Those softanks look great-I looked into them a bit. Like Daox said, you need a lot of tanks (or a lot of $ for a big one). If you have more than one tank, you can't take advantage of the simplicity of stratification. I doubt the advantages of multiple staged tanks outweigh the benefits of a single simple stratified tank-I suppose it would depend on the situation.
The most efficient storage shape, considering volume inside divided by surface area, is the sphere. The next best is the cylinder, like the softanks. The closest easy to fabricate shape is the cube. Heat loss is a function of surface area, temperature differential, and the heat conductivity of the whole package. The heat loss that really matters, though, is how much you lose vs. how much you can store, assuming you have a heat source large enough to bother with storing anyway. A 4x4x4' tank holds 478 gal and has 96 square feet of surface area, for 0.2sf/gal. An 8x8x8' tank holds 3,830 gal and has 384sf of surface area, for 0.1sf/gal. A 16x16x16' tank (sorry, I couldn't convince Charmaine to let me build it!!!) holds 30,640 gallons and has 1536sf of surface area, for 0.05sf/gal-1/4 of the loss area per volume! So if the purpose is to store heat when you can get it to use when you can't, and any heat you lose through the tank does you some good anyway in 6-9 of the 12 months (meaning the tank is within the building envelope), it makes sense to build as large a tank as is practical so your loss area compared to storage capability is as favorable as possible. Multiple 60-120 gal round tanks? Don't even get me started!!
|