More Solar Cover Questions

[MrLeadFoot]

I think, because of your interest, you should be the Guinea pig and report your findings. This is the way many of our processes and recommendations have been established. (I'm not joking).

I actually thought about it, but I think it would be a bit difficult to do a reat "test", because I'd have to get two covers and try to duplicate scenarios, which will be difficult due to nature factors including, but not limited to, light hours during the day, wind, temps, etc. This morning I was actually thinking of taking two white 5 gallon buckets, and putting equal amounts of chlorine in each, a small piece of pool cover in one, and nothing in the other, fish tank pumps of the same size set on low, and placing them side by side in the sun for 6 hours, and testing chlorine before and after, and checking temps after. Not the best setup but at least both samples would be subjected to the exact same conditions. Problems is that the water column would be so small they might get heated up by the fish tank pumps, even if I were to try and insulate the buckets from ambient temperature as well. I then thought about using two aquariums, but the two empty ones I have are two different sizes.

I think someone who has tried each color cover on a pool for a summer season would be able to provide more realistic results, even if the two seasons were to differ a bit both weather-wise, and pool use-wise. Yes, it's a long shot to come across someone who has used both colors, and actually noted temperature differences, not to mention noticed FC effect differences, but I thought I would see if anyone had, hence why I created this thread.

 

[M T]

There will be many variations in the use of the covers and in the environment. Especially in California, a location difference of ten miles can dramatically affect your annual and daily temperature and sun exposure ranges. In my case, I live in an environment with June & July average high temperature of 77 and average low of 58, zero rain and clouds only in the morning. I have a similar requirement for the pool temp to be in the upper 80s which would require heating except in the occasional hot spells.

I've had my pool 40 years and been through covers mostly on the two-year cycle. I've got a almost-kidney-shaped pool with no hope of a reel, but we do pull the cover to one end (folding it in 3' widths). Maybe your method of rolling it up in the water would preserve it better but it seems cumbersome to me (how do I get it out?). I have used different colored covers (blue, gray, silver) but I'm not able to say much about FC loss. It is the UV blocking of these covers that prevents FC loss.

I've used the (36'x18') heavy and very heavy (thick) covers, but I wouldn't go back to them. Way too much effort to drag them off the pool (a 2-person job) and they don't last longer, nor do they cause the pool to be warmer. The effort meant that I didn't use the pool as much. I've been using one of the 8mil blue covers which is easy for me to uncover half the pool by myself. I do not trim the pool cover to match the pool shape but instead fold the excess back over the pool. I have considered using two pieces but never felt it would make things easier. I did consider the cover circles (like lily pads) as that would be relatively easy to remove but I'd think squares would be easier to cover the water.

It is hard to compare year to year, but I feel the 8-mil cover I have now is probably the best for having warmer water. The pool water gets warmer than the air's high temperature.

Besides heat, one of the other reasons I keep the pool covered is to prevent loss of water. We've been through some extended periods of drought in California and I don't want to have to keep topping off my pool. We keep the pool covered except when we swim, I keep the CYA about 20 (too low for an "outdoor" pool, at the upper range of an indoor pool). That entails a lower FC level (both normal and SLAM).

But there are some downsides to keeping the pool covered. Virtually all pool chemistry discussions seem to assume no cover.

• The gases in the water don't balance as quickly with the air with a cover on the surface. If the CO2 (generated as part of sanitization) can't leave the pool, the pool will tend to be acidic. You can aerate to deal with this.
• This site's ABC's of Water Chemistry says "CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight." This suggests that sunlight is necessary to break down CC.
• I suspect the SLAM instructions should specify the cover should be removed during the process. This is when you're likely to generate a lot of CC and CO2. But a pool owner will think a cover will keep the FC levels higher and more consistent during the process.

These differences from an uncovered pool may cause frustration when your pool works differently from what you read about.

