Am I OK using refrigeration type flexible copper tubing instead of schedule K or L to make a home-made heat exchanger for my unpressurized thermal storage? I plan to use 3/4' OD flex tubing, probably two 100' coils in parallel. Seems like the thin wall refrigeration type would offer better heat transfer. It's also quite a bit less expensive. Is there anything to worry about in this kind of application?
Type of Copper Tube for Heat Exchanger
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I have heard most people using ref copper for their heat exchangers coils and it seems to be just fine. I would say just one concern would be to make sure the inlet and outlet connections to the tank are well supported so you are not relying on the structure of the copper.
What dimensions are you making the tank and what is your placement and configuration for the heat exchanger are you going to use?
What dimensions are you making the tank and what is your placement and configuration for the heat exchanger are you going to use?
Thanks for the response AFBlue. This will be a 700+ gallon tank framed w/3/4' ply and lined with EPDM, based on an online set of plans and pics. Not sure of the complete setup yet, just in the planning stages. Any suggestions for design are very welcome.
I used the refrigeration tubing for 4 150' coils. It was fairly easy to work with, finding the fittings was the only pain, 3/4 ref is not 3/4 plumbing. I did develop a pin hole leak in the DHW coil but my water is very acid and I have had problems with my regular plumbing as well.
I find that 2 150' coils work well in my 1200 tank. I mostly got my numbers from STSS. I also have one 150' coil for DHW and one for solar.
I find that 2 150' coils work well in my 1200 tank. I mostly got my numbers from STSS. I also have one 150' coil for DHW and one for solar.
I don't think you would need to waste your time with a coil heat exchanger in a non presurized tank. Simply run an open hose underwater to bottom of tank. Than for return line it will be a suction copper or pex sucking from bottom of tank, no worry about heat exchangers that way and the tank gets hot because water is circulating, so simple. I don't know why no one talks about that design?
chesterewers said:
You still need a heat exchanger to separate the pressure/non-pressure sides of the system along with an extra pump. I also believe there would be cavitation on the non-pressurized pump suction due to flashing of steam in the inlet, especially at higher temps if you don't have pressure there. The pump's life would be really cut short.
steam man said:
okay would you have a drawing or diagram of how to plumb it? I currently just have a loop going to a forced air heat exchanger back to the tarm. The diagrams that I found are for zones. Thanks
A friend of mine, i.e. "Maine" who also posts on here did exactly what you are thinking. He uses an unpressurized storge tank with "dip" tubes, heat exchanger, forced air heat exchanger, and underfloor radiant. He claims it works great. Do a search on here for "Maine" post and I'll also mention this post to him so he can comment on the details.
chesterewers said:
Seems to me if your systym is open with no hx in tank your tank would have to be higher than any othe plumbing or it would overflow.
steam man said:
did a search for maine and came up with 11 pages on results, would you have the exact post link to copy? Thanks
woodsmaster said:
I have seen this work with the tank on the same level. Not sure of the details but the heat exchanger I've seen is at floor level. Perhaps a foot valve in the suction line is used. The tank can have enough reserve capacity for any flow back to the tank.
chesterewers said:
Probably true after thinking about it the tarm has 15 psi up to 35 and that would cause an overflow if the hose is left open in storage tank. I will definitely need to see what the man from maine did.
Whate the flow rate?
@ 10 GPM for 3/4K my drop table shows about 17 ft drop per 100 ft of run.
The velocity is about 7 ft/sec which looks OK.
Is there a spare 34 ft head left in the pump?
I dont have the drop curve for 3/4" refrig piping, but I am assuming that the tube will be a little smaller than 3/4K.
I would tend to go larger on the tube size to minimize head loss. Also the residence time in the heat x increases which should help transfer, however some will argue that laminar flow from the low velocity will hurt.
Also remember that it is recomended that you assist stratification in the tank by sending hot water in the top and cold water in the bottom. I have used a 4 way reversing valve for this.
@ 10 GPM for 3/4K my drop table shows about 17 ft drop per 100 ft of run.
The velocity is about 7 ft/sec which looks OK.
Is there a spare 34 ft head left in the pump?
I dont have the drop curve for 3/4" refrig piping, but I am assuming that the tube will be a little smaller than 3/4K.
I would tend to go larger on the tube size to minimize head loss. Also the residence time in the heat x increases which should help transfer, however some will argue that laminar flow from the low velocity will hurt.
Also remember that it is recomended that you assist stratification in the tank by sending hot water in the top and cold water in the bottom. I have used a 4 way reversing valve for this.
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