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Single long temp sensor well in storage tank?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by chew72, Jan 21, 2013.

  1. chew72

    chew72 Member

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    I have an idea for a temperature sensor well. The storage tank is 1200 Gallons, horizontally. 19.5 ft long by say 40 something inches. Use a long temperature sensor well on the vertical something that almost reaches the bottom. Place the sensors in the well at the heights you want, then fill the well with transformer oil to help conduct heat. The same stuff used on pole transformers.

    It's nonconducting electrically so the sensors should be fine. You only need one well and can place the sensors at any height. I was thinking something 3/8" in diameter for the well. The top would have a compression fitting to keep water out.

    Thoughts?

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  2. maple1

    maple1 Minister of Fire

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    Might be able to make something like that by welding a long tube onto the bottom of a bushing - then just thread the bushing in the port. Have no idea if the multiple sensors in the one port will give accurate readings though - no idea about the oil either.

    Seems to me someone had a thread on here a few months ago about something very similar...
  3. ewdudley

    ewdudley Minister of Fire

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    Nice idea. I doubt you need to fool with the oil.

    Needed room for three senors at top of storage, used a 1/4" x 1/2" copper X male adapter drilled through so the copper pipe could extend inside. Worked fine but I seem to recall seeing better ways to do it, just can't remember them.
  4. Triangle tube uses long drywells for their tank in a tank indirects. Should be able to find one the right size through them.
  5. mole

    mole Member

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    Chew,
    Sounds like it should work. But there may be a simpler way which I haven't read about at all here on the forum...... Has anyone out there ever tried mounting their thermocouples on the EXTERNAL surface of the tank, under the insulation? This might sound silly at first, but I have a limited amount of data that suggests it would work:

    I have a few standard Honeywell aquastats mounted with a thermowell in my piping system and a regular dial thermometer which inserts directly into the supply line. I also have 6 places in my system where I've taped naked thermocouple wires to the surface of the 1-1/4" black pipe in my boiler loop, then covered it very well with a heavy fiberglass pipe insulation. The naked wire thermocouples agree with the dial thermometer well and appear to pick up temperature changes faster than the Honeywell aquastats or the "strap on" type aquastat. They would also be very easy to tape to your tank surface with aluminum foil tape. In my storage tank, which is EPDM lined and insulated with 5" of polyiso board, I mounted three of the naked wire thermocouples behind the EPDM liner. I taped the wires to an electrical box knockout "slug" with aluminum foil tape (for more even heat transfer) and hung them on the polyiso board wall at various heights (top middle bottom) before I put in the liner. I figured the temperature change in the tank is not lightning fast, so a little lag time of heat transfer throught the liner is not critical. These thermocouples work great in my tank and the temperatures agree well with the other readings in my system.

    With this approach, you don't have to buy any expensive thermocouples or thermowells. You just buy 100' or so of type J or type K thermocouple wire and make your own thermocouples: You cut the wire to length, trim the wire insulation of the last 1" to 1-1/2", and simply twist the exposed bare wire tips tightly to assure good contact and foil tape it tightly to the surface. This gives an average temperature over the 1" length of the twisted wire. The type K thermoucouple wire 24AWG is $.30/ft at Davis Instruments (davis.com) I bought 150' of wire for about $35 if I recall correctly. I also paid $29 for a used thermocouple reader on e-bay which shows a digital readout of whichever of the 10 thermocouples I put the selector switch to. You may prefer to get three individual meters if you want to see all three temps at once like some folks do.

    So what I know for fact is that the naked wire thermocouple works well on my 1-1/4"black iron pipes. They also work well reading through the EPDM liner in my tank. So the unknown is ......what is different about your tank that might make it NOT work? I suppose if you're not insulating your tank well, (for instance, if you wanted some radiant heat to warm the room of the tank) then it would not work. There would also be more vertical heat transfer through the steel tank than my EPDM lined tank, but since we know that these tanks maintain their temperature striation, then that wouldn't be a real problem.

    I dunno, I think it would work! Maybe others have thoughts on that?
  6. maple1

    maple1 Minister of Fire

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    Yes, even if you could do the deep well, I think I would go strap on or surface mount. I think they read just as well (with some insulation over top), be easier to service, and not have to worry about more potential leak spots.
  7. taxidermist

    taxidermist Minister of Fire

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    Mole,
    All of my temp probes are taped to my tanks with foil tape and they all work fine.

    Rob
  8. stee6043

    stee6043 Minister of Fire

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    I too use a highly complex and heavily engineered method to adhere my temperature probes to my tanks - duct tape.
  9. maple1

    maple1 Minister of Fire

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    I went with house wrap tape - it's a nice red colour.
  10. I used foil tape, but it's failing after about three weeks. Been thinking about jb weld.
  11. mole

    mole Member

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    I didn't know anyone else tried it that way. Cool.
  12. taxidermist

    taxidermist Minister of Fire

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    Mines been on for 4 years
  13. chew72

    chew72 Member

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    Ok well I think I've totally over thought this lol. Looks like sticking the sensors one the side works perfectly well, and now that I think of it, why not.
  14. stee6043

    stee6043 Minister of Fire

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    It seems so often in life that the simple solutions are the best solutions. No need to overcomplicate!
  15. maple1

    maple1 Minister of Fire

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    I cut a short piece of 1/2" pipe insulation in half lengthwise and taped that over top. Partly for insulating & getting better temp feedback, and partly for protection.

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