Solar water heater idea

[nwcpro]

   I just hooked up with the local grocery chain's maintenance guy, and he is going to let me take a bunch of 2'x4' double pane glass doors to play with.  I was thinking of using them as solar water heaters.  They have about 1/2" gap between the panes.  Why couldn't I just paint the outside of the back pane flat black, insert some pipe into the gap, and voila!  Somebody tell me why this won't work, because most of my ideas don't for one reason or another.

   Heck, I'm mostly just looking for an excuse to hang out on this site!

   He also has a HUGE curved glass frame (8'x'8') that looks like it would make an AWESOME parabolic reflector, but I'm not sure my wife will let me bring that home....

Ideas?

[picmacmillan]

check out my files and there is a couple pictures of some store bought water heaters i had given to me...i took one apart to see what goodies were in there, and it was like you said, just some half inch copper pipe and some bigger pipe(guessing 3/4'), around the outside..it had fiberglass insulation behing the pipe and dark aluminum painted sheets over the pipe itself...the thing was covered with glass...the only specialty item on it, was a little gizmo attache to the outside pipe..you will see it in my photos, and apparatnly this thing is a sensor to circulate the water once it gets 17 degrees hotter than nomal...if you need any extra info, just give me a shout, and i am sure i can get some info on it.....i will be putting these to use this summer and i will do some testing to see how hot it gets....any model babes out there want to do some experimenting with me, please leave email and qualifications and i will get back to you   pickster

[scottsAI]

Start of a good idea.

You don't need an excuse to hang out. You already have one. Your interested!!!

 The problems here is what is painted black will get hot, which is the glass. Glass is not a good conductor of heat, not a good insulator either. The pipe needs to be thermally connected to what is black. The glass will get hot, but not so much the water in the pipe. The glass may have a problem getting so hot. Very difficult to put the pipe in between the pains of glass. Black poly hose may work. Still not recommended.

The pipe needs to be mounted on metal, the metal should be painted black. The glass above helps isolate the heat in the metal/pipe. Need insulation below the metal.

A pipe <1/2 inch will have head loss, need a stronger pump to push it through. $Power.

Solar Hot Water for Mich could use two 4 x 8 panels, should supply close to 100% hot water. Down south only need one panel needed. If in a cold climate then using a double insulated glass panel above the pipe would make it more efficient. Down south would reduce eff. Not the heat loss, Glass blocks the sun.

Keep the ideas going. You learn from what works, you will get better at it.

Have fun.

[nwcpro]

   Well, I wasn't planning on heating water in a pipe so much as just filling the gap (with the back side black) with water.

   What if I remove one end of the edging and slide a black metal plate into the gap?  Sun comes in, heats up plate, water in gap gets hot.  Thoughts?  

[Jeff7]

Make sure the glass is tempered, or else it might shatter when heated.

An 8 foot wide parabolic reflector ought to be fun. Incredibly powerful, but fun.

[picmacmillan]

Below is the 8x4' water heater i have



I took the glass off and below is the aluminum sheeting covering the pipes..notice the dark coloured paint on the sheeting, and attack dog





Here is the corner raised up to show the piping andinsulation underneath is hard to see...hoped this helped to see what it looks like..pickster





below is the little elctrical gizmo that supposedly tells the pump to turn on when the water gets to a certain temperature ot circulate...hope this helped to see what it looks like..pickster

[scottsAI]

Exactly one of my ideas back in the 70's!

Never tried it.

I hear you suggesting:

Glass

water

Glass painted black.

I think you can skip the metal. The metal is used to transfer the heat to the pipe, here the glass is the pipe, thus no need for the metal.

Might work. Water should not be allowed to get too hot.

In other words, make sure you have water flow.

How are you going to seal the edges, water tight?

If you live in a cold climate then may need another glass layer on top to insulate the panel and some insulation under it and edges.

Warm climate, might not need anything. It's hot already!

Remember you can't pressurize this glass sandwich, not even a couple pounds, 1 psi * 4 x 8 = 32 pounds lifting the glass up!

If it was this easy, I know of another that had this same idea. Nobody I know has tried it. You would think if two, now three people had this idea, then others would have had, somebody would have tried it. I conclude it must not work.

But, that said, I don't know why. Would love to know if this works. Or why not.

I just remembered a problem, this only applies to the insulation glass panel (third or top one). Most glass has iron (or is it lead?), which blocks the sun somewhat, Not recommended to put over solar cells. Here, the glass is part of the pipe, so no problem for the lower two layers.

