Back to the main Barra Box page...
This page gives a couple days worth of results after adding the change package A changes.
In these results, the fan is working, and appears to have its set point set to about 52F -- I had intended to make it higher than this, but it did not have a calibration in degrees on its face.
The added outside insulation is also in place (see change package A).
The logger that senses when the fan motor is on is the aqua colored square wave in the plot below -- when its up, the fan is on.
The fan is blowing up from the room into the bottle chamber.
Full 2 days -- see below for each day separatley.
Day 1 from plot above.
Day 2 from plot above.
Some tentative observations:
- The room temp thermostat is apparently set to turn the fan on at about 52F.
- When the fan turns on, there is a brief rise in room temp (which seems good), followed by a slower fall off than was occurring before the fan turned on (which seems somewhat good) -- it looks like the fan cannot quite move enough heat from the bottles to the room to completely offset the heat loss from the room, but its pretty close. I would guess the step drop in bottle temp when the fan goes on is because the sensor is taped to the outside of the bottle and sees some influence from the air being blown over it.
- During the collection periods (sunny part of day), the room temp seems to want to follow the bottle temp -- perhaps the air mixing problem Nick described.
But, the room temp still says well below the collector in temp, so there is not full mixing going on -- eg when the temp of the air flowing across the ceiling is 100F, the room temp is down at 80F.
- Overall it looks like the room temp is somewhat better controlled than it was -- now the fan keeps it from going much below 50F, and it only climbed to about 87F during the day -- of course, if the bottles had been hotter, it probably would have risen more. Still, better controlled than Nick's house :)
- Observing the backdraft damper when the fan is running -- its plastered against the hardware cloth -- apparently doing its job of preventing fan flow into the collector area where heat loss would be great.
- The south bottle temps do not vary drastically from the north bottles -- from the thing I did earlier on my garage thermosyphon, I expected the south bottles to be a good deal hotter than the north -- this more uniform bottle warm up seems good to me?
- This has been fairly easy weather for the Box -- some sun each day, and ambient temps in the 30F ish range. I don't think the Box performance is up to keeping the box at 70F (or probably even 50F) with the current gains, bottle absorption, and insulation levels. What does the simulation say about this????
How well is the collected heat being transferred to the bottles?
We have about 2.4 sqm of effective collector area.
On the 2nd day, it looks like about 5 hours averaging about 600 watts/sqm of sun, or about (600 watts/sqm)(2.4sqm)(6 hours) = 8640 watt-hours = 24K BTU input.
If one assumed 40%(?) collector efficiency, then the heat input to the room and bottles would be about 10K BTU.
The bottles warm up from about 60F to about 90F, or about (3 rows)(18 bot/row)(2 liters)(2.2 lb/liter)(1 BTU/lb)(90F - 60F) = 7200 BTU into the bottles.
Well, that does not seem so bad?
Heat loss from box
Back 32 sf, E side 16 sf, W side 16 sf, top 32 sf, bottom 32 sf, front 32 sf
Heat loss per degree F:
Walls at R 23 (32 + 16 + 16)/R23 = 2.8 BTU/hr - F
Top at R26 (32 ) / R26 = 1.2
Bottom at R23 (32 )/ R23 = 1.4
Front at R16? (32 )/ R16 = 2
Total = 7.4 BTU/hr -F
At 60F in and 25F out, (7.4 BTU/hr-F) (60F - 25F) = 260 BTU/hr, or, 6200 BTU per day --
Does not seem too far out of whack with bottle gain? Especially considering that loss from top area would be higher due to bottle temps being higher than 60F.
Well, this seems like some progress to me??
I'd be up for one more change package -- what do we want to do? Or, we could just claim victory here?
I'd still like to see a simulation that tracks this well to give some confidence for the dCube if we do that project?
It does seem like the proposal to add a back duct and a false floor duct as Nick proposed might work better?
This seems like it would avoid the mixing problem, but how would room temp be controlled?
Similar to the diagram below? -- or, how different? Fan?
Or just control loss rate from bottles to room somehow, but how?
Had a random thought about doing a dCube (or pre dCube) in the SE corner of my barn/garage. Idea would be to close off an 8 ft square that made use of the existing south and east walls, ceiling and floor. Add the north and west walls inside. This would come equipped with two bays of the existing thermosyphon collector. ???
Gary January 21, 2010