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Very Quick question on passive solar water heater....  RSS feed

 
gardener
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Location: Upstate NY, zone 5
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Having had a couple of January vacations in the Bahamas/Virgin Islands/Puerto Rico when I was young, I understand the climate there. Even in January, most days will have at least some sun if not a lot, with probably a shower in the afternoon. It never gets much below 70 degrees - all the warm Gulf water moderates the temperature amazingly. Cool cloudy weather for days will probably be rare.

I think you will be safe to assume that most days your collector if well built will be able to get the holding tank to 140ish or more. The best collector piping aside from copper will be black HDPE - it can stand decades in the sun. It does get softer when hot, and will not take much pressure then, but you have a very low-pressure system.
I might consider a coil of HDPE on the roof spread out for exposure, connected to top and bottom of an insulated holding tank on the roof or a foot above it. I might slope some of the pipe up so there is hot water priming the circulation. The bigger the pipe diameter, the easier it will be to get the thermosiphon going, though the less effectively it will heat the water in it. Running a pipe with an easily accessible shutoff valve up to the top of the tank (with an air gap so there can be no back-siphoning from the collector system) will allow easy topping-up of the system. You could either inspect regularly to see how fast it loses water, or just give it a shot of fresh water now and then until you see it overflow.
A 10' coil of 3/8" copper tubing submerged in the tank near the top and plumbed into the hot water supply will allow enough flow for one modest fixture's use at a time while heating the water quite well.

How's that for cheap but effective (and safe)?
 
Glenn Herbert
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A further thought: I think you would be wise to buy a coil of HDPE at home and set it up like you would expect to do for real, to see what results you can look forward to before you are out in the boonies far from suppliers. You can probably find out how much of what size of pipe will give the heating you are looking for. If you don't have further use for the test parts and it is not practical to ship them to St Croix, you can probably recoup much of the cost on craigslist. It may be practical to put a coil of 3/8" copper and a few valves and fittings in your luggage...
 
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- still searching and thinking....
-- Here in Minnesota I have a well system - and the water out of the tap is 110 degrees.
-- Might we have legionaires?

Is there any credence to the "copper argument"...?

chuck
 
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Charles Heller : I have been guilty of spoon feeding you information as you ask the questions . I have gone to the permies tool box at the top of the page

between the Permies banner and the permits video of the week and used Our search function to find you a more definitive article on Legionnaires D.

There is an ongoing argument between the E.P.A. who wants water heaters to be set at 130ºF (I Think ) because above that temp the young the old, and
people with immune compromised conditions can be rapidly scalded!

The C.D.C. wants the temp set at 140ºF to protect wait for it ---- ! The young the old and immune compromised !

Any way link below :

http://www.permies.com/t/2607/energy/alternative-hot-water-legionnaires-disease

I'm kinda thinking that you can take over the searches, but that does not mean that I or your other Fellow Members will not be here !

Yes Copper is at least Bacterio-static, the germs stop growing and multiplying, if every hand rail in america had a thin copper plating we could stop the spread
of lots of germs.

Eventually the copper would wear away and the railing could be turned over or replaced ! Big AL
 
Charles Heller
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- Sorry, I missed Glenn's posts earlier.....

So - I remain boggled... My first question is "Really??!!" - a 10' 3/8" copper coil would provide enough heat transfer that you could run COLD water through it and take a shower at the same time?! Am I understanding that correctly??

and #2..... It sounds like my idea of putting a hunk of copper in the holding tank aint necessarily that dumb? - - How about a few thousand pennies??...



 
allen lumley
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Charles H. : I think that you could probably rigt up an experiment starting with water at 150 degrees and Some copper tube, but I would think a finned
heat exchanger would be hard pressed to do it in 50 feet, and with out a high pressure pump a 3/8ths inside diameter shower would be a get wet then
soap then rinse type shower !

