Water-to-water Heat Exchanger. Wow, soft copper pipe is expensive

[markmudd]

I have two 60 ft coils, 120 ft total. They are supplied by 1 inch copper line in parrallel, in that water does not run thru first one and and then the other, but that each coil recieves same temp water by dividing the 1 inch line into two 3/4 lines then reuniting lines after coils. I know That is less than a lot of folks with technical expertise recommend, but it works good for me. It is controlled with valve in that I simply adjust flow to tank coils based on heating situation and then whole system slowly cools and supplies heat after fire is gone. Obviously not a high tech system and I would probably use primary secondary type of plumbing if I had to redo but I did not know of this site when I did it. I ahve a royal 6150 boiler which is a good unit, but again not a gassifier. Missouri climate is moderate and I have lots and lots of wood.

TAnk is 500 gal made out of 2x4 with 3/4 plywood and 2.5 inches of polyurethane insulation and 1 inch of blue board foam on exterior (between 2x's) and 1 inch blueboard on interior behind liner oer 3/4 plywood with osb on exterior. Have a single top center support to keep tank from speading on top and 2x4's run horizontal and are bolted at corners. For top I layered 5 1 inch thick blueboard sheets with EPDM on innermost top panel.

Do not recommend use of blue board for high temp. Use the Polyscianate stuff (spel?) I also messed up on installing my liner and need to re do it to have a better seal around top edge. but it holds heat well. Plan to fix liner this summer.

 

[Duetech]

Sorry to say I don't share the "real world" consensus concerning coiled copper. Seems like a terrible waste of cold cash. It would be a lot of work but hard copper and solder will make a submersible heat exchanger of probable equitable (or better) output for a lot less money. Look at an air/water heat exchanger like used in a fossil fuel furnace plenum. A custom "built to your size tank" exchanger using 1" reduced to 1/4" and back (like in the above mentioned exchanger) will extract or collect large btu's. It is labor intensive but you can place your exchanger in the tank right where you want the conversion to take place and not through a portion of the tank that is prone to rob efficiency. The hard copper exchanger will take up less room and cost less to build. IMHO

I priced hard copper and soft copper. Soft copper was cheaper. You can get hard copper a lot cheaper where you are? How much less it it than soft copper?

Foot for foot it is probably not cheaper going to 1" hard copper from soft but the point is to look at a heat exchanger like they use for air/water as in a furnace plenum/boiler conversion. In a simple 1" 20" x 24" air/water exchanger there are usually two 1" tubes and about 16 quarter inch tubes to transfer water from one 1" tube to the other 1" tube. The smaller tubing is what passes through the fin medium that transfers the heat to the air as it passes through the fins. (the heat is transfered through surface area...imagine trying to put 240 feet of copper tubing in a plenum for heat transfer...lol). If a person were to build a similar tubing arrangement for heat transfer inside of the storgae tank it would of course be bigger but would not need 240 feet of 1" tubing and water is probably much better than using fins. Example: in a 4' x5' by 5' tall tank you would position a home made exchanger near the top and one near the bottom of the storage tank. Each exchanger could have three (or two* if you know you can get the tank water to flow at a rate to keep up with the heat transfer) 1" pieces about 5' long and fourty-eight (or 36*) 1/4" pieces about 4' long (to go across the tank and back* and across again). That is a lot of cutting and 1' to 1/4' tees and a lot of soldering but the 1/4" copper will give you 4x of the surface area of 1" copper and the heat transfer would be superior to 1" copper. If a person were adept at bending they could eliminate a lot of soldering. In my area 1/4" is cheaper than 1" and that is what I was refering to about being cheaper to build. Soft copper could probably be used but then you have a lot of flaring and fittings to account for. Sorry for the confusion.

 

[jebatty]

The Tarm Solo 40 states 140K BTUs, but is that input BTUs? Assuming 80% efficiency and that being input BTUs ....

This is the output rating, not input. You probably can use 70-75%, not as an efficiency number, but as average output over a burn. At high burn the Solo 40 can output more than 140,000 btuh, but that won't last very long. Humming along at around 100-110,000 btuh for a good part of the burn should be about right.

As to actual output, I determined that last year when I had a flowmeter installed, since removed.