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Pool heating

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Snowmelt
Snowmelt Member Posts: 1,416
I called the place where I bought my hot tub, the sales rep was very knowledgeable. So I asked him how big of a bool heater would you need for a 16,000 gallon pool. He told me for his 15,000 gallon pool he sells 135,000 pool heater. I am now very confident that a 200,000 btu pool heat exchanger will do just fine. I will be using a navien 200,000 btu boiler. (NFB) The boiler will also be doing the house heat and will fire down to 20,000 btu the boiler does have small zones I would like to add a nice size buffer tank. I’m thinking the smallest zone might be 4,000 btu, if the smallest zone is 4,000 btu and the minimum fire rate is 20,000 what size buffer would you use?

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  • Zman
    Zman Member Posts: 7,573
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    I think a 20 gallon would be the minimum. If you use outdoor reset, your minimum loads will be much lower on the warmer days. That, however, does not affect the on cycle much.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Ironman
    Ironman Member Posts: 7,379
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    @Zman
    Where did you get the buffer tank simulator?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 7,573
    edited July 2020
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    It's part of this package.
    https://www.hydronicpros.com/downloads/index.php?id=21
    I find the pipe insulation calculator very useful as well.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Ironman
  • hot_rod
    hot_rod Member Posts: 22,258
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    I would go with a 3 pipe buffer, direct to load, like this.
    You have options for tanks, HeatFlo builds a nice 22 gallon, 4 port. I'd upside the ports to 2" for your load connections.

    Shop for tanks, often times the "on the shelf" models are less $$ compared to special orders.

    https://www.heat-flo.com/documents/buffer-tank/buffer-tank-spec-sheet.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ironman
    Ironman Member Posts: 7,379
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    Zman said:

    It's part of this package.
    https://www.hydronicpros.com/downloads/index.php?id=21
    I find the pipe insulation calculator ver useful as well.

    Have you found it worth the $ investment?

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,258
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    Ironman said:

    Zman said:

    It's part of this package.
    https://www.hydronicpros.com/downloads/index.php?id=21
    I find the pipe insulation calculator ver useful as well.

    Have you found it worth the $ investment?

    I think HDS has one of the best heat load calculators. It allows you to build wall assemblies, indicate basement details, how much exposed wall for example.

    The load calc, exp tank sizer, circuit simulator, and buffer sizer are the modules I use most often.

    If you have a copy of Modern Hydronic Heating, it walks you through examples on how to use HDS modules. Not by accident I suspect.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Ironman
  • Zman
    Zman Member Posts: 7,573
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    Ironman said:

    Zman said:

    It's part of this package.
    https://www.hydronicpros.com/downloads/index.php?id=21
    I find the pipe insulation calculator very useful as well.

    Have you found it worth the $ investment?

    It absolutely is. The heat loss module is great, I really love the circuit simulator, especially for trouble shooting imbalanced older systems. I have the older version and will probably upgrade to get all the new circulators included.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Ironman
  • Snowmelt
    Snowmelt Member Posts: 1,416
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    Ok great do my next question would be do I grab ( place ) a tee before the buffer tank for the indirect water, also since the pool heat exchanger is large would you also grab that before the buffer tank.
    In my head those two items would be the biggest load and would be using a lot of btu’s therefore not really short cycling at all the rest of the house would be.
    I was looking at the Utica buffer tank and the 22 gallon has 1-1/4 Tappens.
  • Zman
    Zman Member Posts: 7,573
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    I think I would tee both of them before. That way you don't need to heat up the buffer water in the summer.
    I did do one project where I put it after. In that case, I had mixing valves downstream feeding extremely micro loaded towel warmers. My thinking was the 180 degree water left in the buffer after DHW call would satisfy the low temp micro loads for a good long time.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Snowmelt
    Snowmelt Member Posts: 1,416
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    My customer has one of those zones the small bathroom which never goes because the heat from the rest of the house heats that bathroom, I am sure I could keep that zone open all the time so when any other zone opens the bathroom would heat up. The problem is that he has 4 pumps existing then a few zone valves. I’m thinking of switching it to all zone valves.
  • Zman
    Zman Member Posts: 7,573
    edited July 2020
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    If you pipe the DHW through the tank and don't have mixing on the zone side, you just end up sending a big slug of 180 degree water from the DHW call into the low temp zone after the call for heat comes back on line.For your setup, maybe Tee the DHW before the buffer and the pool after? It sound like DHW would be the priority and the other loads will run simultaneously?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 22,258
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    Here is an option, IF the pool HX and DHW circulators move exactly the same gpm as the boiler, 100% of the boiler could go to those loads. So, really no interaction with the tank, it would stay at setpoint.
    The DHW would want to be on priority. Maybe lock out heat loads during pool call if you want 100% boiler output to that HX.

    On heat call, the coldest possible return goes to the boiler for best efficiency.

    Same applies to the heat call, interaction with the buffer only when the load is not matching the boiler output. You might lock down the boiler firing rate to the highest heating load requirement, buffer would only be in play on lower load days and micro zones calling.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Snowmelt
    Snowmelt Member Posts: 1,416
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    Z man can you draw a little diagram.
    Hot rod, your saying take the house heat before the buffer tank and return after. I want to just stick to basic, is it Possible to have the radiant floor on all the time and get a mixing valve to have outdoor reset. ( I know it’s possible) I was questioning the bathroom radiant floor being on all the time.
  • hot_rod
    hot_rod Member Posts: 22,258
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    Really doesn't matter which load you pipe first, they are in parallel off that low loss header. Run the tank at set point at the highest temperature required on design day, pull the load off with any motorized mix valve with ODR. The Taco i mix valve for instance.

    For DHW the boiler goes to high temperature, high fire via priority. If your indirect can take all that boiler can give, (gpm/ btu) there will be no flow into the buffer, it will stay at setpoint. Even if it creeps, no big deal the heating is taken off via a mix valve.

    For the pool I would size the HX to supply the required BTU, whatever the boiler output is, at a low boiler temperature to maximize condensing. With close approach HX sizing you could run the boiler 5° hotter that the pool temperature, that boiler would condense like crazy running 95° supply! You would have a 97% efficient pool heater.

    Use a HX simulation program, most have pool specific sizers. Try 95F on the A side of the HX, 85 pool side, see how it looks.

    A swimming pool rated flat plate is what I would use, they are more efficient than a tube and shell type, more surface area and the chevron plate pattern encourages high turbulence, for excellent heat transfer.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Snowmelt
    Snowmelt Member Posts: 1,416
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    Hot rod, your so informational.
    So I think your saying that the micro zone you have before the buffer tank? How would I manipulate the boiler to fire at a low temp for the pool heater while leaving the indirect at high fire, I may have to get you boy John Serlerno to step in and help me
  • hot_rod
    hot_rod Member Posts: 22,258
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    You can do it🛠
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,258
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    The boiler will go to high fire when it sees a demand from the indirect. Check the manual, most all mod cons have an indirect function and wiring terminal to allow that.
    All the heating zones return to the lower right side.

    Properly sized and pumped the indirect and pool HX May never interact with the buffer, really no need to. You want all the boiler hp going to those loads for quick recovery on the indirect, and max boiler to the pool. May as well use all the boiler power in those non heating loads.

    Use an indirect with a large coil, a reverse indirect or a triangle tube tank in tank. Any of those should be able to handle that boiler output easily.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Zman