Have fun!

[Ungrounded Lightning Rod]

IMHO you'll do a LOT better with the double-pane glass if you put both panes, followed by an air gap, between the outdoor air and the collector plate.

Heat goes right through glass.  The point of the double-pane system is to interrupt the heat path with a layer of gas that is too narrow to convect, and thus does a rotten job of transferring heat between the panes.

What I'd do is build a wooden box, line the back and sides with insulation, and put a collector made of black-painted sheet metal and pipes in the box, leaving a small gap above it.  Then I'd put the double-pane over the top and seal it to the box.

Sunlight (visible and near-infrared) goes right through the panes and is absorbed by the black-painted metal.  It comes back as heat and far infrared.  Far infrared bounces off the glass and gets re-absorbed.  The heat in the metal plates is conducted to the pipe and heats the water, and also is conducted to the air in the box and heats that.  But the sides and back of the box are insulated, so little escapes there, while the double-pane glass doesn't conduct much from the inside to the outside air and little escapes there, too.  Result:  Most of the heat ends up in the water and can only exit the box when the water does.

If you put the water between the plates of the glass you've lost most of your insulation.  Most of the heat flows right from the water to the outer pane, through the glass, transfers to the outside air, and blows away.

You've also exposed the water to the paint and the metal and other materials of the frame.  Not good if it ends up in your drinking water plumbing.  (In the alternative I described above the water stays in drinking-water rated copper pipes.)

For pipe I'd use household copper water pipe.  For a plate I'd use a thin sheet of copper, which can easily be soldered to copper plumbing.  (A solder joint transfers heat as well as it does electricity, since heat in metal is carried mainly by conduction-band electrons.)  If the copper is too expensive I'd use sheet aluminum and try to make a good, broad, mechanical joint between it and the pipes, maybe caulked in with heatsink compound.  Aluminum conducts heat almost as well as copper.  A mechanical joint doesn't conduct as well as solder but if it's tight and has a large contact area it's still no slouch.

[Kwazai]

If your grocery store guy is letting you have glass doors- they probably came off of a freezer/fridge of some sort and he is probably needing to dispose of it also. I would check with him to see if you can 'recycle' the condenser coils from them (after gettting rid of the refrigerant. painted black and made out of aluminum, rated for pressure,etc. they would be inexpensive coils for the water side. just my .02$.

Mike

[nwcpro]

   Yeah, I'm going to work on him for the copper coils (there are tons of them there, and I don't think they are going to be reused.

   Thanks for all the tips, everyone!  I think using these as a faceplate for a wodden collector box is the best plan.  I pulled the aluminum edging off one door and inside is a nice compact "sandwich" which will be easy to deal with (and I can recycle the aluminum).  Now to find some cheap copper pipe.  Hmmm....  

   Luckily, cold weather is not a problem here in Southern Oregon.   It sorta froze once last winter (I think).  Shoot, we were out in the old rabbit convertible in our T-shirts in mid-February!  That's the problem I have with Alt energy here: no wind, no creek, just lot's and lot's of sun 10 months out of the year.  The obvious answer is PV, but I'm scared of the prices.

   My incentive is this:  4 kids, one income, stuck in the city, no gas.  When they estimate how much electricity an average family uses, we're off the charts.  Also, the current house we're moving into has no real heating or cooling system.  Some moron in the 60's decided to put in radient CEILING heat - not floor, mind you, but electric coils in the ceiling!  Gives you a sinus headache in minutes.

[nwcpro]

Thanks for the pics!  They give me another idea......

[pyrocasto]

I've already forgot. How do you keep the pipes from freezing in the winter at night, if I want to use a open loop system?

[ivandenisovich]

I was reading a book called "Solar collectors, energy storage, and materials" (MIT press, 1990).  There was a section about dying the heat transfer material black and running it past clear glass panes.  Another option was to suspend small particles in the HTF.  It turns out that this method is slightly more efficient that conventional absorber plates.  

Of course you would need to use a closed loop system.   I don't think there is any way to use an open loop system in a freezing climate.  Your best bet would be some type of drain back system with a heat exchanger.  I installed one of these last year and it cut my electric bill in half.

The "back" of the collector would also need to be heavily insulated because in direct contact with the HTF, glass would be a good conductor of heat.

Paul