Installing a Passive Solar Heater

In this blog post I will be discussing installing a passive solar heater. I created this design to collect sunlight into the black heat painted cans. The cans are open on top and bottom and glued together with high temp silicone.

Applied STEM and Problem Solving

This design is frankly very simple. It took me a weekend to build and 18 months to test it through winters and summers. Once I had data that it would work, I committed to installing it.

This design allows cold air to enter through the bottom and as it rises it heats up inside the black cans. The volume of the box at the top under the glass and reflected by the shiny foam insulation gets warm quite quickly. There is an opening at the top where the hot air will flow into a lower pressure (i.e. colder) space.

This installation is primarily to heat the area of my classroom at Mezzacello where I store batteries and servers in the winter. To that end it does a great job. In spring and summer I vent the air out the top. This system is analogous to the greenhouse effect of the earths atmosphere.

Prior to committing to installing the solar heater with permanent steel, I tried a lean-to using the banister in the attic I repurposed. It looked bad, but data is data whether one likes it or not. I spent all my budget on the box, I wanted that to be the point of these 18 months.

As part of my commitment to modeling sustainability and applied STEM I will be adding blogs like this to my web site. I learned all of this from youtube. Sustainability mandates that I share as much as I can in the hopes that we all will as well.

How To:

You need to build a large box (mine is wood as it’s easy to build with) 1 m x 1.5 m 30 cm (39″ x 59″ x 11″) and make it durable. The box is lined with reflective foam insulation and the corners are reinforced. There are holes cut into the bottom that line up with the black can tubes.

Each can is an aluminum soda or beer can that I ground the bottoms off and glued end to create a tube. Then I glued them together into 9 tubes 1.45 m long using high temp silicone glue. Lastly I spray painted each tube matte black with high temperature spray paint.

You position the bottom of each tube on that hole. Place some stays under the tubes to make sure hot air can circulate around the tubes as well. The glass is sealed in place with silicone caulk and mechanically fastened to the frame.

Lastly there is a slit to allow the hot air out the top. I attach a duct to that and into the shed. Two DC powered computer fans draw the hot air into the area of the shed with the batteries and servers.

The Hardest Part

It really is that simple. The hardest parts were finding the NON-UV reflective glass and sourcing 90 aluminum cans. I live in downtown Columbus and I don’t drink soda or beer. Finding cans is tough when you are competing with recyclers who want to sell the aluminum cans!

Luckily my friends drink soda and beer and I was able to beg them for the cans. This is a great project to work on with your kids. You learn a great deal about math, volume, geometry, environmental science and thermodynamics in a fun and natural way.

Future Plans

I will definitely be building a few more of these. I will also be adjusting their installation height as heat rises. In the chicken coop, a lower installation makes more sense.

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