Regarding the dissociation of FC by light, my understanding is that chlorine breaks down from light in the 250nm - 450nm wavelength range (UVB, UVA through violet). I suspect any solar cover would block this but I don't know for sure. A decade or so ago, I did see some covers that specified their UV blocking quality. Last time I bought a cover, I didn't run across any that specified that info.

 

[Rancho Cost-a-Lotta]

I think someone who has tried each color cover on a pool for a summer season would be able to provide more realistic results, even if the two seasons were to differ a bit both weather-wise, and pool use-wise. Yes, it's a long shot to come across someone who has used both colors, and actually noted temperature differences, not to mention noticed FC effect differences, but I thought I would see if anyone had, hence why I created this thread.

This forum member commented about his the difference between clear and opaque covers:

Running a 55K Gal SWCG at 75% just to maintain a 4.0 CL level in a 17K gal pool

last year I barely needed to run my SWCG at 25% for 2 hours per day and this year running it at 75% for 6 hours. So running it 9x as much to maintain the same level of chlorine. The only difference is that last year I had a solid gray solar cover and now have a clear one to produce more heat...

www.troublefreepool.com

 

[hwy17]

I have the same experience as you OP - blue cover on all the time works great. So that's what I keep doing. I don't have the same experience on longevity! I get a new one every year.

On daytime covering, I have some thoughts. My experience is the same as others that night time covering is more important to the temperature of the pool. Initially this led me to the conclusion that there must be more evaporation happening at night. But, the scientifically educated people I know assure me that if you take 86 degree water in 80 degree ambient vs 50 or 60 degree ambient, the water in higher ambient temps will evaporate more. I believe it is an under-appreciated fact that there is actually more heat loss by evaporation during the warm day than there is at night, and this is what leads to our experience that covering at all times when not in use is in fact the most effective method. Counter arguments would include that the cover increases reflectivity which I don't buy or that the cover increases radiative losses, which I don't buy either as long as the pump is running and keeping the covered surface closer to the water temp.

As for blue vs clear, my less thought out gut opinion is that it doesn't matter much at all. If you were to look at them with either a blue blocking filter, or an infrared camera, I think they would be indiscernible and somehow (less thought out) this indicates there is an indiscernible difference in heat absorption.

On chemical consumption, I do notice the difference, but both pale in comparison to a truly opaque cover like I use over winter which can hold chlorine even in a warm pool for probably weeks. Given how stark this difference is, my gut estimation of the effect on chemical consumption is that it is small, maybe 10-25% or something.

Cal poly's pool research center would seem ideal to settle all of these debates, and I wish they would. I wonder if they have decided the layout is not good enough for rigorous scientific standards given different wind loadings and the pools being too close together and sort of stopped using it at all.

 

[Oreodane]

I've had my pool for 23 years and, for many of the years, I would cover the pool for heat. Believe it or not, in all this time I've only bought two covers, both of which I think have lasted between 5 and 7 years. Neither of them fell apart by separating at the seams nor did either of them disintegrate. The bubbles simply started gradually popping over time until they became holes, and when a few holes developed I tossed them. Both covers were the blue covers from Leslie's.

I just threw out the second one, and I want a replacement for two reasons this time, heating the water and slowing FC breakdown. Now, I know some people don't believe covers do much in the way of heating a pool, but with a cover on my pool for a few days, my temp can get to 88F. In fact, I have to turn my pump on to circulate the water when the cover is on or the top of the water gets super hot, to the point where it wouldn't be good for the cover to sit on the hot water.

I'd like to hear opinions from those who have had covers in regards to the questions below.

1) Do the clear covers really heat the water MORE than blue covers? The blue ones work really well in generating, not just trapping, heat, and I find it hard to believe a light colored one like clear can even get hot, let alone generate more heat than the blue one. If they really do, I'd like to hear from you.

2) I suspect blue would be better, but will blue or clear be better to slow FC breakdown?

3) I've come across posts on here, and reviews on shopping sites, that say these covers are "disposable" because they disintegrate in a year, but that's not been my experience at all! They seem to last a LONG time for me. Have the quality of covers gone down that badly since I bought my last one?

