First let me say I don't know how long I'll keep referring to the builds by number as that will get boring after a while but it does help me keep them straight in my mind.
Third build is complete. Once again I built a two layer screen collector. These are very quick and easy. A little different this time as I was trying to build as inexpensively as possible and still get reasonable heat out of the collector. This one is a smaller collector. I found a few sheets of 28” by 76” tempered glass (shower doors) on CL so it’s only about a meter and a half in area. Had to work a bit to get clear glass. The guy who had them said they had been sitting in his yard for about eight years. After a couple of good hard wash downs I still wasn’t happy with the clarity. Pulled out the paint buffer and some fine grit polish and that got the rest of the grime off.
Not sure how the picture got turned sideways. Looks ok in my picture folder on my computer. Anyway this is the final product. It makes a really pretty mirror in the shade, but lets the sun in wonderfully when there is nothing covering the top of it.
Cut the boards for the collector box out of some reclaimed OSB so no cost for the wood unless you count the couple of cents for electricity and slight wear and tear on the saw blade. One layer of the screen was free from a reclaimed screen door and the other layer is what was left from my previous build so I’m calling that 5 or 6 bucks. I did have to buy insulation and that seems to be the most difficult material to source for free. I have seen a sheet or two here and there, but always too far away to make it worth the drive. While I only used half the insulation there is probably just a third of the sheet left that will be usable for another build. So I’m calling that a $12 expense.
All the miscellaneous items (silicon, screws, paint, brackets, door insulation and starter collars) come in at around $40. So this build has around $60 into not including the fan and ducting that will be necessary to connect it to the house.
In an attempt to get by without paying for foam door insulation I looked around the house to see what I could use as a sealer between the wood and the glass. It occurred to me that I had a lot of old dead bicycle inner tubes laying around and that they might work. So I cut strips out of a couple of them and adhered them to the frame with some silicon. They would have worked just fine if I had cut my wood with just a bit more precision. One of my boards is just about a sixteenth of an inch taller than the other three and rather than tearing the box apart to fix it or trying to plane it down I broke down and splurged for regular foam door gasket material.
Electric rotary scissors makes cutting the inner tube lengthwise go pretty quickly.
Because this is tempered glass I thought it might be a good idea not to try to drill through it as I’ve read that almost no one can do that without causing it to blow out. So I made a few little brackets out of ¾” aluminum angle. I also placed angle at each corner because tempered glass, while very strong on the surface, tends to shatter relatively easily if hit on the edges.
This is one of the corner brackets with a piece of inner tube glued on where it will hit the glass.
I’m not as certain about my test results this time as it has been really hot here lately and testing has been getting done at around 92 degrees. I think I’ll just wait til it’s cooler outside to retest and verify my numbers as I believe my results are too good. Oh, I’m coming up with 87% efficiency during testing using a six inch fan blowing through a four inch opening. The four inch fan gave about half the output of the six inch so I’ll probably need to change the collar size at a later date also. If the thing isn’t putting the heat I think it should when it gets cooler outside then I plan to add a reflector on either side of the vertical component which in this case will be the 76” length.