Heating a pool with an air conditioner

Discussion in 'Home Repair' started by DerbyDad03, Dec 8, 2012.

  1. DerbyDad03

    DerbyDad03 Guest

    Ask This Old House showed the installation of a system that captures the
    heat from the AC unit to heat a swimming pool. The AC refrigerant line runs
    through a coil inside a canister. The pool water runs through the canister
    and the heat is extracted.

    OK, that's all well and good. Efficient, free heat heat for a pool which is
    shaded by trees and gets very little sun.

    Let's think about this. When it's hot out, the AC is running and pool gets
    heated. When it's cool out, the AC is not running, so the pool does not get
    heated.

    Sure, there's some advantage to heating the pool on a hot day, even into
    the hot night. However, on a cool day or cool evening, when the owner would
    really want the pool heated, he's right back where he was before the system
    was installed. Early and late in the season, when it's not hot enough for
    the AC to be running for any length of time, there is no heat available for
    the pool - right at the times of the season when you would want it.

    Considering that it takes a certified AC tech to capture the refrigerant,
    adapt the AC piping and recharge the system, is it really worth installing
    one of these systems? I don't have a pool, so I don't know how cold the
    water in a shaded pool would be on a day hot enough for the AC to be
    running.

    After a few days of cool weather, how long would would the AC have to be
    running for it to heat the pool to something that would be comfortable?
    Yes, I know it depends on the size of the pool and how cool it was. The one
    in the show was a decent sized in ground pool. Is it a matter of a few
    hours or would it take all day or longer? I know there's a number of
    variables involved...just looking for some idea.

    It just seems kind of bass-akwards to only have heat available on hot days.
     
    DerbyDad03, Dec 8, 2012
    #1
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  2. DerbyDad03

    Guest


    You may not have a pool, but I say you're on the right track.
    You're right, durintg the times you are most likely to want to heat
    the pool, the AC will not be running much. When the AC is running a
    lot, you're not likely to need it much to warm
    the pool. Here in NJ the AC is running a lot in Jul and Aug,
    precisely the time you typically don't need to heat the pool.

    Also take a look at the BTUs of a typical pool heater.
    I have one here that is gas, 400K BTUs for a 48,000 gal
    pool. You can scale that for other sizes. They don't
    put 400K btu heaters in for nothing. It takes a hell of
    a lot of energy to heat all that water. A 4 ton AC by
    comparison is only 48,000 BTUs, an order of magnitude
    smaller

    And also a lot of the heat from a pool is quickly lost,
    so you can't keep building it up over days.
    So, if you have a couple days of putting heat into it
    with the AC system, then days where it doesn't heat,
    in a day it will be cooled down again. That can be
    slowed by using a thermal pool cover, but that is
    yet another obvious pain to put up with.

    So, yeah, I'd say the whole thing is dumb and
    I would not spend a nickel on it.
     
    , Dec 8, 2012
    #2
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  3. DerbyDad03

    DD_BobK Guest

    DD & Greg are both correct. In concept it's a good idea but whether
    it really works well & pays is all about the numbers.
    How much energy does the AC remove & when, seasonal & daily basis.
    How much energy does the pool need & when, seasonal & daily basis.

    How well these two systems "match up" will determine viability.

    Even a very large AC load (5+ tons) would still be much smaller than
    most pool heaters.

    But, the "heat" from the AC is essentially free once the system mods
    were made.
    Providing a few tons (24,000 to 50,000 btu/hr) would lower your
    natural gas bill.

    Like, Greg, I see this AC pool heater as supplying some sort of
    baseline heating with a gas fired unit also being required.

    imo, the AC pool heater would lower yearly energy costs but not
    eliminate the need for a conventional heater... unless the owner was
    satisfied with a "greener" but lower performing pool heating system.

    cheers
    Bob
     
    DD_BobK, Dec 8, 2012
    #3
  4. DerbyDad03

    gonjah Guest

    I can see it working but, summer before last, I was trying to cool my
    pool down. Now I use "Sun Sails" and cover the majority of the pool with
    shade.

    Nat. gas is so cheap here it doesn't seem like the savings would cover
    the cost of the conversion anytime soon.

    Interesting idea though, and maybe I should be watching "TOH" more.
     
    gonjah, Dec 9, 2012
    #4
  5. DerbyDad03

    Guest

    Is the refrigerant coil made of copper?
    How long will that coil last in
    chlorinated or salted water?
     
    , Dec 9, 2012
    #5
  6. If we're talking a heat pump here, then in the winter, the HP is going to pull
    heat out of the pool which may have a very nice financial payback...it's going
    to work like a geothermal pump but not as expensive. Downside is that it may
    take longer to heat the thing up in the summer and will make the pool unusable
    in the winter
     
    Malcom \Mal\ Reynolds, Dec 9, 2012
    #6
  7. DerbyDad03

    DerbyDad03 Guest

    Make sure you watch ATOH or the The TOH Hour. Just watching TOH won't get
    you what I saw.
     
    DerbyDad03, Dec 9, 2012
    #7
  8. DerbyDad03

    DerbyDad03 Guest

    They did indeed say the the AC unit will run more efficiently.
     
