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Location: When you take flak it means you are on target
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Just wanted to run this by the forum.
I live in the AZ desert. It is over 100 for about 7 months a year and in the 110 plus range from June until September. We are thinking of by-passing our hot water heater.
I was thinking of just building a stainless box of 50-100 gallons - say 6 inches thick by say 6 feet square, or whatever it took to get the volume, like a fuel tank (maybe just buying a square fuel tank).
We'd just paint it black and strap it to the car port roof (ours has 6X10 beams) weld some input and outgo tubes and pipe it into the system - with bypass valves by the water heater. Then we could just shut off the electric heater and run our regular pressure water through the solar box.
Our overnight lows are above 90 degrees for about 3 months and about 80 for about 5 months. So we'd have warm to scalding hot water 24 hours for much of the year. Even in winter we'd have hot water by midday and it wouldn't cool until early evening.
I figure we'd save about $150 a year in electric costs - and still have the heater as a back up if needed - I doubt it would be.
Hmmmm, I'd say you're missing about $150 a year in water heating costs! If I had your temperatures (which I could never tolerate, even with AC), I would have set up one of these solar systems! I assume the heat is from solar radiation, duh...as that's what will heat the water, not the outside temperature. I assume you've looked up this stuff on YouTube:
I live in the AZ desert. It is over 100 for about 7 months a year and in the 110 plus range from June until September. We are thinking of by-passing our hot water heater.
I was thinking of just building a stainless box of 50-100 gallons - say 6 inches thick by say 6 feet square, or whatever it took to get the volume, like a fuel tank (maybe just buying a square fuel tank).
We'd just paint it black and strap it to the car port roof (ours has 6X10 beams) weld some input and outgo tubes and pipe it into the system - with bypass valves by the water heater. Then we could just shut off the electric heater and run our regular pressure water through the solar box.
Our overnight lows are above 90 degrees for about 3 months and about 80 for about 5 months. So we'd have warm to scalding hot water 24 hours for much of the year. Even in winter we'd have hot water by midday and it wouldn't cool until early evening.
I figure we'd save about $150 a year in electric costs - and still have the heater as a back up if needed - I doubt it would be.
Seems pretty simple.
What am I missing?
On average, water heating costs are about 30% of a family's electricity expenditure.
You do not need a steel box and it does not need to be on the roof.
Find an old water heater, remove the core, strip the outside paint, paint the outside black.
Build a wooden box big enough to put the painted water heater in, insulate box, put glass on top. Face south standing up or lying down so that glass is obviously facing south. Plumb new solar water heater so that water flows through it into your internal home water heater. The idea is to "pre-heat" the warter outside, relieving the inside water heater from most of its work.
One of the issues with a large volume is getting the heat to transfer to the water fast enough. Instead build a box with plexi glass front, paint the inside black. Run a series of copper finned tubing or simply some coiled pex tubing inside the box. Never did this with solar so research it to find what works best.
Let's suppose this box could be placed at an angle on the ground in an area that gets a lot of sun next to a wall where the hot water heater is. The higher end of the tubing goes to where pressure relief valve is on the hot water heater, be sure you installation incorporates the PRV. The other end goes to where the drain valve is on the bottom of the hot water heater.
As the water inside the tubing in the box heats up it will thermosiphon into the top of the hot water tank, the colder water is pulled into the tubing.
This is the basic idea, they have the tank on it's side but it can be straight up and down.
Two very important points, the collector needs to be below the storage tank and it should be as close as possible.
We use the same setup for small solid fuel stoves with perhaps a two foot coil inside the stove, you can easily heat a 40 gallon tank of water in 12 hour period. Now if you wanted to maximize the amount of water heated by solar and still have all the hot water you would need you can use a two tank system like this, just put the first tank outside by the collector.
Just imagine the stove here is your collector, note there is two relief valves listed here. You only need one.
The benfit of this is you leave the hot water heater on, all of the water going into the hot water heater is pre heated.
Last edited by thecoalman; 08-30-2015 at 08:07 AM..
Make sure to put in a pressure relief valve, as heating water too far makes steam, which can cause a deadly explosion. In fact, if you did not already know this, I would strongly recommend that you really spend some time researching the project, for your own safety. Solar hot water is a simple thing, but there are a few things that can kill you if you get it wrong.
as heating water too far makes steam, which can cause a deadly explosion.
Technically in an application like this it can't make steam as the water is occupying that space, the water will want to expand into steam but it can't so pressure will build as it's heated. If it keeps building beyond the capacity of the water vessel then it goes Boom! and you have steam.
Steam heated systems work at very low pressures and they are not completely filled with water.
Technically in an application like this it can't make steam as the water is occupying that space, the water will want to expand into steam but it can't so pressure will build as it's heated. If it keeps building beyond the capacity of the water vessel then it goes Boom! and you have steam.
Steam heated systems work at very low pressures and they are not completely filled with water.
This is true, as long as there is no air in the system. My statement was not worded the best, to be sure... The general premise that relief valves are needed is valid, however, which is what I was attempting to convey.
Location: When you take flak it means you are on target
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Thank you folks for the suggestions.
And NO, I hadn't thought about the pressure relief valve (though I know regular heaters have them) - so thanks countryboy and coalman, may have kept my head from being blown off!
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If I had your temperatures (which I could never tolerate, even with AC), I would have set up one of these solar systems! 
I assume the heat is from solar radiation, duh...as that's what will heat the water, not the outside temperature. I assume you've looked up this stuff on YouTube:
The general premise that relief valves are needed is valid, however, which is what I was attempting to convey. 