4) The first cover I got, I trimmed to fit the challenging shape of my pool, as seen below, perfectly. I split the cover at the narrowest point between shallow and deep, to make it easy to simply roll up and remove each piece, or just let them float rolled up. Leaving one end covered enabled the family to enjoy one end or the other without uncovering the whole pool, too, when applicable. The second cover was narrower and followed the curves out of the narrowest point of the pool just enough so the cover could be held in place by the shape of the pool, but more of water in the round parts of the pool were exposed, especially in the shallow end. I don't think it mattered as far as heating is concerned, but will more exposure defeat the purpose of using the cover to slow FC breakdown? The narrowest part of my pool is about 14.5' and the length is 34, so I could get 34x16, and keep the curves in the deep and shallow ends exposed. If I want to cover all of the curves, though, I'd need at least 20' wide, and the cutting could become tedious if I really do have to replace these newer covers every year. What are your thoughts here?
View attachment 491546

Solar covers do not heat the water from the sun. They prevent or reduce the cooling of the water due to evaporation. I'm unsure if they reduce the breakdown of FC, but if they do, it's probably due to the filtering of the sun's UV rays by the plastic the cover is made out of. I don't think the color of the liner would have any effect on the chlorine breakdown, which is just my opinion.

 

[MrLeadFoot]

Great post. Thank you for that.

I've had my pool 40 years and been through covers mostly on the two-year cycle. I've got a almost-kidney-shaped pool with no hope of a reel, but we do pull the cover to one end (folding it in 3' widths). Maybe your method of rolling it up in the water would preserve it better but it seems cumbersome to me (how do I get it out?).

Most of the time I push the rolled up halves to the side of the pool. I have a pretty large pool so this gives me plenty of room to do laps. If i want to play "horse" with the kids using the basket you see in the pic, we move the rolls to the deep end against the same side as the basket and they're out of the way. If I want to remove a half, once rolled up, I first lift one end up out of the pool and drape it on a lounge chair which puts the roll at a vertical angle and allows most of the water collected in the roll to drain down and out of the other end back into the pool. If I'm doing this alone, I then fold the upper end of the roll over and onto the lower end and, because now it is light with the water removed, I then simply lift it out. This is the only time any stress is put on the cover (when I fold it) but it is obviously minimal, judging by how long a cover lasts me.

I have considered using two pieces but never felt it would make things easier.

There is absolutely no way I'd be able to move a cover around on my pool by myself if it was one piece. Look at the weird shape of my pool. It's way more curvy than a kidney shaped pool, so even when putting it on, even with multiple people, would be a real PITA. I hated having a cover when it was one piece.

Before I started cutting them in half, I couldn't even roll them up without folding the sides in first, which REALLY creased and undoubtedly compromised the integrity of the cover. So, I cut the first one out of desperation. I was hesitant at first because there's no going back once you cut it. But, it turned out to be the best thing I could've done. Rolling it up is a breeze, especially when you're in the water, but I can still roll it up when I'm not in the pool. Putting it back on, and getting it to fit into all the curves is a breeze now, too, because I just unroll a half and can easily slide it around to fit into the curves.

Even better is that the curves I used to curse I now count as blessings. If I want to use only one end of the pool, the shallow end for basketball games or the deep end for diving, I can simply roll up one end and move the roll wherever I want, including sliding it up onto the remaining half. I cut mine right that the narrowest point between shallow and deep ends, and since the cover is trimmed to fit into the curves, cutting it at the narrowest point ends up ensuring that either remaining half doesn't move out of position by virtue of it fitting the form of the pool. Even the wind or motion of the water from splashing and diving doesn't effect its position.

If you're unsure about cutting yours, I suggest you wait until you're ready to discard your current cover, then split it and play with it a bit. As the cliche goes, I bet you kick yourself for not having done it sooner.

It is hard to compare year to year, but I feel the 8-mil cover I have now is probably the best for having warmer water. The pool water gets warmer than the air's high temperature.

