Friday, January 4, 2013

A DESIGN CHALLENGE for pop can and downspout collector builders

Solar air heating collectors that use columns of aluminum soda pop cans or that use metal gutter downspouts as the absorber are quite popular. 
pop can collector
Greg's pop can collector in work
In this design, the supply air flows into a plenum at one end and is distributed to the pop can columns or downspouts, the air then flows up the pop cans.  The sun striking the outside of the black painted cans heats them up, and this heat is transferred to the air flowing up through the cans. 

One of the challenges for an efficient design is to get the same flow in each of the pop can columns.   Having unequal flows in the columns makes for a less efficient collector with some parts of the collector running hotter than they need to and losing heat out the collector glazing.
When I built a downspout collector for testing against other collector types, I was unable to come up with a plenum design that gave an even flow in the downspouts...  I think that this may have been a significant part of why the collector did not do so well in the testing compared to the screen absorber.

Sooooo, if you are building or have a pop can or downspout collector, how about testing the flow in each column, and see how the flow comes out on yours.  If its not close to the same in each column, maybe you can experiment around with changes to the collector to get the flow to even out? 

Testing for even flow is easy to do, and coming up with a collector/plenum design that provides even flow to all the can columns would be a real benefit to a lot of collector builders. 

On my prototype, I measured the flow by making a small hole in each column, and then read the column air velocity by inserting a wind meter in the hole.

The results looked like this...

Flow in each of the 13 columns.

January 4, 2013


  1. What about putting the entry all the way over to one side and then putting the exit all the way over on the opposite side like they do with solar pool heating collectors. I would think this would force a more uniform distribution of flows.

  2. We did a flow distibution equilization from a manifold project in another media by having various sized aperatures at the transition plane.

  3. I got the idea above from a Borla exhaust system for a fourth gen Camaro. They had a series of plates to tune flow between exits.

    1. Hi -- How did you do check the flow in each of the exit? Seems like the problem with a solar collector where each can row has to be adjusted individually is that you have to have a good way to measure the flow and that its going to take a lot of fiddling?



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