Storage copper coil advice needed

[gorsuchmill]

I'm considering making a storage tank for this coming winter and am likely to use a coiled copper heat exchanger (like the STSS set up). I need approx. 2, 180' coils. I can get 100' coils of 3/4" type L copper for $220 each or 3/4" refrigeration tubing for $120 each. I realize there would be slightly less surface area in the refrigeration tubing given the OD v ID size difference, but other than that is there any reason not to use it given the significant cost savings ($400)? If so, I'm inclined to go with the refrigeration tubing and use compression connections or braze to copper pipe for the few connections that would be required.

If this works, it would make the copper coil setup very price competitive with the external hx setup, after consideration of pumps, hx and operational costs, not to mention having fewer moving parts in the mix.

Your thoughts?

 

[Nofossil]

I used refrigeration tubing for one of my coils. I machined a copper fitting to the right ID so that I could solder it in - no problems.

 

[Bad Wolf]

I made 4 150' coils and used adapters to go from 3/4" refrigeration tubing to 3/4" plumbing pipe.

 

[gorsuchmill]

Thanks for the vote of confidence. An STSS system would suggest 2, 180' coils. I was thinking of 3, 150' coils to make up for some of the lost surface area from the smaller pipe diameter. These would go into a 1,000 gallon tank fueled by a Solo 40. Does that sound about right?

 

[Bad Wolf]

You are not losing that much surface area. 3/4 refrigeration has .198 ft2 per liner foot. Type K has .229 ft2 per liner foot. So a 180' type K would equal about 208 ft of refrigeration tubing.
I put in a TARM excell 2000 with 1200 gallons of storage and 2 150' coils of refrigeration tubing. (the other 2 coils were for my DHW and solar) Once in a long while when I'm up at 170 storage temp with a real hot fire the blower might shut off because it can not transfer heat fast enough i.e. not enough surface area. But thats with a 10 degree delta. My Excell is rated at 102,000 btu while your Solo 40 is rated at 140,000 btu. (thats in a perfect world) so 450' of refrigeration should be more than enough.

 

[gorsuchmill]

Thanks Greg and Nofo, you've confirmed my thinking on this. For about $500 I can have enough tubing to create adequate exhange for a 1,000 gallon tank. I'm guessing the cost of pumps and an external h/x would be a little cheaper (in the $300+ range) initially, but would also have the disadvantage of higher operating costs, more potential mechanical breakdowns and a greater risk of lost efficiency over time in the exchanger unit. For the extra couple of hundred bucks I'll go with the simpler coil design.

Lee