flue, and sucking our efficient heat away. So 2 of the exterior vents are blocked off, to reduce thermalsiphon loss.
The oddest thing, is that in summer, we have 3 tons of brick/masonry at 65F sitting, creates a chilled space to hang out, when it's 95 outside.

[J.P.M.]

The inner core is pre-cast refractory material. Shell is brick, flue is common flue tile.
When burning normally, the inside walls are pale white, the soot burns off, and off the door glass too,
From a cold start, it's recommended 5 or so, "seasoning" fires, to slowly drive out any accumulated summer moisture, and to not shock the thermal mass, and slowly heat the mass up. And yes, several days to cool down. Spring and fall are tricky, we have to watch the weather forecast and fire according to the forecast, not what we feel. The thermal flywheel also is forgiving of not having to fire every 12:00 hours, generally, evening fire at 5pm, morning fire at 8am and the mass evens it all out to a delicious warmth.
We do have 3 feed vents for outside air, but since Calif has some odd rule that dampers can only be closed 70%, we have 30% thermal siphon going up the flue, and sucking our efficient heat away. So 2 of the exterior vents are blocked off, to reduce thermalsiphon loss.
The oddest thing, is that in summer, we have 3 tons of brick/masonry at 65F sitting, creates a chilled space to hang out, when it's 95 outside.

Thank you. The damper thing is a safety issue. The 65 F. issue in summertime may have it's origin in night time circulation and the device thermal time constant (or thermal flywheel, or thermal inertia) being ~ the same as the building's but sort of pi/2 out of phase from daytime thermosiphoning aided by the 30% open flue. The greater the time constant of a lumped mass, the closer will the temp. be to some long term average characteristic temp. - perhaps the outside average temp. over several days. Hard to say.