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Garage_Hermit

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Reply with quote  #11 
Thanks for the Moral Support, Dan

CMV = Controlled Mechanical Ventilation, it is a fan that sucks air out of plumbed rooms, using extraction spouts.  Supposed to take the humidity out of the house, but it ALSO takes a lot of heat with it !

So watch this space, I am off to install a heat exchanger in there pretty soonish !

Warm bedrooms are not too good for one's health -- guess it's the computer going 24/24 and the sound-mixing console that keeps the heat up !

Still, mebbe he'll pay *my* fuel bills when I'm OLD ! ha ha !

Looks like you had a great weekend ! U must B a Solar Militant !

G_H

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EcoMotive

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Reply with quote  #12 
Hey Dan, 

A question/concern about your shed cold air trap if I may...

Regarding the placement of the cold air inlet below the hot air outlet. It seems to me that air could still establish a reverse thermosiphon flow despite the cold air trap you built. Even though the cold air will have to travel upwards to get out of the trap, it will be pushed along by the "head pressure" of the column of cold dense air in the collector above it.
The idea I'm getting at is similar to a P-trap in the drain of a sink. The trap will hold a portion of water and prevent it from flowing out but if the faucet is being used and the water level in the drain rises over the highest point of the trap and the head pressure of that higher water pushes itself out of the trap and into the rest of the sewer system.
Since the cold air in the collector is presumably more dense than the ambient air in the shed I think it could produce a net-positive pressure that establishes flow out of the trap.
The only remedy I see to this is to bring the cold air ducting all the way up above the hot air outlet and then back to the floor where the inlet would be. It would look like a giant S-trap for a sink.
...or I could be totally wrong here. I guess the real question is... have you observed reverse thermosiphon flow despite your cold air trap or does it seem to be working as planned?

Lance in Newfoundland

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solardan1959

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Reply with quote  #13 
Lance,
   I should have made it higher as you suggested by another foot to be on the safe side,  and as you said exceeding the hot air input may be even better.  I still hope/think the cold heavy air will just sink to the lowest point and the three feet or more of rise will prevent most of the air from developing a flow.  I have not noticed any flow but it would not be very high anyway and may be hard to detect. With my garage panel, it just had vents at the top and bottom and the flow very noticeable.  I am not sure a a good way to test it, a candle?  Maybe three temp probes, one at the output, one at the lowest level, (panel inputs), and one at the trap input and compare temp levels.  If the lowest level and the trap input are the same then I guess you have reverse flow. 

edited 6:13 PM  Lance, I measured at the input to the panel and got 41, the input to the cold air trap was 47, the output of the panel was 67 and cooling.  Right now it seems fine, I'll check it when the panel is a lot cooler and see if it gets worse.

The best info I have found and what I loosely based this on was here: http://www.iedu.com/Solar/Panels/  (The Zen of Passive Solar Heating Panel Design  by Morris R. Dovey )  He has some nice info on cold air traps.  I can not find much else on the subject or info on the design of one.


The main problem I have had with it is I have not had one good day to test it, today will be the first full day of sun to see how the panel is putting out. I got to about 90 at the output yesterday with intermittent sun but mostly clouds. The best I have gotten in the shed is about 50 in the two weeks since I modified it. This morning it was 10 degrees F out and 15 in the shed.  High of 35 today with two feet+ of snow on the ground.  I think we are at 3 feet snow fall for April, a new record.
  But looking for a good Sun day today so we will see how it goes.
Dan
solardan1959

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Reply with quote  #14 
Another interesting thing I noted today is the Sun's reflections off the glazing. It would have been hard to see before with no sun...but I digress.  The Glazing is old patio door panels so they may have been treated with something.  I did not notice the same effect on the pole barn heater or my glass garage heater.  It may be the sun is still slightly more filtered here because of the trees also, (I think it's just the snow is slightly sloped towards the shed).  The panel output temp was 76 at the time with input temp of 26 degrees F. 


My Garage panels all read at least 70 to 83 with ~ 96 CFM. (I do not see any reflections here)



Dan

Decided to add a solar powered fan in cold air trap to try and get a little better output.  The output current temp was about 104 and dropped to 98 after I added the fan.  The fan just increases flow upwards though the cold air trap, hopefully.



The panel was put in the window as this is just a temp experiment anyway.  Also note the tree shading but I am not going to cut everything down.



This was the starting temp of the shed and the temp three hours later.  I expect to get to 60 F by the end of the day.  The outside temp is thirty five degrees.


edit, 3:50 PM,
Did not quite get there, only got to 58, shed is 17X19 feet and it increased by 43 degrees so I guess I can't complain.  The panel output temp increased back to around 112, max 115, after the shadows above went away.
Dan
Garage_Hermit

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Reply with quote  #15 
Great to see your results, Dan !

