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sundug

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Reply with quote  #1 
SAM_0775.JPG  Attached are a couple of pictures of my newly built evacuated tube solar water heater for the spa. Spa chemicals do not mix with metals, so I had to use only plastic and glass in contact with spa water. Glass tubes bring the cooler water from the hot tub to the bottom of the ET, warmed water exits the top thru a 2 hole stopper.  This prototype setup has a differential controller that only allows the 20 watt panel to run the Topsflo 15 watt pump when collector temps are above spa temp. I also included a heater thermostat in that circuit to cut off the pump when spa water temp hits 104*F.  I say prototype because I still have to figure out if all the plastics can withstand stagnation, and I have to figure out freezing. I had filled evacuated tubes with water and left them out in the sub zero temps we had last winter, with no damage, so I think they will be OK, I just will have to insulate and maybe heat tape the hard plastic plumbing. Doug
 


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Garage_Hermit

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Reply with quote  #2 
Hi, Doug !

That looks interesting !

will be taking a look around my garden tomorrow, to see where I could put one of these spas !

Happy Summer Solstice !

G_H

P.S. I took your "house tour" video, you have a great home and some brilliant ideas, just love the little log wall & your bedroom wall is beautiful!


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sundug

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Reply with quote  #3 
The evacuated tube array turned out to be too small to keep up with spa heat losses during the winter, and I had to use a PVC manifold to combine the flows from each tube, and that couldn't be allowed to freeze, so I went to a 4' x 8' glazed steel stud channel and twinwall collector with 300' of 1/2" irrigation tubing coiled in it.  This can freeze without damage, but will overheat the tubing during stagnation. I installed a roll up shade to control that, so it is hands on. Sundug


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jpeg SAM_1356.JPG (421.15 KB, 55 views)
jpeg SAM_1357.JPG (422.25 KB, 56 views)


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tomhoffmo

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Reply with quote  #4 
I would be interested in seeing more detail about the  4' x 8' glazed steel stud channel and twinwall collector. Is that something you built yourself? Thanks!
sundug

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Reply with quote  #5 
Quote:
Originally Posted by tomhoffmo
I would be interested in seeing more detail about the  4' x 8' glazed steel stud channel and twinwall collector. Is that something you built yourself? Thanks!


Hi Tom, 
 Yes, I built the collector. I bought steel stud channel  and 5/8" polyisocyanurate foamboard as a backer board. I initially wound 300' of 1/2" black poly tubing into the collector, fastening it every so often with U shaped pieces of wire which I bent after poking them thru the backer. I used a 20 watt PV panel wired thru both a differential thermostat and a high limit switch. The high limit switch was a mistake, as altho it prevented the tub from overheating above higher than desired temps, it allowed the collector to stagnate and overheat and melt the poly tubing. I went to Type A PEX and wired around the high limit switch to solve that problem. Now I use a roll up shade to regulate high temps. The twinwall was from Menards, PEX I got online, all other materials  at home centers. Doug

http://www.builditsolarblog.com/2012_03_01_archive.html

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stmbtwle

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Reply with quote  #6 
Yes hot tubs have their own set of challenges. My 2×4 ARETHA regularly hit 160F when the tub was at high limit. I was always worried about the computer fans, but they have held up fine.

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