Poly Pipe for Solar Thermal Collector

[(unknown)]

(this is a repost from water heating... )

Yes I know...

Everyone says you can't use plastic pipe for a medium temperatur solar collector. But still... I wanted to open a discussion...

The small copper tube/plate collector I built for testing was expensive. Over $100 for a 1' x 10' collector with only plastic scrap sheeting for glazing. The copper in these systems is annoyingly expensive. Fittings, solder, paste and then paint... is there another way???

So there I am, back at Home Depot, starring at the 100 foot coils of poly pipe (black plastic pipe often used for underground sprinkler systems). I look like one of those guys on "One flew over the Cookoo's Nest" with a small puddle of drool quietly spreading on the freshly waxed concrete floor... but I digress.

At about $15 for 1" x 100ft or $40 for 1" x 300ft, it entices the imagination. Can one solve the problems associated with poly pipe so that it may be used as a main solar collector for supplimental water heating.

The main grievances seem to be first... overheating, second UV radiation.

If the overheating can be solved, I say big deal on the radiation. So what if it doesn't last ten years. You could replace it every two years and still save a bundle over buying or building copper plate solar panels.

As for efficiency... size over quality. Make 'em big!

Ok... the floor is open.

Let's hear some creativity!

Ross

[Gary D]

Hi Ross, there have been people who string black plastic on their roofs, according to an earlier post. I think your biggest concern if you don't pressurize it, would be to keep the water flowing during peak heating hours. Any hose clamps might need to be retightened after a few hours/ days and you definately want the copper for your transfer medium. It was discussed that btu exchange would remain the same at any flow tho return to the collecters would be higher, so it would seem that a higher flow would be better in this case. I think it will work, but be able to open the collecters for unexpected fixes. Gary D.

[wooferhound]

 I made a pool heater from Black ABS plastic pipe, I am including a picture. I made this 4 foot x 10 foot structure as pictured for a little less than $100.oo

The complete story is here...

http://www.fieldlines.com/story/2003/7/8/19177/93125

I used 100 feet of 1.5 inch pipe in all. I painted it all Flat Black before I put it up, but after 1 year in the weather I am seeing the paint is turning Grey and areas of the pipe that did Not get painted are still nicely Black.

Today I am installing an underlayment of black plastic, and then a clear plastic cover over the entire structure to help try to capture more heat and hold it in.

Does anybody know of a Black Paint that will Stay Black ?

[Ross]

Hi Woof,

Thanks for the feedback. I like the tube collector. It is VERY similar to one I put together out of 1.25" PVC several years back. It was a very basic parallel tube system (such as yours) with a manifold pipes top and bottom. To keep the flow rates through each pipe as even as possible, I put stainless steel washers in each tube off of the manifold so that a measured amount would flow through each pipe.

The PVC needed no real support other than the roof so I painted it all black (I used BBQ paint) and threw a couple of hooks in to support the thing. Then I plumbed it down to the pool pump (much the same as you did with valves I could turn on or off as needed for hot water) and flipped the pump on.

I was suprised at how well the pump handled the head pressure. It did just fine getting up there and then after a few minutes had flushed out most of the air and equilized itself well.

The dissappointment was that for my 17' round pool, it really made very little difference. The water would come out hot initially but would cool quickly. My choices were simple... let the pump run continuously (expensive) or put a controller on the thing to wait for the collector water to heat and then turn the pump on every time the colletor temperature was at some differential above the pool temperature. This way I get the heat without the lengthy run on the pump.

The collector was uncovered and I suspect that if it had been boxed in, it would have done a much better job. It was roughly the same size as your own... 10' x 10'. I think it needed to be tripled in size to do what I wanted.

Thanks for your feedback!