I took a look here... http://www.wikihow.com/Calculate-BTU-Per-Square-Foot
Guessing your shed height is 8 foot, then U have 2500 cu.ft
and U went from 15°F to 58°F which is a TD of 43 °F which gives.... 107,500 BTU air !

Guessing U ran for 4 hrs, that is around 27,000 BTU/hr

The "real" amount of heat required is probably around 55 BTU x 2500 sq.ft = around 20.000

so at 27,000 you can consider yourself to have arrived !

I kind of like the shadow of the tree - Mother Nature Exerting her Influence over Man's Technology
(however, she also sent lots of nice snow / reflection, to make up for the shadow anyhow !)

Glad to see you staying warm
cheers,
G_H


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(1)  "Heat goes from hot to cold, there is no directional bias"
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solardan1959

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Reply with quote  #16 
Hermit,
   Let's just say it's working okay. while the air was 58 higher up it was probably 47 at floor height so a small ceiling fan would help mix things up.  Also drywall and sealing things up better will probably help to but it's a far cry from the dirt floor shed/garage it used to be.
   The big problem is without storage and 10 degree nights two much heat is lost when there is no sun.  While I could add more panels or maybe change the glass to get more heat out you would have to make it uncomfortably hot during the day to try and make it through the night comfortably also.  I have no real mass in the building like a concrete pad, the Pole barn does a much better job of retaining the heat because of that, so I need to come up with a plan for night storage.  One idea I just came up with would be a two inch slab on top of the current OSB, (chipboard), floor I currently have.  I could run pex through it and add a 4X8 hot water collector on the roof.  No storage, just the heater, loop, and an expansion tank for safety.
  Upon further reflection, I do not really need a 2 inch slab but could make a 1 inch edge/frame, run the pex loops, and use some medium like concrete or sand for heat storage to fill space between the loops and put another layer of flooring over that.  If I used concrete I could just lay some linoleum over it.
  One other idea I've been thinking of for parts of the pole barn and garage is laying pex on the concrete with in a 1 inch frame and laying a plywood floor over that like a 1 1/2 inch platform to apply more heat to the floor.  The platform would be along benches etc where you would not drive a vehicle but would give you a better working environment.

Or I could leave it alone...
Dan
Garage_Hermit

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Reply with quote  #17 
Dan,

Great to have the info. Shame about the lack of thermal mass, as that is what it's for, slowing down the heat !
The ceiling fan sounds like a great idea !  Personally, I would just insulate the floor real good, with some styrofoam and OSB.

Course, you could make a lot of themal mass dead quick and easy, using water - how about a "warm wall", comprising a row of shelves full of jerry cans of water, behind some insulation or drywall,, and get a fan blowing your warmest (ceiling) air into that lot, to store some heat in the water... The heat would eventually find its way out, but after a few hours...  maybe put a little fan in there for pushing boost when it felt a little too chilly !  You could even augment that warm wall with a 100-watt light bulb.

Less pain than an additional slab...

The alternative to a warm wall, if you are feeling flush, would be a thermodynamic DHW tank, with a radiator attached to it, but that would cost some !

Or you could maybe build a gravel bed outside somewhere near to the shed, probably about 4 cubic yards, and shove all of your heat into THERE, and then blow it into the shed, either direct or over a heat exchanger.  The gravel bed would need some really good insulation...

Enjoy trashing the ideas, ha ha
G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
solardan1959

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Reply with quote  #18 

Late Spring update? 
Shed temps been running 70 to 80 but finally with the leaves on this heater it gets little sun.  But it appears that Mother Nature Approves, (well at least some of her friends).
See the nest at the top right of the collector.

solardan1959

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Reply with quote  #19 
Just an update due to issues with another project.  In post #5 above I talked about using landscape fabric for the absorber in my shed heater.  I again used this material in what started out as a cheap preheater for my pole barn heater.  Due to the unconventional design I had problems with this landscape fabric and will not use it again.  It melted when I did not have good flow through the collector, I would assume the off gassing is not good for you also.  It has held up good in the above mentioned shed heater though.

So as mentioned I have made additional modifications to the pole barn heater, info can be found here:
Solar Web Page > Forums > Solar Hot Air Collectors > Pole Barn Heater Test Bed

And more interesting is the Sunspace I added to the back of the garage shown in the first photo, details can be found here: Solar Web Page > Forums > Member Projects! > Solar Dan's Sunspace 
Dan
Garage_Hermit

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Reply with quote  #20 
Hey, Dan,

Nice update, ties up loose ends !

How come I never saw the bird's nest before !
Somebody appreciates your heat, anyhow !

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
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