Safety cover vs solar cover heat

[alben]

For the past 10 years I have always used a safety cover year round on my 18' X 36' inground pool. My current safety cover is:
Protex - heavy duty cover with 98% shade.

Previously, when I bought the house, the pool had only a bubble solar cover. However after having pocket gophers, muskrats, squirrels, and rabbits falling and subsequently drowning in the pool, I decided to purchase a safety cover and leave it on permanently. Also this offered another level of safety when we became parents to a toddler/child. The only time the cover comes off is when we are using it.

My question is if anyone has data on how much solar heating BTUs I am missing out on. I realize I am not getting the effects of heating during the day on sunny days, but by how much? My current safety cover is dark green, a very tight weave (98% shade), and does not touch the water surface. The air space between the cover and the water surface gets very hot and is humid. So I am assuming the I am minimizing heat loss via evaporation and the hot air space "may" be helping with heating the water.

Any comments on using a safety cover versus a solar blanket regarding heating and heat retention? Would adding a solar blanket under the safety cover help with heat retention?

 

[chem geek]

Welcome to TFP!

It's a good question. First, the easy part. A relatively thin safety cover seems to have about half of the insulation capability of a bubble-type cover. This is my estimate based on my own safety cover compared to others' experiences with bubble covers and the relative temperature loss overnight (accounting for pool vs. air temperature differences). So having a bubble type cover might cut down your overnight heat loss (and temperature drop) roughly in half. This can result in a substantial net temperature gain between heating during the day and a lower loss at night.

The harder question to answer is how much heat gain you are missing out on due to not having a mostly clear cover. I made technical calculations here that show that an uncovered white plaster pool absorbs around 60% of the sun's energy. If there is no cover, then you get this full amount of absorption (and with a dark pool surface, you get even more absorption and therefore heating), but with no cover you also lose heat from evaporation. So in theory, a clear cover that let infrared and visible light through, but blocked UV to protect chlorine breakdown and also prevented evaporation, would be ideal. The problem is that I don't know how much light is lost through use of a clear bubble-type cover. My best guess estimate is that it might be as much as half since even clear or light blue covers don't seem to fully transmit light through. So instead of a peak heating rate of around 0.7ºF per hour with a perfectly transparent cover (and no evaporation), the peak heating rate might be 0.3-0.4ºF per hour for a white plaster pool.

Richard

 

[dayhiker]

It's been very mild in central AL this week with highs around 70. Lows have been as far down as 45. From today on it's supposed to be mid 80's. I had my mesh saftey cover on AND the bubble cover to try and hold heat in. I won't do that next year, btw because the bubble cover is a nasty mess. I took the safety cover off on Sunday, but left the bubble cover on and the pool temp has gone from 60 to 65 in 3 full days of sunlight (M, T, and W).

I'm out of town until Sun night but will try to give an updated temp when I get back. It's supposed to be warm and bright over that time period.

The cool temps seem to allow us to compare the sunlight only, so 5 degrees sounds like the difference is significant.



I put the bubble cover on in late March to try and start retaining heat. What I learned is that it's a waste because of the shading. Also, the pollen goes through the mesh and just sits on the bubble. Next year I'll leave the pool as-is until after Tax Day. That seems to be about the time that the oak blooms are finished. I can take the mesh off, run the polaris for a day, vacuum, put the bubble cover on, get the solar in gear, and by May 1 I should be swimming. Ahh, lessons learned. This is year 2 with the pool, so I'm getting there with the help of this place.

 

[PaulR]

the bubble cover is a nasty mess.

Amen. I made the additional goof of putting mine on without skimming first, so there's leaves and gunk on the underside of the cover too. At some point I'm going to have to pull it off to hose it down top AND bottom.

But the temp is 77... definitely getting there!
--paulr

 

[dayhiker]

the bubble cover is a nasty mess.

Amen. I made the additional goof of putting mine on without skimming first, so there's leaves and gunk on the underside of the cover too. At some point I'm going to have to pull it off to hose it down top AND bottom.

But the temp is 77... definitely getting there!
--paulr

Once I took the safety cover off I flipped the bubble cover so that the side with all of the pollen would now be face down so it could at least start the process of getting washed off. I also pressure washed my slab this week so now I have some of that crud blown in the pool too. The coping, diving board, and steps look dang good now though.