storage tank chosen- now evaluating HX options

[pybyr]

Hello all--

I've settled on a design and source for my storage tank

since I have to get it down a bulkhead hatch and into my low-height old house cellar, it's going to be a sectional 6 x 6 x 5 foot unpressurized metal tank, holding about 1350 gallons, although after you factor in the expansion, it'll only be about 1275 gallons of "cold" water. Insulation will be 8 inch polyiso board (4” + 4”) underneath and on sides, maybe more on top (I have a whole bunch that I got used for free, in decent shape)

now I need to make the decision on type and configuration of heat exchanger, and I'd like to solicit all of your insights. I know it’s been discussed a lot and various people have pursued various paths, so I am hoping to learn from what you all have considered and tried (I _have_ tried to read all the threads, but at times it's a bit of "info overload" especially when trying to sift relative pros and cons and how much is difference in technology itself vs deployment details)

Copper coils are out as far as I am concerned- the material is too expensive

I’ve been leaning towards a plate heat exchanger with two back-to-back circulators for reversible charge & draw directions, as WoodNotOil is doing (so as to be able to try to maintain stratification in the tank)- but would appreciate further confirmation that this is likely to be a good way to go

I occasionally come back to the idea of PEX coils- with the main appeal being slightly less complexity than the plate HX, but I wonder if the coils will sag, or just be a big hassle to make/ install/ support

For the plate HX, if I go that way, I would appreciate suggestions on inlet and outlet configurations (into and in the tank) that’ll flow well while preserving the stratification of the tank as much as possible; it seems like I'll want to draw from/ flow to broad horizontal "zones" at bottom and near the top, with as little turbulence as possible, and I am trying to think of non-complicated ways to do that.

Thanks in advance for the input

 

[Nofossil]

The dual pump system seems like it will work fine.

As far as stratification, I'd think about a horizontal capped pipe with a bunch of holes along the sides, above (or below, for the bottom) a flat plate that extends a goodly distance to both sides of the pipe.

 

[WoodNotOil]

I am planning on using the horizontal pipe with holes to slow the flow down and reduce mixing. I had not thought of capping it, good idea. I am going to skip the flat plate over the pipe because my tank is almost 12' long which I hope will slow the flow enough. If not, I can add the plates later.

Just a word of caution about a 5' tall tank. For some of this work you have to get inside the tank. Mine came out at just under 4' and it is hard enough getting in and out. Depending on ceiling height this may or may not give you trouble.