Anyone use a solar cover with an auto-cover?

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gtemkin

gtemkin

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LifeTime Supporter
Jun 7, 2008
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Seattle, WA
Wonder if this has ever been tried. It's for next year's season.

I had solar covers for many years. I found they gathered and retained heat very well. I now have an auto-cover which is wonderful for keeping the pool clean and convenient to open and close but worthless at retaining heat.

I was thinking of having a solar cover floating on the water, coming off of a reel that would be at the opposite end of the pool than the auto-cover. The loose ends of the solar cover would have to be "tethered" with easy disconnects to both ends of the pool.

So, would a solid auto cover slide over a solar cover? I'm thinking it would put a lot more drag in the system that it wouldn't be practical and it would over-stress the auto cover system. Anyone have any pros or cons?
 
Really all "solar covers" mostly do is reduced evaporation and thus retain heat. So your auto cover should accomplish the same thing ... at least at night. If you want to add heat, it is usually best to have no cover on while the sun hits the pool.
 
jblizzle said:
Really all "solar covers" mostly do is reduced evaporation and thus retain heat. So your auto cover should accomplish the same thing ... at least at night. If you want to add heat, it is usually best to have no cover on while the sun hits the pool.
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So not to stir the pot...but I've seen this a few times posted, and in my testing I just don't see it. (OP does not either)

My brother and I both have similar pools, he has an auto cover and I have a 16mm solar cover (yes I know, it is thick but whatever).

We both live in the same climate and he runs his heater WAY MORE than I do to maintain the same temperature. He has gas vs. my HP, but still - we compare heat loss, etc...and I blow him away with my solar cover.

Most other variables are DEAD the same....so are we 100% sure that an auto cover and solar cover show similar performance. Heck, the OP brought this up because he has first hand experience with both and the auto cover was much less efficient.

So just curious why I keep seeing this data that seems to be flawed.....
 
I agree that the solar covers I've used have provided much more heat gain than having no cover during the day. I've had both clear and colored, clear working the best. I think there may be a lensing effect that is not being accounted for.
 
Bama Rambler said:
My personal experience mimics yours. I gained more heat with a clear cover on than with no cover. I think it's because it negates the cooling from the wind.
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Yes, thats another big part of why a solar cover appears to do better than just being uncovered.
 
Fair points. With no wind (maybe rare) no cover should add more heat ... maybe that is too ideal. I imagine the humidity level also plays a part in this.

If the cover its left on all day, then the solar cover will certainly allow more heat to be added than an opaque safety cover that does not let the sun in.

For the OP I do not think having both covers on will have any benefit assuming the auto cover is opaque. Unless you intend to open it during the day and only have the solar cover on.
 
Yes, opening during the day would be my intent. My pool gets sparse use - twice a week typical - so I would be benefiting from the solar gain during the day and use the convenience of the auto cover to fully cover the pool over night. It might get more use if I could get and keep it warmer without much additional expense.
 
gtemkin said:
Yes, opening during the day would be my intent. My pool gets sparse use - twice a week typical - so I would be benefiting from the solar gain during the day and use the convenience of the auto cover to fully cover the pool over night. It might get more use if I could get and keep it warmer without much additional expense.
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Quick question...why did you add the auto cover...simply for "safety" or was it just the keeping things clean angle ?
 
Thought it would be convenient, which it is, but the loss of solar gain is a big loss for me. Guess I also fell for the bling factor. Have been pleased with the cleanliness benefit, although I hadn't considered that before buying. Safety wasn't much of a factor - although I am very big on safety - because our backyard is completely wall fenced and it's not viewable from outside the yard.
 

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gtemkin said:
Thought it would be convenient, which it is, but the loss of solar gain is a big loss for me. Guess I also fell for the bling factor. Have been pleased with the cleanliness benefit, although I hadn't considered that before buying. Safety wasn't much of a factor - although I am very big on safety - because our backyard is completely wall fenced and it's not viewable from outside the yard.
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So if you HAD to do it over.

And your OPTIONS WERE (exact same price)

Fence with Solar
No Fence and Auto Cover

What would you do ?
 
There may be insulated/solar auto-covers but knowing the price of a non-insulated auto-cover I'd say it would likely be many many thousands of dollars and because of increased thickness it probably wouldn't fit in the existing underground chamber it lives in now.

That's why I came up with this hybrid solution which would be comparitively inexpensive. If someone has tried it it be nice to hear if it worked or not.
 
gtemkin said:
There may be insulated/solar auto-covers but knowing the price of a non-insulated auto-cover I'd say it would likely be many many thousands of dollars and because of increased thickness it probably wouldn't fit in the existing underground chamber it lives in now.

That's why I came up with this hybrid solution which would be comparitively inexpensive. If someone has tried it it be nice to hear if it worked or not.
Click to expand...


One does exist, but I can't find them again...if I do I will post.
 
I am curious to know if you tried your solar blanket under the automatic retractable cover idea. If the bubble cover can act as an insulator between the water and the vinyl cover, wouldn't that decrease the heat transfer to the vinyl cover and wouldn't that theoretically lower the convective heat loss? Or are solar blankets really just evaporative barriers? I have an opaque cover so I'm not interested in solar heat gain, just in minimizing my losses. Anyone with any info?
 
