SOlar Hot Water - Copper or CPVC?


Old 09-17-08, 02:34 PM
Thread Starter
Join Date: Sep 2008
Location: Zephyrhills, FL
Posts: 1
SOlar Hot Water - Copper or CPVC?

I just acquired a nice solar system, 80 gallon tank with backup electric heater, differential controller, 4x10' collector panel from a house that was under renovation. Ihave all the parts - just need to install it.

They had the system all installed with copper/soldered joints. Should I stick with copper or can I use CPVC to run the plumbing from the tank to the collector?

My concern is the length of the run, the collector is at opposit ends of the house from the tank, probably 50' each way to run. Does it matter? which I use as long as I insulate them up in the attic?

thanks for any advice

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Old 09-18-08, 06:50 PM
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Join Date: Apr 2008
Location: Oklahoma
Posts: 1,698
shouldn't matter as long as it is rated for hot water. try to set it up to drain in freezing weather.

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Old 09-19-08, 09:14 AM
Join Date: Nov 2005
Location: USA
Posts: 2,459
Hey there. Happy owner of a solar hot water system.

CPVC or PEX? No. It cannot handle the long-term abuse of the high temps of a solar system. The industry has been there and tried that.

Copper, sure. Or stainless (see below).

However, the big question is how this system is supposed to work. Is it drainback or closed loop?

If it is drainback, then you have to pay close attention to pitching everything properly, and you will need to plan for a control strategy for filling the system and then running it. Typically, this is done by having two circulators to fill the system, and once siphon/circulation is established, turning one off and circulating with only one. Some differential controllers have this functionality built in. Others don't.

If it is closed loop, then assuming you're in a climate that experiences freezing weather, you need to provide a means to fill and maintain the system with a 40-50% propylene glycol and water solution (that's the non-toxic, food-grade kind. NOT automotive glycol which would kill you should it ever leak into the potable side). The nice thing about closed loop is you don't have to worry about two pumps, or pitching everything just so. Or having a drainback reservoir, etc. etc.

For a closed loop system, I'd suggest piping with Caleffi SolarFlex for the run from near the tank to the collectors.

I have this stuff. It is fantastic. Supply, return and thermistor cable all in one insulated and plastic-coated unit. High-quality stainless. Cut a huge amount of time off the installation. Hook it up, secure the run, and go.

A 50 foot run is not a big deal, but you will need to make sure you end up with the right flow rate and size the circulator accordingly. The panel will have a head loss curve, as will the piping (there are standard formulas for copper pipe and fittings), and the tank manufacturer should privde the head loss through the heat exchanger. Usually, you want about 1-2 gpm. The head loss through 3/4" pipe would be much less than 1/2" so you should probably consider 3/4" for whatever you choose for a 50 ft run.

Mount the panel so you have room to add more. In the temperate U.S., the ratio of panel area to gallons of storage can be 1:1.5. You're at 1:2. You could add another small panel to increase production.

Warning: solar energy is highly addictive.
Old 09-19-08, 07:05 PM
Join Date: Nov 2005
Location: USA
Posts: 2,459
Now I see that you're in central FL. Possible you could just use water. I think some controllers have a "light freeze" setting that on cold nights will run the system to prevent a hard freeze up. Basically, it draws down the temperature of the storage by using that heat to warm the panels and piping. Steca controllers have a "vacation mode" that works the same way.

Also, in FL, you probably want to be at 1:2 for panel:storage.

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