Step 4: Insulate the Back

Now we will make a frame to hold the foam and insulation board on the back of the panel. Cut your frame material into the same dimensions as the main frame, using the 2' sections made from the 1x2's (gives an extra 1" for the corrugated tin to fit) and longer sections with the 1x3's. Build the frame the same as you did for the main one too. Secure the frame in place with wood strips cut from the leftovers of the 1x2's and 1x3's, nailed/screwed to the side of the main wooden frame, and then nailed/screwed into the sides of the new frame. To seal the ends, use two or the foam insulation strips (the ones that fit the tin's corrugation).

Now the fun: use your spray foam (the stuff for "Big Gaps" is probably best here) and go back and forth along the troughs in the corrugation on this side. One can will not come close to filling the box, so use it mainly to fill the troughs and act as glue to hold a slab of foam board insulation.
Do you think this would work with a garden hose rather than the irrigation pipes? I have about 100 ft of black garden hose and thought this would be a good use for it. Thanks.
<p>I'd be cautious with material choices, hoses can leach toxic chemicals into your tub !</p><p>Ever drink off a hose on a hot sunny day (without letting the water run enough) </p><p>Plastics with a bitter odor are very toxic, and are in a lot of &quot;imported&quot; plastics.</p>
It probably would, though it might kink easier (especially when it heats up) and not transfer the heat quite as well. If its just laying around, couldn't hurt to give it a try, and it will likely help some. Think how water in the hose comes out steaming hot at first if its been laying around in the sun, same principle is at play here. Just make sure it doesnt get too hot and melt holes in it!
<p>Thinking about reverse engineering this for a different climate. Here in Canada, we use our hot tubs mostly in winter, one problem is that the deck usually gets covered in a lot of snow. looking at doing something like this;</p><p>drop a large pond pump in the tub, attach it to a long garden hose and lay over the pathway to the tub. cover the hose with raised decking.</p><p>return the other end of the hose to the hot tub.</p><p>Connect the power of the pump to an Insteon or z wave outlet (GFI) so when snow is forecasted, just turn on the pump and let the water from the hot tub melt the snow.</p><p>The hot tub will heat the water as it goes. </p><p>Looking for something I may have missed....seems kind of simple...</p><p>Chris</p>
<p>should work, its the same basic concept as heated flooring. I would mostly be concerned about the water freezing in the pipes and bursting, you would then have a siphon that would drain the tub unless the walkway is higher than the tub. If you made it with a closed-loop system using anti-freeze it would likely avoid that problem, just put a segment of the tubing in the tub to warm the anti-freeze and run it with a closed-circuit pump instead of the open-circuit pond pump.</p>
<p>After 4 years, do you have any measurements or estimates of how much heating this saves at various times of year? (Best in KWh rather than dollars, as rates vary)</p><p>Thanks</p>
<p>Regarding your concern about overheating the pump, I suggest a bubbler (a.k.a., aquarium air pump) inserted into the base of the rising tubing. The bubbles rise and move the column of water upward. The water at other end of the tubing flows freely downward towards the tub creating the necessary gravity assist to complete the water flow.</p><p>Regarding the sagging clear corrugated plastic panel, I suggest to run a tight insulated wires, as if they were guitar strings, length wise across the top of the box, then you lay the clear panel over that. The wire, if placed correctly so that they fit into the valleys of the panel would help keep the shape of the panel when or if it overheats and tries to sag. </p>
The problem with a bubbler is that it would pump air into the coils, which will reduce the surface area of water touching the tops of the coils. It will also break the siphon (doesn't take much air to do this) and end up just draining the entire setup. So far the pump is still working, going on almost 4 years now. There really isn't much to one of these, its basically a brushless motor with an impeller on the rotor shaft. No real electronics inside, just coils of wire to drive the permanent magnets of the rotor all sealed in waterproof potting material. <br><br>As to the sagging: good idea. It would need a screw or nail at each peak to get them high enough, but would prevent the sagging. Also using real glass or polycarbonate would probably work and be better suited to this application. My clear PVC is getting hazy now and has several cracks and chunks that have broken away. My next upgrade to this will be either of those. I almost got a glass lid replacement from an old glass storm door someone threw out, but it shattered on me while trying to get it on the roof (search youtube for tempered glass explosion, thats what happened). I bumped the corner on the concrete just a little too hard and poof, glass everywhere.
Is there anyway of doing this but convection rather than using a pump?
If you had your water storage (hot tub in this case) above the solar collector, you could work through convection. You would also want to simplify the flow path of the collection piping. Instead of spirals, have vertical piping that are connected at the top and bottom. As the author stated, though, this will give far more opportunity for leaks.
OK just wondering. Thought maybe too much friction loss anyway.
Would using copper pipe help with the heat transfer thereby heating the water more? I know it would increase the cost but it sounds like it might allow the panel to be in the sun without running water in it also.
Oh, and about the part of not letting it sit in the sunlight without running water: Its mostly a problem with the transparent PVC lid. The poly pipe itself gets softer, but isnt under pressure enough to cause problems (it might flatten out a bit from vacuum, but will return to normal when the water turns on again). The lid, on the other hand, sags from the heat built up in the box, which without any water running in the system to remove, gets quite hot, and would regardless of materials the piping is made of. This sagging is the problem I try to avoid, as it actually deforms the lid and starts collecting rain water in the depression. The Polycarbonate option I mentioned might avoid this, as glass certainly would.
Copper would dramatically increase the cost (and weight) of the project. <br>The design is similar to commercial ones (wikipedia: http://en.wikipedia.org/wiki/Solar_thermal_collector ) but with the collection tubes in front of the &quot;absorber plate&quot; since I used a corrugated panel instead of flat, and plastic tubing instead of metal, all to reduce costs. Once you get into copper, the price approaches/exceeds that of commercially available panels (see http://www.amazon.com/SW-37-Solar-Water-Heater-Panels/dp/B0041VM58E ). If you have it laying around though, sure, use it instead, paint it black (just be sure to use a pipe bender to avoid kinking it.<br><p><br>There would be gains in conductivity (coefficients of 400 vs 0.5), and since the copper is thinner, there would be gain in that as well (Q=kA&Delta;t/x , heatflux = conductivity * area * temperature difference / thickness). http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html has a good description of how this works out. It is a bit more complicated because instead of a (relatively) simple heat exchanger, its a heat exchanger with a radiative input power on the air side boundary layer. This adds in another Q on the right hand side of the equations.<br></p><p><br>Disclaimer: I was an ME in school, but fluids and thermodynamics were not my favorite courses. I could work all this out, but it would give me a headache and the numerical answers are already mostly done if you search the internets.</p>
Sounds like a great idea but in the UK, irrigation piping has holes in it. Is this correct or do you mean what we would call hose piping which doesn't?
Definitely do not want leaks in the panel, as any water that gets out of the piping will not make it back to the tub, and will also create condensation on the transparent lid (which is an easy way to tell if you have a leak), and will eventually fill the box with water and will start leaking everywhere. This is the non perforated tubing, sometimes its also called &quot;Poly Pipe&quot; as its made of polyethylene, or &quot;Funny pipe&quot; since its like pipe but flexible. Its sold in rolls and can be bent easily (more so if its warm).
I love this....I have been contemplating something similar, but your method is much easier to accomplish that what I had been planning. I think I will follow your instructible this winter and live up to the old motto of 'keep it simple stupid' <br> <br>Thanks, 5 of 5
This a good idea. I saw something similar on a greenpowerscience video on youtube.

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