Building THE Ultimate Storage Tank

[skidsteer]

Moore questions on Building An Ultimate Heat Storage Tank
I'm using a 1270 Gal Steel Tank Going to spray foam tank to insulate it & berry it .Tank is non pressurize totally enclosed.
I have a question now on the coils that I'm going to make . I'M going to use 3/4 in soft copper bought in 100ft lengths IM going to bend them into coils .AM I better off having two to three smaller coils all series ed together placed in a circle around the tank .Or am I better to make ONE big coil say two to three-hundred ft long and then place the proper size coil into the center of the primary coil to transfer the stored heat to my heating system. And how do i figure how many feet in each coil do i need to supply the proper amount of btu's needed to heat a1270gal storage tank to 180 deg and the same to transfer enough hot water to the house.

 

[heaterman]

RE your coil layout....

You have a couple things to consider. If you pipe 300 ft of tube end to end, you're going to develop some pretty substantial head or flow resistance. You will also be limited to about 4-5 GPM at best through that length of 3/4 tube. The temp rise/drop across that coil would obviously be the highest you can attain all other things being equal.

If it were me I would pipe them in parallel, reverse return, for better flow rates, smaller pump and equal distribution through all the coils.

I assume that you are drawing your usable BTU's from the storage and not the coils.

 

[skidsteer]

I know I need the coils to be hooked to my woodboiler to transfer the heat to the storage tank . what is the best way to get the heat out of the storage tank to my heating system ,if you dont want a pressurized storagetank ? another coil or a hx

 

[Nofossil]

I know I need the coils to be hooked to my woodboiler to transfer the heat to the storage tank . what is the best way to get the heat out of the storage tank to my heating system ,if you dont want a pressurized storagetank ? another coil or a hx

As suggested above, I'd do two 150' coils in parallel, Id use the same coils for charging and discharging - flow top to bottom for charging, bottom to top for discharging. I have a setup that does just that - check out the diagram on my site. Need an extra pump and zone valve to make it work. Let me know if you have any questions.

 

[Jersey Bill]

Skidsteer,
The STSS setup is 2- 120 ft 3/4" coils in parallel which, they claim will transfer 150 MBH with a 20 degree delta @ 15 gpm. (this checks out mathematicaly)

Since the flow is parallel, there will be 7.5 gpm per loop.
From my flow table, thats a pressure drop of 13 ft/100 ft, or 15.6 ft drop across the loops.
Then you have to add the pressure drop through the valve @ 15 gpm, if there is one, and that is what your pump should be sized at.
Allowing a few feet for the valve, (19'@ 15 gpm) in Taco land, its a 013 IFC, a grundfoss is a UP 43-75.

By me, 3/4" soft coils are available in 60 & 100 ft lengths. To reduce the pressure drop to the pump, I was considering using 4- 60 ft coils.
That is only 3.75 gpm per coil. From the table its 4.6 ft/100 ft, or 2.76 ft total. Adding a few feet for the valve, (7' @ 15 gpm) I come up with a taco 014ifc, or a grundfoss up 26-64

It is important that you charge the storage from the top, and discharge from the bottom.

 

[skidsteer]

Jersey bill, Like your thoughts about using smaller coils #1 it cuts down the resistance and #2 since I started digging around on making the best possible storage tank I can I was concerned about putting one or two coils into a six Ft dia tank x six high it to me would not transfer heat well in my mind .
Now since I Posted this latest Blog Yesturday Sven from STSS had E-mailed me back . About a month ago I had contacted him for some help and a price quote .
I got impatient and began scrounging up materials from the info from all of you guys to start building my own system after not hearing back from him.
Now I am already on my way I have some soft copper to start my coils but didnot purchase all of it .Sven had quoted me 957gal tank with three 180Ft coils based on my heat load one coil is for domestic which at this time im not going to do because the way im going to pipe my system I dont need it I already have a boilermate .
That sparks this question should I put six 60ft coils in my tank to = the amount of the two 180 ft coils OR Is that a total over kill
My tank is 1270 Gal

 

[jebatty]

I considered the stss tank and copper coil hx. I asked my Tarm dealer for info on how much copper I needed. FWIW, following is a copy of the reply:

Here are some answers to your questions:

The first one dealt with how many feet of 1" copper would be equivalent to 360' of 3/4" copper. I don't have a direct answer but do have some thoughts. One is that 279 feet of 1" copper is equivalent to 360' of 3/4" copper. The other answer is that the transfer rate will be dependent on flow rates. I've included a little of my figuring below.

--100' of 1" copper--Tarm USA recommends the 3/4" parallel 180' configuration.

Heat loss per foot of 1" copper "water to air" is about 85 Btu/hr/ft. Heat loss for 3/4" copper "water to air" is about 65 Btu/hr/ft. I wasn't able to find a "water to water" figure but the heat exchange ratio for the two diameters should be in the .76-.77 range. The other way of looking at it is:

1" copper (1.125 OD) has a circumference of 1.77", 3/4 copper (0.875 OD) has a circumference of 1.37".

So, the surface area of 1" copper is 1.77 in x 12 in/ft = 21.24 si/ft
The surface area of 3/4" copper is 1.37 in x 12 in/ft = 16.44 si/ft

360 feet of 3/4" copper is 5,918 si, equivalent to 279 feet of 1" copper.

What happens if you don't have as much? Slower rate of heat exchange. This can be improved if you increase the flow rate through the tube, though I don't have the equations on hand to advise. Look at some of the internet sites under solar thermal storage.