I never would have thought that about a thinner cover. But I can't help but wonder if I did go thinner that it would not last as on given the way I move mine around.

Besides heat, one of the other reasons I keep the pool covered is to prevent loss of water. We've been through some extended periods of drought in California and I don't want to have to keep topping off my pool. We keep the pool covered except when we swim, I keep the CYA about 20 (too low for an "outdoor" pool, at the upper range of an indoor pool). That entails a lower FC level (both normal and SLAM).

Fortunately for me, I have auto fill so I don't have to worry about topping off. I like to keep mine covered, too, to maintain the heat.

But there are some downsides to keeping the pool covered. Virtually all pool chemistry discussions seem to assume no cover.

• The gases in the water don't balance as quickly with the air with a cover on the surface. If the CO2 (generated as part of sanitization) can't leave the pool, the pool will tend to be acidic. You can aerate to deal with this.
• This site's ABC's of Water Chemistry says "CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight." This suggests that sunlight is necessary to break down CC.
• I suspect the SLAM instructions should specify the cover should be removed during the process. This is when you're likely to generate a lot of CC and CO2. But a pool owner will think a cover will keep the FC levels higher and more consistent during the process.

These differences from an uncovered pool may cause frustration when your pool works differently from what you read about.

Didn't know some of this, and maybe why I always felt that if I cover it too long it makes it easier for algae to take hold. I always thought it was because of the warmer water. I'll have to monitor more carefully to ensure things are balanced. Maybe I can take it off periodically during the day when I can to help mitigate any negative effects. I always keep it covered during the middle of the day because I've found that that's when it helps generate the most heat, but I can certainly "let it breathe" before and after.

Regarding the dissociation of FC by light, my understanding is that chlorine breaks down from light in the 250nm - 450nm wavelength range (UVB, UVA through violet). I suspect any solar cover would block this but I don't know for sure. A decade or so ago, I did see some covers that specified their UV blocking quality. Last time I bought a cover, I didn't run across any that specified that info.

Yes, that's the question I have regarding clear covers. I'm thinking it would be nice to have clear for a change, especially if it helps warm better, and so I can see into the pool better. Being able to see how my Baracuda cleaner is doing with the cover on would be nice, too, but I can't help shake the nagging suspicion that clear might be a weaker material. Maybe it's just that colored LOOKS more substantial, and that clear looks like fragile bubble wrap that makes me THINK clear is more fragile, I don't know. Lowering FC usage is a benefit to me, too, not having SWG, so if clear reduces that benefit, then I wouldn't want clear.

 

[MrLeadFoot]

This forum member commented about his the difference between clear and opaque covers:

Running a 55K Gal SWCG at 75% just to maintain a 4.0 CL level in a 17K gal pool

last year I barely needed to run my SWCG at 25% for 2 hours per day and this year running it at 75% for 6 hours. So running it 9x as much to maintain the same level of chlorine. The only difference is that last year I had a solid gray solar cover and now have a clear one to produce more heat...

www.troublefreepool.com

Thanks for finding this!

 

[MrLeadFoot]

I have the same experience as you OP - blue cover on all the time works great. So that's what I keep doing. I don't have the same experience on longevity! I get a new one every year.

On daytime covering, I have some thoughts. My experience is the same as others that night time covering is more important to the temperature of the pool. Initially this led me to the conclusion that there must be more evaporation happening at night. But, the scientifically educated people I know assure me that if you take 86 degree water in 80 degree ambient vs 50 or 60 degree ambient, the water in higher ambient temps will evaporate more. I believe it is an under-appreciated fact that there is actually more heat loss by evaporation during the warm day than there is at night, and this is what leads to our experience that covering at all times when not in use is in fact the most effective method. Counter arguments would include that the cover increases reflectivity which I don't buy or that the cover increases radiative losses, which I don't buy either as long as the pump is running and keeping the covered surface closer to the water temp.

