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POOL AND HOT TUB HELP

KeenGreenKeenGreen Member Posts: 24
I am a Hydronic System Designer located in Vancouver BC.
When designing a Hydronic System for a house, I am always stumped by sizing a pool and hot tub heater. BTU's required.
I have completed a heat loss for the heating and domestic (DHW) for the 3 level house. 94,000 btu's.
The house has a separate INDOOR pool and hot tub.
Now I am trying to figure out the btu's required to heat the pool and hot tub.
The pool is 23' x 9' x 6' deep. Temp should be maintained to 82deg.
The hot tub is a 4' x 6' x 4' deep. 104 deg.
They want to use one boiler for the domestic, heating, pool and hot tub.
I've tried to use the online guides but I thought I would get better info from the pro's. Mentors if you will.
When I get a btu load for each load, I can then size my boiler and heat exchangers accordingly.
Once I get a plan of attack I will record this and use it for all of my future Designs.
Thanks in advance.
Jeff

Comments

  • nicholas bonham-carternicholas bonham-carter Member Posts: 7,823
    Is the pool/hot tub inside or outside, and will it be heated all year round? What is the design temperature in your area?
    If outside, is there any insulation around the pool underground?
    Is the location one which is easy for servicing, such as in a major town, with a stocking wholesaler for at least one make of boiler?
    If on an island, or other remote location, then a cast iron boiler, or two might be easier in the long term.—NBC
  • Larry WeingartenLarry Weingarten Member Posts: 1,483
    Hi, An old rule of thumb is that 90% of a pool’s heat loss is from the water surface. Getting a good insulated cover on it will help a lot. I’d ask the pool cover maker how their product affects heater sizing.
    Yours, Larry
  • KeenGreenKeenGreen Member Posts: 24
    @nicholas bonham-carter
    It's an Indoor pool. Vancouver area design temp is 19F.
    Major town and I am the stocking Wholesaler.
    How do you size pools and hot tubs?
  • Jamie HallJamie Hall Member Posts: 10,377
    Take a look at this handy dandy reference. It isn't as hard to wade through as it looks.

    The reason for looking at it is that the difficult part of calculating the heat loss from a pool is the heat lost to evaporation -- which can be considerable. Once the evaporation rate is found, calculating the amount of heat that represents is simple enough. Direct conduction into the surrounding ground is rather small, if the pool is below ground, provided you don't vary the pool temperature much -- it will take a long time to come to equilibrium, though, like days or weeks (if it's free standing as the hot tub might be, the standard formulae for heat loss is completely applicable).
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • hot_rodhot_rod Member Posts: 11,369
    All the pool heater manufacturers have sizing guides, Raypak, Laars, etc. Generic ones from some of the energy orgs.

    With indoor pools if the room is heated it covers much of the pool load. If the pool is heated, it covers some of the room load.

    Remember dehumidification, by far the most often missed component of indoor pools design.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • pecmsgpecmsg Member Posts: 718
    Indoor Pools require SPECIAL SYSTEMS to control humidity, room & water temperatures.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 5,706
    Rather than using a boiler a system like a dry-o tron. basically a heat pump that dehumidifies the indoor space and uses condenser heat to heat the pool water
  • ratioratio Member Posts: 1,951
    Seresco, Desert Aire, & Pool Pac (IIRC) are some others. Some of them have natatorium design documents on their website.
  • ZmanZman Member Posts: 4,853
    edited May 31
    I've been doing quite a few of these lately. This raypak calculator gets you pretty close. They only spec their equipment so you have to do a bit of reverse engineering. https://apps.raypak.com/gas_sizing/Raypak_gas.php

    Keep in mind the expectations of the management. I have one customer that wanted to be able to do a water change in the hot tubs in < 6 hours and the pool in < 24 hours. I ended up oversizing the heat exchangers and running condensing boilers. The boilers run nice and cool on outdoor reset and modulated down most of the time. When the pools are cold, outdoor reset and snowmelt is disabled. The boilers ramp up and it is quite a show.

    That system saved 35% annually over the pig that it replaced.

    Check out these pool links as well
    https://www.leaktools.com/evaporation-index.html
    http://www.b2ce.com/uploads/3/4/2/9/3429384/natatoriums_white_paper.b2ce_inc.pdf

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rodhot_rod Member Posts: 11,369
    Zman said:

    I've been doing quite a few of these lately. This raypak calculator gets you pretty close. They only spec their equipment so you have to do a bit of reverse engineering. https://apps.raypak.com/gas_sizing/Raypak_gas.php

    Keep in mind the expectations of the management. I have one customer that wanted to be able to do a water change in the hot tubs in < 6 hours and the pool in < 24 hours. I ended up oversizing the heat exchangers and running condensing boilers. The boilers run nice and cool on outdoor reset and modulated down most of the time. When the pools are cold, outdoor reset and snowmelt is disabled. The boilers ramp up and it is quite a show.

    That system saved 35% annually over the pig that it replaced.

    Check out these pool links as well
    https://www.leaktools.com/evaporation-index.html
    http://www.b2ce.com/uploads/3/4/2/9/3429384/natatoriums_white_paper.b2ce_inc.pdf

    In visited HTP years ago when the Munchkins were first hitting the market. The owner told me he used one on his own pool, no HX, as I recall just pumped, probably with some bypass for the GPM required for the pool flow.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,492
    I've used Dektron. The dehumidification from cooling, the condenser just puts the heat back into the pool water. Workes very well. You get the added benefit of compressor heat added to the pool. Consider that if your room is 72F, then the pool will essentially stay at 72F without and heat input. You are only concerned with the temp difference between pool set point and room temp.

    I'd consider an indoor pool as almost a no load for sizing calcs. A generous HX to bring it up to set point may cost you 60,000 btu/hr. The electric heat input from dehumidification should come very close to what youd want.

    Outdoor pools are an entirely different story.
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
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