Wednesday, February 20, 2013

Solar Can Heater Build Part 1

Some time long ago I saw a solar can heater on the internet. I thought - that's cool.

Then I started, inexplicably, collecting soda-water cans. I found myself locating and measuring a scrap piece of ply-wood to serve as a backing. I did a math problem with my kids figuring out how many rows and columns it would take to cover the board with 12 oz. soda cans. I found some old windows which matched the size of my board. Then I started thinking... we can build one of those there thangs!

The basic idea  is that you make a thin box containing stacks of cans that are punched or drilled to let air flow through them.  The face of the box is a sheet of glass or Plexiglas.  I have some old double pain windows which I will re-purpose for the  face.

As my journal entry notes, I have a few things to figure out.  I want to have a mechanical thermostat to control the vent, so when the air temperature exiting the heater drops below a set level, the vent will close and prevent cool are from cycling into the house or the draft from reversing.  Maybe just a foot valve will do if it's light enough to open when warm are is  flowing out the top outlet and strong enough to resist a draft pulling back the other way.

I also want to incorporate an air filter on the inlet to keep dust out.  I have to also come up with a good mount, window adapter and manifold to handle routing air.  Ideally, I'll draw cold air from the basement and vent warmed air into the house, but we'll see how many holes the missus will let me put in our cottage.
Notes from my Project Journal

4 x 5 x 5 = 100 cans
So, I've got two large cardboard boxes full of clean cans now. I drink soda water a lot. Can't do beer, don't like pop. Soda water has the pleasant carbonated effect that I miss from beer, so I go through cases at a time.

Gettin' jiggy wid it.  Sorry. 
I've taken my time figuring this project out.  I don't have all the pieces in place yet, but I have plenty of ideas where I'm heading with it.  My buddy Ken suggested a jig and aluminum tape instead of glue for setting up the cans in columns.  I tend to agree - it's less messy than the build I've seen that used construction adhesive and the jig I came up with is just two conduit pipes with some 1x2 spacer held together with zip ties.

Measure, cut, repeat.
Here we have two cans butt together, lined up perfectly thanks to the jig.  Next I'll cut a length of aluminum tape.  I figured the distance the easy way.  Marked the board and a can, rolled the can, marked the board where the mark on the can was towards the board again.  I checked it a couple of times to make sure I had it right.   Worked out perfectly.  The tape is basic dryer vent tape which has pretty good heat characteristics both in terms of the material and the glue.  I chose the "made in the USA" brand on Ken's advice (He's a Dryer Vent Wizard franchise owner and knows his vents) as imported brands let loose under heat, unfortunately.

rollin' rollin' rollin'
 To apply the tape, I start on the side of the cans facing me with the tape curled to ensure a perpendicular seat at the joint.  Then, I just roll the cans on the jig to smoothly lay the tape down.

 When done, the tape mostly lines up with the other end but because it's so much wider than the joint and  the length is specific to the diameter of the cans, it's no worry and looks nice and tidy.

Air Flow
Bottom right is a shot of the bottom of the cans.  To punch them, I simply put a counter-sink bit in my drill press and didn't even turn it on, just pulled the press down into the center of the can.  I punched 200 cans in about 20 minutes I'm guessing.  Repetitive... reminds me why I'm glad to have left factory work behind me in the 1990's.  The punched hole is offset from the tab hole which will serve to slightly baffle the air flow as it rises through the cans.  This will slow it down and give it more time to soak up heat from the cans which will be warmed by the sun.

When all of the stacks are assembled, I'll give them a coat of stove-black paint, which as you might guess is hi-temperature paint that should hold up.  I will likely give them a once over with some hi-grit sand paper to etch the aluminum enough to hold the paint.

When I get further along with the build, I'll post some more pictures.  My projects tend to wind out over weeks and months in my free-time (which is scarce and sacred) so be patient.