What Material Would You Use ?
I like this design of a solar air heater. It uses 160 soda cans to make a solar collector that heats air. I know that you’re thinking, this is going to be one of those “You may be a Redneck…” jokes…. It’s so simple, it’s great, but the commercial version is a bit pricey….
The main considerations would be the cost of the required UV rated clear sheet of polycarbnate, the bonding agent that attaches the soda cans together, and what to make the collector’s framework from so it can withstand the constant dry heat inside and not start a fire…. ;>)
What type of heat tolerant material would you use to make the framework from?
Any idea what to use to bond/seal the thin wall cans end to end?
What do you think the price would be for the special UV stabilized Polycarbonate?
Thanks for your help, Bill
http://www.liveleak.com/view?i=CB_1222457435
http://www.cansolair.com/
Replies
Hi,
There are plans for several versions of the pop can collector on my site here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm#Active
Just search down the page a bit for "beer can solar"...
I think the Hungarian version is a good one.
There are also a number of other air collector designs in this same section you might want to look at.
The one titled "Wayne's Solar Air Collector" is a similar design without the need to glue together hundreds of soda pop can.
I use wood for my collector frames. I've never had a problem with degrading the wood or overheating. I've never heard of a fire in a non-concentrating solar collector, and have looked hard to try and find any reports. There were thousands and thousands of them made in the 70's, so you would think there would be reports if it was a problem.
Some people use the materials that are used to make steel stud walls. Its best to use the sill plates, as they don't have the pre-punched holes in them. Here is one example water heating collector that uses galvanized steel sill plates for the frame:
http://www.builditsolar.com/Experimental/MTD/MTD.htm
For glazing, the cheapest high quality choice is SunTuf corrugated polycarbonate. Home Depot handles this -- its a bit over $1 per sqft. I've made several collectors out of it, and I think its a good material. Its polycarbonate, which is good to 270F, and is tough. It is UV stabilized and guaranteed for "life". My oldest SunTuf glazed collector is 5 years, and the glazing looks just like the day it went up -- no yellowing --its this one:
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
The only down side of the SufTuf glazing is dealing with sealing the ends of the corrugations. They sell strips for this, but your design has to allow for these seal strips.
This is how I do it in my water heating collectors:
http://www.builditsolar.com/Experimental/CopperAlumCollector/CopperAlumCol.htm
This is about as simple as it gets -- you can build one in an afternoon (maybe a long afternoon :)
I think that dual wall polycarbonate glazing is also a good choice. Its the stuff they use on greenhouses a lot. Very nice to work with.
I used it on this collector:
http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm
and have been quite satisfied with it.
Its about $2 or a bit more per sqft.
Shipping can be expensive if you can't get it locally.
Thicker sheets of polycarbonate should also work. I think its a good
idea to curve the polycaronate to give it some stiffness -- I think that the Cansolar and the Hungarian collector do this. Be absolutely certain that you get polycarobonate that is treated to resist UV -- it will yellow if not UV treated.
Glass is also good (its the best from a longevity point of view). You can sometimes get good deals from glass shops on sliding glass door panels that have been pulled out or new ones that are miscut.
You have to plan the collector around the glass, since you can't cut the tempered glass.
Some more stuff on glazing materials here:
http://www.builditsolar.com/Projects/SpaceHeating/Glazing.htm
Solar air heating collectors are a very good project. Cheap and simple to build -- very good payback period.
Gary
Yer a pretty handy guy, now go put the soffit on the barn's ends(G).Spheramid Enterprises Architectural Woodworks
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Gary, thank you for your great insight and comments.
Several years ago, I bought a few of those double pane, metal framed, glass vertical freezer doors for pennies on the dollar. They are identical to the ones seen in most supermarkets, these days.
Do you think they would work on this type of air system inspite of the heat?
Bill
Edited 8/3/2009 7:42 pm ET by BilljustBill
Hi Bill,
I think they would probably be fine. I'd guess they are tempered glass just from a safety point of view, and that would be good.Glass with a high iron content is not good for collectors because it absorbs too much sun in the glass. I'm told that you can tell if the glass is high iron by looking at the edge -- the higher the iron content, the greener it will look. Gary
High iron in the glass..
Gary, thanks for the insight of the green color... I remember as a kid, of seeing the edges of all those green glass shelves in the 5 & Dime stores....
Thanks for the tip,
Bill
My question for you is ... why bother in Texas? A lot of effort for little return, it seems. Your heating load can't be very much. Are you also planning a thermal storage or just heat when the sun is out. Even when you might need heat, it will be mostly in the night hours.
I think your biggest issue is bonding the cans to the substrate. Plan on temps in there of say 220++ I've tested air collectors before that easily got up to that temp. In the summer, it may be way more.
An option for the frame would be to have your sheet metal guy bend you up a box. Insulate it w/ e.g. polyiso ... and you are ready to go.
why bother in Texas? A lot of effort for little return, it seems.
