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followup regarding a thermosiphon panel - Page 3

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Posted by schooner on November 2, 2006, 10:06 pm
 
I'd agree, you don't want the insulation heating up, you only want the
absorber to heat and better to reflect it back that have it absorbing it
itself.



Posted by M&M on January 1, 2007, 7:54 pm
 
I have a question.
Could anyone comment on this please?  The video is newsey, and I am
asking for opinions please. Does anyone have additional input into
this, or using it ?
http://www.jointhesolution.com/usasolarenergy ,  Thanks!



Posted by Morris Dovey on November 2, 2006, 3:00 am
 Tater (in 1162421607.591770.90220@e3g2000cwe.googlegroups.com) said:

| hi gary, you are gonna love this. two identical thermometers one at
| inlet, one at oulet. zero difference in temp.

Unless you're taking measurements in full dark, there's something very
wrong here. My thermosiphon panels are all 6' tall and at this time of
year, I see temperature differentials of around 100 degrees.

| I dont think the air velocity is strong enough to spin a vane on a
| wind meter :)
|
| putting my hand as close as possible to the output vents does
| register heat. it also registers the mildest of air movements. the
| plastic bag one way flaps do move open to about 45 degrees.

Without a temperature differential, there /shouldn't/ be airflow.

| I really got to get some clear polycarbonate on the panel, but have
| been comming up empty on that end.

Yuppers. Keep looking - it'll be worth the trouble.

|| Thermosyphon collectors should do fine on efficiency, but they are
|| sensitive to following the design rules, which are roughly:
||
|| - Fairly tall -- 7 or 8 ft is good.

Taller produces higher internal temperatures - meaning that the
additional height will not operate as efficiently as the part below.

| mine is six feet, the roof slopes so i could not get it any taller,
| when i expand i should be able to go 7ft for the next 4 ft wide
| panel, then 8 ft for the next 20 ft of panels
|
|| - collector depth about 1/15 or more of height (for an 8ft high
|| one, 96/15 = 6inches deep)
|
| a bit less for mine, used 2x4s for depth

I build both 4" and 6" panels. The 6" panels do perform better - but
only slightly better (and certainly nowhere near 50% better).

|| - absorber that absorbs well, but has low flow resistance (2
|| layers of black window screen,
|| - The air flow path is through the absorber
|| - The air flows from the south (glazing) side to exits on the
|| north side.
|
| just like the one you described in your article. only difference was
| that i used plastic film instead of polycarbonate(as described in
| another article)

There's a photo of the polycarbonate glazing that's worked best for me
at http://www.iedu.com/DeSoto/sc_materials.html

|| - The entry and exit vents area at least half of the cross
|| sectional area.
|
| each or total? I approximated the same as what yours were(per your
| article)

Hmm. I'd suggest intake and discharge openings the same area the other
plenum(s). Anything smaller will inhibit airflow.

|| And a glazing the transmits light :)
|
| light does get through, but the film is milky white, and I am
| guessing that it is blocking a bit of IR. like I said, i want to get
| polycarbonate, but havent found a local source.

More than light, please. Make that beast absorb everything you can!

| *IF* it was working correctly, my follouw-up would have been about
| me stockpiling materials to expand the one 4ft panel to 4-5 more of
| them to heat up a garage half the size of the shop you heated in
| your article.

My shop is a 50'x50'x14' aircraft hanger. I have one 6' tall by 12'
wide panel (photo at top of
<http://www.iedu.com/DeSoto/collectors.html> ) that provides about 1/3
of the heat needed to make the shop "shirtsleeve comfortable" through
the (central Iowa) winter. The hanger is drafty (the 45'-wide door
doesn't help much) and I would expect that with 6'x24' of panels you
should be roasting by mid-day in winter.

| as it is, I am glad I went with this approach rather than shelling
| out hundreds of dollars to completely converting my garages south
| wall to a solar collector. now is my time to perfect the design,
| then let 'ol Sol carnk out the BTUs

Absolutely! Prove the design first - then expand.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto



Posted by nicksanspam on November 2, 2006, 11:10 am
 

Polyethylene film is fairly transparent to IR (the NRAES greenhouse manual
says 80% vs 2% for polycarbonate and 4% for glass), which hurts efficiency,
given a hot absorber.

Nick


Posted by SJC on November 2, 2006, 1:34 pm
 

  The white looking poly is for construction. Lowe's has 4 mil white and
2 mil clear. The difference in insulation is not important if you use two
layers with a gap of sealed air. Two layers of 2 mil clear separated by
only 1/2" of air could make a lot of difference.

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