Author Topic: Solar water heater panels (Read 5365 times)

oak leaf · « **on:** January 28, 2009, 01:23:47 AM »

I was talking to a co-worker and he told me he had two solar water heater panels and wanted to take them off his roof. I asked what he wanted for the panels and was told nothing just help me take them down and patch the roof. These two panels are 4' x 10'. I also got two pumps with the panels. He had chopped the tank up the week before we talked. I did not get any of the controls either, but that is not a problem I am very handy in that area.

I got the panels home and hooked up a water hose to one of them and found two leaks. I took the panel apart and silver soldered the leaks. I cleaned the flat plate and painted it with flat black paint. When the weather gets better I will put this back together and start on the next panel.

I want to get a tank with a heat exchanger but it is expensive and I can't afford it at the moment so my question is: If I do not have a tank can I use an old water heater for storage while I save up for a tank with a heat exchanger. How would you recommend setting it up. I would not set it up until the freezing temps have stopped; early March. I would want the new tank before next winter.

Thanks,

Harlon

wdyasq · « **Reply #1 on:** January 27, 2009, 08:34:24 PM »

Build your own 'tube in shell' heat exchanger and go on with your life.

Ron

MattM · « **Reply #2 on:** January 27, 2009, 09:34:44 PM »

Google builditsolar and check out their projects. Some of them are quite affordable. And once you cut the gas bill it will free up money for the next project....

zap · « **Reply #3 on:** January 27, 2009, 09:34:54 PM »

GO HERE!!! Read, read, read.

fcfcfc · « **Reply #4 on:** January 28, 2009, 06:21:44 AM »

Hi:

I have GL-30's diff controllers for sale at $99 and sensors for $12. I believe I have the lowest price:

www.WeAreSolar.com

You don't want a tank with an internal exchanger. For one when you loose the xchanger, you loose the tank or vise versa. You stated you already have two pumps. Go with a used standard electric tank as your preheat tank and use a $75 external flat plate xchanger (ebay).

Go closed loop glycol. Head loss through the xchanger won't be an issue with a small system if they are 120VAC pumps. Get the controller, expansion tank, valves, check valve etc.. and your done...

.....Bill

ptitchard · « **Reply #5 on:** January 28, 2009, 08:32:10 AM »

Harlon,

The way I did it in the UK was contact a plumber.

A lot of people over here are switching boilers to the "on demand" combi's types which mean that the old hot water tank is removed by the plumber.

You will still have to pay a little bit because the plumbers get scrap value for the copper, which with the current world recession the price has dropped considerably.

Anyway good luck with the project it is one of the cheapest and most effective RE system going.

Ungrounded Lightning Rod · « **Reply #6 on:** January 28, 2009, 12:50:03 PM »

If you have an old water tank and can temporarily take the insulation off you can convert it to a heat-exchanger.

Pull the case and insulation. Take some copper pipe. Wind it around the inner tank in a spiral. Solder it into place. (You may have to clean the tank surface before this step.) Apply a protective paint if you feel a need. Reapply the insulation and case, bringing the new pipe out near the top and bottom.

= = =

Regardless of whether you use a heat exchanger or build one onto a tank, you'll want to run it "counter-current" to get the best heat transfer. The incoming antifreeze-laden water from the panel goes one way (down if the exchanger is vertical), the water from the tank (if pumped into an external heat exchanger) goes the other way.

If you build an external, vertical, heat exchanger right next to the tank you may be able to get away with convection for the tank's water.

I understand the code doesn't like the "pipe-in-pipe" type of heat exchanger for drinking water because it has a single wall between the drinking water and heat transfer water. A defect in the inner pipe means you get antifreeze (or whatever is circulating in your panel's loop) into your water supply.

oak leaf · « **Reply #7 on:** January 28, 2009, 05:28:17 PM »

Thanks for the comments.

I am just wondering, how big of a flat plate to get?

How many raps around the tank should I use?

How big of a tube-n-tube should I make?

All of the ideas that have been posted are good ideas and are easy enough to do, but which would give me the best heat transfer?

The easiest to do would be the tube-n-tube, and the best heat transfer, I think. But is the pipe failure a real concern? Or is it hype on the code makers part? I have worked with copper pipe for a long time and have not seen it unless the pipe has frozen. The pressure should never get very high. I do not know if I want to be the test dummy, the only way to find out would be to get real sick or die, not good.

