Hi everybody!

This is my first post, so go easy on me.<EDIT>: it looks like Gary updated the original link June 11 '09, about five days after the last post in this thread.

I'm pretty sure the panel keeps draining back into a (thermal) storage tank, that has a 300' coil of PEX pipe submersed in it. The PEX coil is plumbed inline between the supply service and the hot water tank. When the collector is warming the water in it, it travels through in to the storage tank, and the seperate coil (with potable water) takes on heat from the storage tank, on it's way to the HWT.

I'm not sure if that's right, or makes sense, but here are a couple of pics from a link on the site mentioned above;

http://builditsolar.com/Experimental...DiagramDHW.jpg
PEX coil not to scale, lol. P is for pump and V is for Valve. The valves are there should he need to by-pass the solar collector.
http://builditsolar.com/Experimental...0567_small.JPG
The PEX in the tank with it's inlet and outlet connected to house plumbing.
http://builditsolar.com/Experimental...0569_small.JPG
You can see the white drain pipe in the middle of the picture, at the corner of the storage tank. The (cooler)water gets pumped from the tank bottom up into the collector, then drains (warm) into the top of the tank.

http://builditsolar.com/Experimental/PEXColDHW/Overview.htm

Thanks for the in-depth tour Gary. If I get some time in the Spring, I'll take a crack at this!

alg

I am a newbie to solar, I have been reading a lot and Gary's design really caught my eye. I live in Vermont with my wife and three daughters (teenage years are coming so hot water is going to be in short supply at my house). I heat my house 90% of the time with a Vermont Castings Defiant wood stove located in the basement next to my current hot water tank. I also have an oil fired boiler that I use for heating my DHW and base board heat. I am in the process of installing a secondary hot water tank that will feed the primary tank. The water in the secondary tank (80 gallon electric tank that will not be wired) will be preheated by circulating water through a heat exchanger on the back of my woodstove.

I had seen quite a few people that had put an exchanger inside the stove, but that just scared me, we lose power occasionally and I really did not want to come home one day and find pieces of my stove in the living room because it blew up.

So now you know a little about my setup, here is the solar question. Since I have a way to heat my hot water in the winter months with the woodstove heat exchanger could I use Gary’s PEX panel design to preheat my water in the summer months? I know it would have to be drained in the winter and I would probably move it into the garage. It would be considered a Direct Pumped System.

I know a couple of things would need changing, like the fact that I can’t use PEX-AL-PEX for potable water so I would probably use 1/2” PEX with elbow on each end. I would also have to put a pressure release valve and probably an air vent at the top of the panel where the water exits. I would utilize the same secondary tank and circulator so I think I am looking at about $300 to create the panel with enough pipe to bring it into the cellar. Any thoughts?


I had a couple of links to show examples but it would not allow me to post them, so if you have a question on my design please email me or post a reply. Thanks

Hi Trevor, if you will be circulating potable water through it I would recommend you use the copper style collector as normal pex wont hold up. you will need a temp differential controller(turns pump on when collector is hotter then the tank and off when tank max temp is reached) and a pump designed to circulate pressurised water (gerfundos?) when max tank temp is reached the pump stops running and the water just bakes in the collector(stagnate condition) and can get up to about 200* or more in strong sun, and I don't know about you but I have 80 psi water pressure and that would put me right at the 200* 80psi limit of standard pex. I think what would work good for you is batch heater as long as you drain it before the freezing weather or just build the $1k drain back system and not use the extra hot water heater. This is right off Gary's site:
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It is easily bent in to tight turns AND it retains its shape without spring back. This is a very nice feature.

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It has higher working and burst pressures than ordinary PEX.
The PEX-AL-PEX I used (Mr. PEX) is rated for 160 psi at 200F.
Standard PEX is rated at 80 psi at 200F, and 160 psi at 73F.

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It has better thermal conductivity that regular PEX -- this should result in somewhat better heat transfer from the aluminum fins through the PEX to the water.
PEX-AL-PEX 3.1 BTU/h-ft F for half inch tubing
PEX 2.6 BTU/h-ft-F for half inch tubing

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It has a much lower coefficient of thermal expansion than PEX, and is more compatible with the expansion rate of the metal fins.

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It may be somewhat more tolerant of freezing. It will probably withstand several freeze thaw cycles, BUT will NOT withstand continual freeze thaw cycles.

so regular pex would be less efficient and wouldn't be a good idea to subject it to such conditions. By the way I have seen the pictures of the blown up wood stoves and they all didn't put a pressure relief valve in-between the shut off valves and the heat exchanger

I have built half a dozen solar hot water heaters, active solar systems with no pumps. They all worked well, I built some in the late 70s and one a couple of years ago. Copper is the best but it will not tolerate freezing water. If you will be using a thermosiphon (no pumps) system and you are sure you will drain your system before the first hard freeze go with copper. Personally, I'm interested in pex and might build one to see how it holds up mostly because of the freezing issue. The last system I built for an organic farm (not for profit) and it keeps busting out either the line or a sweated fitting. Also, I use glass from discarded patio doors and build the collectors to fit them. They are free, often easy to find, easy to use and the most efficient. I used a fiberglass product called Calwall in 1979 which lasted 10 years but turned an ugly yellow, cutting down the efficiency, I'm sure.

Interesting ideas Miguel, and welcome to the site. :)