Storage tank symmetry important?

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mapratt

New Member
Jan 12, 2011
45
Coastal Oregon
Gentlemen -

Finding used propane tanks; my guy up in Tillamook thought he had "locked in" two 500-gallon units, but one slipped away.

So, question - when installing two tanks for thermal store, how important is it to have symmetry in the capacity and in the size / shape? The one he has locked in is an older one and is not the current sort-of-standard size (it's a bit wider and shorter than normal).

Thanks much!
 
One other thought to add to the query... I'm planning to install the tanks vertically, and to plumb straight out of the very top and very bottom.

thanks again -
marilyn in coastal Oregon, the sheep dairy lady

(I tried to search for an answer, but wasn't clever enough on my search criteria...)
 
Marilyn said:
One other thought to add to the query... I'm planning to install the tanks vertically, and to plumb straight out of the very top and very bottom.

I can't see any significant problem with one tank being shorter than the other. Imagine that you had two identical tanks side by side, but one tank is two thirds of a tank higher than the other. When charging with hot water the top of the higher tank would fill first, then both tanks, then the bottom of the lower tank. There would be some effect from the piping not being absolutely symmetrical, but when the pumps are off everything would settle out.

Since you're going through the trouble of having ports installed at the apexes of the ends of the tanks, may as well go with at least 1.5" for the ports themselves in order to minimize flow velocities entering the tanks. The piping to and from the tanks can be smaller depending on your boiler capacity, but the ports themselves ought to be big to cut down on any jetting effects.

--ewd
 
I would try to find the same size and shape If possible. either way be sure to plumb them as evenly as you can. I didn't get my plumbing perfect and have to throtle one tank back to make them charge evenly. I went with 1 1/4 fittings on my tanks and get very little mixing.
 
Tarm Sales Guy said:
I think the only way to deal effectively with dissimilar sized tanks is to plumb them in series instead of parallel. I would appreciate hearing others' thoughts on this. Chris

Imagine a pair of tanks, each shaped like a wine bottle, side-by-side, one right-side up and the other bottom-side up.

Plumb them in parallel with reverse-return or some other symmetrical piping. No problem.

Now replace the the necks of the tanks with sections of pipe. No problem.

Now replace one of the tanks with a full height tank whose height is the same as the other tank plus its pipe neck. Still no problem.

--ewd
 
I think Eliot's suggestion to weld in larger ports is very good. The cost of the fitting itself and the welding would only be very little more to use larger ports than the rest of the piping.

I would use 2" (biggest size that is easily available ) and run into the tanks with 2 or 3 feet of 2" pipe before the tank to give the water a chance to slow down before it gets to the tank.

Piping them parallel would probably not be a problem but I think doing them in series would always be optimal and not subject to minor effects of the piping not being balanced.
This may be why you see so many European schematics on the web done in series. But if for some reason parallel is easier I wouldn't worry about it. Just try to get all the round-trip runs to each tank and back to be the same length and with the same fittings.
 
If you can plumb them parallel it will reduce the flow velocity into the tanks, and reduce the mixing, Plumb them in reverese parallel if you do. Have the output to the emiters come off the higher tank because at steady state, the heat will thermal syphon to this point, and you want to draw from that. If you are going to plumb them in series, because its easier, then the size/shape difference of any tank combo will make absolutely no difference.
 
plumbed in parallel 2" fitings are overkill unless your moving a masive amount of water per min. I get very little mixing with 1 1/4" on my verticle tanks even if I turn My circulaters on high.
 
Tarm Sales Guy said:
I think the only way to deal effectively with dissimilar sized tanks is to plumb them in series instead of parallel. I would appreciate hearing others' thoughts on this. Chris

The only problem I see with series would be with the distance that you keep the tanks from each other. I only have 1 1/2" between my tanks as I wanted a small footprint for the tanks so I could maximize the insulation around the exterior of the tanks and I could wrap the tanks with a cable to secure them together. With this, if you plumbed them in series, you would have a large temp variation between the tanks at the bottoms until you had them completely charged. I like the idea of series as it would be allot easier to plumb, and you don't have to worry about getting the water flow balanced with two (or in my case four) tanks. I think the ideal would be multiple tanks plumbed in series with each tank insulated independently so one tank could be at 180 degrees and then next one at 100.
 
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