Has any one made a storage tank by rapping copper around it? What were the results?

Thanks,

Harlon

jonas302 · « **Reply #8 on:** January 28, 2009, 05:41:48 PM »

A ten plate exchanger will do the job no problem

General non-code wisdom is your water mains are presserized the solar side isn't so if there was a hole your solar tank would overfill long before you die

I'm pretty sure someone has posted the coil around water heater method before try the google search

jonas302 · « **Reply #9 on:** January 28, 2009, 05:50:17 PM »

http://www.fieldlines.com/story/2008/2/3/82549/38059

oak leaf · « **Reply #10 on:** January 28, 2009, 06:43:14 PM »

Thanks jonas302,

I looked at the link you posted, not good. I will make a tube-n-tube. I will put a pressure gauge and let you know what I get on the collector side. I think it will be fine to get me by until I can afford something else.

Harlon

Gordy · « **Reply #11 on:** January 28, 2009, 11:43:02 PM »

Harlon,

I wish I had a link for you. But a twin wall heat exchanger is not all that hard to build.

You'll need,

, pieces of copper pipe 1/2", 3/4", & 1"
, T fittings, on the straight through part of the T you'll need 3/4" on one end and 1" on the other. The third will depend on the plumbing coming to the heat exchanger from the solar collector.
, 1/2" to 3/4" adapter

You'll probably need a piece of 1/2" and 3/4" steel bar stock. To drive through the fittings, so that the pipe's will slide all the way through the fittings. Using a round file will weaken the fitting's.

Assemble the 1" pipe with the 3/4 pipe inside of it, then put the T's on each end. You'll want at least 1" of the 3/4" pipe sticking out of the T's. Solder this together, it'll be your antifreeze jacket. Now insert the 1/2" pipe all the way through the 3/4" pipe and slide on the 1/2" to 3/4 adapter and solder. This will be the bottom of you heat exchanger. Again leave at least 1" of extra pipe sticking out each end to hook in to your water lines to the tank.

There will be a gap between the 1/2" and 3/4" pipes, that you will want to fill with a heat transfer medium from the link above if they have something pourable or use mineral oil. Mineral oil may not be the best for heat transfer but it's better than air and it's safe, one of it's uses is as a laxative.

If you want you can install a 1/2" to 3/4" adapter on the top, but do not solder it. That way if the 1/2" or 3/4" pipe were to spring a leak it will flow out the top, and you'll know about it.

I hope I made this easy to understand , And that you find it useful.

Gordy

fcfcfc · « **Reply #12 on:** January 29, 2009, 06:22:25 AM »

Hi:

You would be better off with a flat plate exchanger, better heat transfer. Tube in tube without the spiral extrusions tends to develop laminar flows. Flat plate exchangers are very turbulent, thus good transfer. Spend the $75 on the 10 or 20 flat plate and put all that time on to the other parts of the system and design. It would be time better spent...

.....Bill

wooferhound · « **Reply #13 on:** January 29, 2009, 06:23:48 AM »

Lots of heat exchanger projects on this page . . .

http://builditsolar.com/Projects/WaterHeating/water_heating.htm#Components

Bruce S · « **Reply #14 on:** January 29, 2009, 08:51:22 AM »

Oak Leaf;

You could just to be very safe, use proplylene glycol ( found at RV centers) for the solar side, it's usually good to -50F and is reguarded as safe. The added plus is most of them I've helped winterize come in a fashionable pink. Letting you quickly know that you have a leak :-)

Ethylene glycol is the poison stuff :-/

Stay Safe

Bruce S

Tritium · « **Reply #15 on:** January 29, 2009, 01:38:31 PM »

I remember when I was a kid proplylene glycol was on the list of ingredients on a Dr. Pepper can.

Thurmond

Barb · « **Reply #16 on:** January 29, 2009, 06:44:47 PM »

I was wondering why you don't circulate your hot water through the old wtr htr as is using it as a pre heater? Not enough room or the solar panel won't handle the well or city water pressures? If you have the room circulate your water from the panel into the top of the water htr and take off the return from the bottom. Take the pre heated water from the top and pipe to your existing wtr. htr. Of course the system must be drained in the fall if you live in a freeze zone. But by that time you will be set up with the antifreeze and heat exchanger tank and all the other goodies, right? Using a Grundfos wet rotor circulating pump or B&G will handle the head pressures without costing more than five or ten cents a day to operate. Use a timer to turn it off before sundown and back on again an hour after sunup.

