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Thread: FACT OR URBAN LEGEND - dark liners

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    FACT OR URBAN LEGEND - dark liners

    Do darker liners actually retain/heat your pool faster?

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    Without having a scientific reply , I can only say our current liner is darker than our original liner and if there was / is an increase in temp , I havent noticed . So my answer is no .

    THe solar cover however has made a difference

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    I am no scientist but...

    I believe it is a fact that a darker color will absorb more heat and reflect less, the opposite being true of a lighter color. I would therefore speculate that a darker color will absorb more heat that will then be released into the water through convection/conduction whereas a lighter color will reflect more heat away.
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    Quote Originally Posted by HappyWino
    ....a darker color will absorb more heat and reflect less, the opposite being true of a lighter color. I would therefore speculate that a darker color will absorb more heat that will then be released into the water through convection/conduction whereas a lighter color will reflect more heat away.
    I have always thought along the same line however, like Ctoon, I now have a darker vinyl lined pool whereas my last pool was a light colored fiberglass (moved) and the temperature is about the same with the same amount of exposure to the sun. Kind of blew away my deduction but it always seemed logical?

    Dave

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    I wonder whether the fiberglass and liner has too little mass to absorb enough heat to matter? In a gunite/plaster pool there is a lot more mass to absorb (and store) heat.
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    JasonLion's Avatar
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    A darker color will absorb more sunlight than a lighter color, no question about it. However the difference is not going to be large enough to do much for your water temperature. The water already absorbs some sunlight and reflects some sunlight before it ever gets to the liner and sunlight reflected by the liner has to go through the water again, with more of it getting absorbed on the way out. Plus evaporative cooling is more efficent the warmer the water is, which cancels out much of what gain you do have. By far the largest effect on temperature you can have is using a solor cover. That stops the evaporative cooling at night, which is the main source of heat loss.
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    I would say that it would help a bit but it also depends on how deep the pool is. Water absorbs the sun's energy and the deeper it is, the more energy it will absorb. Any energy reflected back upwards gets absorbed as well.

    So the deeper a pool is, the less likely a dark bottom would help. You can visualize this by comparing the water color in a deep end vs the shallow end for a light color pool. The shallow end is lighter because more light is reflected off the bottom and makes it back to your eye. Deep ends in white bottom pools are darker which means most of the energy has been absorbed. Water absorbs more energy in the red end of the spectrum, which is a good thing for heat, so the water looks blue.
    Mark
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    Maybe, but if you feel the walls/floor below the water line isn't it the same temperature as the water even if in direct sun light?

    Dave

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    Since dark-colored objects both absorb and radiate heat more readily than light-colored objects, I would think whatever additional heat might be gained while the sun is shining (if any!) would be offset by similar losses when it is not.
    Currrent pool under construction: DIY Kafko steel/vinyl IG 26kgal 20x40 Kidney, sand filter, Triac spillover spa, Aqua Logic SWG
    Previous pool: IG vinyl 20x40 rectangle. Made all the mistakes - now reformed (mostly)

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    Quote Originally Posted by DavidD
    Maybe, but if you feel the walls/floor below the water line isn't it the same temperature as the water even if in direct sun light?

    Dave
    This is true but it has more to do with the energy conversion and heat transfer. The pool surface temp will not be that much different since heat transfer is pretty quick from the pool surface to the water. So the pool surface will absorb energy and thermally conduct it directly to the water. So even though the temp difference is small, the surface will still transfer BTUs to the water.
    Mark
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    Quote Originally Posted by chatcher
    Since dark-colored objects both absorb and radiate heat more readily than light-colored objects, I would think whatever additional heat might be gained while the sun is shining (if any!) would be offset by similar losses when it is not.
    This is also true but there still may be a net heat gain since the water takes the heat out of the surface almost instantaneously so the dark surface will be at the same temp as the water (see above). Any remaining energy in the pool surface that radiates back, some of it will be absorbed by the water again.

    At night most of the heat loss will not be radiative but evaporation from the surface which is why a cover is necessay to maintain the heat.

    There are so many processes going on with heat transfer that it is really difficult to know for sure if there is heat gain. However, I have read from many sources that you can get close to 1-2 degrees of net heat gain with a colored surface so I do think it has a small effect on temperature.
    Mark
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    Quote Originally Posted by mas985
    .....since heat transfer is pretty quick from the pool surface to the water. So the pool surface will absorb energy and thermally conduct it directly to the water. So even though the temp difference is small, the surface will still transfer BTUs to the water.
    Good Point.

    Quote Originally Posted by mas985
    .....I have read from many sources that you can get close to 1-2 degrees of net heat gain with a colored surface so I do think it has a small effect on temperature..
    Yes, as have I. When buying our new house, I even commented to the wife that with the dark liner, this pool should actually stay warmer. It doesn't feel that way yet but it has been getting down into the 60's on some night. I guess the wife is really missing the heat pump.....

    Dave

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    Quote Originally Posted by mas985
    ...At night most of the heat loss will not be radiative but evaporation from the surface...

    ...There are so many processes going on with heat transfer that it is really difficult to know for sure if there is heat gain...
    A lot of people use their solar panels to cool the water at night, which I would think work mostly by radiation.