Ross

[RobD]

My plumbing supply sells those 1" black coils. I was wondering why you're not running the coil in one flat expanding circle? That was my idea.

robD

[BrianK]

I had some of that black plastic pipe laying around and just for the fun of it I took an old window pain layed it out cut some plywood and some 2x4's made a box painted the inside black used about i think 25 or so feet of the pipe coiled up nicely in the box it heats up to about 150degs not bad. make the water move it will warm up a 5 gal bucket to about 85degs give or take. This was just a small test to get my brain going on plans for something larger.  HUM the roof of my house is nice big and black might be a good location one side is 15x30 facing south nice angle also a garage with east west roof 20x40 also looks promising to me  woo hoo

     .

[Norm]

  Roof gets pretty hot why can't you run water down the roof...course it all depends what you're going to use the hot water for......

             ( :>) Norm

[Coolluke]

Hi Ross

I just finished my solar panel using one inch poly drip, although I am getting reasonable results from this system, I have come to realize it's limited potential.

http://www3.telus.net/teeoff/solar

I have been looking into retrofitting my box with a cross flow design made out of ¾ copper pipes.

The problem with copper is the price, I just checked with my supply store and for ninety eight foot lengths of 3/4 pipe it's going to be $1000 this does not include the 180 fittings I would need at $1.80 each. (These are Canadian prices)

There has to be a cheaper way!

I'm now looking into 3/8th. Plastic tubing to use as stringers between two 1 ½ inch PVC pipes, I would like to get 100 tubes in an eight foot length. This would give me 2.6 times the diameter of the 1 ½ PVC.

If I'm not mistaken this should reduce the head pressure at each individual connection in the system and limit the chance of a failure.

This project is still in the design stage and I hope to start building it in Feb.

Clear skies

CL

BC. Canada

[RobD]

I'm thinking about the natural effect of using parallel tubes. the inlet is on one end and the outlet on the other with all the tubes tied to a common pipe on each end ( one common inlet and one common outlet). This way there would be a natural circulation without a pump.

Why not run the tubes in the attic attached to the bottom side of the roof sheathing with a insulated holding tank, say 50 gallons, right there.

RobD

[dconn]

I've got a small collection of house wall-mounting radiators.  I was thinking about putting a painted single panel one behind a double-glazed pane and seeing what it would do - if they work well giving heat wouldn't they be a cheap way of getting it?  and gravity flow should work if one outlet is down and the other up (which would mean standing a radiator on its side)?





Derek

[StanB]

Guys, if you want to heat water in 30-40 gallon batches, then just use 2x6's to make a rectangle to fit whatever free plate glass you can get..

Put some blue foam insulation under it and then line the box with black plastic sheet.

When you seal it all up and add water, it will heat up to 185 F in moderate summer sunshine.

In low angle winter sun, you can get up to 140 F water. Just heat it in batches and then dump it as needed.

Does this make any sense??

Stan

[laskey]

Hey why not use bendable copper tubing and coil that  instead of ... eep.. $320 worth of fittings!

Cya,

Chris

[bkrahmer]

I'm planning on building a set of collectors, perhaps next year, about 145 ft2.  My current theory is this:  Use a wooden 2x6 frame, plywood on the back, low-iron glass for the front, insulated on the sides and bottom (bottom as if the box was laying on the ground).  On top of the insulation at the bottom, you add a layer of metal.  Aluminum would work if you can thermally and structurally bond the aluminum sheet to the copper tubing (I haven't made a prototype, maybe soldering or brazing?).  The copper tubing would be flexible tubing bent into a serpentine.  The copper tubing and the base sheet would be painted with selective coating (like Solkote).  There would be six separate panels, but all parallelled together.

That configuration should give great performance for a pretty decent price.  The way I think of it is this: 1. Minimize your tubing, especially if you're using an inferior thermal conductor.  Tubing is only for carrying the energy away.  2. Selective coatings are not that expensive, and should give much better results than paint.  

cheers

[wildman]

Wow have been working on this for awhile.  I used 1/2" black tubing for sprinklers, started with 250'and hung it on my wood fence.  Worked great for a about 5 min then cooled off.  Went to 500' then 750 feet.  Now I have the hottest pool around.  The tubing is really cheap.  looks kinda... well everyone talks about it and then gets in the pool.  

Less than 100 bucks and it works!