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Bradley

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Posts: 9
Reply with quote  #1 
I have a question concerning the cpvc solar collector video i watched on youtube. I am considering building a collector and have looked at several different designs and the one that interest me from a labor stand point is the one using 250 to 500 feet of pex in a spiral configuration. The draw back i can see is friction on the water travel but if i have a solar pump doing the work i don't see the draw back. Can someone enlighten me on why i should build a cpvc collector system instead. What am i missing? Thanks

cwwilson721

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Posts: 303
Reply with quote  #2 
The spiral one I thought of hasn't been built nor tested yet. It was a "thought experiment". Whether I build it or not, I don't know. Any pluses or minuses are unknown at this point (the pex and the glazing are the odd things. As you said, can the pump handle it? What about stagnation? Etc.)

The CPVC is a known quantity, and has been built in many configurations.

Basically, it comes down to:

Do you want to use a known/understood design, or do you want to experiment?

I may build the pex spiral later, but right now, I've got my hands full 
Bradley

Registered:
Posts: 9
Reply with quote  #3 
I would circulate the heated water into a storage tank thinking that would handle the stagnation if i understand you correctly. concerning the pex of course that is designed for plumbing so i don't understand your concerns, please explain i am new at this. 
Bradley

Registered:
Posts: 9
Reply with quote  #4 
I guess the real question is what do you mean by glazing?
Bradley

Registered:
Posts: 9
Reply with quote  #5 
What am i missing here? Why is it so hard to post to all and navigate this site it is ridiculous. Am i the only one that feels this way?
cwwilson721

Registered:
Posts: 303
Reply with quote  #6 
Glazing:

If you look at the typical "solar pool heater" (some of which are spirals), they tend to be just the coil. No frame or glazing. Glazing comes in when you want heat to be produced when the temperatures outside are cold. The glazing (glass/whatever) helps hold in the heat to increase heat transfer to the coil (Think of your car in the sun. It gets ALOT hotter with the windows rolled up. Same principal)

Stagnation:

Stagnation happens when there is no circulation, or if the temps in the collector reach REAL BAD LEVELS. Usually 180+, and materials used in the collector, or even the water/fluid itself, causes failures/boiling/melting of components.
Some causes are pump failure, controller turns off the pump because your storage temps have been reached, or an unforeseen issue with the design causes the liquid to boil in the collector, causing failure.
A REAL good example of the last one is the "2xCPVC" collector that was tried earlier. A design issue caused the failure due to the way it was put together. In a 'normal' collector, all would have been fine, but a totally unforeseen stagnation event was caused due to a "2nd loop" that made a steam "bubble" as part of the circuit. This caused the water to not flow in one 'loop', and the heat in the collector/fluid got REAL hot (200+F), making the CPVC melt/soften. I was as shocked as everybody else when this happened. It looked like a great design, and looked like it should have been fine.

But, that's why we test. And test. And test...

There are many ways to mitigate stagnation events. Just look around in the forum.
Bradley

Registered:
Posts: 9
Reply with quote  #7 
Thank you for your reply. If i have a closed loop system and i do regulate my water temp in the collector and a pump circulation is there really any concern for stagnation or degradation of the system?
cwwilson721

Registered:
Posts: 303
Reply with quote  #8 
Testing of new designs by us here in the Forum is just about mandatory.

We're not (by and large) engineers or rocket scientists (some exceptions) or brain surgeons.

We're people with a desire to use solar, but not pay the amounts the commercial systems cost. We use 2x4's and nails, spray foam cans to seal, and old sliding glass doors as glazing. Or even Saran Wrap. Hey, if you got it, try it. You never know.

We try to build this stuff using either stuff we already have on hand, or can easily and cheaply buy at the local home improvement store. And then figure out a way to make it work.

Sometimes, it's BRILLIANT (look at the window screen collector. Easy, cheap, and fast)

Sometimes, it's "Well. I SHOULD have NOT done that..."

We're all learning. And we test...And test...And fail..And try again. And test...




Bradley

Registered:
Posts: 9
Reply with quote  #9 
Thinking about it now, It really sounds like what i should design is a solar collector and storage passive system and not worry about all the other issues. What are your thoughts? (Just learning, Stupid Question) Like to hear your thoughts.
cwwilson721

Registered:
Posts: 303
Reply with quote  #10 
Depends on where you live.

Myself, in Alabama, where summer temps get FREAKING ridiculous, I use a radiator (possibly 2. My full system is not online yet) as a heat dump when my storage temps get to where it's not calling for more heat. The controller flips a valve, and the collector pump just pumps the fluid to a fan-assisted radiator, and it happily cooks the birds as they fly overhead. So far, for me, it works.

Stagnation IS a possibility. Even if you have T&P valves/etc, avoiding the event is preferable to having it happen.

Would you rather pay $400/wk for car insurance, or have brakes?

BUT, every system is different. We all build things different. What works for me, may not be appropriate for you. Or, even if it is, you may have different skills, or money, or your site setup may not be the same.You may have different heat requirements than I do, or not enough space to put in a huge storage tank. Or, you can't use a separate tank, and need to use something else. You may want to use a pex for your heat exchanger in the tank, or a copper coil. Or, use a stainless steel "self contained" heat exchanger unit. You might have access to a old farm that has stuff in it to scrounge for free. All situations are individual.

I have all the standard safety gear in my system. The T&P valve, the expansion tank, etc. Plus a few I've added (BTW, the thermostat thing works as an air temp relief gadget in the collector). I use a closed loop system. And I use the glycol too. BUT, I monitor temps closely to reduce acidic decomposition in the water portion of my system. Temperatures cause this. And a stagnation event REALLY messes with it.

There is ALWAYS cause for concern for a stagnation event. Let's say the power dies, or a mouse eats the leads to your pump. Temps rise, and eventually, you're at the critical temps. Now, your T&P valve opens, and sprays boiling liquid all over your roof. It drips down and pours all over the wife's million-dollar rose bush. Well, used to be, because now it's dead. Now, you're divorced, the wife has all your money and half your stuff, you STILL have to replace the fluid in the system, plus fix whatever broke, etc, etc, etc...


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