They make special filters out of copper and silver another bacteria-static metal , but you need contact time again to make it effective and all these devices
need contact time ! Sorry that research you will have to soon your own ! Big AL
 
Glenn Herbert
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I have about 6' or so of 3/8" copper from my water heater to my kitchen sink, and even when I had my well pump set for 15-30 psi, it ran a decent stream. It wouldn't power a blastem luxury showerhead, but it would take care of a modest one. And part of the reason to use 3/8" instead of 1/2" besides cost is the great heat transfer area compared to volume. I can't quantify it, but 10' of that running through a 140 degree water tank would absolutely warm up continuously running water and may make it hot... that depends partly on what the water starts from. I was assuming something near 70.
 
Charles Heller
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Okay..... One thing I just found out from my sister is that the "supply line" is actually a buried pipe (so not the hose laying on the ground I thought) - so that's good. And I have finally grasped the idea that a coil of some sort's main advantage is that it takes away the idea that any of the shower water would be "stagnant" - assuming regular use....

So - it seems like I'm down to size and length of coil (- seems like I could cram more than 10' in most tanks...?) - how large a tank I should put it in - and whether a "bread box" batch heater or a self siphoning collector and storage tank would be most likely to give higher temps...?

??

Thoughts?

Thanks!!
 
allen lumley
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Charles H. : My vote is for an insulated, and reflectix type material- lined box, with a drop door also with reflective material, that can be infinitely adjusted to Shine
the suns light energy through a glass or other transparent panel onto a Black plated metal drum, the kind with a clamp to secure your drum end!

This would allow the domestic coil to be mounted on that flat end to promote a good seal ! the drum head may need to have its gasket replaced with a solid bead
of RTV type Food grade Silicone Seal !

I think thats about the best I have for you ! Big AL
 
Charles Heller
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I DO appreciate all your help and thoughts with this - and Glenn's too.
I will definitely let you know what I end up doing and I'll try to post pics....
So - final questions before I continue my investigation via other forums.
I've been picturing a 20 or 30 gallon tank - that sound about right? (I picture a 55 gal. drum smashing through the roof...)
Should I go with plastic or steel? (Does it depend at all upon whether I go with batch or thermo-siphoning?
Coil length and size - any more opinions on that? -- How about as much 3/8" copper as I can cram in there? (- within reason)...?

Thanks once again...
Chuck
 
allen lumley
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Charles H. While trying to find you a picture of a domestic hot water coil or sometimes inaccurately called a 'sidearm' or 'sidearm water heater' I found this.


see link below :

http://www.reuk.co.uk/Solar-Hot-Water-Heat-Exchanger.htm
http://www.reuk.co.uk/Solar-Hot-Water-Heat-Exchanger.htm


If you had a drum of the type I tried to describe earlier, and then used this coil to steal hot water heat away from the barrel ( inside the insulated bread-box
-batch heater ) to supply hot water to your shower, you should be able to have nearly unlimited hot water on a sunny day and mostly stay above the
comfort zone of L's Disease !

I expect that a (thick wall) plastic drum will not have a removable end and will be insulating so I am still thinking metal 30 gallon barrel. I picture a separate
piece of new construction located adjacent to but separate from your main building if only to make the shower more useable, this part of the plans has to fit
with your ideas and that of your Sister et al

Again hopefully you can make some phone calls to a boiler installer who may have some used domestic coil heat exchangers and only wants a few more
dollars than the scrap Copper price to make the transaction worth his while ! Most of these units if you can find them will be 1/2'' to 3/4'' inside diameter

I picture you trying this at home and then needing only to take a heat exchanger and some fittings, air freight on a Drum will probably be near the same full
or empty

Hope this helps a little ! Big AL
 
Charles Heller
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allen lumley
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Charles H. : O.K. heres a thought, the wort chiller looks like it would be a transitional size between a very dedicated home brewer, and an Artisan Craft Beer Brewery/
Pub Enterprise.

