This is a picture of a downspout collector from Scott's site...
But, the last advantage of lots of surface area to transfer heat from downspouts to air is only true if the heat from the sun side of the downspout gets conducted around the sides and back to warm them up. This test was done to see if that happens -- that is, is there really good heat transfer around the full circumference of the gutter section so that heat is transferred to the air by the full surface.
The not very ambitious test setup consists of 3 downspout tubes connected to an air supply plenum. Air is supplied to the plenum by a small fan, and the temperatures of the front ant the back of the gutter tubes is measured with a thermal imaging camera (my new
The insulation panel on the back is to better simulate the actual collector environment -- it is quickly removed before taking the temperatures on the back side.
These are thermal images of the front and back while the collector is in operation.
|Front of the collector|
|Back of the collector|
More details and analysis on the test of the downspout collector here...