    DerbyDad03, Dec 9, 2012
    #8
  9. It's not about heating the pool, it's about the cooling the house. Air
    conditiioners are heat transfer devices. They move heat from one location to the
    other. Transfering heat by means of a fan to the outdoor warm air is far less
    efficient than transfering it to cooler water.
     
    Robert Neville, Dec 9, 2012
    #9
  10. DerbyDad03

    DerbyDad03 Guest

    No, it was about heating the pool. Watch the latest episode of Ask This Old
    House when you get a chance. The system was installed for the sole purpose
    of heating a shaded in-ground pool. It was plumbed in before the pool
    filter and included a sensor that only allowed the refrigerant to flow
    through the canister's coil when the pool water needed heating.

    The fact that the AC would be more efficient when it was heating the pool
    water is just an added bonus. If it was about cooling the house, then the
    sensor would not have been installed.

    The fact that
     
    DerbyDad03, Dec 9, 2012
    #10
  11. DerbyDad03

    harry Guest

    Well you'd only be using the pool on warm days.
    So makes perfect sense.
     
    harry, Dec 9, 2012
    #11
  12. The Daring Dufas, Dec 9, 2012
    #12
  13. DerbyDad03

    DerbyDad03 Guest

    DerbyDad03, Dec 9, 2012
    #13
  14. DerbyDad03

    Guest

    I think those of you that think this is going to make
    a substantial difference in cooling costs to the house are
    barking up the wrong tree. It's true if you had the same
    size condenser that you could get more cooling out of
    it by using water on the condenser instead of air. But
    the condenser the AC unit already has consists of a coil
    and fan that are sufficient and sized so that it brings
    the refrigerant temp down close to that of the outside
    ambient air. It does that with an electric fan
    that probably uses less energy than the pool pump
    would. If you feel the pressure line where
    it enters the air handler it's around room temp. A
    pool in the months when you need AC is going to be
    around 80F. So, you're not going to drop the
    refrigerant temp any more than that by passing pool
    water over it. In other words, I don't see it making
    a difference.

    And the suggestion to use the pool with a heat pump
    to get heat in the winter is pretty much a non-starter,
    IMO, too. In the climates where it would make the most
    impact you have freezing temps. Pools and the existing
    pool eqpt are not designed to operate in freezing conditions. I
    guess you could do it in FL, but given the climate, little
    need for heat, why bother? And as for heating the pool
    down there, in the months when it would work, they
    actually are cooling some pools because they get too
    hot on their own, no?
     
    , Dec 9, 2012
    #14
  15. DerbyDad03

    Guest

    We can add pools to the list of subjects you obviously are
    clueless about.
     
    , Dec 9, 2012
    #15
  16. Was it stainless steel? A lot of guys I know will call any heat
    exchanger "the coil" even though the item may be in different forms
    but I did not pay close enough attention to the coil in canister bit,
    my bad but I'm sure the coil in canister wasn't bare copper. The flat
    plate exchangers I posted the link are not made of copper but rather
    stainless steel. **I found the heat exchanger you mentioned, it's not
    stainless steel, it's freaking "titanium". The video link is there too!
    I always use flat plate heat exchangers in the systems I work on so I
    automatically think of that type. I've never used one made of titanium
    and I think it's so cool(no pun). o_O

    http://www.hotspotenergy.com/pool-heater/

    TDD
     
    The Daring Dufas, Dec 9, 2012
    #16
  17. Heck, the only time I have a pool out back of my shack is when it rains.
    'course we can put thick plastic in the bed of the pickup
    and fill it with water. ^_^

    TDD
     
    The Daring Dufas, Dec 9, 2012
    #17
  18. DerbyDad03

    gpsman Guest

    Via the AC, which is obviously woefully insufficient to heat the
    standard 16x32 ±20K gallon pool.

    Seems it must be a system auxiliary to a dedicated heater.
     
    gpsman, Dec 9, 2012
    #18
  19. DerbyDad03

    Guest

    After posting this, I realized there was one aspect
    I overlooked. I compared the electricity to run the pool
    pump with the electricity to run the pool pump. But
    the electricity used by the pool pump can probably
    be ignored because the pool pump typically runs 6 or
    8 hours a day to filter the pool water anyway. So,
    it can be filtering while doing the AC.

    In which case, I can see the system saving basicly
    whatever it took to run the fan motor on the AC
    condenser. Which is something. But the whole thing
    appears very impractical to me for a variety of reasons.
    The biggest obstacle being the mismatch between the
    periods when you need it most and when the AC is actually
    running the most. For example, here in NJ, when the
    heating is most useful is late May and June at the
    beginning of the season and Sept to extend the season
    for a few weeks. Those times the AC is not running
    all that much.
     
    , Dec 9, 2012
    #19
  20. DerbyDad03

    gonjah Guest

    I think this is the episode. It's the 3rd scene selection:

    http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20652494,00.html

    Titanium.

    FWIW: My pool heaters heat exchangers are copper.
     
    gonjah, Dec 9, 2012
    #20
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