trickle collector idea.

Question:

>I was thinking fairly thin piece of copper. I was hoping that copper >oxide was a good absorber and poor emitier.   I could use a copper >header and footer without a reaction of the other metals.  I liked >copper because of heat transfer, but aluminum would probably be just fine.

If heat only travels through a thin layer with sun on one side and water on the other, practically any material would work well, eg polyethylene film or EPDM rubber. >Honestly, I may just get a corrugated metal roof that alternates >relatively flat areas with a ‘hat’ every 9".    The channels are 3" >wide.  I am not sure how well galvanized steel will transfer the heat >if runs in a little rivlet down the middle.

That’s a different situation, with heat traveling sideways through the material. Thicker materials allow wider tube spacing. >I have not heard that polycarbonate is a problem with long term water >exposure.

GE sent me some graphs from a lab which show serious embrittlement in the presence of warm water vapor. It might wear out in 2 vs 20 years. Nick

Response:

I just ordered issue #59. I was thinking fairly thin piece of copper. I was hoping that copper oxide was a good absorber and poor emitier.   I could use a copper header and footer without a reaction of the other metals.  I liked copper because of heat transfer, but aluminum would probably be just fine. Honestly, I may just get a corrugated metal roof that alternates relatively flat areas with a ‘hat’ every 9".    The channels are 3" wide.  I am not sure how well galvanized steel will transfer the heat if runs in a little rivlet down the middle. Aluminum seems to be more challenging these days to get corrugated in. I have not heard that polycarbonate is a problem with long term water exposure. Eric

Response:

Robert.  Thank you so much for your help.  Here are some of my responses (My first answer is a bit Nick S.).  For example, how are you going to force the water to stay dispersed? I could place 1/8" nylon weedeater cord ($8.79 for 1500′ at ACE) every 4".    It is a 20′ run from header to footer.  Total area is around 700′.  Storage is a 4500 gallon tank. Perhaps you are planning on a DHW preheater? If so, use a double-walled heat exchanger. Yep You wouldn’t want to do that anyway because a continuous stream of new water will eventually corrode the copper, which is one of the least resistant materials to corrosion What about my 50 year old copper plumbing pipes?  What material would you use?  I liked copper because copper oxide seem to be a good absorber with low e.    How about aluminum, galvanized steel or stainless?  How about black plastic (25mil thick with foil behind that? Are you going to use the solar energy for space heating?  If so, then how do you plan on transferring the heat to the air?  This is a preaheater for DHW and heating via hydronic.

Response:

- Hide quoted text — Show quoted text ->My family is always acusing me of reinventing the wheel.  I think I >have a good idea for a trickle collector. >Basically the water runs down a flat sheet of copper.  The copper sheet >is covered by a layer of polycarbonate 2 wall sheet.  The space between >them is something on the order of a 1/8th of inch apart (beads of >silicon?). >There is a header with holes in it spaced every inch or so. (not sure >how to calculate the size, but perhaps 1/16th" is a good place to >start.  The footer has bigger, more frequent holes.  The  edges are >held tight by ‘H’ channel with a big bead of silicone. >Looking at thermal expansion coeficients, it looks like the >polycarbonate will expand 1/4" more over 50 degrees. >Does anyone else see problems with this idea?  It shold be pretty >cheap. > The details can make or break such an idea.  For example, how are you > going to force the water to stay dispersed?  If the sheet is flat, the > water will tend to gather into channels, or run off to one side, which > may leave large areas unwashed.  If the sheet is slightly grooved, > then the water will stay spread out, giving more even coverage.

There is a collector described in HomePower issue 59 that uses two sheets of corrugated metal spaced close to each other and fed from a manifold.  The flow might be somewhat similar to yours.  This is a short quote from the article: "Water spreads out through capillary action to gather solar heat from between the two pieces of metal. Gravity carries the heated water eight feet to the bottom of the black painted metal roofing. When it gets there, it is around 140

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