A question for Brady....

[myxpykalix]

Brady,
I am drawing up plans to cut a box out of plywood for my solar air heater, you know, like the plans you have, so let me ask what might be a dumb question.
The ones i've seen all talk about using empty pop cans, but i can get a mountain of beer cans here.
Is there anything special or different about using beer cans instead of pop cans? Since I don't drink I don't know if there is a difference between the two? (if you know) :D thanks

[Brady Watson]

Nope...pretty much the same. BUT...Instead of bees hovering around the pile of empties, you'll have stray dogs looking to lap that last little swig in each can :D

It's the thin-gauge aluminum and air chamber created by the can that you are after. Personally...I don't feel like cleaning, drilling & painting all those cans. I'd rather make a little male/female 'squish' mold out of MDF and use thin flashing (on the roll) to make 2' long U-shaped pieces that can be overlapped & then painted. The can AL is so thin, that material this thin would be a dream to stamp in a make-shift mold. Can probably use 'Quick clamps' to mold it.

These inverted U shapes can then be secured to a backer that has 2 dadoes machined into it, so that the inverted U will be held into each dado by spring action. A little dollup of sillycone will keep it all in there.

But....that's just how I would do it... ;)

-B

[harryball]

If you have the evil little critters in your area, toss the cans near a fire ant mound and kick the mound. They'll clean every last drop of whatever is in the can out. Also works for conch shells and pretty much anything else with organics you need to strip clean. Keep if off the mound and check it the next day so they don't fill it with dirt.

FYI, I find they don't like diet sodas so much. Probably a good hint why we don't need to drink them either.

/RB

[myxpykalix]

Brady,
Sometimes when people describe something you see it instantly, sometimes you don't. I can't visualize what you are describing. You don't have a picture of anything like that do you?

Also i got to thinking, you know the rigid thin aluminum pipe you have on dryer vents? Could i use something like that?
Since i don't understand the thermodynamics(?) of this my assumption is that by drilling the offset smaller holes it somehow makes the air swirl and move around, so a long unobstructed pipe would not work.

edit: While trying to visualize what you were describing I came up with this. Top part is the pipe with the baffles offset in it and bottom is a view inside the pipe at the baffle. Am I on the right track?

[Brady Watson]

The end result is more like a 10' long PVC pipe that has been ripped in half on a table saw...Except you make a mold that can be used with clamps or a hydraulic press to make 2' sections that can be glued together.

You just need a material thin enough to be quickly heated and a means for air to move via convection. It's REAL simple...

-B

[geometree]

Every winter when I get cold, and poor I start thinking of how to make some solar collectors. It seems to me that the designs with tubes to direct the air are overly complicated with no benefits over a more simple single chamber design.

I am leaning towards a design something like the one here http://www.iedu.com/DeSoto/SC_Madison/

I think he's a shopbotter but haven't seen him here in a long time.

[myxpykalix]

shawn,
I recall seeing this some time ago but at that time wasn't interested in it. I think there was more info available but doesn't seem to be there now. I have been watching several youtube videos and getting advice here.:D

[gerryv]

Shawn, a key aspect of the tubes is the importance of creating turbulence within the tubes to maximize the number of molecules coming in direct contact with the aluminum. In other words, laminar flow such as occurs in a smooth, straight passage is said to be less capable. Besides the environment benefit of recycling, this is why the fellow that first developed these used pop/beer cans. By using a wedgie opener in several spots on both ends, he was able to ensure the turbulence.

This dude appears to be making a good buck with these things. Apparently he even wangled a government grant to set up shop so good for him. If I recall correctly, he explains the process on his website or in the video.
http://www.cansolair.com/

That's how it was explained to me anyway. Personally, I think he was also highly skilled at opening these cans and enjoyed the repeated pffft sound and simply found an innovative way to justify his indulgence to his better half :D

I looked at the link you posted but did not see any info on the makeup of the panels; did I miss something?

[myxpykalix]

Brady,
Your advice is needed again. I have located a source for scrap aluminum parts that look like beer cans but are a bit thicker. Other then creating some type of smaller opening between the cans (which they may have something) can you look at these pics and stats and tell me if you think these might be a better solution then regular beer cans?
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Small Cans = D 1 1/2", H 4.75", weight is 0.1615 lbs each, Asking $0.25 each
Medium Cans = D 2 3/8", H 5 1/2", weight is 0.2000 lbs each, Asking $0.30 each ******
Large Cans = D 3 1/2", H 5"+, weight is 0.338 lbs each, Asking $0.50 each

The medium cans are going to be the closest in size to a soda can, just a little narrower and a lot heavier in weight (thicker walls, can't be crushed by hand unless you are the Hulk).

These are basically manufacturing scrap from an aluminum can manufacturer
----------
I'm not concerned if it is a bit more work to use them if it will make a better product. I was unclear on whether because it was thicker that might not make for a better heat transfer?
I appreciate you taking the time to help me with these questions since you seem to have more experience with this stuff then me thanks!

[Brady Watson]

The thinner the AL the better. You want to leverage the quick conduction of thin AL & it's ability to dissipate that heat quick enough to create a convection current that will cause the heat to rise & basically 'pump' the air from bottom to top.

Thicker wall AL setups would benefit from less velocity, and will yield lower performance than thin wall setups. This is because it takes more energy to heat up the thicker AL...and thicker is less efficient. Our goal is not to heat up the AL. It is to transfer heat from the outer surface of the thin wall to the air inside of it. Think membrane here...

Imagine wall thicknesses of 1"...it would be very cool to the touch until the sun heated it up enough to start generating some heat. Even so, it still may not heat up enough to provide any additional heating at that thickness.

So...It appears that a soda/pop/beer can is the ideal material for this type of project. The fact that they neck down a little at the top of each can really doesn't do much over a can or cylinder of the same wall thickness. This neck DOES however provide structural support for the can walls, in conjunction with the top & bottom rims.

There's a lot to be said for doing your own experimentation...that's where you separate fact from internet fiction & make advances.

-B

[myxpykalix]

Thiat why we should call you "Mr. Wizard":) the scientific facts make sense and I do appreciate the explaination. My thought was that a thicker wall would hold heat longer but now as you explain the conduction/convection aspects it makes better sense to use the thinner wall cans.

I have seen several videos on how to make one of these but none go into the "science" behind it.

"There's a lot to be said for doing your own experimentation"
I can appreciate your sentiments however by getting advice from you has saved me a ton of time and some cost by not going and buying these aluminum castoffs so once again thanks much for the info...:)

[Brady Watson]

No problem - glad I could help. I will eventually be doing some of these myself - except on a much larger scale than is commercially available. Post up some pics & results when you get to that stage.

Also...K.I.S.S. - The pop/beer/soda can method is a proven design. No sense in reinventing the wheel, especially if you want to make a test/practice one 1st.

-B

[servant74]

I like the DeSoto hot air units. I guess because it is totally passive and needs no fans to force air through them. According to the information I have read on that site, it doesn't send much warm air in in the summer vs winter. In the Winter snow actually helps in the heat collection due to it reflecting more light onto the panels.

But that one also benefits if you have eaves that shield them in the summer but make sure they are free from obstruction during the heating season!

I don't have a place to use them currently... to bad.