My Tank construction and experimental Hex

Where did you get the liner?What is the temp.rating?

Hi Sparky I am very impressed with your incredible ability to get right into a project , design ,construct ,test ,improve . Do you have a crew ? Your back yard looks great for a solar project . Anthony

You might want a bit more insulation once it's done to reduce standby loss - especially in the summer.

Two questions:

1) What provides the 'hoop' strength to resist the water pressure?

2) How will you prevent evaporation?

sparke said:

nofossil said:

You might want a bit more insulation once it's done to reduce standby loss - especially in the summer.

Two questions:

1) What provides the 'hoop' strength to resist the water pressure?

2) How will you prevent evaporation?

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1. Do you mean system pressure? If so, the hoops are tie wrapped every 2 inches on the 3 vertical supports. The tensile strength of the tie wraps are 40lbs.
Do you think this is going to be a problem??

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I believe he's asking what will provide resistance against the sides of your tank falling outwards when it is filled with water. The taller the tank, the more hydrostatic pressure is exerted.

Just a little advice regarding the insulation... any foil faced insulation should be facing out towards an air barrier. Remember, aluminum has a very high thermal conductivity... so if it is in physical contact with another solid it will promote heat transfer from your tank.

The reason it is used against an air gap is, air has such a low thermal conductivity, heat conduction does not represent a large loss even with the increased conductivity of the foil. The foil, however, has a very low radiative emissivity, meaning it will radiate very little heat to its surroundings. So the idea of foil faced insulation is, by putting it adjacent to an air space, the air itself prevents against conductive losses, and the foil reduces radiative losses.

Probably not a tremendous amount... it just won't help any, but having a thing layer of very conductive material in your insulation should be much penalty being surrounded by very thermally insulative materials.

sparke,

Why did you chose 800' of 1/2" pex? Did you compare heat transfer rates with copper?

Are all four 200' coils reversible - used for both heat in and heat out?

Did you research the "submersible" quality of the pex?

For my 600 gallons of unpressurized storage, I am thinking of using 1000' of 1/2" pex for $290 http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200205852489 instead of 180' of 1/2" copper for about the same price (actually more for completed auctions) http://cgi.ebay.com/1-2-60-ft-TYPE-L-WATER-Copper-Tubing-Coil_W0QQitemZ140212959413QQihZ004QQcategoryZ63902QQssPageNameZWDVWQQrdZ1QQcmdZViewItem.

Very cool setup and thanks for posting,
Steve

sparke said:

Liner - Polypropylene 45 Mil

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Before you install your tank lining, I suggest you research independently and carefully the temperature rating of the poly liner. My quick research on polypropylene liners, including 45 mil, shows very good low temperature performance but most specs do not even indicate a hight limit, as this material seems to be principally sold as a pond liner or similar application.

This site shows a melting temp as low as 142F and a softening temp as low as 95F. The site also indicates the poly extends into much higher temp ratings, so different grades of poly appear to exist. Check out your liner specifically, just to be sure. http://www.polymerprocessing.com/polymers/PP.html

You would not want to find that your liner was dissolving into your hot water return line, to congeal or be deposited (if that happens) in your plumbing/boiler, etc.

This cite talks about poly liners for steel tanks. Since the focus is for this specific purpose, I would be cautious about giving the temp rating too much credence, if your liner is for ponds and not tanks. Also take a look at the info on stress as the temp changes. http://www.fisherutah.com/technical-docs_files/Polypropylene.pdf

I investigated polypropylene tanks for my hot water storage and decided against poly tanks. I found that most of the tanks within a reasonable price range softened at around 120F and could start melting at 140F, which is consistent with the above cite. I did find that high temp poly tanks were available, but they were very expensive and way outside the price range I was willing to pay.

Unless you are sure about your poly grade temp rating, think again about EPDM, which appears to be fine in temp rating for boiler tank lining. https://www.hearth.com/econtent/index.php/forums/viewthread/14864/

sparke said:

SteveJ,

Why did you chose 800’ of 1/2” pex? Did you compare heat transfer rates with copper?

When STSS did a quote for me , they quoted 240' of copper(2-120' coils). I think copper transfers around 3X that of pex. So that was 720' fo pex and I just rounded up a bit. 200' per coil worked out perfect with the height of my tank.

Are all four 200’ coils reversible - used for both heat in and heat out?

Yes, I will post a schematic later. I am changing my system from series to parallel. The project got a bit more time consuming when I decided to do that.

Did you research the “submersible” quality of the pex?

No, I got the idea from EricJeeper who uses pex in his tank.

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That 3 times number just doesn't seem correct to me for conduction. If the the link I've attached is an indicator it would seem like they vary by a factor of ~ 800 times. Perhaps I'm missing something ....over or underthinking as usual.

Hugh

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

sparke said:

Were you using the polyethylene? I agree that math does not work but something is awry. Maybe because they are just comparing the material in its raw form, not cross linked, or anything else they do while manufacturing, etc...

EricJeeper says his 500' of 1/2" pex in a 600 gallon tank works like a champ.

Since there is no hard data besides peoples experiences - This is why I am calling it experimental

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sparke,

All of the "plastic" types seem pretty consistant in regards to their conductivity. Cross linking is used for strength purposes not heat transfer purposes.
That said, I have always thought that the copper heat exchangers were often way oversized if there is a fair amount of convection going on near the tubing in the tank. If this is so then if might account for Eric not having problems with pex his installation.

I would love to see a link to a reliable source that shows copper only having 3 times the conductivity of PEX.

Hugh

I continue to have trouble understanding why the choice to go with a big coil hx when a flat plate for about 1/3 the cost can perform so well. I know an extra pump is needed, but pumps today are very economical. The flat plate 5 x 12 x 30 plate I use (pd $200) will load my 800 gallons of storage from 80 to 150-160 in about 6 hours, and at the low end and until storage input to hx reaches above about 130 can take all the heat my Tarm Solo Plus 40 can deliver without idling.

What are the benefits of the coil hx over the flat plate?

Jim,
Is your 800 gals open or pressurized?

I am moving from unpressurized to pressurized. The boiler side is pressurized already. Storage will be soon, as I move to a 1000 gal LP tank.

My plate hx feeds hot water into the top and draws cold water out of the bottom of the tank, which should result in about as much stratification as one can get. I intend to do the same with the pressurized LP tank.

Jim,
Have you thought about welding a tankless DHW coil such as you get with an oil boiler into you propane tank?
Just something I'm thinking about.

Ed