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Old AC Evaporator Coil as an air handler?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by deerefanatic, May 2, 2008.

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  1. deerefanatic

    deerefanatic Minister of Fire

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    I've got an old A/C Evaporator Coil from a local HVAC guy for really cheap.. Could I use it as an air handler coil for hydronic heat? I plan to redo the piping so that instead of a serpentine pattern, it makes 10 parallel passes.... Should reduce flow rate and head needs that way......

    It's a 20X20 inch A-Coil with two radiators 15X17 in size....... Copper tube with aluminum fins......

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  2. Redox

    Redox Minister of Fire

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    As circuited from the factory, no, it won't work very well. Refrigerant stays the same temperature as it is boiling, so you want a longer circuit moving from bottom to top. Hot water temp drops as it gives up its heat, thus requiring a shorter circuit. If you recircuited it, you have to go from side to side and the return bends of an evaporator aren't made this way. It could work, but may have a high pressure drop or other problems, like the copper disintegrating when you hit it with the torch. Evaporator tubes are very thin. For all the work involved, you probably want to look into a real hot water coil. They aren't THAT expensive.

    Chris
  3. deerefanatic

    deerefanatic Minister of Fire

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    Yes, I knew what you mentioned...........

    Well, expensive is a term of perspective I guess........ $200 for water coil vs the $10 I paid for this is a large difference.........

    I plan to set it up so that the water splits........ If you look at the tubes of an evap coil, they go across, bend, and run back. The other side of the coil is all open and they solder the turn-arounds on to it, so I can just de-solder them to make it a parallel flow unit......

    I'll try it and let yall know what happens.
  4. leaddog

    leaddog Minister of Fire

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    If it don't work it is worth about 35 to 40 bucks for scrap if you cut off the copper and take all the steel off. copper over $3 lb and the fin tubes $1.50 lb
    leaddog
  5. Redox

    Redox Minister of Fire

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    Most refrigeration coils are made by bending the tube 180 degrees into a "U" shape. This means that one side will have no solder, just loops. These loops will go from top to bottom and you need them to go from side to side. Also, they are put together with hard solder which will require a lot of heat to melt (think oxyacetylene hot). Unless you are very good with a torch, you will wind up just burning a hole in the tube. Don't ask me how I know this... :)

    Chris
  6. deerefanatic

    deerefanatic Minister of Fire

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    Actually, my a coil has the tube running in the desireable side to side orientation......

    Yes, they are brazed. I've figured this out... Already been able to get a few of them apart so it looks good for me... Your's must have been a cheapy specimen! :) LOL!!
  7. heaterman

    heaterman Minister of Fire

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    You'll be far better off finding another 2 or 3 evap coils, buying them and selling them at a scrap yard. That'll give you enough $$ to get a real coil like you need. You should get one sized to provide the required heat at 140* water. Beware of sales guys that make wild claims about undersized coils. If it sounds to good to be true, it probably is. Don't waste your time on the evap coil, it's not the right piece of equipment. You'll get very limited temp rise across it.
  8. Redox

    Redox Minister of Fire

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    See! And he's an expert! :)

    It will work a little, but the extra pump and fan hosepower you will need isn't worth it. If I was going to the trouble of cutting a coil into my ductwork, I would save my pennies (and melt them down) and make sure it's the right coil. Your boiler will thank you for it later.

    We're just trying to help you make the right decision and I hope you don't think we're beating up on you. Lotsa good experience here in the Boiler Room!

    Chris
  9. deerefanatic

    deerefanatic Minister of Fire

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    OK, I give in! :)

    So even with a good flow of water though it (I.E: Rerouting the the lines) it wont raise the water temp much? Not enough surface area or????

    -Matt
  10. Redox

    Redox Minister of Fire

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    This is going to be hard to explain in a short space...

    Even though they both appear to be doing the same job, a refrigerant coil is a whole different animal. You need a long contact time with a refrigerant for it to do it's job and this is counterproductive where water is concerned. Water needs a much shorter contact time. If you had unlimited resources. lots of patience and could plumb that coil so that the circuits were only two passes long, it would work better, but still would have a lot of air pressure drop and other potential issues. Evaporator coils are much thicker (more tubes across the thickness) than water coils and this makes a big difference where you are concerned. Look at a hot water coil or a car radiator; they are only 1 or 2 tubes deep and only make 1 or 2 passes, while an evaporator is usually 3 or 4 tubes deep with many passes and the tubes will be a bigger diameter to reduce water pressure drop. All these differences add up to something you are probably not going to be happy with.

    Hope this helps and good luck with your project!

    Chris
  11. deerefanatic

    deerefanatic Minister of Fire

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    I'll have to get a picture........ The coils are in a serpentine pattern and only 1 row deep........

    It would be fairly simple to plumb it for only two passes........

    Anyhow, it's a moot topic now... I've purchased a 20x20 water coil on eBay today as well as two sidearms... :)
  12. heaterman

    heaterman Minister of Fire

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    A good hot water coil will have 4 rows in it, a mediocre to average coil will have three. Most of the really cheap coils you see on the market are 2 row and designed for use with steam. 215*+ coil temp.
  13. deerefanatic

    deerefanatic Minister of Fire

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    The one I bought is a three core.........

    It'll work for $200............
  14. heaterman

    heaterman Minister of Fire

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    Did it have a rating on it? For example.........58,000 btu @ 140*F Just curious.
  15. deerefanatic

    deerefanatic Minister of Fire

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    185,000 btus....... Yah right!!

    Probably closer to 100,000 btu's........... It's being sold by an OWB dealership.
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