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Old 10-16-2008, 10:08 AM   #1
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Solar Hot Water Heater


i'm building a solar hot water supplement system, similar to the one shown. except mine will be taller and thinner. about 6 feet upright. will also have boiler type temp and pressure gauge and temp/pressure relief valve outside on unit.

A: i'm wondering if cpvc (made for hot water) in 2" size with primer and glue will stand up to possible excessive heat and expansion and not leak?

(i know, copper....but i hate copper sweating, and it's cost prohibitive.)

B: another option is 2" black steel with hi-temp dope or teflon tape, but my concern there would be rust in the HWH.

my preference would be cpvc though.

any suggestions here would be helpful, thanks!

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Old 10-16-2008, 11:18 AM   #2
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Generally, I think PVC/CPVC has a max temp rating of something like 140F. Seems low to me as a HW heater can put out 140..

http://www.engineeringtoolbox.com/pv...res-d_796.html

Ran across this company which makes high temp/pressure CPVC that may work.. I'm sure other cos. make it too, but not sure of cost, availability, etc.. http://www.harvel.com/piping-cpvc.asp

PEX I think is usually rated 180F. Also saw this blog entry on PEX w/aluminum.. http://www.pmengineer.com/CDA/Articl...00000000435978 Probably expensive though.

I'm no expert here, but thought that might help.. You'd probably want/need at least a 200F rating, and a higher PSI than normal CPVC.

Black steel with definately rust.. Even galvi would probably not do so well for ya..

PS - No idea how reputable any of those links are, but I'm sure someone will jump in..

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Old 10-16-2008, 01:59 PM   #3
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Copper. That is the only way to go. Temperature in these systems can exceed 210 degrees and that will melt pex which has a maximum of 200 degrees @ 60psi. CPVC will dry out and crack. You can go galvanized if you want to but that is harder to work with unless you have the equipment to make your own lengths.

Yes copper is expensive.

Barrier pex (aluminum liner) will not work as it will still soften the poly.

You will also need a pressure tank (5 gallon will work for large systems and 3 for smaller systems), pressure/temperature release valve, steam vent, air scoop, pressure gauge, hight temperature pump, Delta T differential relay, valves to isolate the system for maintenance and flow restriction for the pump, and a high point to putting more fluid in the system.

If you are building the collector use copper for sure and you can get some snap on aluminum panels that will help gather more heat that are designed for pex. Put in glass to keep the heat in and change the heat from radiation to convection. Insulate behind the pipe to keep the heat in. Use board insulation. Seal it as best as you can but not totally sealed as it needs some air movement.
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Last edited by Marvin Gardens; 10-16-2008 at 02:04 PM.
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Old 10-16-2008, 02:08 PM   #4
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Can you use aluminum?

You could use copper fittings, and flare the aluminum tube to connect to it.
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Old 10-16-2008, 02:27 PM   #5
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Originally Posted by gp_wa View Post
Can you use aluminum?

You could use copper fittings, and flare the aluminum tube to connect to it.
I am not aware of any copper aluminum connections that would work for this situation.

These expand at different rates and don't think they would survive the expansion contraction process.

There are options like SolarFlex but that is really expensive and makes copper look like CPVC in comparison.
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Old 10-16-2008, 02:54 PM   #6
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Quote:
Originally Posted by Marvin Gardens View Post
You will also need a pressure tank (5 gallon will work for large systems and 3 for smaller systems), pressure/temperature release valve, steam vent, air scoop, pressure gauge, height temperature pump, Delta T differential relay, valves to isolate the system for maintenance and flow restriction for the pump, and a high point to putting more fluid in the system.
thankx Marvin, please elaborate on this paragraph?
got pictures of these things? p/t valve i know, pressure gauge i know, why a pressure tank? and the rest?

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Old 10-16-2008, 06:14 PM   #7
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thankx Marvin, please elaborate on this paragraph?
got pictures of these things? p/t valve i know, pressure gauge i know, why a pressure tank? and the rest?