If your water is corrosive or really hard then it will find all those pin holes in your solar panel. Obviously you are skilled or you wouldn't have used silver solder. I'm wondering why you didn't use 50/50 or 95/5?

fcfcfc · « **Reply #17 on:** January 30, 2009, 02:04:18 PM »

Hi:

Don't take this wrong, but it is a VERY BIG MISTAKE to rely on draining anything manually in order to avoid freezing. Murphy sees a situation like that and he salivates, sits back and just waits for the right opportunity....

Using a timer for on off will also loose you energy on cloudy days... Diff is way superior... if money is really that tight then you might want to hold off on the project, unless it is really just for fun or an experiment...

.....Bill

huntedheads · « **Reply #18 on:** January 31, 2009, 05:52:17 AM »

In case your wondering what that looks like (I did) here is a picture, just can't remember who I got it from?

It's also what I built. Put the tank as close to the basement ceiling as you can so you get all the exchange area as possible I ended up with 4' 7". I pump the solar into the top and let the storage tank thermalsyphon. Works pretty darn good too!

Airstream · « **Reply #19 on:** January 31, 2009, 02:31:39 PM »

In a sealed loop there should be distilled water and inhibited Propylene Glycol (food grade) meaning when the collector gets stagnant at boiling temperatures there will be no metals reaction, making it especially aluminum safe and will allow even steel to be used continuously for 10 years. DowFrost is recommended for the panels I have, from MSDS: Propylene glycol 57-55-6 > 95 %; Dipotassium hydrogen phosphate 7758-11-4 < 5%...

Airstream · « **Reply #20 on:** January 31, 2009, 02:37:52 PM »

And... the neat thing about a product like DowFrost is they do not really want it freeze proof, the antifreeze itself does not carry enough heat year round so they want to maximize the water content, then at low temperatures that actually allows some of the water to freeze into slush (condensing the anti-freeze liquids) which then allows some circulation to occur when the pumps come one and allows the lines to clear on their own... Pretty sneaky.

Gordy · « **Reply #21 on:** January 31, 2009, 05:45:58 PM »

My only experience with the pink stuff was last winter, while working on a crude oil pipe line in MN. We had to use water/ trash pumps all winter, at the end of the day the pumps were drained of water then 1/2 to 1 gallon of RV pink antifreeze poured in them. The pumps were started and run for a few minuets to work it around. The next mourning at 10* or lower the pumps were frozen solid, would not turn over. and the new jugs of RV pink had turned to slush, At -10 the new jugs of RV pink were frozen solid. We started using elcheapo windshield washer fluid, as it would still be liquid at -27 and no more problems with the water pumps. I'm not saying to use washer fluid in your solar system. Just form what I saw that pink stuff is crap IMHO.

Gordy

Airstream · « **Reply #22 on:** January 31, 2009, 07:06:34 PM »

There isn't a good comparison to be made. -60°F freeze point for a 60% solution...

SolaHart Fluid Details (PDF)

SolaHart PDF source page

DowFrostHD Fluid Details (PDF)

Dow PDF source page

huntedheads · « **Reply #23 on:** February 01, 2009, 05:47:45 AM »

Screwed that one up!!! Here are the pictures.

KEG · « **Reply #24 on:** February 01, 2009, 12:47:03 PM »

I made this a little over a year ago and so far it is working great. The 3/4" outer tubes are 5' long.

huntedheads · « **Reply #25 on:** February 01, 2009, 01:40:53 PM »

There is where I got the picture from!!!

Catch66 · « **Reply #26 on:** February 08, 2009, 06:36:44 PM »

Hello, Oak leaf.

My couple of cents worth. I Also suggest a flate plate heat exchanger, with a closed

glycol system. I built a tube and tube exchanger 1/2" x 3/4" for my system,in beginning but have since purchased 2 flatplates from e-bay they out preform by a lot. like said before counter flow the separate fluids.

I also struggled with glycol price. check out NAPA stores for Sierra brand they make

a polypropylene for automobiles it is friendly "to us" and it handles temps to 250 degrees. Go with a preheat tank any electric will work well.

Like fcfcfc said the Gold line-30 work very well & will control your water side.And at a good price too.

Take care,

Chuck

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Author Topic: Solar water heater panels (Read 5365 times)