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Old 11-02-10, 12:38 PM   #1
Daox
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Default Incredibly cheap solar hot air panel

So, I've been thinking about using solar hot air panels for my garage. I took some time and thought about the least expensive way to make these panels. Below is what I came up with. The construction is incredibly simple and requires very few parts.

You need:
1 - 4'x8'x1" polyisocyanurate foam board
4 - 2"x4"x8' pine boards or 3 - 2x4s and 3 1x2s
2 - 4'x8' clear polyethylene film (construction plastic)
screws for the frames
round cap roofing nails to stick the polyiso to the 2x4 frame
staples for the polyethylene film
aluminum cans

Having to buy everything new (except the cans), you should be able to make a 4x8 panel for around $40 and much less if you have a few thing laying around. Now, you can fill it with aluminum cans like most people do and you got yourself a nice solar hot air collector.

Of course, there is a downside to it. The polyethylene film melts not too far over 200F. This means you'll need a blower with the system. Not that a blower is a bad idea to begin with because a blower will increase the panel's collection efficiency. If you don't have a blower, there is a good chance the polyethylene will melt.

If I end up going with hot air panels, I'll probably end up making a few of these to heat up the garage.






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Last edited by Daox; 11-02-10 at 12:47 PM..
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Old 11-02-10, 02:40 PM   #2
TimJFowler
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Here are a few more solar hot air panel designs

A commercial product (the Sun Aire brochure explains the design in sufficient detail) - AAA Template

A quick and dirty DIY design - Almost Free Solar Hot Air Collector.

I've looked over both of these designs and think a good DIY solution could be derived from them.

FWIW,
Tim
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Old 11-03-10, 09:04 AM   #3
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The instructables one is nice and very cheap. However, they're pretty small collectors, only 2'x4' or 8 sq/ft. One of the 4'x8' panels is 32 sq/ft. To heat my ~750 sq/ft garage I was thinking I'd need at least three of the 4x8 collectors.
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Old 11-03-10, 11:27 AM   #4
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Hi Tim,

Nice -- like the idea of seeing how low the cost can be for a functional air collector.

If it turns out that it runs to hot for the poly, you might just go with single glazing -- with only one layer of the poly, the outside of the glazing is always going to have the cooler ambient air to help keep it cooler than the collector internals. Single layer glazing might get the cost all the way down to $38.50

I think you may need something to control the airflow inside the collector -- the pop can approach works and its cheap, but lots of work.
Window screen or perforated aluminum soffit material work well as flow through absorbers, but increase the cost. But, if you have well sized vents top and bottom they will thermosyphon nicely and don't need a blower -- so that keeps the cost down.
Just adding some baffles to make sure the air flows to all parts of the collector, and using the back wall of the collector as the absorber might work pretty well and would be very cheap.

Another variation. Build the collector right onto a south facing wall, and do away with the polyiso insulation -- just paint the siding a dark color. This won't work for vinyl siding (the heat would damage it), but should be OK for wood siding. My vertical collector built in somewhat this way only gets to 185F when stagnated in the summer.
The back insulation is not needed if the space behind the collector is a heated space anyway.

Another one in the spirit of cheap air collectors:
Have always liked the simplicity of this Mother Earth one:
THIS $30 SOLAR SETUP HEATS A 30 X 40 WORKSHOP FOR FIVE HOURS OR MORE EVERY SUNNY WINTER DAY

If you get the cost down to (say) $1 per sqft, and 1 sqft of collector harvests about 900 BTU per sunny day, the payback period for $2.20 propane would be about 1.5 months!

Gary
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Old 11-04-10, 10:28 AM   #5
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Yeah, the cans are a pain and lots of work. However, they are free. Being a incredibly cheap design its hard to beat free. Also, most guys glue all the cans together. I don't see that as necessary. They also force the air to go directly through the cans vs just anywhere in the panel. I also see this as unnecessary. I think if you put the cans in the collector in an organized manner, pinch them at the top and bottom with a 2x2 or something, and you should have a good enough collector.

You could definitely cheapen up the design if you had a wall that you could work with. Unfortunately, I do not. So, this is what I came up with.
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Old 10-03-11, 03:59 PM   #6
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Not to bring back a thread from the afterlife, but...

Another option for low-cost collector parts is free windows.

Two of the window installation businesses in town leave the old windows out back behind their establishments and encourage people to help themselves. (Saves them disposal costs.) Mostly they put out old single pane wood windows, but occasionally there is thermal pane stuff.

Of course then you have to build your project to the size of the available glass.

But it's another low-cost (free) option if you're worried about melting the plastic film.

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