Solar Air Heater - DIY

[likes to eperiment]

Paint coatings and heat absorbing/transfer

One other almost always over looked area of heat transfer inefficiencies is the paint coating department. Much of the paint commonly used for collector assembles contain heavy polymers that actually are slow to absorb heat and transfer heat just as poorly. Think condoms and paint coatings act similar. Highly polished black chrome is very nearly the most heat absorbent surface available. Just tough to make an aluminum can polished to high luster, however the increased performance would be mentionable.
I just made a post offering interesting possibilities in the absorbing and releasing of solar radiation with different materials in the beer can collector thread. Its certainly food for thought.
Interesting to think about would be an aluminum can similar to a florescent bulb only larger in diameter. Polished to a high degree with a smooth and black finish. The paint should contain a high degree of metalic bits, cover well with a single coat, be nontoxic, and cheap to use. The black can/gutter assembly works well enough to be of use but you can see the room available for improvement.
Stay safe, don't burn anything up or down, and never quit experimenting!

[Naptown]

beer cans ar much thiner than the gutter spouts will this lessen heat transfer .. all burnt here.....

Incorrect
Heat transfer across a medium is a function of the thermal conductivity of the material, temperature differential and THICKNESS OF MATERIAL.
Look at any heat transfer material the BTU rate is dependant on the thickness of the material. The thicker the slower the transfer.

[sunburnt]

my thought and i dont think much but

beer cans ar much thiner than the gutter spouts will this lessen heat transfer .. all burnt here.....

[Accipiter82]

true but in the interest of quality control it is also better to wait a bit between the emptying and the building of the panels.

Agree This is my goal panel_od_limenki_19s.jpg i find good tutorial and just to wind one more friend that will help me to empty all 100+ beer cans

[Naptown]

For some reason, it seems to work better if you empty the beer cans yourself!

true but in the interest of quality control it is also better to wait a bit between the emptying and the building of the panels.

[inetdog]

You can us empty beer/soda cans to build solar air heater

For some reason, it seems to work better if you empty the beer cans yourself!

[Accipiter82]

You can us empty beer/soda cans to build solar air heater

[nobody]

i'm in the stages of doing another one of these for myselves. we have two that are made on 4x8 plyboard. i was wondering if it might help to heat the air more if some how you put a U shaped tube connecting the can roles. say the first role of cans you leave open in the return header space. then you link the first role to the second, on the other end of the second you link it to the third role and so on till the last role is open on the end the hot air is piped out of. the air remains in the painted flat black cans longer getting heated more and more as it moves through the cans.

the thing we keep talking about is there has to be a happy medium for the output fan size. to big a fan and the air doesn't have enough time to heat up enough. to slow of a fan the air gets very hot, but it doesn't blow out into the room to be heated well.

this may have been bruaght up before and if it has i'm sorry. just me thinking again. the first one i did is hooked up on my chciken coup in the winter monthes. yep. my chickens live a pampered life. the second one i gave to a friend for his cabin. this one will go on my out biulding. i have been using small dc computer fans and a small solar panel to run them. they turn on in the day and off on thier own at night.

i have the intake hooked up so that the heated air is being reheated again and again. it seems to work alot better than pulling cold air in and trying to heat it up. i have the output hose run to the furthest side of the chicken coup. when i do my out building i will do it the exact same way. also the intake is high up on the roof of the chicken coup. the output is down next to the floor.

[JennyRox02]

The Solar Sponge is a low cost Do-It-Yourself active Solar Air Heater designed to heat your home using energy from the sun. The sun provides heat all year round, so why not use solar in the winter too! Solar air heating can supplement your regular heating system and can dramatically reduce your heating costs. Air in your home is circulated through a collector on the exterior wall where it can gain up to 30 degrees before being vented back into the room. These 4'x 8' collectors look like large doors and should be mounted on a sunny south facing wall or roof.

[CarrieTaylor]

i can advise you on that i would do differently and would cause a big difference would be to actually pull the warm air from inside the house then warm it up more and pump it back in, at the moment i am getting the outside cold air and warm it up and pump it into my house and usually has a guideline to my system if its 15c outside(air intake) its pumping 30c into my house

Thank you!

