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Thread: How to slow evaporation without heating pool?

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    How to slow evaporation without heating pool?

    OK, I have a solar bubble cover, and I use it in the spring and fall. But, during the summer here in Austin TX, I would like to slow down the evaporation rate of the pool without heating it up. Just solar heating with no cover usually keeps our pool between 83 and 89F. If I were to keep the solar cover on, the water would quickly become too warm for comfortable summer swimming. There is a nearby pool guy that sells 4'X4' pieces of thin, white foam (looks to be about 3/8" thick) for $15 each--it is not rigid, but probably originally comes on rolls, like the kind used for package cushioning. Good idea, but I suspect the wind would easily catch them--that would be a mess.

    Anybody ever seen the 60" round "sun ring" style solar covers, but with a reflective surface (instead of transmissive) which would presumably stop solar heating as well as evaporation? Maybe a few of those on the pool would help. BTW, I understand after reading this forum, that the liquid stuff is pretty much useless, especially when windy.
    Bill Long
    Jack of all trades / Master of none
    14,000 gal. 34'X12' gunite w/SunStone quartz aggregate plaster, Hayward 425sf cartridge filter, IntelliFlo VS-3050 pump, IntelliChlor IC-40 SWCG, EasyTouch controller, Polaris 280 cleaner (w/booster), Rheem 5350 heat pump, PoolSkim

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    UnderWaterVanya's Avatar
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    Re: How to slow evaporation without heating pool?

    What about taking a bubble cover and painting it silver or white to reflect most of the light?
    Alternately perhaps you could glue a white or silver layer to a bubble cover.
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
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    JasonLion's Avatar
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    Re: How to slow evaporation without heating pool?

    Most of the "heat gain" from using a solar cover is because it stops evaporation. Only a relatively small portion is due to actual solar heating. You lose a lot of heat to evaporation. So anything that stops evaporation will "heat" the pool relative to what you would have had with evaporation.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: How to slow evaporation without heating pool?

    If you had a white or reflective cover on the pool during the day and then took it off at night when the sun was no longer hitting the pool then that would cool it off and tend to keep it close to the average day/night temp or somewhat below. During the day there is evaporation cooling the pool and sunlight (absorbed by the water) heating it. Which one dominates depends on the humidity of the air and the amount of wind.
    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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    Thanks for inputs and suggestions

    I like the idea of using a few "sun rings" because I have stowed our reel and cover for the summer, and my wife and I swim once or twice a day. So minimizing the hassles of removing the stuff is essential.

    Right now, our pool typically warms from 82-84 in the morning to 87-89 by late afternoon (breezy). That's with a breezy, 75 low overnight. So, it is losing heat at night, but is that mainly evaporation or conduction? Any daytime evaporative cooling is obviously being offset by solar gain.

    I guess what I really want is to minimize evaporation, without causing the pool to overheat. A cover, or sun rings, will inhibit both evaporation and night conduction, thereby reducing their cooling effects. So, I guess that anything I put on the surface will always have the net effect of raising the water temperature. Does that sound right?
    Bill Long
    Jack of all trades / Master of none
    14,000 gal. 34'X12' gunite w/SunStone quartz aggregate plaster, Hayward 425sf cartridge filter, IntelliFlo VS-3050 pump, IntelliChlor IC-40 SWCG, EasyTouch controller, Polaris 280 cleaner (w/booster), Rheem 5350 heat pump, PoolSkim

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    cramar's Avatar
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    Re: How to slow evaporation without heating pool?

    You could add solar heating and use it at night, this would allow you to keep the cover on during the day and reduce evaporation, by using the panels at night it would cool the pool and counteract the the daily heat increase.

    One of the members here mentions cooling tanks, or cooling storage, something like that. Not sure how that works but sounds like he has some sort of water storage that cools the water, maybe search and figure out what he has.
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    Re: Thanks for inputs and suggestions

    Quote Originally Posted by stbasil
    So, I guess that anything I put on the surface will always have the net effect of raising the water temperature. Does that sound right?
    No, if you have a very reflective cover, then the pool would reach a temperature that was the average of day/night temperatures. There would be no heating of the water from the sun (with ideal reflectance) and no evaporation for cooling. There would only be conduction to have the water temp equal the average air temp.

    When we had a somewhat light tan cover, the water temp pretty much followed that rule of being the average day/night temp until I turned on the solar system for the season. Now that we have a dark blue cover, the water gets warmer than the average and even when heated the cover adds one or two degrees of heating so the solar system shuts off earlier than it used to when I had the tan cover.
    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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    Re: How to slow evaporation without heating pool?

    It's hard to predict exactly what wind, humidity and other conditions do to temps. I have Sun Rings. I'm quite satisfied with them. Easy to take on and off and keep heat in the pool at night better then nothing at all. They have a clear side and a dark blue side with an air space between. Here's what I have observed as far as heat gain using them. I'll list those observed effects from maximum heat gain to lowest heat gain.


    Best heat gain is no rings
    Clear side up with pump running
    Clear side up without pump running
    Dark blue side up with pump running
    Dark blue side up without pump running

    The above effects are when conditions are conducive to heat gain on a typical summer day here in the Philadelphia area. As far as evaporation I think it's a wash by covering during the day and uncovering at night.
    Bill
    18'X4' 7600 Gal AG
    3/4 HP Pentair Pump
    Hayward S166T 100 lb sand filter

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    UnderWaterVanya's Avatar
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    Re: How to slow evaporation without heating pool?

    Quote Originally Posted by yeggim
    It's hard to predict exactly what wind, humidity and other conditions do to temps. I have Sun Rings. I'm quite satisfied with them. Easy to take on and off and keep heat in the pool at night better then nothing at all. They have a clear side and a dark blue side with an air space between. Here's what I have observed as far as heat gain using them. I'll list those observed effects from maximum heat gain to lowest heat gain.


    Best heat gain is no rings
    Clear side up with pump running
    Clear side up without pump running
    Dark blue side up with pump running
    Dark blue side up without pump running

    The above effects are when conditions are conducive to heat gain on a typical summer day here in the Philadelphia area. As far as evaporation I think it's a wash by covering during the day and uncovering at night.
    So you would leave them off in the day and then toss them in as the sun left the pool in the late afternoon/evening if you were trying to gain heat - correct?
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: How to slow evaporation without heating pool?

    Quote Originally Posted by UnderWaterVanya
    So you would leave them off in the day and then toss them in as the sun left the pool in the late afternoon/evening if you were trying to gain heat - correct?
    Yep. I imagine there would be conditions where taking them off during the day would be counter-productive to heat gain but I haven't experienced that yet. We don't get too many days of low humidity and high winds.
    Bill
    18'X4' 7600 Gal AG
    3/4 HP Pentair Pump
    Hayward S166T 100 lb sand filter

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    Re: How to slow evaporation without heating pool?

    One year we used solar shade we bought from Home Depot. It virtually stopped the evaporation and kept the pool cool, even in August in south Texas. Our problem was keeping it from dropping into the pool...we where trying to have it "hover" over it. We not sure what chemicals are used to produce it. Still working on it.

    - - - Updated - - -

    Are solar reels difficult to use?
    Pool size = 16,000 gal, IG Fiberglass, 2 speed hayward pump with cartridge filter

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