Solar Pool Heater Project

[Mike-Mat]

Hello All,

I'm new to this forum. Please be nice if I screw up. .

I'm building a solar pool heater based on the concept of PVC irrigation tubing, coiled up into 3ft diameters. Similar to these http://www.gullsolar.com/index.php?page=suncoil I plan on at least 3 of these to start with. They will be mounted on a board.

My question is... Which will produce more heat...
1 - Painting the mounting board black? or
2 - Covering the board with a sheet of aluminum?

The Aluminum I'm looking at is in sheet form .032" thick x 48" x 6'. The standard finish is a mill grade (as rolled, not polished), but it can be polished. Thought I might mount it to the board and then polish it myself.

Looking forward to your input. Thanks in advance.

Mike Mattera

[Mike90250]

I suspect the insulative quality of the plastic, will prevent you from seeing much gain when you have water flow. I think 1/2" copper tube, coiled into a spiral, and painted black, on a white surface, will give a lot more gain. Obtaining a half degree of gain, is better that more, as you have a higher gain, you re-radiate the heat back out.

There are solar thermal pool collectors made commercially, get a look at those, see how they do it.

Mike

[Mike-Mat]

Hi Mike,

Thanks for your input. I agree copper would be better. But I dont have copper. Based on other peoples good results using PVC irrigation tubing, I've used that as my starting point. In the future, when budgets allow, I might try using copper.

I dont mean to be difficult, but the real question was...
Would Aluminum reflect more heat than a Black background?

Solid experience on this is not necessary. I dont expect a scientific analysis. Your opinion as to which might be better would be very helpful to me for now.

Thanks again,

Mike Mattera

[Mike90250]

question was...
Would Aluminum reflect more heat than a Black background?

I think white would be as good, or better, then polished aluminum in this case, considering how long the aluminum would stay polished outdoors

Black would NOT be a good reflector.

[Mike-Mat]

That's a good point. I thought about that also. With no coating on the Alum. it will start to oxidize the minute I finish polishing it. Probably wouldn't be more than a month before it starts to loose it's shine. PLus the Aulm. adds to the cost of my budget conscience project.

So with that, I would think a black board will radiate heat better. 300ft of black tubing on a shiny black board should pick of some of that great Phoenix AZ sunshine.

The final incarnation of this heater will consist of 2 banks, with 3 coils in each bank (100ft/coil. .600" dia.). My pump will move 650GPM thru a 1" pipe. So far I estimate the total project will cost about $250 tops.

Mike Mattera

[Mike90250]

The black board will heat itself up. None will transfer thru the pipe to the water.

White, will reflect light, and the black pipe can absorb it, heating it a bit.

If you had a black metal plate, soldered to metal tube, then the black back will do useful work.

Leave a gap between the coils, about 1 diameter worth, that will allow light to reflect to more sides of the tube.

[Mike-Mat]

I see what you mean about the metal plate being in contact with the tubing. It has me re-thinking it a little bit. I looked at my local metal supplier and found 20 guage (.032") x 48" x 72" steel for $40 each. I figured steel (painted black) would absorb and radiate the heat better than Aluminum (does that make sense?). Do you think a .032" plate is thick enough to radiate the heat efficently?

So I could mount the steel sheet onto the backer board and then mount the coils directly onto the steel surface. Perhaps using some steel straps in an "X" fashion to hold it down.

One of my concerns is the weight. I'm putting this on the flat roof of my patio. Most likely I'm have to move the pieces up there and then build it in place.

Mike Mattera

[Mike90250]

I'm not sre how to explain this better.
Metal plate soldered to metal tubing OK

Metal plate to plastic tube = useless (no thermal conduction path)

Black painted background - No reflection, only the background gets hot & no thermal conduction path

WHITE painted background - reflection to tubing, some gain.

And steel is a poor heat conductor. don't bother with it.

With plastic collection pipe, a light (white) color background is your best friend.

I'd suggest white painted aluminum. Paint both sides before placing on top of the wood backing. The aluminum will take weathering much better than the painted wood will.

What's your expected lifetime of the tubing?

[Mike-Mat]

Thought you might find this interesting.

So I have 4 coils containing about 120' (each) of PVC irrigation hose, connected in series. The black PVC is mounted on a black board. Water is pumped out and thru the coils.

Preliminary Test:
Water going in is 57

[Mike90250]

Reducing the flow rate thru the coils should allow it to pick up more heat.

While that "sounds" right, in reality, it's false. Heat "flows" from hot to cold. The greater the difference, the more "flow". if your water is flowing faster, it would accumulate even more BTU's, faster, because of the differential. Also, the hotter the pipe is, the more it will re-radiate the heat away from it.

Fast flow rate, and low difference, will over a day, acquire more gain than
slow flow, high difference.

[Moofer]

i like this, looks simple and cheap. With a solar powered pump, its gonna be free warm water in the pool.

[tonytheroofer]

[QUOTE=Mike-Mat;5325]Thought you might find this interesting.

So I have 4 coils containing about 120' (each) of PVC irrigation hose, connected in series. The black PVC is mounted on a black board. Water is pumped out and thru the coils.

Preliminary Test:
Water going in is 57