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mattie

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Reply with quote  #11 
Thanks for the swift and detailed reply ,some insightful reading ahead.
Regards Mattie

baothaitu

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Reply with quote  #12 
I got a question about the collector, what is the advantage/disadvantage of run the copper pipe continuously vs. in parallel (header). I thought that by running the pipe in series would be a sure way to get all the heated fluid back to the heat exchanger. I am ready to built mine, just a little confuse on the design. Any thought on this?
N4KIT

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Reply with quote  #13 
Hi Bao -

Here is what I know about the two methods of plumbing a collector - some others may be able to chime in with some efficiency comparisons...

Serpentine (one continuous pipe back and forth):

Pros - easier to plumb, takes less fittings, cost is slightly lower  Cons:  piping must be carefully laid out to ensure complete drainback

Riser (2 "headers" with "risers" in between):

Pros - water residence time from input to output is the same no matter what path a discrete particle of water takes through the panel, and much easier to ensure complete drainback when the system is not running.  Cons:  More difficult and time-consuming to plumb, cost is slightly higher.

All commercial flat-plate collectors (that I know of) are of the Riser design.

Hope that helps,
Chris

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SolarInterested

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Reply with quote  #14 
Another 'Con" with the Serpentine design is that there is much more flow resistance through the collector due to only one path versus multiple flow paths in the 'hiser' design.
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baothaitu

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Reply with quote  #15 
Thank you very much, I will do the Riser design then. I have a plumber friend that so interested in solar heat but was hesitate on up front cost, so he volunteer his time to built my system to see how it work first, so the difficulty level is not my main concern. The ease of operation is what I looking for. Again, thank you for your quick responses.
baothaitu

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Reply with quote  #16 
I got another (stupid) question! (Well, like most of you guys suggest, read a lot, ask a whole bunch of questions [biggrin]). As I stumble around the forum, I saw that the CPVC / Aluminum set up that if you put the pipe closer (say 3" apart) then you don't need the Aluminum fin. So, how about I built the copper / aluminum with the riser prototype with the copper sit 3" apart? My plan is 1" header, 3/4" copper sit 3" apart and aluminum fin bottom and top, polycarnonate double wall for glazing, that way I only need to built one 4x8 panel instead of two 4x8 panel, and still have the same volume of of heat transfer fluid being heated on the collector. Would double the copper pipes on the collector make the fluid less hot?  I thought that puttting the copper 6" apart is kinda waste of space in the collector!
Garage_Hermit

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Reply with quote  #17 
Hi, baothaitu,

Quote:
Would double the copper pipes on the collector make the fluid less hot?


Basically, Yes, U answered your own question !

What determines the amount of heat absorbed by the collector, is its AREA, in square feet, and the "insolation" or "solar flux" = specific to your location (and
the season & time of day & the weather conditions etc.). 

Basically, you will get "so many watts of power per square meter"

The idea is to make the collector as efficient as possible, in order to get as much of that energy, out of the collector and into your system !

So depending on your collector efficiency, you will get a certain output -- by designing and building, you are in fact choosing whether to heat a small quantity of water to Very Hot, or a LOT of water, to less hot...

In any event, you ought to avoid oversizing the collector in the first place, it leads to more expense and all sorts of other problems...

Your collector should in fact be sized according to your Heating Requirement...

G_H


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N4KIT

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Reply with quote  #18 
I would go with 3/4" or 1" headers and 1/2" risers.  The materials are cheaper and I think you would get better heat transfer to the HTF (heat transfer fluid) with less mass.

Also, when you mount your collectors, be sure they are tipped a degree or so, with input on the low bottom corner and the output on the high top corner.  This will ensure the collectors drain back to the storage tank properly when the pump is not running.  The return line should slope consistently toward the tank with no sags or low spots, again to ensure proper drainback.

Good luck - we look forward to seeing your progress!

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baothaitu

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Reply with quote  #19 
I plan to built two 4x8 vertical riser, 1" header with 3/4" copper, closed loop with 40% glycol as HTF. Inside is a 20x20 water coil with 2 radiator fans mount directly on the coil push air through it. Two bi-metal snap disc will regulate the pump and the fan (90-130 degree). There is no thermal storage tank, The fan and the pump will run as long a the temperature above 90 degree. Of course, there will be an expansion tank, temperature pressure relief valve and an air bleeder somewhere on the pipe. I currently have no plan to use it in summer time yet (hopefully by then I come up with something). I kinda hope that I do not overheat the system or freeze it overnight!
netttech

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Reply with quote  #20 
Baot,

Have you decided where/how you plan on mounting the snap switch?

Some mount it to the flashing, others the copper pipe. On my current water panel my switch is mounted to the flashing, that is directly below a flat portion of copper soldered to the tubing. I wanted the switch to activate based on the heat of the pipe.

That being said, I'm not happy with the location & activation. Although its gotten better I still believe mounting the switch directly to the flatten copper has better perfomance.

I'm also not happy where the switch is located on the panel. It's about 12" away from the exit. That means the entire panel has pumped out the heated water & replaced it with cold. It takes longer to re-activate the switch again.

About 1 hr of cycling the pump, the water heats up enough so it sustains constant pumping. My panel is only 10'L x 5'T. You panel being bigger may not have that issue. 

Personally, I think the switch should be located on the panel further away from the exit.

Jeff
Central IL
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