DIY solar hot water pre-heater

[spinningmagnets]

The solar water pre-heater has been consistently rated as one of the most cost-effective upgrades to a hot-water heating system. If building one of these only cuts your water heating bill in half, even though that may not sound like much, the cost of a DIY pre-heater is so low, the payback is quite short.

Since the stock system pressure moves water through it, no additional pumps are needed. The key elements are a tank that can hold the normal municipal water pressure, an insulated box, and a glass (or UV-Polycarbonate) glazing.

The best glazing is a salvaged glass door, and the best candidate for the tank is an electric water-heater tank that a plumber has upgraded to gas-heat, and he would normally discard the perfectly fine old tank.

Since this solar “batch” collector is positioned before the homes stock water heater, the stock system will ensure your water is always as hot as it was before the upgrade. However, on sunny days it takes less energy to heat up warm water than to heat up the cold in-coming water.

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Batch

 

[jonathanm]

I love this kind of thing. There is a long way to go before PV technology can truly meet the demands of the applications expected of it, but why complicate things? IF you can use solar energy directly then that has got to be a good way to go.

Passive solar FTW.

 

[vanilla ice]

I was thinking of using old propane tanks for this.. coil your water tubing through, fill it will salt water and paint em black. Stick em up on the roof where they wont uglify your yard.

 

[CrazyJerry]

In the grand scheme of off-grid it's small potatoes but it's also one of the more rewarding projects. I finished mine recently and really love it!
http://diesel-bike.com/Solar_Shower/Solar_Shower.htm
~CrazyJerry

 

[maydaverave]

I was thinking about just coiling some black water hose in a box as described above. More surface area, simpler and everbody has tried drinking out of a water hose thats been lying in the sun as a kid

 

[amberwolf]

If you don't plan on drinking or cooking with that water, the hose'll work fine. But it tastes awful after it's heated up in the hose.

FWIW, that was one of my original plans for a preheater--just laying out all the hoses I have on the nearly-flat roof of my back room, and running them as a valve-switchable loop to/from the water heater tank.


Given the way my pocketbook is heading these days, I'm probably gonna have to turn off the gas (and the phone) and go pure solar for the water heater (whcih is the only gas item in the house anyway). Then I can reroute the plumbing so the heater basically becomes just an insulated storage tank, and wrap it in blankets/etc (since it will have no internal heating anymore to burn anythign with), and pump the water out of the tank back to the roof loop for reheating periodically during the day once the tank drops to a certain temperature, swapping the water from the loop back to the tank.

Ideally I'd like to get at least one more old heater for it's tank, but I haven't been able to get hold of one with an intact tank yet. (or one I could fix)

I should be able to use old washing machine valve solenoids to control the flow, cutting off the input pressure from the water main to the tank, and switching the input and output of teh tank up to the loop, with a pump from a washing machine moving the water back up to the roof (aided by the water from the roof pushing back down the other side of the loop).

I'll probably have to use garden hose for the majority of this, until I can find enough metal water pipe to put up there instead, and paint it black. More efficient if I lay it out in a reflector tray, but it'll work even without that here in Phoenix.

 

[Harold in CR]

I used to build and sell those passive tank systems. The local hardware store would get old tanks when the new ones were installed. 9 out of 10 would have a tiny leak, caused by flux covering a pin hole in the weld. Chip off the flux and just a touch with the welder electrode, and, tanks good as new. Too much heat might crack the glass lining inside the tank.

Try to find a used GAS water heater tank. That way, you get to have the how air also travel through the chimney pipe and heat the water a little quicker.

I also laid an electric heater on it's side. Be sure to turn it, so the elements are installed from the bottom of the setup, and, use the folded elements, which are shorter. Put a 90° fitting for the pressure relief, and now, that is still the highest point of the tank for blow off, if needed. Now, you have the solar and also the electric to keep the water temp topped off.

Also, living out in the country, made a wood furnace from a Propane tank, and mounted a gas water heater tank, laying down, right above the furnace. Plumbed it into the house system, and ran a tube from the propane tank up and 90'd through the chimney tank on the water heater tank. Now, I had direct flue running through the tank, besides the radiant heat from the furnace tank. Worked VERY well.

 

[vanilla ice]

How hard is it to pull the tank out of an old water heater? That is why I would go with something else.. seems like a major pain. I've messed with one curb side before and the sheet metal and insulation seemed it take a few hours of hard work to get through.

 

[Harold in CR]

First, look for USED, NOT OLD, heaters. The ones I got were less than a year old. Leaked and replaced under warranty.

Never took me more than 15 minutes to strip one down.

Also, instead of welding, you could also carefully drill out the defect and use a Galv. or Stainless metal screw with washer and rubber bit, to stop the leak. Put a little dollup of yer favorite leak stopper goo on the screw, as you run it in, and, yer good to go.