[Crumb]

Check out simplysolar - they have lots of wild ideas and some really fruitcake suggestions.

The wire thingy sounds like a waste to me.

I am willing to test it in the real world, side by side, later this fall when I build it.

One straight black pipe. One pipe with aluminum windings, one with copper windings.
Just for fun we can do black plastic sewer pipe with windings too to specifically measure the effect of the windings regardless of the aluminum gutter? We'll see.

I doubt I have anything accurate enough to measure the difference, however, I will report back.

Most of my temperature measuring stuff is +/- 3%, But - hey, I like the idea enough to try to take it a little further.

EDIT: May also try slots with L shaped strips of aluminum on alternating diagonals. One surface gets black and put on the sun facing surface. This may be less tedious than the wires. I am excited about the idea but have my hands full on a solar build right now.

Update 9/7 - Project abandoned. My surface requirements are too great due to thinner air above sea level to be worthwhile. Thinner air means less thermal mass to move the heat into, and even less efficiency. Even radiators and fans are less effective out here. I forget this often.

Now, solar-to-water might be a better candidate but that's another headache for another day.

By the way - Tests on black spraypainted cardboard, cardboard with a copper "stitch" and aluminum "stitch" - favored the copper wire by quarter to half a degree hotter on the backside of the corrugated cardboard than aluminum or nothing. Meter was +/- 3% so I really can't conclude much other than a "maybe/dunno." Did not do any timing to see which cooled quickest, but they were roughly the same in just a quick check after about 15 seconds out of the sun.

If I ever tackle any of this I'll put the heat into water first, then into the air - it's a little different out here than most places.

[russ]

For any others following this - you will be far better off looking at www.builditsolar.com and using one of their plans.

This is getting a bit strange for virtually zero gain.

[Crumb]

I'd like to see a reference for this !

The type of surface - it's emissivity is what controls absorption / radiation .

The base material is what controls the CONDUCTION

best to worse :
silver
copper
aluminum
the rest aren't worth mentioning.

I have seen this laid out my way with references, but it was years ago and it would take me all afternoon to find it.

I think we might be agreeing, at least partially.
Copper has the better conduction, no doubt - we agree there.
I am pretty sure that aluminum, while being a less efficient conductor of heat, is marginally better at wanting to give it up. I think it was by using a different measurement than surface/emissivity like you were using.

I havn't looked in years, but I think it had something to do with (specific?) heat capacity and maybe there was a caveat in there of "by weight" or somesuch?
Would that make better sense to you if that were the case? Again, its been years since I saw the references.

I didn't write the book on thermodynamics, nor did I read it - I am just instinctively good with it. I can't be positive, but I remember having the same surprise that you did- when I heard it. The explanation was convincing enough for me. I remember seeing graphs showing aluminum just a whisker better in some cases.

I think the study I saw was about this: If you want a heat sink based on thermal mass alone, (big dumb lump) you want copper.

If you want a finned heatsink in an airflow with lower thermal mass and lower overall weight and not a giant lump of copper you are better off with aluminum- And it wasn't much - A few tenths? A few percent? In those terms - it made total sense to me.

I welcome any references to the contrary, because what I know might not specifically apply here using the different set of measurements you are talking about.

In our scenario copper wire should be okay and work nearly as well, but if you are going to all that trouble - why not built in a little more heat transfer if you can help it?

The performance is close either way, so I certainly wouldn't frown on a system using copper, I just wouldn't do it that way and would recommend otherwise.

[russ]

I can suggest an improvement (how I would/will do it) :

Check out simplysolar - they have lots of wild ideas and some really fruitcake suggestions.

The wire thingy sounds like a waste to me.

[Mike90250]

Why aluminum wire when copper wire is easier to find and absorbs heat better?
It is a trade off, like anything else. Copper absorbs heat better than aluminum. Aluminum gives up heat better than copper. Sometimes it is just better.

I'd like to see a reference for this !

The type of surface - it's emissivity is what controls absorption / radiation .

The base material is what controls the CONDUCTION

best to worse :
silver
copper
aluminum
the rest aren't worth mentioning.