As for blue vs clear, my less thought out gut opinion is that it doesn't matter much at all. If you were to look at them with either a blue blocking filter, or an infrared camera, I think they would be indiscernible and somehow (less thought out) this indicates there is an indiscernible difference in heat absorption.

On chemical consumption, I do notice the difference, but both pale in comparison to a truly opaque cover like I use over winter which can hold chlorine even in a warm pool for probably weeks. Given how stark this difference is, my gut estimation of the effect on chemical consumption is that it is small, maybe 10-25% or something.

Cal poly's pool research center would seem ideal to settle all of these debates, and I wish they would. I wonder if they have decided the layout is not good enough for rigorous scientific standards given different wind loadings and the pools being too close together and sort of stopped using it at all.

Nice post. While 25% less chlorine usage is nothing for those of you with SWG, that's significant for less fortunate folks like me, who have to schlep to the store to buy liquid chlorine as the costs keep going up, and having to constantly add it to the pool on a regular basis. So, if a blue cover saves me a bit on all fronts here, and helps warm my pool, as it has been doing all these years, it's looking like so far blue is pulling ahead of clear.

 

[Newdude]

I'll vote that my 'clear' / opaque white cover was hideous. It called my attention to it from anywhere in the yard, where if I had been mowing the lawn, a blue cover would have blended in that a pool was over there out the corner of my eye.

I found that the clear cover did exactly what it was supposed to do, along the same lines as everyone reports with a blue cover. Nothing magical happened due to the clear cover. If it was cool for an extended time, it was a moot point that the water was warmer than it would have been with no cover, yet still an undesirable temperature for swimming.

 

[JamesW]

But, the scientifically educated people I know assure me that if you take 86 degree water in 80 degree ambient vs 50 or 60 degree ambient, the water in higher ambient temps will evaporate more.

Heat loss from water to air through conduction and convection increases as the water temperature difference from pool (Higher temperature) to air (Lower temperature than pool) increases.

You also have to calculate heat loss from evaporation, which depends on the humidity of the air and air velocity.

You might have lower humidity during colder weather, which will increase evaporation.

Hotter weather can cause evaporation by providing some of the heat that water needs to evaporate.

So, you can get more evaporation during hotter weather, but the air and sun provide some of the heat.

Warmer air can hold more water, which can increase evaporation depending on the humidity.

During hotter weather, the air can provide heat to the water rather than remove heat (conduction and convection).

Also, during the summer, the sun provides a lot more heat than in the winter.

You also have radiation losses (thermal infrared) which are probably reduced significantly with a cover.

So, there are multiple different effects that have to be considered when calculating heat loss or gain.

Evaporation from a Water Surface

Evaporation of water from a water surface - like a swimming pool or an open tank - depends on water temperature, air temperature, air humidity and air velocity above the water surface - online calculator.

www.engineeringtoolbox.com

Swimming Pool Heaters

Calculate outdoor swimming pool heaters.

www.engineeringtoolbox.com

 

[JamesW]

5. Conclusion

In this work, comparison has been made between experiments and simulation of a swimming pool under dynamic conditions.

To override the influence of the heater (a heat pump in this case) and of solar gains on the time dependent behavior of water’s temperature, specific tests have been made during summer night so as to properly evaluate heat losses.

Among the various contributions and in accordance with the literature, the identified most important one is evaporation, which accounts between 55 and 70 %, depending on the 4 different tested cases.

It has been demonstrated that wind velocity and relative humidity in the ambient air have the most important influence on this specific phenomenon.

The second one, also in accordance with the literature is the long wave radiation from the swimming pool to the surrounding areas and in particular to the sky (20 to 40 %).

In the 4 investigated cases, the analysis led to an almost identical value whatever the conditions.

The third contribution to total losses is convection and accounts for less than 10 % mainly because of low values of wind velocity during the experiments.

The last part represents between 1 and 2 % and corresponds to losses through the walls and also to the input of district water that offsets evaporation.

https://pdf.sciencedirectassets.com...31d5103500404540601&rr=7c7cf0dd4fc0c070&cc=us

 

[JamesW]

the water in higher ambient temps will evaporate more.