 

[maydaverave]

My water heater is on the fritz and I am broke till fall also I live in florida. So it shouldn't be to hard to rig up something to warm up cold spring well water to a nice temp on a hot day. Thanks for the ideas.

 

[Evoforce]

Just be very careful to have a pressure relief valve incorporated into your system. Water heaters can explode!

 

[vanilla ice]

Hrm, the one I was messing with was old and rusted. All I had was a bike multi tool. What do you guys use to open up the water heaters? Sawzall??

 

[torker]

Here is what I use for my pool. These were made in the 70s for domestic hot water. I found these with a pv panel and a 1 amp 12 v Taco pump for 60 dollars. I run my 1 hp pool pump to them @ about 20 gpm. Lately I have been running them at night to cool my pool. We just hit 30+ days of over 100 F here.

 

[Harold in CR]

Top and bottom covers should have sheet metal screws. Take them out, and take off the top cover, turn upside down and pull off the whole outer cover, and the bottom section. You may have to cut a slice from the bottom of the outside jacket, up to the drain pipe, so the cover can slide around it.

If your tank was really old, it was probably all stuck together with rust ???

 

[amberwolf]

I have found a few tanks here and there that were "re-insulated" using spray-foam expanding stuff squirted between that outer metal cover and the core tank, making it difficult at best to get the outer cover off of it, at least for in-the-field salvaging operations. At home, I'd have no problem with it, but the less I have to fit on the trailer, the better, and a whole heater usually won't fit as one piece (which is another reason why I haven't managed to snag one yet).


FWIW, I have been experimenting a bit with water pressure on the shower head, and find that if I have it at about 2/3 valve open, I can take a full shower on just the "cold" water still in the overhead (roof crawlspace) pipes that's been heated (to nearly scalding) by the sun, at midday, without even turning the hot tap on at all. In morning and much past sunset, there's not enough to do it, but if I could run that water into an insulated tank....

And it only takes about 10 minutes or so at midday to reheat that water in the pipes; 20-30 at 9am or 3-4pm, and maybe an hour at 7-8am or 6-7pm (since the air is already hotter in evening, it works better later/longer than it does early morning).

I can also do my dishes (hand washed) and kitchen cleanup on just that water. I could also do a load of laundry on hot-hot, but the pipes to the room with the washer don't run thru the roof crawlspace, they run directly from under the house, so that water really *is* cold. I'd have to move the washer into the kitchen or bathroom, or outside, and add taps I could screw onto for the washer hoses to one of those rooms. If I had to do that, it'd be easier to just replace the standard water heater with the solar one.

 

[newRMW]

If you don't plan on drinking or cooking with that water, the hose'll work fine. But it tastes awful after it's heated up in the hose.

FWIW, that was one of my original plans for a preheater--just laying out all the hoses I have on the nearly-flat roof of my back room, and running them as a valve-switchable loop to/from the water heater tank.


Given the way my pocketbook is heading these days, I'm probably gonna have to turn off the gas (and the phone) and go pure solar for the water heater (whcih is the only gas item in the house anyway). Then I can reroute the plumbing so the heater basically becomes just an insulated storage tank, and wrap it in blankets/etc (since it will have no internal heating anymore to burn anythign with), and pump the water out of the tank back to the roof loop for reheating periodically during the day once the tank drops to a certain temperature, swapping the water from the loop back to the tank.

Ideally I'd like to get at least one more old heater for it's tank, but I haven't been able to get hold of one with an intact tank yet. (or one I could fix)

I should be able to use old washing machine valve solenoids to control the flow, cutting off the input pressure from the water main to the tank, and switching the input and output of teh tank up to the loop, with a pump from a washing machine moving the water back up to the roof (aided by the water from the roof pushing back down the other side of the loop).

I'll probably have to use garden hose for the majority of this, until I can find enough metal water pipe to put up there instead, and paint it black. More efficient if I lay it out in a reflector tray, but it'll work even without that here in Phoenix.

That is a brilliant idea to use old washing machine parts to control the flow path! I was googling for DIY plans to build a solar pre-heater for my outdoor hot tub spa and realized while I was reading your posting that I had an old washing machine with a broken agitator transmission coupler. I was storing it in the garage until I had time to arrange disposing of it.

 

[amberwolf]

I had an old washing machine with a broken agitator transmission coupler. I was storing it in the garage until I had time to arrange disposing of it.

FWIW, those are super cheap parts and very easy to replace. There are a number of types, but one of the most common is a GE / Kenmore / etc type like this. The images below show the "upgraded" version that has a metal core in case the issue is a rounded out hole, but usually the arms break off instead. They make all-metal ones too, but if there isnt' any weak spot in the coupler to be a "fuse" then if something siezes or jams you can instead have a motor fire.

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They also make a version with a layered-rubber/cloth shock ring, if the problem you have isn't that the arms of the plastic break off but that the rubber disintegrated.