Between November and February, it can get down to the teens around North Texas. When Propane was $2.65 a gallon, I began looking for lots of options!!
I have a newer Lopi fireplace insert and blower, but getting the heat down the hall is a problem, so half the house is warm, but the rest is cooler. Good for Winter night sleeping, but the fewer moving parts of this kind of heater would help equalize the heat during the Winter daylight hours. With wood heat supplementing most of the heat, thermal mass to store daylight heat isn't an issue.
To bond all those cans, end to end, I wonder about those high temp. red-colored silicone sealant, of if they sell "J/B Weld" in quarts and gallons... ;>) By building it myself, the actual costs would be much lower, so ROI would/should be fairly quick.
I have two 4x7'-5" thick sections of surplus government aircraft aluminum honeycomb with only $20 invested in both...So, with the $10 metal framed, double pane, freezer doors, I'd be out the insulation, metal framework, 100 cfm blower, and insulated ducting, making the low cost less of a problem whatever the efficiency would be.
Thanks for your insulation idea, too.
Bill
I wouldn't bother bonding the cans. Stack them up and run four fine wires through them. Anchor the wires to an X frame on both ends (and maybe put an X spreader in the middle somewhere). Tighten the wires until the cans seal tightly to each other -- a little air leakage likely won't do much damage.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
I caught a statement made in the video. He said they put a twisted piece of metal through the stack.
I'm guessing that the twist works like a gas hot water heater's piece of long twisted metal inserted between the burner and the vent hood on top of the water heater. The twist slows the rise of the hot combustion air so the heat has time to transfer through the hollow vent tube and into the cooler water at the top of the heater...
So, I'm thinking that all those metal twists are a must for higher efficiency and may not have room for those tensioned wires. Maybe the twisted metal could be made to pull/hold the stack of cans on each of the lengths... The vendors of this model said they have been working on their design for 20 years and making them for sale the last 10 years. Lots of places where the DIY'er has to re-invent the wheel as he tries to copy their ideas without the advantage of knowing their learning curve wisdom... ;>)
Bill
Hi,
Some no doubt highly biased opinions on solar air heating collectors:1) Everyone who makes a solar air heating collector has 10 reasons why its the most efficient design ever. This is especially true of the expensive ones, and the Cansolar one is very expensive. The thing that is in short supply is test data that shows efficiency curve for the collector -- very few of these for air collectors.
You might check the SRCC website and see if the Cansolar one has been certified -- if so, it will have the efficiency curve that you can compare to others.2) This is Wayne's design:
http://www.atlanticenergy.ca/projects/WayneLangilleSolarAirCollectors/tabid/72/Default.aspx
He has made an honest attempt to measure performance, and it looks to me like the collector performs well. It uses tubes instead of beer cans and does not have any "turbulators" -- but, it still works well.
It looks a lot easier to build than the beer can collectors.3) If you look at the TEA design:
http://www.builditsolar.com/Projects/SpaceHeating/TEACollector/TEAConstruction.htm
Its very well thought out, and they have real test data for it, and it does fine. Its a backflow, flat sheet metal absorber -- so, this is another totally different design that also performs well.4) There is a paper listed here:
http://www.builditsolar.com/Experimental/AirCollectors/AirCollectors.htm
That shows efficiency tests done on various kinds of flat plate absorber collectors with various kinds of baffle systems. Some of them do very well indeed.I guess my point is don't get taken in by somebodies line about having found the only way to get an efficient air heating collector -- there are lots of ways. If someone claims that have the greatest thing since sliced bread, and they have not done the testing to establish the efficiency curve, then they don't really have anything.In the end, you want to build a collector that is a good design (lots of these), but mostly you want to make it BIG. People loose track of the fact that what really makes a collector produce a lot of heat is a lot of area. DIY air heating collectors are cheap to build, so you might as well make it really large.Gary
I see what you mean about data and efficiency ratings, seems like everyone has the "best one".... ;>)
Thanks for all your help, too.
Bill
That first link is a collector, all right. What kind of collecting have you been doing??
I built a 40 gallon solar preheater back in the early '80's from a set of plans in the magazine called "New Shelter". Back then, getting a large window of just single pane glass was a major undertaking; double pane glass was way too expensive. With just one pane, I could run the system from about the last frost of early spring to just before the first hard freeze of early winter. Our well water is about 58 degrees, so any preheating helped before it went into the cold side of the standard hot water heater. I had an inline temp. gauge and often the incoming preheated water was hotter than what the the waterheater was set. I wrapped and covered the entire surface of a galvanized pressure tank (one without the bladder) with a special blackened copper with a heat transferring adhesive. That one worked so well, it would cause the pressure relief valve on the solar tank to open to release the hot water. I had to go in and spray a black paint on the tank that was more shiny to prevent the overheating...;>) It lasted until we had a serious hail storm in late 80's, even the glass was still intact. When the new roof was put on, I had the roofing crew tear out the tank and send the rest on the dump trailer filled with the old asphalt shingles....
Why did you ask?
Bill