Richard Heiliger gives a very complete description of two versions of the Modified Trickle Down (MTD) collector that he and John Canivan have been working on over the past couple years. These new collectors designs are based on the Thomason Trickle Down collector design, but use less expensive materials, and are easier to build.
Update Dec, 2011: Update on Richard's MTD Collectors
Update Oct, 2009: Report on Richard's MTD Collectors after 2 full seasons...
Overview of Richard's MTD collector
The absorber component of the MTD is dramatically different than the Thomason design, using a plastic and felt mat to spread water rather than the corrugated metal absorber of the Thomason collector. The MTD also includes an inside glazing layer keeps water vapor from condensing on the outer glazing and makes the collector more efficient.
Here is a sampling of pictures of the internals that give an idea how unique this collector design is -- download Richard's article to see the full details.
Download Richard's full 44 page pdf describing the collector in detail ... (pdf 2.6 MB). Very detailed construction sequence.
This version of the MTD uses corrugated galvanized metal roofing as the absorber. The corrugated absorber has a layer of black felt applied to it that spreads the water evenly over the full surface of the absorber. A distribution manifold supplies water to each corrugation. The outer glazing is corrugated polycarbonate, and an inner Mylar glazing layer seals in the water and prevents condensation of the outer glazing.
Here is a sampling of pictures of the internals for Version 2 that give an idea how unique this collector design is -- download Richard's article to see the full details.
Download Richard's full 41 page pdf describing the collector in detail... (pdf 2 MB) Very detailed construction sequence.
The spreadsheet below provides performance data for one sunny, mid-winter day. The performance is for a bank of 6 collectors, three of the collectors are Version 1 and three are version 2. It appears to me that the performance is quite good, and very comparable to high quality commercial collectors.
Download the Performance spreadsheet ... (Excel 0.3 MB)
I have had a few questions on how I plumed the feed lines on my trickle down collectors, below a simple diagram of how I did it. Might answer a few questions.
This is a note from Richard that provides the results of the stagnation test he has been running on the MTD collectors:
I ran water thru the collectors today, July 8th. After over three weeks of stagnation in 90 to 98 degree temperatures with clear skies. I had no leaks. Although the seal between the Mylar and back pack polyester separated at the very top of the funnel it did not leak. The side and bottom seals appear as good as when they where made. Perhaps some type of mechanical connection needs to be added at the top of the funnel. Such as the rivets I have along the edges. With the success of the steel collectors I am not going to spend more time on the back pack type collectors.The steel collectors had no problems what so ever. I will also mention that the acrylic felt turns a deep purple with constant exposure to the sun, but still seems to disperse the water just fine. I did notice the acrylic felt was turning purple even before the stagnation test. I am hoping that the polyester felt I have on order will not fade. The spec on the polyester felt states that it is fade resistant. Will put a piece out in the sun and see what happens. Just hope it disperses the water as well as the acrylic. I will also note that I have polyester fleece in two of the collectors. The fleece does not disperse the water at all. It also has turned purple.Also the PEX I have inside the collectors appears to be in very good shape yet. With the heating and cooling it has a developed a few curves on the way up, likely needs a few more tie points. I originally used nylon tie wraps to hold it in place. The sun deteriorates the nylon and it breaks. Metal conduit straps would likely be a better choice.I also drained the storage tank today. The water was slightly cloudy but saw little indication algae or such had developed. There was some pink strings of some kind occasionally. It looked like suspended fiberglass. But I used yellow fiberglass insulation. So I am not sure what it is. I painted the inside of the steel storage tank with red rustoleum, perhaps that is what it is. I still think that draining the system twice a year would be a good idea. I had a problem with a line to my radiator got partially plugged with a chunk of silicon from somewhere in the system. I added strainers between the storage and pump inlets.
I looked at the temperature on my controller, which has the LM34 in the bottom of the collector most every day, never saw it above 225, I also took a couple afternoon temps at the top with a candy thermometer, 275 was the highest.The collectors are at 58 degree angle.RD
John Canivan and Richard Heiliger have been working on the MTD design for some time, and are about to release an MTD book through Mother Earth News. John's website also offers a book and additional detail on the MTD design, and pre-made absorber mats for sale.
John's website: http://www.jc-solarhomes.com/
You can send comments, questions, or ideas to Richard at: rdheiliger AT msn DOT com (replace AT with @, and DOT with a period)
Thanks very much to Richard and John for this work!
Gary Jan 21, 2008
Added Version 2: June 27, 2008