I recently finished building and initial testing on a Solar air heater, and the results are promising. Being from Colorado solar heat makes a lot of sense. The collector is based on a design that can be found many places online as well as one that is manufactured in Canada by Cansolair. From there I made some changes that I believe will increase efficiency.
Like most, it is approximately 4' by 8 foot.
The main heat collector core is made from recycled soda and beer cans.
Here is where the difference lies. My design uses 192 cans instead of the normal 240.
Most collectors have the can columns right together with no space between them. My feeling is, with the sun directly in front of the collector each column has 50% surface showing, and 240 cans.
The sun is only directly in front for a short time. The rest of the time the sun is hitting at an angle and each column is partially hiding the one next to it.
In my design I have spread the columns apart to eliminate the shading up until almost 45 degree sun angle, which was my target. I then put a reflectorized, insulated panel behind the Columns to reflect light, and thus enegrgy to the back side of each column. This way even though I have 20 percent fewer cans, I get 50% coverage at 45 degrees and far greater at lesser angles. pretty much 100% at times. This spacing is seen often in Solar water heaters.
The above photo shows that at about 9:30 in the morning, with about 68 to 70 degree ambient temp. I was producing 150 CFM of 100 degree air.
I also increased my blower size by 50% (to 150 cfm) and use a blower instead of an axial blade fan. A blower is more efficient with higher volumes and handles static pressure better.
At these settings the fan runs constantly but I am getting a virtually 100 percent heat exchange. With the panel laying on it's back to mimic mid winter sun angles, during constant operation and 100 to 110 degree output, the Polycarbonate cover stays about the same temperature as the ambient air. This tells me that there is no heat being generated in the cabinet and being lost through the front.
If I shut the fan off for a few minutes the temperature rapidly climbs as high as 140 degrees. To decrease the electrical requirements I could cycle the fan as there is a 20 degree differential fan switch installed (above). In this scenario I would be outputting less air, but it would be hotter. The down side would be there would be some heat loss through the cabinet front. I have not yet figured out how to calculate the best operating methods.
In the next few weeks I plan on getting the collector installed and running, and will also post a link to a website I am creating with better instructions, should you want to build your own. I estimate the cost of this system at about $350.00
There is a fair amount of labor involved but is not that hard for someone that is a little handy.