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AMG

Bubble Cover Installed Upside Down (Bubbles Up), How Much Does It Matter?

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Okay, stupid me. My pool is not symmetrical so I cannot flip it. I installed with the bubbles up. How much difference do you think it really makes? If it is just a little less effective, I'll leave it. If it is basically not effective, I'll trash it and buy another $129 cover. There is no reason to keep it on there if it is useless to me, but if its 80% as effective or whatnot, I'll leave it.

I remember seeing chemgeek post a while back, if he reads this, I'd love his input too :)

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You lose some effectiveness, but probably not that much. You may be right at 80% effectiveness. What you are losing is the insulation from air pockets in between the bubbles that would exist with the bubble-side down. So the area of the cover in between the bubbles (and the lower part of each bubble) does not have still air insulation. However, unless you've got persistent wind, the air in between the bubbles may still somewhat insulate even with the bubble side up.

It's not at all a disaster. At least half of the heat loss will still be prevented since evaporation will still be virtually eliminated and the bubble insulation will still cut down a lot of conduction/convection.

You can just see how it goes and whether you are happy with how you are keeping your pool warm.

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The whole purpose of a solar cover is to reduce overnight heat loss from evaporation. It doesn't matter if the bubbles are up or down, they just keep the cover floating on the pool. They do not significantly insulate against heat transerfer out of the pool nor do the concuct heat into the pool. The cover merely floats and stops evaporation. The significant heat loss in a pool is from evaporation.

Best practice is to cover at night to minimize heat loss and uncover by day to maximize heating from sunlight. An uncovered pool will heat faster in sunlight than a pool with any type of cover. However, in windy/dry conditions where evaporation is high during the day as well then keeping the cover on will minimize heat loss by evaporation both day and night.

So, If you are in a hot, humid place like Miami, Florida cover at night and uncover during the day. IF your are in an arid, windy place like Las Vegas, Nevada you will retain more heat by keeping it covered all the time since evaporation heat loss happens both day and night. If you are in between see what works best for you.

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Thank you both so much. I appreciate it. The pool was 68 when I covered it, and it's supposed to warm up this next week. We'll see if this thing works :)

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I wouldn't expect it to last quite as long, not a serious hit on life span mind you, but the added direct contact of the plastic sheet that gives it it's tensile strength with they water will likely have an impact.

Scott

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I wouldn't expect it to last quite as long, not a serious hit on life span mind you, but the added direct contact of the plastic sheet that gives it it's tensile strength with they water will likely have an impact.

Scott

Not a problem. If it was infective, it's lifespan would be 1 day as I throw it away. If I get 1 season I'm fine with it. Thank you.

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They do not significantly insulate against heat transerfer out of the pool nor do the concuct heat into the pool.

Though I agree that the primary purpose of a cover is to stop evaporation, I disagree with the above regarding losses via conduction. Still air is a reasonable insulator and is how double-pane and triple-pane glass works to insulate better. I have a thin mostly opaque electric safety cover and it loses at least twice as much heat as those who use a bubble-type cover (as determined by temperature drops overnight in similar air and water temps). If you feel the surface of my cover, it is warm like the pool. If you feel the surface of a bubble-type cover, it isn't usually as warm and feels more like the air temp. In fact, we are strongly considering getting an additional air-pocket or other type of insulating cover to put on top during the extended season to cut down on gas heating costs.

This link gives the thermal conductivity of various substances. PVC has a thermal conductivity of 0.19 while window glass is 0.96, but still air is only 0.024. For a 9ºF temperature difference (5ºC), a 1 centimeter air bubble will conduct heat at 0.024 * 5 / (1/100) = 12 Watts per square meter while PVC (vinyl) will lose 0.19 * 5 / (1/100) = 95 Watts per square meter or 8 times as much.

Now the bubbles being up still slow down heat conduction through the bubble so it is only the "in between" areas that conduct faster and as I wrote the air may be still and not convecting much without wind.

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They do not significantly insulate against heat transerfer out of the pool nor do the concuct heat into the pool.

Though I agree that the primary purpose of a cover is to stop evaporation, I disagree with the above regarding losses via conduction. Still air is a reasonable insulator and is how double-pane and triple-pane glass works to insulate better. I have a thin mostly opaque electric safety cover and it loses at least twice as much heat as those who use a bubble-type cover (as determined by temperature drops overnight in similar air and water temps). If you feel the surface of my cover, it is warm like the pool. If you feel the surface of a bubble-type cover, it isn't usually as warm and feels more like the air temp. In fact, we are strongly considering getting an additional air-pocket or other type of insulating cover to put on top during the extended season to cut down on gas heating costs.

This link gives the thermal conductivity of various substances. PVC has a thermal conductivity of 0.19 while window glass is 0.96, but still air is only 0.024. For a 9ºF temperature difference (5ºC), a 1 centimeter air bubble will conduct heat at 0.024 * 5 / (1/100) = 12 Watts per square meter while PVC (vinyl) will lose 0.19 * 5 / (1/100) = 95 Watts per square meter or 8 times as much.

Now the bubbles being up still slow down heat conduction through the bubble so it is only the "in between" areas that conduct faster and as I wrote the air may be still and not convecting much without wind.

One point to consider, solar covers FLOAT on the water surface, electric covers don't. Yours is, as you said, a safety cover to prevent people from falling in. Solar covers won't! You are really comparing apples and oranges here.

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Actually, most of the electric safety cover does float on the water and is designed with slack to do so. Only about 6" to a foot on the sides is up above the water (attached to aluminum rails on the underside of the coping in my case) with the rest riding on top of (i.e. floating on) the water. It does that so standing on the cover or other objects on the cover are at least partly buoyed up by the water rather than all stress being on the cover edges attached to the rails.

If the flat side of a bubble-type cover is down on the water, then it's similar to my cover except for the insulation of the bubbles on top. When the bubbles are down on the water they are floating keeping the flat side up away from the water thus trapping additional air in between the bubbles for even more insulation. That was my point.

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I think I am clear on the concept. Of course this is not to scale at all, but the area shown where the bubbles are up, you have direct surface (outside air) to solid plastic, to water. It prevents evaporation but there is no insulation similar to a double pane window. With the bubbles down, the idea is that the bubbles float the top solid plastic sheet so not only do I get the double pane window style insulation in the bubbles but in between the bubbles there is air in that channel, so really the whole thing is providing that. So I lose a little bit, oh well

BUBBLE SIDE UP (incorrect, but still effective to some large degree)

bubbles_up.png

BUBBLE SIDE DOWN (most correct)

bubbles_down.png

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Still my point is that the difference is going to be so small since the majority of the heat loss is by evaporation that the difference in heat savings in only going to be a degree or two at best. The difference between a covered and uncovered pool wil be more like 6 to 10 degrees daily! I would not loose any sleep over it now. Covers last one to three seasons normally. When you replace it you will know which way is up!

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Wow AMG, you can draw! Those are great illustrations and yes, you've got the concept exactly and yes, waterbear is right that most of the prevention of heat loss is from cutting down evaporation. Additionally, the part that is from cutting down conduction is still mostly effective with the bubbles up and you're not likely to notice a difference with the cover on upside-down.

I've measured the overnight temperature drop in my own pool with the cover off losing 6ºF and with the cover on losing 3ºF while a neighbor's pool at the same water temp but with a bubble-type cover losing only 1-2ºF (probably something like 1.5ºF but couldn't tell for sure).

Of course, when the time comes for you to replace your cover and have it be bubbles-down next time, you can let us know if there's any measurable difference in heat loss (if any of us remember this by then :-)

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