Heat bank design
Heat Bank Concept Sheet
Copper Coil Schematic
(please note that the it should read "one 1.5 and one 2 foot diameter" in the figure above)
By nesting two copper coils in this way we can fit over 80 feet of 3/4" pipe into a 2 ft. cube. The outer coil will have a diameter of 2 ft. with 8 loops giving us 2*3.14*8 = 50.24 ft. of pipe. The inner coil will have a diameter of 1.5 ft. also with 8 loops giving us 1.5*3.14*8 = 37.68 ft of pipe, for a total of 87.92 ft. Our calculations indicate that this will provide us with a significant increase in the temperature of the main water before it enters the electric hot water heater.
The Finished (almost) Product
We ended up reusing the 30 feet of 1/2 inch copper pipe from the experimental phase as we were running short on time and couldn't find a supplier of 30 foot sections of 3/4 copper pipe. Since taking this picture we have added two more support bars so it looks less off center. We also cut the hole in the big plastic box and the copper section fits in nicely.