Solar Hot Water Heater design for 120 ppl

[Saxomasaurus]

I built a solar hot water heater (The SunSpa) this year for our camp, and in spite of my firm convictions to the contrary, it worked like a charm! The heater brought 100 qts of water from ~70 degrees to ~110 degrees in about 4 hours, enough with one refill per day to provide hot water for all the showers and some of the dishwater our camp of 120 people needed over the course of a day.

This way, our camp managed to wean off those wasteful shower bags (5 gallons per shower!) to a 1.5 gallon pump-sprayer, and still have hot water.

The reservoir is a 100 qt Coleman cooler, with the drain plug removed and replaced with a garden hose bib. I used a simple PVC fitting to thread onto the bib on the inside of the cooler and seal the drain.

A small 12V pump inside the cooler circulates the water through the solar accumulators via 3/8" braided vinyl tubing. The tubing enters the cooler via inserts that are drilled into the cooler and caulked into place.

The accumulators are 50 ft copper air conditioning coils, mounted on thin sheet aluminum with plumbing strap, all inside wooden boxes and painted matte black. I am no carpenter, so getting the boxes square and all of the recessing done was probably my happiest accomplishment! I used a table saw to notch out the top surfaces of the walls of the box so I could mount the glass flush.

I used 1/4" tempered glass panes, and I made the panes removable to get at the mechanical in case there were issues. To seal them up, I used window seal, and simple baggage straps from Ikea to cinch down the glass panes. The boxes stayed sealed so there was no dust on the black surfaces, and I left a brush near the collectors so that any camp member could wipe the panes clear throughout the day.

To improve this design, I would use a larger reservoir so it didn't need to be refilled during the day, and starphire ultra-clear glass. My pump operates on 12V from an AC adapter, but a smaller pump could operate directly from a small solar panel and be completely self sufficient.

Please feel free to use, improve, and tell me how you did it!

[GreyCoyote]

Thats an awesome build. I like the idea of the Coleman as a reservoir. Well done!

Copper is getting darned expensive. How do you think black plastic irrigation tube would have worked instead of copper? Dirt cheap stuff, and if it worked you could go bigger for less bucks.

[Saxomasaurus]

The design was based on a concept that used PEX pipe, so it's indeed possible:

http://rimstar.org/renewnrg/diy_pex_sol ... mal_dn.htm

I wanted maximum absorption in a compact design that I could fold up into a suitcase (the wooden boxes are hinged and have a clasp so that this can be done) to deal with the hassles of BM travel and packing, but if you have lots of transport space and a team to move the thing around, a bigger box with more pipe would accomplish the same goal.

The concept design used 300' of 3/4 PEX tubing, whereas I used 100' of 1/2" copper. Note that the cost of each is approximately the same ($150 at Home Depot). You also need more paint for the PEX.

Note that most of my design considerations went into the glass. If it breaks, you're system is busted and you won't find a replacement on playa. The larger design requires a much more expensive piece of glass, and it would be much more awkward to move around a lot; mine were standard 2'x2' panes.

[GreyCoyote]

Well done, and well considered.

Btw: I was actually talking about black PE irrigation pipe which is lots cheaper than PEX and doesnt need paint. But I see where you were going and I like the choices you made.

Good stuff.

[Traveller in Time]

And then I stumble in, just having searched and calculated about PVC, PE and copper pipe kind of posting lag, some dinner and two postings came in between.


Copper 385W/mK (thermal resistance value) while PVC 0.2W/mK (drainage), PE 0,5W/mK (underfloor heating )
This would suggest you would need to scale up some 1000 times.
However there is another factor; time and as water only does 0.6W/mK the upscale should be limited. You have the whole day to heat the water
Also smart is the glass covers no dust and trapping hot air.
Perhaps pressing the tubes against the aluminium would also increase the efficiency.

Hope you dont mind, made some schematic

Waterheatercirc1.png

[Saxomasaurus]

It wasn't clear from my description, but I did use aluminum sheet backing behind the coil, the entire area of the wood boxes.

