Copper fridge heat exchanger as solar collector

[niffa]

Hi,

I have collected used fridge heat exchangers (the tubes at the back of the fridge) and am painting them black, connecting 20 or so together with a  copper bus pipe top and bottom.

 I know this collector will need to be pumped to over come the pipe friction losses but should heat up well?

I intend to have a reflective backing plate so both sides of the head exchanger will see the sun. Lots of thin copper tube under glass got to work?

Please comment, as I have no experience. Sorry no photo as no camera.

Phil

[georgeodjungle]

sounds like it would work.

but i think a flat black backing plate might work better by heating internal temps up.

build two and let us know.

[Volvo farmer]

Painting them black? Every one I've ever seen already is black. What are you pumping through them and what are you going to do with it when it's hot? There's mineral oil (possibly contaminated from burned out compressors) in them there coils and I think it would be unwise to use them for potable water.

[coffeyw]

Most I've seen were glossy black.

I assume you're painting them flat black.

The best exchanger (condenser) rigging I've ever seen in use as a solar collector was made from old condenser units from residential and commercial air conditioner units.  When this type of condenser unit is painted flat black it ends up being a black hole to the sunlight.  The condenser fins are manufactured very close together, so there's no sunlight that makes it through the fins to warrant using a mirror on the back of the unit.  I remember this unit was in an insulated box with a glass front.

[Jeff7]

If you do paint them, I suggest a high-temp paint, like something meant for grills. Regular spray paint might get gooey in sunlight, especially when it's absorbing most of it.

[niffa]

Thanks for the comments.

The heat exchanges I have are all white, but what the, I am spray-painting them with black zinc paint. Good point about cleaning the tubes, as I will be circulating potable water through them. I have acid wash cleaners as used in cleaning industrial milking plant but will take care.

I estimate 80% coverage of collector area by copper tube so the reflector idea may be of academic interest only I will post results (if I don't poison myself)

Cheers

Phil

[niffa]

Thanks I had't thought of that. I will try the black zinc on a tial one first.

Phil

[Mary Ann]

Hi there, if you are talking about the condensor on the back of the fridge, they are not copper.  I am a retired appliance tech. when changing the compressor we had to solder onto the condensor and it is steel so we had to use a silver high temp solder to hook the copper line to the condensor.  I don't know if this makes a difference to what you are trying to do. hope this helps  

[cyplesma]

*

The condenser fins are manufactured very close together, so there's no sunlight that makes it through the fins to warrant using a mirror on the back of the unit.  I remember this unit was in an insulated box with a glass front.

*

Those fins are basiclly a heat sink to help pull heat away from the pipes, I don't know if it would work the other way, but worth a try for those who have the materials and time.

as far as using a reflective back or black back behind the pipes, definitely try both.  You might want to consider some form of magnifying glass. or several. there pretty cheap in the dollar store market in the states.

or a little more expensive magnifier is a cosmetic mirror you can find in the womans makeup section of a department store. 15x, 10x 7x, and 5x.

I helped a daughter make a solar stove to cook a hotdog. with a small cardboard box lined completly inside with aluminum used a hanger to angle the cosmetic mirror into the box. her hot dog was burnt in 3 minutes on a party cloudy day with a drizzle of rain.

[niffa]

Thank you for that I checked my condensors and they are steel the only copper is the first foot or so.

 I will have to re think the plumbing layout now as I had intended to run potable water through the heater. Not a good idea now I know the tubes will rust over time. I will have to set it up closed loop with anti freeze.

Thanks again, will post pics soon.

Phil