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Coiled Copper Conundrum

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by SteveJ, Nov 27, 2007.

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  1. SteveJ

    SteveJ Member

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    Okay, I am convinced to use a storage tank and coiled copper as the hx.

    So, now the issue:

    Boiler to the house is 3/4" pex.

    I want to keep costs down as much as possible and based on the hot water heat carrying capacity of copper tube, I see that 1-1/2" copper has 6 times the heat carrying capacity of 3/4" copper.

    So, does this mean that I can use 1/6 the as much 1-1/2" coiled copper as compared to 3/4" coiled copper?

    Based on the Type-L used by STSS, 180ft of 3/4" coiled copper delivers a hx rate of 39,600 BTU at 120F, does this equate to 30ft of 1-1/2" coiled copper?

    I have found that Type-L coiled copper is $2.74/ft for 3/4" and $7.42/ft for 1-1/2" at PlumbersStock


    Does this mean for a 39,600BTU rating I can either spend $493.20 for 3/4" or $222.60 for 1-1/2"?

    What about stratification?

    Thanks,
    Steve

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  2. hkobus

    hkobus Member

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    The numbers you are using are for the "volume" of heat carried. this is closly related to the restriction and the surface area of the cross section of pipe. The cross section of a 1.5" pipe is 4X that of a 3/4" The heat emission from the pipe will be related to the surface area of the outside of the pipe, the thikness and the temp difference between the fluids (or gas). The site you refered to, has that information as well.
    The articles on the pex HX in the hole has me thinking, I also found some info on nylon tube(air line tube on highway trucks) used in HX, it is thinner walled than pex and had has good strength and heat resitence. I will try to find the article and post the link sometime.

    Henk.
  3. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    As Henk alludes to, you want the opposite. The lower the carrying capacity, the more surface area, which means more heat transfer. Carrying capacity is great for getting heat from point A to point B with minimal losses. In the case of a heat exchanger, you want losses. A whole mess of really thin tubes (in parallel, to keep the pressure drop low) would be best.

    Joe Brown
    Brownian Heating Technology
    www.brownianheating.com
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    I checked out the PlumbersStock website and it's interesting. It's the only place I've seen online where you can buy pipe and fittings at the same time.

    But those don't look like wholesale prices to me. They're about what you would pay at Home Depot or Lowe's, plus shipping, which may or may not offset what you save on local sales taxes. But they appear to have a complete selection of stuff, which is more than the big boxes around here can say. You pay slightly more around here at the heating supply houses if you just walk in off the street.

    One reason I checked out the website was to price 1" gate valves. I need about 6 of them. The other day I ordered a package of 8 from an Ebay store for $50 with free shipping. I know I can find a use for the other two. On the website, 1" gate valves are going for more than $12 each. So I would recommend Ebay or an Ebay store for that kind of stuff. Close to one third the price when all is said and done.
  5. Nofossil

    Nofossil Moderator Emeritus

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    I've said this before on other threads, but I'll risk censure from the site admins and say it again:

    I did my tank with copper. Lots of copper. Even without today's copper prices, I wish I had gone to a few scrapyards and scrounged finned stainless heat exchanger tubing. It seems to be pretty common, and is vastly superior to copper in terms of effectiveness per foot.
  6. SteveJ

    SteveJ Member

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    Thanks everyone for pointing me in the right direction...

    I like nofossil's suggestion about the finned stainless.

    Short of that, what about refrigeration tube? Anyone using?

    Price seems right 3/4" < $2/foot

    Any issues submerging refrigeration tubing? Issues circulating 180F water/glycol?

    Thanks,
    Steve
  7. leaddog

    leaddog Minister of Fire

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    refrigeration tubing uses od for size l and k uses id so 3/4 refrigeration is smaller. Just so you can compare apples to apples.

    leaddog
  8. Nofossil

    Nofossil Moderator Emeritus

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    I used refrigeration tubing for my DHW preheat coil. I had to machine my sweat fittings to mate with it - non-standard OD. Otherwise, no problems.
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