Water needs heat to evaporate.

This is why we sweat to cool off.

As sweat evaporates, the heat comes from our skin, which cools us off.

As pool water evaporates, the heat mostly comes from the rest of the pool water, but some can come from the air and from the sun's thermal radiation.

So, even if you get more evaporation, the pool water is not necessarily losing more heat because the heat is being supplied by the air and the sun.

As noted, the humidity and air speed are very important.

With zero airflow or 0 air velocity, the humidity above the surface increases and reduces evaporation.

 

[JamesW]

Heat pumps actually work better with more humidity because they cause the water in the air to condense, which releases the heat in the water as it goes from vapor to liquid.

This is why heat pumps produce so much water.

It’s basically the reverse of evaporation.

 

[MrLeadFoot]

I'll vote that my 'clear' / opaque white cover was hideous. It called my attention to it from anywhere in the yard, where if I had been mowing the lawn, a blue cover would have blended in that a pool was over there out the corner of my eye.

Sorry if I wasn't clear previously. When I say "clear", I am referring to the ones that are transparent/slightly translucent not an opaque white. In fact, I didn't even know there was an opaque white. But, since you pointed it out, your description makes sense. I agree that I would not want something white.

I found that the clear cover did exactly what it was supposed to do, along the same lines as everyone reports with a blue cover. Nothing magical happened due to the clear cover. If it was cool for an extended time, it was a moot point that the water was warmer than it would have been with no cover, yet still an undesirable temperature for swimming.

Ok, I take away from your post that the clear cover doesn't help heat, or trap heat, better than a blue cover.

 

[Newdude]

Ok, I take away from your post that the clear cover doesn't help heat, or trap heat, better than a blue cover.

Exactly.

The 'clear' cover is white-ish and/or opaque at best. Maybe it hazed up quickly and then ladted for 4 more years. Or maybe my 16 mil cover was less transparent than the 8 mil. I dunno, but it was hideous. Lol.

 

[MrLeadFoot]

Water needs heat to evaporate.

This is why we sweat to cool off.

As sweat evaporates, the heat comes from our skin, which cools us off.

As pool water evaporates, the heat mostly comes from the rest of the pool water, but some can come from the air and from the sun's thermal radiation.

So, even if you get more evaporation, the pool water is not necessarily losing more heat because the heat is being supplied by the air and the sun.

As noted, the humidity and air speed are very important.

With zero airflow or 0 air velocity, the humidity above the surface increases and reduces evaporation.

All great info, and none of it surprises me. Thank you for chiming in!

 

[MrLeadFoot]

Exactly.

The 'clear' cover is white-ish and/or opaque at best. Maybe it hazed up quickly and then ladted for 4 more years. Or maybe my 16 mil cover was less transparent than the 8 mil. I dunno, but it was hideous. Lol.

I would love to see pic of your pool with the hideous cover on it, so if you happen to come across one, please post it so we can all freak out. I sure could use some entertainment after the serious natures of this thread that I started!

 

[Newdude]

I would love to see pic of your pool with the hideous cover on it,

Sadly those pics were taken on a sliding keyboard phone and didn't transfer to my first smart phone back when.

 

[MrLeadFoot]

Sadly those pics were taken on a sliding keyboard phone and didn't transfer to my first smart phone back when.

I think I had that same phone!

 

[MrLeadFoot]

This forum member commented about his the difference between clear and opaque covers:

Running a 55K Gal SWCG at 75% just to maintain a 4.0 CL level in a 17K gal pool

last year I barely needed to run my SWCG at 25% for 2 hours per day and this year running it at 75% for 6 hours. So running it 9x as much to maintain the same level of chlorine. The only difference is that last year I had a solid gray solar cover and now have a clear one to produce more heat...

www.troublefreepool.com

I noticed that he also went to a clear cover that year over opaque in an attempt to generate more heat. I wonder what he found, as a result. I will ask him on that thread.