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Garage_Hermit

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Reply with quote  #11 
Willie, you sure got me to put my thinking cap on !

[image]

G_H

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stmbtwle

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Reply with quote  #12 
Are you really going to try to push air through 25m of 18mm copper tube, or is that coil for something else???
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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #13 
Willie, you must be winding me up !

it says "circ pump" on it !

The 18/16 copper is circulating... wait for it... WATER [rolleyes]


(OK, guess I am a bit at fault - I should have made it clear that the 120-liter wheely bin is full of... WATER...)


G_H

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stmbtwle

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Reply with quote  #14 
Sorry G_H I wasn't sure.  Your parts list makes no mention of the elbows and parts to make a "coil" out of downspout, though I think that approach would work pretty well, if well sealed to keep water out of the downspout.  So it looks like you'll have two HEX's in that wheelie bin, one for air and one for water.   I think it'll work.

After your idea of blowing air through a water/water HEX I wasn't too sure WHAT you were up to! [smile]

Aren't you already pulling hot air out of there?  Might be a way to combine the systems, just a thunk.

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Willie, Tampa Bay
SolarInterested

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Reply with quote  #15 
G_H instead of trying to submerge the down spout in the wheely bin (possible leak and buoyancy problems) you might consider putting the bin inside an enclosure and circulating the air around the bin. I think that gives you a lot more surface area in contact with the water compared to just the submerged portion of the 80mm downspout.

The enclosure could be a simple cardboard box or constructed from faom insulation board.

Mike

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Both temperature rise and airflow are integral to comparing hot air collectors
Garage_Hermit

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Reply with quote  #16 
@willie

Point taken, Willie: I forgot to add the price of the zinc "U" at the bottom : it is comprised of 2 x 90-degree elbows, at 3.80 each, so 7.6 Euros (10 bucks to you !)
In effect, the zinc downspouts are not a coil at all, just a straight "U". The joints are soldered :


Like U said, there are in fact two heat exchanges taking place in the tank: air to water, and water to water.

  • The air-water exchange surface is around 5.5 square foot as stated.
  • The water-water area is the surface of the coil, or 2500 cm x 5.65 cm = 14,142 sq.cm / 6.45 = 2192 sq. in or 15 square feet...
Translation: there  is three times more copper than zinc, so copper should pick up the heat from the tank water pretty double-quicktime... hopefully meaning less heat-loss from the tank.  The latter would need insulating (say, 40-mm XPS etc.)

@SolarInterested

Thanks for the idea, Mike !
However, the wheely bin is made of heavy plastic, so would not conduct too much heat...
In addition, the whole system now gets Very Bulky !

However, I get your meaning: it is what the Danes call "tank-in-a-tank", it is apparently a common heating concept up there.

As I see it, the zinc d/s would be pretty firmly anchored, due to the fact that it passes through the bottom board of the facade (twice...). Any tendency to "float" would be countered by installing a cross-brace in the bottom of the tank, to hold the U bend down.  Careful soldering ought to take care of the leak aspects.

Thanks again to both of you gents for your valued inputs, best way to get the pbs ironed out before forking out any cash [rolleyes]

There is a THIRD heat exchange to consider, at the remote end of the system, since the copper coil has to warm water in ANOTHER tank, thru which the cold water supply to the (electric) water heater is routed, for prewarming...

But that's for another day !
(EDITED:  In fact, looking at the problem again, *THAT* end would be replaced by a brazed FP HEX , mounted direct to the bottom of the HW theater...) [biggrin]
=======
Trying to look at this logically, I suspect I will not actually BUILD this present air/water HEX, but rather go for a copper manifold, inside the slates...

(Which was my original plan...)

The main reason is, although like Willie I think it will WORK ([cool]), I don't actually see me parking a wheelybin out in front of the house, for aesthetic reasons...
On this score, a hidden copper manifold would be 100% better, even if building it will likely present a few problems.

(Which is why I considered installing a flat-plate HEX in there, just to see if it would work first, before getting in to a heavy copper-soldering set-up...).

G_H
(time for a beer...)

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stmbtwle

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Reply with quote  #17 
I think your 25 m of 18mm tubing would work better than the flat plate HEX, if you can somehow make a big coil of it and get it into the space. Just my thunk.
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Garage_Hermit

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Reply with quote  #18 
Thanks, Willie, appreciate your thunks...

Been there before with the coil business, it would be tight...
Whence the 28-mm copper "prongs" mentioned above at Item 4.

Recorded over 50°C (122°F) again in the facade today, guess it stays at that level for 4 or 5 hours in this nice sun we're currently getting...

G_H

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SolarInterested

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Reply with quote  #19 
G_H sorry if you mentioned this in the past but could you vent into your house at the top of the facade and just use natural thermosyphoning? I imagine you don't want all that heat upstairs but it would be simple.

Mike

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Garage_Hermit

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Reply with quote  #20 
Hi, Mike,

Thanks for the suggestion.

Must agree with you, I *could* just vent the facade into the house, but it would be excessively HOT !
I would be getting an extra gigantic load of 50°C air in the lounge, during a sunny day...  That means, 122°F which is simply out of the question...
As it is, being November tomorrow, I already have 24°C (over 75°F) in the lounge during these last days (we are having an Indian Summer).

No doubt much of this heat/solar gain is due to the large windows; however a very high proportion of it is no doubt due to the slate facade, acting as a "trombe wall"...  In effect, I have 100 square foot of south facade behind slate. the structure of that facade being 10-inch masonry units.
I suspect that when the sun goes down, that wall is radiating into the lounge for a good few hours...

If I can "borrow" solar gain from the facade during the day, in the form of hot air and hot water, and transport latter to basement (NORTH part) (= crawlspace...), I would not even be subtracting heat at all, because the slates would just suck up more heat due to the greater temperature difference caused by removing the gain: I am basically sitting on a free source of unlimited heat !

Therefore the only logical place for the heat to go, is in the Basement.
Which means that the logical point from which to draw off facade heat, is through the bottom of the facade...

Whence my idea for the transpirational facade, for air, and the copper battery, for water.

Both of which are conditioned by the need to use the Crawlspce as a heat storage vault.

However, I much appreciate the discussion & the feedback, as it is (slowly...) getting my thinking ironed out [smile]

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
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