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Heat Exchanger Assembly

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Eric Johnson, Dec 25, 2007.

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  1. Eric Johnson

    Eric Johnson Mod Emeritus

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    Kids, don't try this at home!

    I know it's outrageous, beyond the pale, ridiculous, absolutely insane.......

    But making it was a lot of fun, and I appreciate all the design help and advice that everyone offered.

    This is two heat exchangers. The one on the bottom is for heat storage; the one on the top for recovery. In total, there's 110 feet of 1/2-inch copper in each hx, and approximately 60 feet of 1". The storage hx has 1" and 3/4" connections so that I can dump the entire output of the boiler into the tank in the summer. Hopefully. All pressure tested with water and no leaks, of course. Well, OK, there were two fitting connections that I forgot to solder, and they leaked.

    Next weekend it goes into the tank.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    Together at last......

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  3. Hbbyloggr

    Hbbyloggr New Member

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    Where are the wheels ?

    Merry Christmas,

    Hbbyloggr
  4. kuribo

    kuribo Feeling the Heat

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    Merry Christmas!

    How did you calculate the length necessary? Any reason you built something out of fittings rather than simply used coils of copper?
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    It's not all fittings. All the 1/2-inch pieces are soldered into holes drilled in the 1-inch. Basically, that's what I had on hand and it's something I've always wanted to try. All those connections obviously are at risk of springing a leak. I wouldn't recommend a project like this; once I got started, it kind of took on a life of its own.

    Attached Files:

  6. kuribo

    kuribo Feeling the Heat

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    Did you do any sizing calculations on the length necessary to achieve the heat transfer you require?
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    I need to transfer about 200Kbtu at theoretical maximum output, which is pretty unlikely. According to the numbers I came up with, 200 feet of 1-inch copper is the required heat transfer surface for that output/input. So it's close. To decide the spacing on the 1/2-inch, I just calculated the number of tubes on each unit required to move the amount of input, which in this case is one 1" line and one 3/4-inch line. A 180-foot 1" coil or 600 feet of pex would probably get similar results.

    The assembly basically fills the tank, with about a foot all around to spare. The input and output assemblies are positioned to maximize their function in the tank, at least according to the specs I was given by a couple different people. A friend of mine at the Forest Products Lab got me hooked on the two-exchanger approach. I'm going to pipe a bypass into the system, however, so, that I can bypass the tank when desired. I have a one-inch three-way zone valve that I may eventually try to connect to automatically make that decision, once I figure out what I want it to do.
  8. kuribo

    kuribo Feeling the Heat

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    Looks good! Congratulations on completing them- it must have been a tedious process!
  9. Bartman

    Bartman Member

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    I think you should go into metal sculpture, it certainly looks like a work of art. By the way, I need directions to you place, I think there's enough copper there to pay for a new truck........... :cheese:
  10. Bartman

    Bartman Member

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    Man, I've got to get a new keyboard, these keys are so stiff I keep missing lettrs..........
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    I priced 1" soft copper and it was $5.50 per foot. I had a bunch of 1" rigid copper that I got for about $1 a foot about four years ago, and used to pipe my first boiler. I bought some pex-al-pex for about $140 a foot and salvaged 100 feet of my rigid copper. So that's $150 out of pocket for the pex, plus another $1 a foot for the 1/2-inch, so that's another $220. Most of the fittings I had laying around, but let's say I spent another $100 on misc. parts. So that's just under $500. If you don't count the hours of design and assembly time, plus the potential for leaks, I'd say I came out ahead. Plus, I got an exchanger designed for my tank, instead of a two-way coil, which I don't think would work as well. Maybe I'm wrong. We'll see.

    Bartman, I'm about 5 miles off the Thruway, Westmoreland Exit. Drop by any time you're passing by. If you want the copper, you'll have to dig it out of the tank.
  12. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    Eric-

    That's very similar to what I did except I used fin tube. Mine has only been in use for a few days but it seems to be working. My return water is always the same temp as the tank water so I think I'm transferring all the BTU's. It took me a couple of days to get my 750 gallon tank from 50 degrees to 175 degrees. It seemed to average about 3-5 degrees per hour. The Tarm never got up to temp until the tank was above 160 or thereabouts.
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm glad to hear you got it going. Are you saying that you could fire the boiler full-out and the tank would absorb all the output so that the boiler never went into idle mode? If so, that's great--that's what I'm hoping for. Can you bypass your tank so you were able to heat the house while getting the tank up to temp?
  14. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    While I was heating the tank the gas boiler was heating the house. My boiler has not done any idleing yet because the tank is always calling for more. The only time the fan has shut off was when the tank temp was 175 and the boiler was at 190. I'm having a hard time keeping tank temp above 150 but I have not been running the Tarm 24/7.