    I agree it's difficult to know for sure. Unless someone wants to build two identical pools with different color liners in the same environment all we can do is speculate.
    Currrent pool under construction: DIY Kafko steel/vinyl IG 26kgal 20x40 Kidney, sand filter, Triac spillover spa, Aqua Logic SWG
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  14. Back To Top    #14

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    I'm going to say yes, the dark liner DOES make a difference. Both my neighbor and myself have the exact same size and shape pool (his is a few years older). Both are in direct sunlight all day.

    My liner looks like this:

    his line looks like this:

    I can get and keep my pool consistently 10 degrees warmer on average than his, even more with the solar cover. On sunny days its almost better to keep the solar cover off, as it warms the water faster...

    Of course, this all may just be a figment of my imagination...
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    talked to my neighbor yesterday... his temp is 72, mine is 86

    he said his liner is almost white now (12 years old)
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    I bought my house from my husband's aunt and because it is almost thrity years old, we hav a good amount of climate data on it and it has had the liner replaced a few times.
    it's 12' deep and YES, having a dark liner made a significant difference in the overall heat

  17. Back To Top    #17
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    Quote Originally Posted by mathey
    talked to my neighbor yesterday... his temp is 72, mine is 86

    he said his liner is almost white now (12 years old)
    Sorry if I seem skeptical but I think something else besides pool color is contributing to the temp difference. I don't think the physics can support that. Without solar, I doubt very much any pool could be 14 degrees wamer than another without other important factors involved. Pool water itself is fairly efficient at capturing heat. However, retaining the heat is dependent on other things such as a pool cover. Nightime exposure would ensure that most of the heat gained was lost each day. This hapens for me with solar panels when I do not use a cover. For a fair comparison, the following must be true.

    Identical time exposure to the sun (# of hours and time of day) between pools.

    Identical wind exposure between pools. If he gets more wind than you, his pool will be cooler.

    Identical use of pool covers between pools. This is a big one. If you use a cover and he does not, that will make a big difference.

    Identical surface area to volume ratios. The amount of sunlight captured is proportional to the area of the pool but the BTUs required to raise to a certain temp is dependent on the volume of the pool. If you have more surface area to volume than another pool, your pool will heat faster even with the same color.

    Thermometers are working properly in both pools. I have seen too often bad thermometers.

    The highest temp difference that I have ever heard of is 3 degrees for color change. I heard from several plaster installers not to expect anymore than this for a darker color.
    Mark
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  18. Back To Top    #18

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    Quote Originally Posted by mas985
    Identical time exposure to the sun (# of hours and time of day) between pools.
    both pools are located about 300 yards apart, both get full sunlight all day...his faces more north/south, mine more east/west

    Quote Originally Posted by mas985
    Identical wind exposure between pools. If he gets more wind than you, his pool will be cooler.
    i'd say i probably get more wind, he has a solid fence, closer to the edge of the pool, mine is open and at its closest, is 8 feet from the pool...his is also tucked up closer to the house than mine.

    Quote Originally Posted by mas985
    Identical use of pool covers between pools. This is a big one. If you use a cover and he does not, that will make a big difference.
    we just put the cover on last week, and even before then we were at 82-83 (yesterday we were up to 88 with the cover)

    Quote Originally Posted by mas985
    Identical surface area to volume ratios. The amount of sunlight captured is proportional to the area of the pool but the BTUs required to raise to a certain temp is dependent on the volume of the pool. If you have more surface area to volume than another pool, your pool will heat faster even with the same color.
    both are 16x32 grecian style, his corners are not as long as mine, so he may have a tad bit more volume and surface area (I mean a TAD)

    Quote Originally Posted by mas985
    Thermometers are working properly in both pools. I have seen too often bad thermometers.
    I can't speak to this, I know my water is warm, and he almost never gets in his since its too cold.


    Maybe it's all in my head, but I'm very glad I got the darker color liner!
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  19. Back To Top    #19

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    Maybe it's all in my head, but I'm very glad I got the darker color liner!
    It's not all in your head...while my pool was filling with cold water from the hose (municipal water supply), the dark liner walls were considerably warm in the midday sun and the water in the pool was around 78 degrees. This was at the 11,000 gallon mark in a 23,000 gallon in-ground vinyl pool. Perhaps any color liner would have been warm with direct sunlight striking it but I strongly suspect that the dark liner absorbs more heat radiation and releases it back into the water.
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  20. Back To Top    #20

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    There is very little difference between a set of (black) solar panels that absorb 80+ % of the sun's energy and convert it to heat transferred to the water vs. a dark pool surface. If water did not directly absorb the sun's energy, then the two scenarios would be the same (assuming the same surface area and sun exposure for both). So large temperature gains would be theoretically possible.

    The main reason that the above scenario isn't seen quite so dramatically is that the pool water absorbs some of the sun's energy itself so even a pool with a light surface often gains in temperature when exposed to the sun. Of course, this is counteracted by losses from evaporation which depends on wind, among other things. So the black surface does not get the full amount of sun so the "difference" between the two pool scenarios isn't as dramatic.

    The ideal pool surface for gaining heat would be a perfect black that absorbs the broadest spectrum of light possible and is also a good insulator (or has an insulator underneath it) so that the heat is conducted primarily to the pool water. Decent circulation is also important so that the bulk of the pool water is heated and not just warmed at the bottom of the pool.

    Richard
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