I looked at PE pipe; my concern would be melting it.

Others suggested black rubber hose, which would work and be cheap...but then your showers would all smell like tires.

On the subject of temperature, one part that I ordered but didn't get around to implementing was a thermostat. We got water up above 120 degrees, which approaches scalding temperature...theoretically, on a hot day, if you angle your collectors well and don't open the cooler, the water could get hot enough to hurt people. Our tank temp. was moderated by our refills during the day. I ordered one of these:

http://www.titancontrols.net/products/l ... hyr-2.aspx

I like the industrial robustness of it, nice and idiot-proof and simple - it simply cuts the circulator when the water temp hits the set mark. In talking with their engineers, the probe isn't waterproof and needs some kind of solution...I was going to use a sleeve of jb weld.

That schematic is swanky, thanks for making it! I would personally recommend against having an automatic means of draining the reservoir, like a pump. It's way too easy to abuse that way...30 gals attached to a sink or directly to a shower head would disappear all too quickly when people figure out they can use nice hot water to wash their hands, or have a 5-min shower.

We had a manual spigot out of the reservoir so that users had to pour water into a bucket and transfer it to a pump-sprayer. Filling the bucket took a couple of mins, and this kept usage down and we were able to provide hot water for any of the 120 users who wanted it, plus a tub for kitchen dishes. If you plumbed the reservoir to a faucet or shower, I would at least double the anticipated usage/wastage. Maybe more.

[Token]

A trip to the dump and scavenging old refrigerator parts can get the metal for dirt cheap or free.

Good design tho, proven.

[Saxomasaurus]

Another suggestion that was made to me for a cheap metal accumulator was a car radiator.

[Traveller in Time]

Melting of any plastic is not an issue, as long as there is water in it. You can hold a lighter under a balloon with some water in it. Perhaps some outer layers will melt off, only reducing the wall thickness.

Continuous pump
And sorry I did an edit changing the alu as background to pressing the tubes against it. For some reasons the image did not change version (but I tried).

[EGAZ]

We had this same design for our pool when I lived in Michigan. A wooden case made of 2 x 6s & plywood, painted black on the inside, half inch black poly tubing, (heavy walled) hosed clamped to a copper header we fabbed up on both ends, Lexan/plexi for the top, all sealed. It was ten foot long by 3ft wide. Even on cloudy days it put out water temps hot enough to burn your hand. We gained a month of swimming in the spring and fall. We later installed a three way control valve to maintain a desired output temp. It did too good a job...

Great execution Saxomasaurus!

[FIGJAM]

Reduce water abuse by installing an on demand valve.

Meaning the water only runs when a button or lever is held down.

If the lever isn't pressed, the water doesn't flow.

[AntiM]

Impressive. What did you do with the greywater? Was there enough to be a concern?

[DanusLight]

Why do you need to heat hot water

[Saxomasaurus]

Impressive. What did you do with the greywater? Was there enough to be a concern?

The hot water system / reservoir had no direct wastage; users would fill a bucket from it to fill the shower, and all the water got used up. We had a simple tarp for spillage.

The shower was a simple pump sprayer with the wand removed and some tubing and a garden irrigation fitting installed in its stead. The shower sat in its own pond with no evap.

Water was transferred from the shower pond to a second pond (the main pond for our sink outlets) with 4 mesh cylinder evaporators, based on the 2006 design here on e-playa: viewtopic.php?t=12911

One tweak we made was to use hot water tank insulators for the distribution disc atop the cylinders; the tops are perfectly flat, and the eyebolts holding them in place can be adjusted to level the disc perfectly.

The cylinders were amazing; running 24/7 for 8 days, we reckon we evaporated almost 1000 gallons with them. The pump was undersized; as you can see all of the surface area was not wetted by the flow...so there's room for even more improvement.

Why do you need to heat hot water

Because it's cold.

[Traveller in Time]

... not as smart and intelligent like you...

You will have talents for sure

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