If you could explain what you wanted and were clever enough to talk your way into the back room of a craft beer 'shop' you might see one, or even a home made one.
If you could find out how fast it cooled down a batch and feel the waters temperature at the discharge hose you could tell if it would work for you !

While They do say free shipping, There probably is a surcharge for the U.S.V.I. but it would make life simpler if you could get it Fed Ex'd to the Island and have a
tracking number conformation that it was waiting for you, well heck, that would be O.K., wouldn't it !

The price is not bad, check that against what a big box store would do for you. It looks like that unit has brass water hose fittings, While a short piece of large diameter
washing machine hose might be just the ticket, make sure you know which direction of flow its supposed to give best cooling, and then check about 10 times when you
hook it up !

Looking better by the day, and it will be more fun hustling into the back room of a Brewery than a Plumbing Shop ! Big AL
 
Glenn Herbert
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If you can get a purpose-built heat exchanger unit for not too much more than plain copper tubing, by all means do it! My suggestion was for simplicity and accessibility of materials as well as cost.

If you used 3/8" copper for a heat exchanger, you could increase the flow and/or effectiveness by hooking up two coils in parallel. You would want water circulation around all parts of the submerged coil, so there would be a definite limit to how much you can practically fit inside the top half of a drum.

If you have concrete walls and roof as you said, locating the storage or collector drum near a corner would let most of the weight transfer directly to the walls, not stressing the roof.

A piping coil spread on the roof would certainly give faster heat, but if you don't need to constantly replenish it for frequent use a batch heater might be as good, as long as it stores enough heat for your evening/early morning use. You probably don't want any more adjustable parts than absolutely necessary, unless you can count on inhabitants to tend the opening and closing (and angle-setting?) every day.
 
Charles Heller
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Hey - You guys still around?? -- Getting closer to my trip and building the shower. I've decided it's likely I can get the temps. I need to kill the stuff I want to kill, so I'm leaning toward not using an internal heat exchanger of any sort - but, I have another "quick question".. Utilyzing the basic idea in that "Costa Rica design... To what height do you suppose "thermo-syphoning" would be effective? If the collector ended up being on the ground and the tank were on a "tower" 10 or 12 feet above it.... Would that hot water still make it up to the tank
Thanks!
 
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The bigger the height difference, the -more- effective the thermosyphoning will be. If you can insulate the hot line, so much the better. Really, insulate both lines would be better. It will work without the insulated lines, but better with...

Big lines work better than small lines for low pressure differentials like all thermosyphon systems.


troy
 
Charles Heller
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Troy Rhodes wrote:The bigger the height difference, the -more- effective the thermosyphoning will be. If you can insulate the hot line, so much the better. Really, insulate both lines would be better. It will work without the insulated lines, but better with...

Big lines work better than small lines for low pressure differentials like all thermosyphon systems.


troy


Hmmmmm... okay - Thank you!
 
Troy Rhodes
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It is helpful if you understand why it works.

Imagine, as you walk up to the water heater thermosyphon unit, that the hot water line is on the right, and the cold water line is on the left. The hot water expands a little in the collector, and becomes less dense. The cold water doesn't.

So the cold water in the left pipe "outweighs" the hot water in the right pipe. Functionally, it's like they are on a teeter totter. The cold water is the fat kid, and the hot water is the skinny kid.

The cold water will go down, forcing the lighter hot water up. If everything is on the same level, like if the teeter totter board was laying on the ground, the difference in weight doesn't matter, nobody goes up or down. It's the elevation that makes thermosyphon work. And the hottest part has to be on the bottom, in this case, the solar panel. And the coldest part, the storage tank, has to be above it, to allow the cold water to "fall" and the hot water to rise.

More elevation, better thermosyphon action, within limits.


hth,

troy
 
Charles Heller
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Interesting - I was just assuming that it was just "heat rising" - but that make more sense.
Thanks again!
Chuck
 
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