recycling pop cans for heating

[captain nodge]

http://www.wimp.com/interestingsolution/  i dont know wether this has been posted before, but it looks like a good idea

[Bruce S]

Those look very nice.
 Interesting that it says he invented this.
 I cannot say one way or the other since while at work I cannot have volume on, but there's tons of this how-to here and on Gary Gray's site  http://www.builditsolar.com/

Jump over there and have a look. bunch of people posting their results, including Gary's .

Cheers;
Bruce S
 

[captain nodge]

thats a well good and interesting build it solar site, lots of interesting stuff, cheers for that, CN

[GeeMac]

I am in the process of making my own version of that panel. I have discovered that the key to getting it done is the proper drill bit. I bought mine at RONA (For Americans, RONA is similar to Home depot et al).  The drill bit cost me twenty four dollars and change. It is made to drill holes in glass and requires lubrication as it turns (soapy water works) The bit is diamond coated and has almost no teeth.  A bit with teeth, as I found out, just cranks the can into scrap aluminum in the blink of an eye.

Keep haivng fun kids.

[doceanboy]

 I have looked at these many times now here is my question.... why do you need the tin cans at all??? I mean if you fill the box up with rocks, bricks or whatever the sun will heat anything and the air inside the box will get hot... the only things I see that make any difference is the size of the box and how well it is insulated and flat black of course.

 If your going to put it on the side of your house why not just put a window there to let the sunshine in?   

This is the one I built and I pump antifreeze threw it.

https://picasaweb.google.com/repower/SolarHeater#

[drew4justice]

I'm with your thoughts to an extent, doceanboy.  I own a ranch style home in northern Ohio and if I enter my attic on a sunny mild winter day, it's warm and toasty up there just from the asphault shingles on the roof.  Why not pump the air from my 2000+ ft^2 attic instead of putting a small box outside?  It would be nice to gain the efficiency of a fresnal or parabolic lens, but I wonder if the warm air is already there for the taking?  Curious if anyone has tried?  I haven't searched the forums on this ponder nor have I paid much attention to solar heating, but I'm starting to look around a little and find the idea of solar heating intriguiging.  Just my thoughts..

[zap]

...I own a ranch style home in northern Ohio and if I enter my attic on a sunny mild winter day, it's warm and toasty up there just from the asphault shingles on the roof.  Why not pump the air from my 2000+ ft^2 attic instead of putting a small box outside?  It would be nice to gain the efficiency of a fresnal or parabolic lens, but I wonder if the warm air is already there for the taking?  Curious if anyone has tried?...

I've done this for around 15 years?
1200 sqft ranch, 4/12 pitch, framed, hip roof.  Yesterday around 3pm it was around 63° inside, 79° in the attic.  An hour and a half with a box fan (I have 2 attic access "holes") brought up the house temp to 66°.
The main problem is that there's very little mass in the attic so the built up heat doesn't last long once you start exchanging air... I have no plans to add any mass.

[GaryGary]

I have looked at these many times now here is my question.... why do you need the tin cans at all??? I mean if you fill the box up with rocks, bricks or whatever the sun will heat anything and the air inside the box will get hot... the only things I see that make any difference is the size of the box and how well it is insulated and flat black of course.

 If your going to put it on the side of your house why not just put a window there to let the sunshine in?   

This is the one I built and I pump antifreeze threw it.

https://picasaweb.google.com/repower/SolarHeater#

Hi,
The tough thing on solar air heating collectors is to provide enough heat transfer area from the absorber to the airflow to pick up the heat.  Air is low density and low specific heat, so you have to flow a lot of air over a lot of absorber surface area to pick up the solar heat.  If you don't have good heat transfer from absorber to air, then the absorber just keeps heating up until it gets hot enough to lose a lot of its heat out the collector glazing and that reduces efficiency.

Another challenge with air heating collectors is getting a good uniform flow over the whole absorber.  You sometimes see collectors that are just a black box with an inlet and an outlet vent on opposite corners.  These work, but they are not very efficient because most of the airflow just short circuits between inlet and outlet, and a lot of the absorber gets very little airflow and just heats up until it gets hot enough to lose its heat out the glazing.

I think the pop cans are probably one good solution in that they tackle both of the problems mentioned above.  If the manifolds are good and supply each column of cans with the same amount of air, then the get air evenly to the whole absorber, and the effective heat transfer area is large because heat gets transferred around to the back of the cans so the whole can transfers heat to the air. 

Some people have used aluminum gutter downspouts instead of pop cans, and I think this probably works even better because they are thck enough to transfer more heat around to the back.  Aluminum dryer vent also works.  The downspout collectors are more expensive than recycled pop cans, but the collector is much faster to build.

You could, as you say fill the space up with rocks, but generally its not a good idea to add thermal mass inside the collector.  Collectors with a lot of thermal mass take quite a while to get going when the sun first shines on them, and then at the end of the day, a lot of the heat stored in the mass just gets lost out the glazing when the sun goes off the collector. 

I've been working a bit on the downspout version of thd pop can collector:
http://www.builditsolar.com/Experimental/DownspoutColTest/Downspout.htm
and
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColProto.htm
and
http://www.builditsolar.com/Experimental/DownSpoutColProto/DownSpoutColFlow.htm

The last link above is still a bit of a puzzle to me -- if anyone has any ideas, I'm all ears.

