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Thread: Pool Heating which is best open to sun or clear bubble cover

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    Join Date
    Aug 2008
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    Honolulu
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    429

    Pool Heating which is best open to sun or clear bubble cover

    First the pool specs 32 ft x 10 ft x 4.5 ft approx (about 10,000 gals), white plaster.

    Latitude 21.18 degrees, Solar noon today is 12:22 pm.

    Average daytime temperature 78 F (10 am to 3pm), night time 68 F to 70 F in December, slightly lower in January and rising again after February.

    In December, assuming a relatively clear and sunny day and low winds 2-5 mph (rare where I live), is it better to have the clear bubble pool cover on or off, between the hours of 10am to 3pm, to boost the temperature.

    The reason for asking this question is to reduce the heat pump run-time.

    Any help would be appreciated.

    Aloha.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

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    Join Date
    Mar 2007
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    San Rafael, CA USA
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    Re: Pool Heating which is best open to sun or clear bubble cover

    If the air is very humid and the wind is low, then keeping it open to the sun is probably better since low wind and high humidity slow down evaporation considerably and more sun will get into the pool without a cover. If the air isn't as humid or there is wind, then having a clear bubble cover is better because the light that does get through heats the pool but the cover eliminates evaporation which would cool the pool.

    Of course, knowing how much wind and humidity make one option better than another is very hard to know. I can tell you what some theoretical models of evaporation say, but in practice that's pretty useless since there are so many different factors and I don't know how much sunlight is cut down when using a clear cover. Obviously, if a clear cover let all infrared and visible light pass through then clearly using a cover would be better since there is always some evaporation unless the air is at 100% humidity.

    This link would imply that evaporation is 5" in the month of December so that's not as extreme as during summer nor in desert environments. Nevertheless, my gut feel is that a cover would be better.

    Bottom line: try it both ways and see which works better for you. Let us know your humidity and your pool water temperature and we'll then have at least one real world data point.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Aug 2008
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    Honolulu
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    Re: Pool Heating which is best open to sun or clear bubble cover

    chem geek,

    Thank you for your reply. The pool will go down to around 72 F if we have rainy days, 76 F on non-rainy days. Rain is more frequent in November thru February than December. If I keep it covered and boost the temperature with the heat pump I get it up to 78 F. This drops about 2 -4 F at night.

    Here are the numbers for Honolulu:


    Temp.
    (ºF) Relative Humidity

    Average A.M. P.M.

    January 72.9 81% 61%
    February 73.0 78% 59%
    March 74.4 73% 57%
    April 75.8 70% 55%
    May 77.5 67% 54%
    June 79.4 67% 52%
    July 80.5 68% 52%
    August 81.4 68% 52%
    Sept 81.0 69% 53%
    October 79.6 71% 56%
    Nov 77.2 75% 59%
    Dec 74.1 79% 61%

    Annual 77.2 72% 56%

    Rain (Inches)

    Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.

    3.6 2.2 2.2 1.5 1.1 0.5 0.6 0.4 0.8 2.3 3.0 3.8

    Aloha.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

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    revstriker's Avatar
    Join Date
    Apr 2008
    Location
    Texas
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    Re: Pool Heating which is best open to sun or clear bubble cover

    I have about the same size pool as you do except I'm in the Dallas area. I use a blue solar cover in the spring and fall. I'm able to get my pool into the high 70s by the end of March, and keep it in the high 70s until the end of October. My first year with the pool, without the cover, the pool didn't hit those temps until late April, and cooled off by late September. So I figure I get an extra month on the front end, and one on the back.
    10K White Plaster Pool Built in 2007. Hayward Pump and DE Filter, Hayward Navigator, Liquidator (Removed due to issues), Solar Blanket, BBB user.

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    AV8TOR's Avatar
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    Dec 2008
    Location
    Fort Worth TX
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    Re: Pool Heating which is best open to sun or clear bubble cover

    Quote Originally Posted by revstriker
    I'm able to get my pool into the high 70s by the end of March, and keep it in the high 70s until the end of October. My first year with the pool, without the cover, the pool didn't hit those temps until late April, and cooled off by late September. So I figure I get an extra month on the front end, and one on the back.
    That's good news to my ears as I live close to you. I purchased a blue solar cover a month ago. When do you put it on to start the warm up?
    16,000 gal IG Double Roman Plaster Pool (16yrs - plaster redone 2014)
    Pentair FNS-48 DE filter with WhisperFlo 2HP single speed pump
    Polaris 280 robot
    BBB all the way and tested with a TF100 kit
    Pool Calc user

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    budster's Avatar
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    Dec 2008
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    Savannah Historic District
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    Re: Pool Heating which is best open to sun or clear bubble cover

    Poking my nose in here -- The solar blanket actually performs two functions, depending on the factors detailled in previous posts: absorbing sunlight and transferring that heat to the surface, AND reducing heat loss (and evaporation) in the non-sunny times. I second chem geek.
    http://www.swimmingpool.com/

    "Leave the gun...take the cannolis"

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    Feb 2009
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    Honolulu
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    Re: Pool Heating which is best open to sun or clear bubble cover

    Smallpooldad - Where did you get your solar blanket. I live on Oahu and am thinking about getting one for my 20'x40' pool. I have several solar panels, that together with the cover should make for a very warm pool.

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    Re: Pool Heating which is best open to sun or clear bubble cover

    Great info. I am in the Dallas area and just started looking into these covers. Thanks!
    Plano, TX
    20,000 gallons Kidney Bean IG Plaster, Pentair Clean and Clear 530 Cartridge Filter

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