Thermosiphon Solar Water Heater Design?

[nickswanjan]

Hello,

I am interested in building a simple thermosiphon solar water heater to provide hot water for a small camp.  Summer use only, short showers and dishwashing.  Can anyone point me to some good plans for something like this or related info?

Thanks,

Nick

[windstuffnow]

  Check out http://www.homepower.com they have a wealth of information on all types of solar water heating, as well as tons of other stuff related to RE.

.

[Nando]

Visit :

http://www.mne.psu.edu/me415/SPRING02/EPICS10/

http://www.motherearthnews.com/top_articles/1979_September_October/A_Homemade_Solar_Water_Heater

http://www.eere.energy.gov/RE/solar_hotwater.html

http://www.ucsusa.org/clean_energy/renewable_energy_basics/solar-water-heating.html

http://www.eere.energy.gov/consumer/your_home/electricity/index.cfm/mytopic=12850

http://freepatentsonline.com/4213448.html

http://www.nrel.gov/docs/legosti/fy96/17459.pdf

http://www.solarbridge.com/English/Products.htm

http://www.kysolar.org/PDF%20Chapters/Chap%208-%20SWH%20System%20Types.pdf

Nando

[johnlm]

And

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

I wonder how people find  the Otherpower.com discussion board.

[ghurd]

Hi Nick,

It's not hard!

"Camp" implies camping to me.

Meaning showers can be day time, late night hotdog dishes can wait.

Simple.

'Thermosiphon' implies overcomplicated to me.

Have a look at this.  The black drums.

Insulate the lower half, run the hot water line in black pipe over the roof in circles.

Cold water is not cold anyway, so why bother worrying.

This is intended just for storage, but can get hot enough to be 'too' hot. And the pipes don't even run on the roof.

It's not hot in the morning!

This link is 95% not related, but may be informative.

http://www.fieldlines.com/story/2005/8/21/205627/022

G-

[Ungrounded Lightning Rod]

The ONLY point of a thermosyphon is if you MUST have your storage below your collector, to pump the hot water down.  (Typically this means a collector on the roof and a storage tank in the basement.)

Put the storage tank significantly above the collector, make sure the collector's run is sloped, doesn't double back, and has adequate pipe diameter, and convection pumps the circulation loop for you.

Getting the water back DOWN when you're actually using it is no problem.  Whatever is pumping water to fill the tank pushes it down for you, and the difference in density between the cold water going up and the hot coming down amounts to only a miniscule drop in pressure.

As ghurd's post implies:  water tanks have a significant surface area, so paint them black and they become solar collectors in their own right.  Maybe it takes much of the day to heat the water once, rather than an hour or so per turnover if you've got a bigger collector area, but that's fine for a camp site with a limited number of campers.

You don't need to put 'em all that far up unless they're doubling as gravity-fed storage.  If you have a reliable pressurized feed (like a pipe from a spring uphill, able to supply water at the rate your shower uses it) and you're not using an auxiliary collector but just depending on the tank's pait job for solar heat, you can put 'em next to the building containing the shower rather than up a tower.  That also shelters them from the wind and reflects some additional heat onto the tank if you position things correctly.

Sheltering from air circulation means it reaches usable temperature earlier and holds heat later.  (But still figure on showering only in the afternoon if you use a tank-paint-only collector.)

[zap]

"The ONLY point of a thermosyphon is if you MUST have your storage below your collector..."

I thought a thermosiphon was when the storage was ABOVE the collector?

[nickswanjan]

Thanks so much for all the ideas and links!

In this case, "camp" means a 1920's one-room building 24x24 - something like what 'ghurd' posted a photo of.  I have a small solar panel that currently gives me light and water pumped up from the lake.

I am trying to strike a happy medium between a black tank on the roof (no hot water in the morning for a shower, need to reinforce the roof), and the more complex systems.  I was originally looking at building a system with a circulating pump, but the thermosiphon seems so much more elegant, and no sensors or drain on the PV system.

I have a nice 2' x 4' piece of thermopane glass from an old skylight, a bunch of miscellaneous 1/2" copper pipe, and a beer keg (that someone converted to an electric water heater a long time ago, but I'm reforming it).

My idea is to build a pressure treated wood box to hold the glass and the copper pipe, mount that box low on the roof, and pipe it to the beer keg in the attic (liberally insulated with fiberglass).  I should be able to get it easily 2 feet above the top of the collector.  I imagine I will need to insulate the pipe from the collector to the tank (distance will be about 10 feet or so).

1) Am I on the right track?
2) What do I use economically for a backing plate, and how do I bond the pipes to it?
3) Where do the various inlets and outlets go to?  It seems like the cold supply and the cold out to the collector should go in the bottom of the tank, and the hot from the collector and the hot out of the tank should come out the top, but the various diagrams are not so clear on this point.

Most of the diagrams I have seen are for using a thermosiphon system as a preheater for another system, not on their own, and they use more complicated plumbing and diffusers.

[zap]

Nick take an hour or so and look over Gary's site builditsolar.com. The link I provide is to his "solar hot water projects". He has designs from super simple to super complex. What you describe seems very doable and Gary's site offers a boat load of info and I'll bet it will answer all your questions.

[nickswanjan]

Thanks.



BTW, here is an good construction link I found: Using the Sun for all your Solar hot water needs



And here is a thermosiphon (or thermosyphon) installation manual: Installer Thermosyphon Manual



And this looks like a good source for custom collectors (unless I decide to build my own): Sunray Solar Absorber Plates



Any cheaper collector options?



Also, I am not absolutely stuck on the thermosiphon idea, but it has strong appeal since it does not require sensors or pumps.  I'm not into the batch heaters because they cool off too much at night.



I have considered a system that has a small circulating motor directly powered by a small solar panel - but I have not found any designs like this?  Also I have not been able to find a reasonably priced direct solar powered circulator.

[Ungrounded Lightning Rod]

I thought a "thermosyphon" was the hack where you use a heat-transfer fluid (like alcohol, perhaps under reduced pressure) that boils, so the bubbles lift fluid into a chamber at the top of the collector.  This produces a pumping action that lets the heated fluid flow DOWN, powered by the heat of the sun, with no moving parts but the fluid.

A cute hack but it requires good seals and some tweaking and fancy plumbing to get it to work right.  (Essentially a bunch of narrow near-vertical heat-collector pipes, penetrating almost across the inner chamber of a fat manifold pipe across the top of the collector.  Or you can bend them over and enter the manifold from the top.)

[Ungrounded Lightning Rod]

gotta have the right sized bubble of air in the manifold.  Too much and no pumping, too little and not enough pumping, none and no pumping.

[ghurd]

I have seen it both ways, but I think standard 'thermosyphon' was so the heated water raises, moving itself to the storage tank.

This setup is level, concerning the tanks. The heated water leaves the heater through the high pipe, going into the storage tank in a high inlet. Cold water leaves the storage tank through a low outlet, going into the heater in a low inlet.

No pump. No boiling.  Works great.  Coal fed. Storage is a 40 gallon gas water heater (no gas).

G-