DM
A pressure tank will stabilize pressures. Solar panels can get up to over 210 degrees and sometimes become superheated steam. The pressure tank will take out some of that excessive pressure. If the temp or pressure gets to high the release valve will activate. It also helps minimize any cavitation caused by collapsing steam bubbles. Can be anywhere in the system and needs to be installed correctly.

Steam valve will release steam when the temperature gets to high. This can cause a blowout in the system. Usually they are set for about 215 or so. Put it at the highest point.

The Delta T is a device that measures the difference between the temperature in the tank and the temperature in the panels. When the temperature in the panels is higher than the temperature in the tank the Delta T will turn on the pump to move the hot water into the heat exchanger.

The air scoop will pull out excessive air out of the system. This is good for systems that have any ferrous metals in them so that there is less oxygen to help with the rusting process. Put it at the highest point.

The pressure gauges will allow you to keep at least 8 psi in the system so that the pump won't cavitate and die an early death. One before the pump and one after it. I recommend a Taco 007-F5 for a pump as it moves a lot of water and is fairly cheap at www.pexsupply.com (I have no financial interest in this company).

Valves? You know what they are. Put in one before and one after the system. I also put one before and after the pump so that I can replace the canister if it goes bad. Once you have the system air free work hard to keep it that way.

Here are some links.

http://www.greenbuilder.com/sourcebook/HeatCool.html
http://solarexpert.com/dhwpic.html
http://www.siliconsolar.com/amtrol-4...k-p-18049.html
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Last edited by Marvin Gardens; 10-16-2008 at 06:23 PM.
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Old 10-16-2008, 07:10 PM   #8
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i have more something like this setup in mind. seems simpler.

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Old 10-16-2008, 07:20 PM   #9
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Could you use soft copper instead of rigid? With a cheap conduit bender you could save some using so many fittings.

DM, does Michigan have a lot of bright sunshine? Here in Ohio we have mostly overcast days throughout the year. Something like 13 days of clear blue sky a year.

I'd consider solar if we had more bright sunny days and the cost of running a pump would be off-set by the electric/gas saved heating the water.

Did you run any numbers as to what your projected savings might be?
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Old 10-16-2008, 07:25 PM   #10
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plenty of sunshine here! and i hope to shave a couple hundred a year from the cost of elec. heat, and it shouldn't cost much more than $100 or so to build. i have lots free already.

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Old 10-16-2008, 07:26 PM   #11
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Ok, I was typing while you put up your diagram.

That's not gonna work. You need to circulate the water through your "batch" tank to raise the temp. No?
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Old 10-16-2008, 07:31 PM   #12
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? huh? won't work? why not? sun heats tubes, water called from faucet/shower, cold goes into batch heater, hot goes into inside water heater. water already hot, no elec. needed to heat it. i don't follow....

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Old 10-16-2008, 07:51 PM   #13
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How are you going to keep it from freezing?
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Old 10-16-2008, 07:54 PM   #14
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I bet your ambient to sun light ratio is going to make that batch system not work so well. The batch tank will be cold most of the time. If it's cool out, you need some way to collect solar heat without letting the cool ambient air just steal it away. You need proper solar collectors and a well insulated tank.
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Old 10-16-2008, 08:13 PM   #15
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Quote:
Originally Posted by MdangermouseM View Post
? huh? won't work? why not? sun heats tubes, water called from faucet/shower, cold goes into batch heater, hot goes into inside water heater. water already hot, no elec. needed to heat it. i don't follow....

DM
Ok, I'm not understanding your diagram. How many feet of tubing are you running inside your solar heater? If the volume of your tubing is big enough, sitting in the sun, waiting for you to turn the faucet on, and that tubing goes to your hot water tank, then yes that will work.

If that volume of water is going into a separate tank and then into your hot water heater your not gonna gain much. In other words, your not raising the temperature of the (holding tank) water by circulating solar heated water through it.

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