My Tank construction and experimental Hex

[sparke]

I have been working on the tank part time for a few weeks. I am getting close to putting the pieces together and filling it up with water. I made the L shape for 2 reasons. 1. You cant see in the pics but there is concrete on the bottom 1/3 of 3 walls. 2 walls are againts foundation wall. I only need to reinforce the front wall. I will reinforce the walls that have concrete holding the bottoms. The concrete was part of the existing basement.

Ambient Temperature in Basement 60* - 70*

Volume - Approx. 760 Gallons
Tank Material - 2x4 studs, 3/4" Vantek plywood, 16 penny galv. spiral nails, 2.5" & 3" deck screws.
Insulation - R 11 Fiberglass, 1" Styrofoam, 2" Foil faced , bubble wrap.
Liner - Polypropylene 45 Mil reinforced.
Hex - 800' 1/2" non barrier pex (should probably use barrier pex) ( 4 coils - 200" each), 2 - Zurn Pex manifolds,
80' 1/2 copper pipe for support, 6" uv rated Panduit tie wraps ( used UV rated because the temp. limitation was 210* instead of 175* for white tie wraps.

 

[NHFarmer]

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

 

[sparke]

https://www.hearth.com/talk/threads/15568/

The people at Water Saver said it was good for higher temps then EPDM but I could not get a straight answer... The EPDM was not any more expensive so I dont think they were trying to make extra$$$

 

[antknee2]

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

 

[sparke]

No, it is a solo project except the wife helps me hold the frame while we make the coils. Two down two to go. The second one came out much better. It took me a while to figure out how to support the pex. I hope it works because it takes a while to make the coils. As far as the Solar goes. I am sure I am going to get the bug to do do that in the summer. Then I will be asking lots of questions It is my goal to be 100% oil free. I have not burned a drop since I put in the new boiler : )

 

[Nofossil]

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]

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?

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??

2. The lid will be made of insulation wrapped in polypropylene and it will be siliconed to the top of the tank. It will also be covered with plywood for safety.

I do plan on more insulation later.

 

[MarcM]

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?

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??

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.

 

[MarcM]

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.

 

[sparke]

The bubble wrap is foiled on both sides... The tank support is described in original post (even if my thoughts don't translate to paper well)... Basically the tank has foundation support on 5 of the 6 walls. The remaining wall will be bolted to the floor with 1/2' anchor bolts. Then it will have "whalers" (horizontal bracing). The horizontals will then be backed by vertical bracing as well. I don't think the tank is going anywhere : ) Also the pics dont show the 2" of foil wrapped polyisosyanurate styrofoam. Also foiled on both sides...

 

[sparke]

Mark, The 2" styrofoam is indeed backwards. The back side is foiled but it is different then the shiny side. I wonder how much efficiency it will cost me? It is too late to change it.

 

[MarcM]

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.

 

[SteveJ]

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 (broken link removed to 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

 

[jebatty]

Liner - Polypropylene 45 Mil

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. (broken link removed)

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. (broken link removed to 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/talk/threads/14864/

 

[sparke]

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.

 

[sparke]

jebatty, Thanks for the info. I did research it before I purchased. You are right most specs show low temp tolerance only. Scroll down and see where it was tested at 176* C
http://www.google.com/search?source...=1T4SUNA_en___US257&q=firestone+Polypropylene (third link down-open Adobe document)

I will be the guinea pig for this material. EPDM is rated for 175* that is the only reason I went with this material.

 

[SciGuy]

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.

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]

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

 

[SciGuy]

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

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

 

[sparke]

Sciguy,

I do not remember exactly where I read that. For sure on this site and possibly on "builditsolar". I know I have read it at least on 3 sites... I have studied so much on the net I could not possibly begin to tell you where I saw it. I saw cases where pex hex's failed miserably. In those cases the installer used the same amount of pex as they would have copper. Then I have come across success stories like EricJeeper. As you know, there is more involved then just the pex. There are flow rates, head pressure, friction losses, etc...
I made the decision to go for it and see if it works. If it does great I saved about $800. If not I lose about $200 and alot of time. Just look at it this way. If it fails I am taking one for the team I think it it going to work fine.

 

[jebatty]

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?

 

[EForest]

Jim,
Is your 800 gals open or pressurized?

 

[sparke]

I want to maximize stratification. If you explain how to do that with a plate hex and an un-pressurized system I would be very interested.

 

[jebatty]

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.

 

[EForest]

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