You'd have to tie down the solar blanket since it will simply get pushed to one end by the automatic retractable cover since such covers are designed to rest on the water's surface. They expect water to be there to help prop up such covers -- without water, the side attachment could not hold the weight of someone standing on the cover.

With a bubble-type solar blanket you would get better insulation. Roughly speaking, the relatively thin retractable cover cuts down total heat loss from the pool roughly in half, mostly due to eliminating evaporation and only a little from insulating. A bubble-type solar blanket by itself cuts overall heat loss by roughly 75% so while most of this is from eliminating evaporation a good deal is from the extra insulation. If you combined the two then there would only be a little more insulation so perhaps cut overall heat loss by 80-85%. If you had to choose a single cover, you'd choose the bubble-type solar blanket, but of course you don't get the safety cover benefit of preventing anyone from falling into the pool.
 
Assuming a windless day with no significant heat gain from the sun, I calculated that my Gecko controller (4.0 kw) heater could maintain my pool temperature at 88F when the ambient air temp dropped to as low as 56F.

This was based on the following:
the surface area is 14'x8'=210SF
the r-value of the vinyl retractable cover is ~ 0.5 (based on an internet search that turned up a DOE study of a pool in Idaho, who knew)
so working backwards from this formula: surface area x difference in temperature divided by the R-value = energy transferred (BTU)
I figured 4.0 kw * 3400 BTU per w = 13600 BTUs
13600 BTUs / 210*0.5 = 32.4 deg F difference.

So, without a wind and no solar gain anticipated during the day, I figured my pool heater would only start to run continuously when the average air temp dropped below ~56F (from 88-32.4). When the average air temp dropped below this, I figured the pool would slowly drop temp as well, in spite of the little heater that could.
So far, the pool is maintaining its 88F with an average daily temperature now of ~45, expecting to drop further this week to ~40F. This average daily is an average of the high and low for each day.

So, how can this be?
I figured that in reality there is a mild breeze, maybe 1-3mph, but I expect this would contribute to the pool water temp dropping further, not gaining...
Is there a solar effect for an opaque blue vinyl cover (Coverstar) that I'm not aware of, yet seeing an affect of?
Or is the R-value for a vinyl cover really not 0.5 (BTW that study gave bubble covers an R value of 1)? and can you have an R value of 0.5 - shouldn't all R values be greater than or equal to 1?

The sides of this AGP have 3 layers of insulation with 2 dead air layers for an ~ R value of 30. There is just a simple concrete pad underneath, but a Dreamturf artificial turf lawn on 3 of 4 sides - we know this elevates the temp above the ground (think football stadiums and the effect there), but I don't think it contributes anything to the cement pad. The 4th side of the pool abuts a deck of equal height.
 
OK, anyone with ideas on where I went wrong in my calculations?
3 days now with average temps in mid 30's and pool temp still at 88F.
One thing I notiiced but didn't think much of is that the vinyl cover only contacts the water in the midsection of the pool - probably 50% of the cover surface is not in touch with the water - but I wouldn't have thought that would make such a difference...

BTW, I figured my max electricity loss from the itty-bitty heater that could when running continuously 24x7 to be ~$11.50 a day....(about 2.5 Starbucks a day).....it's all relative.

Any input would be greatly appreciated.
 
What I learned this past week from my pool -
1) where you leave the thermometer greatly influences the reading (duh):
  • lying flat on the cover within 1 inch of the surface, either where the cover touches water or not, the temperature was generally within 2-3 degrees less than the pool water
  • standing upright about 3 inches above the cover, independent of where the cover touched the water, the temperature was ~9-10 degrees less than the pool water
  • standing upright 3 inches above the coping which is about 2-3 inches above the cover, the air temp was 20 (sunny day, no breeze) to 50 degrees (night time, clear skies, very light breeze) less than the pool water.
  • when I turned my pool heater off well after sunset and back on well before sunrise (10pm - 5am), with an average air temp of 30F, the pool lost ~ 0.57 degrees per hr (4 degrees over 7 hours).
  • it has taken roughly 2 days to regain the lost heat back up to 88F.

So in summary, it would seem that the opaque royal blue cover does have an impact beyond stopping evaporative heat loss. At least when there is no appreciable wind, during those hours when the sun hits the cover, there is a significant increase in the air temp above the cover limiting the convective heat loss. Definitely above my calculated threshold temperature for my heater of 56F. So while there is no solar gain that might be had with a bubble cover, there is a positive effect with respect to convective heat loss. And it did allow my itty-bitty-heater-that-could to eventually catch up with the loss over the next 2 days and return to just maintaining the temperature. So, I'll be surprised if my electricity bill this winter is increased by the full ~11.50$ per day, as the heater is likely not on the entire 24 hr cycle, but more likely 1/2 to 2/3rds of a day......maybe even less as it is very unusual for there to be a string of nights where the average temp is less than 30F.

Triple insulating the side walls to an equivalent of ~30 R was worth the one-time cost.

Given other discussions in TPF about the costs of alternative heating (gas, heat pumps, solar), including the installation costs, I'll just stick with what I have. Even if I lost power for a week, it's highly unlikely Seattle would experience below 30F weather 24x7 and thus highly unlikely I would have to worry about water freezing in my pool setup.

All comments/suggestions appreciated.
 

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