    Reggie
  15. Bartman

    Bartman Member

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    What kind of heat loss do you guys think you will have with these tanks? Where are they located, outside?
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    Mine's in the basement. It's a concrete cistern with 2 inches of foam insulation and an EPDM rubber pond liner.
  17. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    Mine is also in the basement. It's 8 inch concrete block with the cores poured solid. I used 3 inches of celotex on the outside of the block and 4 inches on the lid. I don't think there will be much heat loss. At some point I'll bypass the storage tank and measure the heat loss over a few days.
  18. leaddog

    leaddog Minister of Fire

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    It would be interesting if you would take some readings of your basement temps before you fire up the storage and after and see if you are loseing much heat that way. I was wondering how well 2in of foam was working. When my son does his we are thinking of putting it in the ground as that seems to be the most cheapest and easiest way to get lots of storage. I'm trying to come up with the best underground insulation.
    leaddog
  19. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    By underground do you mean the top would be flush with the basement slab? If it's new construction you could buy the lower half of a pre-cast 1500 gallon septic tank and insulate it before backfilling.
  20. Grover59

    Grover59 Member

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    That is a great looking HX, it does look like a lot of work you really must take this as a hobbie, I know it is becoming an addiction for me.

    Steve
  21. leaddog

    leaddog Minister of Fire

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    I'm thinking more of a hole under ground with insulation then blocks or poured concrete or treated wood constuction lined with epdm. You could make it 8ft deep to get good stratification and the water would equalize the ground pressure. You could make a 2000gal or more tank that would be out of sight and easy to get to. The cost wouldn't be that great and the outside sq. surface area for heat loss would not be much more than a 1000gal tank. The advantage of a tall tank and not having to reinforce it as much would be a real plus. A septic tank wouldn't have the height and you would still need to line it with epdm as you wouldn't want any leakage to the insulation. The other advantage is you wouldn't have the frost worry because with 2000gal under ground it would take some really cold to freeze.
    leaddog
  22. bbb123

    bbb123 New Member

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    I have the stss tank with the Tarm and during the summer I figured I lost around 1 deg. a day. That has 2 inch foam insulation, liner and aluminum skin. What I did find in the summer on my system the circulator for the storage tank goes off at 160 (pipe temp by Tarm). So heating it much over 160 is a waste cause it just keeps circulating the hot water around the system till it cools down. Reggie I'm getting about 10 deg. an hour into my 800 gallon tank with twin 180x3/4 copper with no call for heat. Mine does not shut off till around same temps 170ish tank. With this recent weather I've been burning once a day about 1 1/2 loads of wood I even skipped the other day when it rained out all day. I'm heating around 2500 sq. ft. of 80 year old 2 story blown insulated, 3/4 blue insul. and new windows house. Ow and my tank is in the basement.

    If I ever did build a new house it would have a 2000 gallon tank built right in the floor (either tank or pour it with foundation). Simple frame over top how sweet would that be. If I only knew there wasn't any info around 2 years ago!

    Nice job on HX Eric I pressure tested the coils with my tank cause I didn't solder them. They were fine but that would suck if I got that all in there and it leaked.

    Good Luck and MERRY CHRISTMAS everyone!!
  23. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    BBB-

    Are you using the Termover valve? Do you keep the ball valve on the return to the boiler open half way? My ball valve has been wide open and I just shut it down to half way. I hope this will send more hot water directly to the tank instead of back into the boiler. you have a lot more heat exchange than I do. I have around 150 feet of 3/4 copper with fin tube. I have no idea how much the fin tube helps.

    Your under slab tank would work well. I almost went that route but I didn't have it all figured out in time.

    Reggie
  24. bbb123

    bbb123 New Member

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    I have 2 termover valves I dont touch anything ever (except the temp dial on boiler). Mine don't send water anywhere till boiler reaches 140. I had the house resided summer before last and still didn't put the oil tank back in yet. Sounds like your getting about 1/2 the heat transfer I am. Are you getting gasification if your woods not somewhat dry they don't work. You can mix some wetter wood in after your up to temp but not much.
  25. kuribo

    kuribo Feeling the Heat

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    I think that ideally, you would want the tank within the building envelope. That way all the heat loss through the tank goes into the building to indirectly heat the structure, increasing efficiency.
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