Heat Exchanger Idea

scottinkn Posted By scottinkn, Nov 3, 2012 at 6:54 AM

  1. scottinkn

    scottinkn
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    Oct 12, 2008
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    Because copper is so expensive & I need so much of it to have adequate heat transfer...

    Could I "make" a heat exchanger from copper flashing? Similar to this: HX.gif
     
  2. maple1

    maple1
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    Could you just try a whole bunch of Pex? I don't know what you are wanting to use this for. It doesn't conduct heat anywhere near as good as copper, but it doesn't cost anywhere near copper either. Someone around here would likely have some figures kicking around relating the conductivity of Pex to copper. Or you might find it with some googling.

    That pic you posted looks like trouble waiting to happen, IMO - but I know not much about what it's actually showing.
     
  3. Paddy60

    Paddy60
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    I have considered using aluminum tubing. No luck finding it though
     
  4. scottinkn

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    Wouldn't aluminum corrode? just a thought.

    I may make a box (or stack of) like above and solder short pieces of pipe ((the thickness of the pipe I use for the "frame") and drill them through like swiss cheese) to minimize warping and promote circulation. I wonder how thin I could go with flashing and how high to pressure test.
     
  5. mikefrommaine

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    Sounds like more trouble than it's worth to me. Hard to beat coiled tubing for an in tank exchanger.
     
  6. scottinkn

    scottinkn
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    You are right Mike, easier & faster. I am just wondering if this could work because it would be like 1/3 the price, maybe even less.
    So if I pressure test a prototype to *?* psi, I should be good? (dont know goal psi, but mine right now seems to run about 18-20)
     
  7. Nofossil

    Nofossil
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    First, do a quick back-of-the-envelope calculation of square footage. You can get more heat transfer by moving the fluids better on each side of the HX surface, but if you don't have enough square inches of HX surface, life may be disappointing. I found that soft copper was breathtakingly expensive, but hard copper pipe was not too bad. I used a mix, though as I've mentioned before I'm contemplating forming clip-on copper fins out of flashing to add to my pipes.
     
  8. ozzie88

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    I still say check e-bay I have seen stainless, allum, and copper tubeing for sale in different sizes different prices and lenghts and different size heat exchangers made up already just drop them in a tank and hook up? Best one i seen was one for a steam-jenny, it had large tubeing and big enough to transfer heat for $300 made up already. Just a thought?? Seems like it be less work and less $??
     
  9. scottinkn

    scottinkn
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    well that is one coil, thanks for the link! But I am probably going to go with 1" or mixture of copper pipe, whatever I can get. (I have a plumber friend that owes me for fixing his computer and he promised me some more pipe)

    So, If I do hard pipe HX (in my round tank) should I make a header/riser (like solar collector) type or 1 long zig zag?...are there advantages/disadvantages?
     
  10. ozzie88

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    Water always takes the easy path,so if a header type setting some water may get heated more than other but when doing a [zig-zag] all water is getting heated evenly, this is how i did my dhw. heater in the tank with 3/4 hard pipe and it seems to be working fine, I only have 24 feet of finned pipe but as long as I have 150* or more it heats water ok, more the better they say.
    When taking shower,dishes,or washing maching running is fine, only thing I notice is when running bath I have to put faucit on about 1/3 back from full cause water will cool some,not much but can notice,so some more pipe would have been better I guess. I made a tank for a guy with 70feet of 5/8od copper and it works great, I dont see why some of these guys use 200-300 or more feet of it?? Look at how small some of these coils are that come in oil boilers,I know there made different but wow, alot smaller?? good luck,hope this give you something to think about?
     
  11. BoilerMan

    BoilerMan
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    Domestic coils in oil/gas boilers are always finned copper. They also need the boiler to be at least 140F to work with any reasonable performance. Usually the boiler must maintain 160F for a bath to be drawn or around 4-5gpm@70 degree rise. This is why guys have lots of copper in the tank, to get a lower delta dur to the greater surface area. Domestic coils are very innefficient (but cheap) and are prone to scale buildup.


    TS
     
  12. ozzie88

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    i ALWAYS CLEAN MY COILS ONCE A YEAR, HAVE TWO VALVES ON THEM AND RUN LIME-AWAY OR CLR THREW THEM GET ALL THE SCALE OUT. jUST LIKE ANYTHING ELSE HAVE TO TAKE CARE OF THINGS TO GET THE LIFE OUT OF THEM. IF YOU HAVE SAY HAVE 300FOOT OF COPPER IN A COIL THE WATER PREASURE MUST BE HIGH OR YOU JUST GET A DRIBBLE OUT THE END WITH ALL THE FRICTION IN THE PIPE?? ALL I HAVE TO GO BY IS TANK I BUILT, LIKE I SAID I PUT 70FEET OF 5/8 TYPE L COPPER AND IT WORKS FINE,I GET ALL HEAT I NEED IF TANK IS 150* WATER COME OUT IS SAME [AND I AM TALKING COLD MAINE WELL WATER GOING IN] SO WHY WOULD 300FEET DO ANY BETTER? JUST REDUCE FLOW IN PIPE, I GUESS MORE IS BETTER BUT REALLY ?? TO EACH HIS OWN,,
     
  13. scottinkn

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    Thanks guys but I still would like to know: So, If I do hard pipe HX (in my round tank) should I make a header/riser (like solar collector) type or 1 long zig zag?...are there advantages/disadvantages?
     
  14. Bob Rohr

    Bob Rohr
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    I would sugget a header with 60 foot loops. If you look at the manufacturers that build high performance coil in tank HX, like this TurboMax brand you generally see multiple loops headered together. Pressure drop is the main reason, surface area and the ability to get a lot of surface area inside the tank is another.

    I see more and more manufacturers using corrugated stainless steel tubing for tank heat exchangers. Not as good as a conductor, but lower cost, more surface area, better turbulent flow inside due to the corrugations, and handles most water conditions.

    Also a shot of a tank built in Kansas for solar HX. They use a sprial tube for addition flow turbulance.
    www.solarheatexchangemanufacturing.com/NewFiles/products.html

    Stainless corrugated tube manufacturer

    easyflexusa.com/2.0/content/water-line-system-0
     

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  15. Fred61

    Fred61
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    I used two 100 foot coils of 3/4 L manifolded and run in parallel. Six feet from bottom of tank to top. Domestic water spends alot of time in the bath. I can shower with tank temperature down to 110*, Mostly hot flowing from shower head of course. I was going to solder some butterflies of copper roofing on that I had laying around but I didn't have the patience. Wanted to GIT ER DONE.
     
  16. scottinkn

    scottinkn
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    Thanks guys I will look into it! ...I actually just might have found like 40' of 2", 150 feet of 1-1/4" & 100' of 1"...I hope that is enough!

    ...For both DHW preheat and boiler HX....
     
  17. scottinkn

    scottinkn
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    Well the large copper pipes from craigslist did not pan out. Damn.

    One thing that did occur to me though, for an efficient, low cost heat exchanger idea, is that I could probably use old cast iron radiators ganged up. Just trying to think outside the box & recycling is good!
     
  18. scottinkn

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    Does anyone think ganged cast iron radiators would work well?
     
  19. ozzie88

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  20. scottinkn

    scottinkn
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    Well thanks for the encouragement!!!
    I still need help with making a decision on using cast iron radiators as heat exchangers.
     

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