Solar Hot water

[Shadow]

I'm going to try  building a small Solar batch heater for hot water.I notice most or all are using copper pipe or tubing. I'm wondering if black ABS pipe or sewer pipe painted flat black will be just as effective?I'm thinking a metal pipe may get hotter, but size is limited by expense.So thought larger plastic pipe may take longer to heat but would produce more hot water in the end.Any thoughts?

[picmacmillan]

hi shadow(you still have the coolest paint jobs on the planet) one thing i think of with black pipe is that the water wouldnt be drinkable..as there is oils in the pipe itself..but if its just for showers or dishes, i cant see why not?..i have 2 store bought hot water panels and they have copper pipe in them,, there is some foam insulation behind the pipes, and it is coloured silver..there is some aluminum sheeting layed directly on the pipes themselves and this sheeting is painted black..i believe the sheeting to be aluminum and it covers the entire inside of the panel and again, this sheeting lays directly on the pipes..it even curves slightly with the shape of the pipe(round), (or half moon i guess)..the whole thing is covered with a sheet of glass and has a small electric device on the out pipe..i was told it is to circulate the hot water once it reaches a certain temperature...lots of this isnt what you asked, but thought it may help while building..in my opinion, black pipe would work fine, may even get alot more volume of water within the unit itself..maybe they dont use copper as 2"(for instance) copper pipe is very expensive? not sure..good luck man on your project pickster

[thefinis]

Not sure what is best for your needs but I am planning on putting in a solar preheater as soon as roof is fixed. I went out and looked at flexible black plastic pipe and came back with these findings. Lowes had 300' 1" black plastic for $118 and 400' 3/4" for $98 most every where else had it in stock only in 100' lenghts or less. They both have the same surface area(heating area) per roll but the 3/4 held less water. I don't remember the exact figures but 30 something gals for the 3/4 to 50 something gals for the 1". It is rated for 160 psi @ 73 degrees but I have used it before and at low pressure 30-40 psi it is fine with solar heated water.

The thicker the wall of the pipe the longer it will take for the heat to pass thru both entering and leaving. Ie the larger the pipe and the thicker the wall the longer it will take to heat up after the sun shines but the longer it will stay hot after the sun quits shining.

Good luck hot water is a nice luxury and even better when it is free to heat.

Finis

[georgeodjungle]

poly & pvc can't handle the heat.

might try cpvc or pex...

but copper is king for heat transfer.

best off to save $ & do her right.

[johnlm]

My calculations show 300 ft of 1 inch id pipe would hold 12.27 gallons.

[harrie]

Hi Shadow. Many years ago, I did just what your are talking about, I did however, use 3/4 Inch copper pipe, horizontal and used 3/4 inch copper elbows to go from one pipe to the next. I think the pipes were about 3 inches apart and 8 foot long. the whole unit was I think 9 foot by 5 foot. I than samwiched the pipe between two pieces of corragated roofing, and bolted the sheets together tight to the pipe. The top sheet was painted Black. than the unit was put into a box with a glass top. and set at about 60 degrees to the sun on my south faceing roof. Also, I had a thermo sencor attached to the top pipe in the box that would read the temp of the water in the pipe, and send a signal by wire to a 3 degree differental control unit that would tell a small grundfos circulating pump to turn on and pump the hot water into a preheat tank that was ahead of my hot water heater. The return water would come from the bot. of the preheat tank. It worked very good when the sun would shine, but here in Northern Minnesota, it just was not fesiable. My brother in law, made one out of black plastic and hooked it up much the same way, and it worked fine also. you can also set one up like that by just using thermosiphion princeable, without all the extra pumps and gadjets. Or you could go the way of a heat exchanger, so you could use anti freeze, but it would have to be propoline Glycol, not ethlene, just incase there was a leak that got into the potable water. Good luck. Harrie

[Clifford]

I've been wondering about heat exchangers vs direct plumbing...  perhaps in the summer it is best to do direct plumbing.  However, if you are concerned about the water in your pipes, then the heat exchanger might not be a bad idea.  Or, of course, paint the white PVC (potable water) with a flat black paint.

As far as heat loss, that should be regulated by the "heat reservoir" in your tank, as well as the single or double paned glass above the panel.   You would want minimal insulation on the actual pipes as it would do more harm than good.

Many plastics do tend to decay in the direct sunlight.  I know that poly rope has horrible sunlight resistance (we had tried some for home-made solar panel shutters and it just crumbled).  I think PVC is ok in direct sunlight, but it might be worth checking.  I don't know about ABS.

Not sure about the "heat" issue.  Might be worth checking.  Water tends to limit the temperature to less than boiling temperature.  I've heard rumors that one can boil water in a paper bag over an open fire...  never tried it.  So, there may be some protective value of the water in the pipes.  But, if you are going with plastic, go for the high temp rated plastic pipes.

Also, you might consider the freeze durability of the pipe.  Copper and Galvanized tend to crack at the most inaccessible joint you have.  PVC will spiral crack and the entire array will likely have to be replaced.  Don't know about pex, but I have heard that there are some pipes that are essentially freeze proof.

I think my choice would still be to go with copper and circulate to a "heat reservoir".

[thefinis]

You are very right! I don't know what I was reading when I pulled that from an online calculator but after going back to the page it must have been cubic somethings. A quick look around and found the right formula for tank capacity.

So around 12.2 gals on the 300' of 1" and around 9.2 gals on the 400' of 3/4"

Finis

[nothing to lose]

Yes you can boil water in paper over a fire.

I used to use like Dixie cups or old paper coffee cups for this when camping.

Styroam does not work of course

If you do not have a paper cup totally full of water it will catch on fire at the level above the water and burn down to the level of the water, but it will not burn below that level.

With plastic pipes you have to make sure they are UV resistent or they will dry out the oils and crumble. Green sewer pipe for example, I had some laying in the yard for awhile. When new you could jump on it or drive over it and it would swash and spring back. After sitting in the sun for however long I one day barely bumped a piece with a motorcycle tire and it crumbled.

It doesn't take much heat to soften cold water PVC pipe, it will ballon up if a  pressure in it or be bendable into shapes. Not sure if hot water pvc is UV resistent but it could be painted and maybe work.

High quality water hose is a fast cheap freeze proof useable item easy to work with. I have some here been in the yard and sun for about 10 years, starting to crack up the outer coating now on some hoses from UV but still does not leak. It been drug around and over rocks, drivin over etc.. used and abused a ton. Frozen solid every winter at least a few times. I was surprised it lasted so long and I still used it. Had to repair a couple cuts and such from rocks, spliced it easy. Driking water safe also.

 Heat transfer certainly is not as good as copper pipe and some other things, but in summer sun here water comes out way to hot sometimes with hose just laying on the ground and does not seem to take long to reheat. I mean you don't want to just grab up the hose and spray yourself down, too hot for that!

[Spelljammer]

yeah, pvc not good for this.  Can't handle the heat or UV rays.  But also, it contains lead that leaches out when in the sun.  I would use a good quality black water hose, but not in a solar box though.  They can't seem to handle over 180f for the most part.  Still, copper would be the best bet.