All that said about the pop-can/downspout collectors, I'm not at all sure its any better than a collector that just uses two layers of aluminum window screen for the absorber -- like this one: http://www.builditsolar.com/Experimental/AirColTesting/ScreenCollector/Building.htm
This screen collector is very cheap and very easy to build -- it will be interesting to see if its as efficient as the downspout collector when run side by side.

Gary

[ghurd]

The last link above is still a bit of a puzzle to me -- if anyone has any ideas, I'm all ears.

This screen collector is very cheap and very easy to build -- it will be interesting to see if its as efficient as the downspout collector when run side by side.

Hi Gary,

Bernoulli's Principle?

The blow duct is so close to the center downspot tubes, the velocity is considerably higher the rest of the downspout tubes.
The blow is sort of focused, and a higher velocity.

The suck duct is so close to the center downspot tubes, it is almost like a weak direct connection.
The suck is not focused, more even, and lower velocity.

I know that is not a great explanation...
Sit 5' in front of a box.  Lots of wind.
Sit 5' behind a 20" box fan.  Not much wind to feel.
Same volvume of air.  One is focused, one is not.

Need to keep the velocity more even near the tube ends.
1st thing that comes to mind is fiber furnace air filter material.  Might try a piece from the glass at the end of the collector, to the back of the collector at the bottom of the tubes.


Speaking of fiber furnace air filter material, it would be interesting to see the window screen solar air heater compared to one with 3 layers of fiber furnace air filter material spray painted flat black.
A college student (in India?) ran some similar tests, and he came up with 3 layers of spray painted flat black furnace filters was quite effective.  It is what I used in the last version of my solar water disstiller, and it worked better than anything else I tried (never did get the heater core and cooler thing built).

G-

[GaryGary]

The last link above is still a bit of a puzzle to me -- if anyone has any ideas, I'm all ears.

This screen collector is very cheap and very easy to build -- it will be interesting to see if its as efficient as the downspout collector when run side by side.

Hi Gary,

Bernoulli's Principle?

The blow duct is so close to the center downspot tubes, the velocity is considerably higher the rest of the downspout tubes.
The blow is sort of focused, and a higher velocity.

The suck duct is so close to the center downspot tubes, it is almost like a weak direct connection.
The suck is not focused, more even, and lower velocity.

I know that is not a great explanation...
Sit 5' in front of a box.  Lots of wind.
Sit 5' behind a 20" box fan.  Not much wind to feel.
Same volvume of air.  One is focused, one is not.

Need to keep the velocity more even near the tube ends.
1st thing that comes to mind is fiber furnace air filter material.  Might try a piece from the glass at the end of the collector, to the back of the collector at the bottom of the tubes.


Speaking of fiber furnace air filter material, it would be interesting to see the window screen solar air heater compared to one with 3 layers of fiber furnace air filter material spray painted flat black.
A college student (in India?) ran some similar tests, and he came up with 3 layers of spray painted flat black furnace filters was quite effective.  It is what I used in the last version of my solar water disstiller, and it worked better than anything else I tried (never did get the heater core and cooler thing built).

G-

Hi Ghurd,
Yes -- the high velocity air creating a low pressure area had crossed my mind as well -- maybe that's the answer.


The FG furnace filter absorber sounds good -- lots of surface area without adding too much air resistance.

Thanks,

Gary

[zap]

You might even be able to cut the filter media as a "solid V" to really tweak the flows?


Gary, how does the screen compare to muslin?

[GaryGary]

Thanks Zap,

The tapered cut does seem  like a pretty easy way to get a progressive adjustment on each downspout.

Have not tried muslin -- it seems like it should work about as well thermally.  Not sure if it would hold up to the collector temperatures.

Gary

[drew4justice]

Hi Gary,

Bernoulli's Principle?


I know that is not a great explanation...
Sit 5' in front of a box.  Lots of wind.
Sit 5' behind a 20" box fan.  Not much wind to feel.
Same volvume of air.  One is focused, one is not.

G-

Glen,

The way I picture this would be to blow through a straw with your hand on the other side receiving the air.   Take a regular sized straw and blow through it and you will feel the air with good pressure/velocity.  Now take a PVC pipe of larger diameter and plow the same amount of air and you probably won't feel it.  I've used this analogy when a friend thought that putting the largest sized carburetor on an engine would improve performance and he just didn't get what I was trying to explain.  After explaining the "straw theory" he seemed to understand.

Now I'm trying to figure out if vegetarians eat animal crackers.  This has me stumped.

Drew

[jondecker76]

I have an idea that might work to actively regulate airflow through the downspouts (though it requires that the downspouts are mounted vertically)

Imagine putting some light, free-swinging flappers hanging down in between each downspout (Something with a good amount of surface area and pretty light - like rectangular scraps of foam insulation)

If the air through one downspout is faster than the downspout next to it, the vacuum created by the rushing air will pull the flappers surrounding the downspout inwards, restricting the airflow a bit and lowering the velocity.  With flappers in between each downspout, they should theoretically all swing to a spot that helps to equalize air flow.


This quick sketch shows the basic concept (note:  its rotated 90 degrees the wrong way, but I'm at work and I couldn't get it to rotate in photobucket... but you get the idea)