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Hot Tub heat exchangers

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Mark Eatherton1
Mark Eatherton1 Member Posts: 2,542
in THE MAIN WALL
THat number comes from Tirangle TUbe Phase Three heat exchanger sizing information. Nt sure what all it takes into consideration, but inasmuch as they base it on exposed surface area, I'd assume it only covers convective/evaporative losses. The consuctive losses will be in there, but at a substantially lower rate than the surface.

In the event that you decide to use a flat plate heat exchanger, I'd strongly suggest you also incorporate a 4 way reversing valve to change the direction of flow through the load side of the HXer to avoid getting it loaded up with gunk.

You're welcome!

ME

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  • Nikolai
    Nikolai Member Posts: 31
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    Wondering if anyone has any usefull information on sizing exchangers for outdoor hot tubs.
    Our outdoor design temp is -36F
    Thanks in advance.
  • Nikolai
    Nikolai Member Posts: 31
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    Hot Tub Exchangers

    Wondering if anyone has any usefull information on sizing exchangers for outdoor hot tubs.
    Our outdoor design temp is -36F
    Thanks in advance.
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
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    build an enclosure??

    Steve,

    With one side at +100F and the other side at -36, that's a huge temperature gradient. Even if you made the tub a thermos bottle, the loss off the surface while soaking at those temps will be unreal. With convective heating, 130F temperature difference and the evaporative cooling, the heat loss would be tremendous. Now add the loss of the tub, the pumps, the pipes in between and I would think you would need a bank vault to pay for the energy to feed this. Even keeping the water above freezing would take a bunch of energy.

    Maybe you need to look the the plan and decide whether it's a good one. I wouldn't do it.

    jerry
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
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    Burrr.....

    You're really planning on using it when its that cold outside? You MUST be a member of the Polar Bears club.

    I believe the number is 8 btuH/sq/ ft. surface exposure for each deg. F difference in temperature. If the wind is blowing, the number doubles. So, if you had an 1 man 5 woman hot tub that was 8' in diameter, then you'd have 16*3.14 = roughly 50 square feet. You want to maintain the tub at 104 degrees F when it's -36 outside, so your differential is 140 degrees F, hence 50*140*8 = 56,000 btuH. The covered standby losses are much less than that.

    A modulating, condensing boiler with the right stuff would be the most efficient gas fired option. THe trick is finding one that will work with the chemical and potential fowling factors (sun tan oil, hair, lint, swimming trunk parts).

    Good Luck and G'Day

    ME

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  • Nikolai
    Nikolai Member Posts: 31
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    Thanks for your help Mark. I will be using a S.S. heat exchanger designed for pool/tub heating off of a condensing boiler that will also be doing radiant in the house.
    1 man 5 woman hot tub....I like the sounds of that. The tub I am dealing with is a 1 man 7 woman tub....1 for each day of the week.
    Do you know if your 8 btuH/sq/ ft. takes a certain amount of insulation into affect around the hot tub?
    Thanks again.
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