Pool Cover Use - Don't want more heat

[skillset]

Have been using a blue solar cover since opening (in NJ) late April. It's done a great job keeping the pool temp up, keeping evaporation down, and chlorine use down. But...

Pool is now a bit too warm for me at 91. I like it around 86-88. So, I plan on leaving the cover off at night at cooler temperatures. I figure evaporation is less at night (can anyone confirm this?), chlorine loss will be minimal because no sunlight, and hopefully the pool drops a degree or two or three.

The question is during the day - am I better off NOT using the cover? I know the chlorine use and evaporation will both increase, but what about the temp? Does the air temperature have anything to do with heat gain/loss?

I also understand that you can use a fountain to reduce the temperature (as well as aerate), but you can't use a fountain with the pool cover on !!

 

[mas985]

Evaporation loss is proportional to the temperature difference between the air and water so it is likely that night time air temps are lower so yes more evaporation at night. After all, evaporation is the primary temperature loss for water. Radiation temperature loss is about half that of evaporation. Overall, most of the temperature loss is through both evaporation and radiation via the surface (~70-90%).

Heat gain through the cover during the day is a bit harder to estimate. The cover will block some of the sun's radiation from entering the pool so it may have less heat gain with it than without it. The cover will also hold the heat in better so it will depend on air temp and wind speed.

In general, if the air temp is lower than the pool, then you want the cover off. If it is higher, then it may be better to keep it on. You might want to experiment a bit to see if it makes a bit difference. I suspect the daytime cover use is incidental and you may just want to leave the cover off all the time for convenience.

 

[sredish]

but, aren't solar covers designed to allow for the sun's heat to get to the water to heat it, then hold it in; therefore making the temps rise even faster?

I have a solar cover for mine but was directed not to use it until the pool temps start dropping below where i want it to. I could be wrong but this was my understanding of the "solar" cover.

 

[mas985]

Well, thats what they claim anyway. The fact is when you put something between the sun and the water, it will reduce the amount of sun getting to the water (cover acts as a filter). However, given that the cover contains heat better than no cover, this may result in a net heat gain. So, the heat gain (i.e. solar gain - heat loss) might be higher with the cover on vs off but it depends on a lot of factors.

If the air temp is less than the water temp then the cover may be better at containing the heat so you will have more heat gain with the cover on vs off. However if the air temp is much hotter than the water temp, you will probably have more heat gain with the cover off vs on since the sun will have more heating power with it off. Wind speed adds another factor which can affect the heat gain. The higher the wind speed the more likely a cover will help.

Color of the cover can make some difference although there are two views on this. A colored cover lets less light through to the water but the cover will transfer the heat directly to the water. A clear cover lets more light through directly to the water so it is not clear which actually provides more heat to a pool. This probably depends on the color of the pool surface as well.

 

[kirbinster]

You want evaporation as that will give you the biggest cooling effect. Keep the cover off day and night till your temperature drops. If you want it to drop even faster hook up a water spray to increase evaporation more.

 

[gonefishin]

You may want to get a solar heater. It can not only help heat your pool in spring and fall. But if you run your pump through the solar heater at night or when it's raining it will take the heat out of your pool and cool it a few degrees.

dan