Okay, physics majors. Will this work?

[BABAR]

My pool is 91 degrees.

Goal is to cool off the pool.


I put a fountain in the pool that runs off the pool sweep pump. So it sprays water up into the air, which falls back into the pool (I have a water regulator that is hooked to a well to replace evaporation. So the cost of the evaporation is minimal.)

So the water goes up in the air, some of it evaporates, and the rest falls back into the pool.

Will this cool the pool, or am I merely cooling off the air AROUND the pool.

I will recheck the temperature tomorrow and let you know the result.

[hornet driver]

My guess would be --If the fountain is big enough and if it produces enough spray/mist to cause a micro atmoshere around the other falling water and pool area --then yes---but it would be a slow process---frankley it probably cools down more at night on it's own through radiation . that coupled with the fountain you can probably maintain a cooler temp and heat up a tick less in the day---clear as mud? If nothing else your o2 levels will go up and you can put something that can live in 90 deg water in there. ---WOW, I was just thinking 91---YIKES. Is this thing above ground and getting sun on the sides? The evaporation rate might surprise you too !! Our pool at the apt.--actually 2 pools joined with a small decoative fountain ----about 4 ft high ---looses about 2+ inches a day to evaporation only ---we're at around 100 deg right now --- but that number is consistant in the warm months with low humidity

[DavidQ]

What's the air temperature?

There's a good chance that the water will equalize to, or get close to, the air temperature before it falls back in. Depending on the time in air, size of droplets, etc, that might make up for any theoretical cooling due to evaporation.

[Zeus-cat]

I had the same thought abouthe air temperature.

Letting the water evaporate from the pool surface might be more effective at cooling the pool. Plus, what is the temperature of the incoming water that you are using to replace the evaporated water? That is probably going to have the biggest effect of any of the variables being discussed.

[Tarasdad]

Aeration will cause cooling but probably not enough to notice due to the volume of the pool. A shallow body like a fountain contains relatively little water by comparison which allows far more rapid circulation of the entire volume. Your best bet will be a reflective or insulating cover that allows the heat to radiate out at night while keeping heat absorption during the day to a minimum.

[rockets4kids]

I am thinking reflective cover is going to be your best bet as well. You could probably float aluminized foam on the surface.

[Nolander]

Since you are already using the electricity you would be better off pumping the water underground and back into the pool assuming you could dig and lay pipe deep enough to take advantage of the temperature differential. That coupled with the suggested reflective cover when not in daytime use, light colored components (liner or paint, inner/outer sides) should limit absorption.

Good luck.

Nolander

[jadebox]

Here in Central Florida, people do use fountains and misters to lower the temperature of their pools. The problem with the idea, I would guess, is that water evaporates quickly enough from a pool without encouraging it.

The cover idea would help lower the temperature while reducing evaporation.

Some people here run their solar pool water heaters at night to expose the water to the cooler night air. If your pipes run through the ground, it's also a version of the suggestion in the previous post.

We used to not add water to our pool during the week when normal evaporation would lower the level. Then, on weekends when we were more likely to use the pool, we'd run water from a garden hose into the pool. It would cool the water enough to make it more comfortable. We were probably wasting water, but I think it was less expensive then and we weren't in a drought condition.

An expensive option is a revisible pool heat pump which can eith heat or cool the water.

-- Roger

[Peartree]

I think that the air temperature is the key. Cooling from evaporation works on the water that mostly will not return to your pool and will cool the air surrounding the fountain. What is more likely is that the water passing through the fountain will move closer to the temperature of the surrounding air before it returns to the pool. If the air temp is hotter than the pool, it will get warmer, not cooler. If it gets cool at night, running the fountain will speed the cooling of the pool. A reflective cover is your best bet. We live far enough north that we had an clear insulated cover to slow evaporation during the day and trap extra solar heat to make it warmer.

[Marc_G]

Also, keep in mind cost. You're using electricity at some wattage to pump the water to the fountain. That same electricity could be used to drive some sort of chiller (perhaps Peltier-based?) at much higher efficiency. Nonetheless, I'm for the reflective cover in the daytime. Cheap, easy, no maintenance.

[boomtube]

It takes apx 4 BTUs or 4,184 Joule to raise one liter of water 1deg C.

Conversely that same liter of water would have to shed that same amount of energy to drop 1 deg C.

How many liters of water does your pool hold?

Multiply that by 4 and you’ll know how many BTUs it would take to heat that pool by one degree.

Simply put; to cool a swimming pool full of water by even one degree a hell of a lot of energy needs to be shed. Practically speaking the method you mention probably can’t shed that much energy faster than the water will be heated by the sunlight and surrounding air.

[Scott Evil]

(I have a water regulator that is hooked to a well to replace evaporation. So the cost of the evaporation is minimal.)

Remove portion of warm water and re-install equal portion of cool water from well to desired taste.

Sounds barbaric but think about it...

[BABAR]

Okay, I have a pool cover. It is medium blue in color. I am not sure if leaving it closed during the day keeps it hotter or cooler, then leaving the cover off at night to allow evaporation into cooler air.

[Peartree]

Okay, I have a pool cover. It is medium blue in color. I am not sure if leaving it closed during the day keeps it hotter or cooler, then leaving the cover off at night to allow evaporation into cooler air.

Blue. Does it have lots of small 'cells' that make it look like the world's largest sheet of bubble wrap?

If so, this is a 'solar cover.' It holds (traps) heat in and reduces evaporation. Good if you are trying to make your pool WARMER. It's what we use up north. I think what the others are talking about is similar but includes a silver, reflective side to reduce evaporation but to reflect the sun's heat instead of trapping it.

[dlb]

Save the money on the pump energy (unless you like it, toss in some lights for at night)
do what I have done for years, use ice and a solar (silver )cover, I find on my 20X40 pool that 10 big bags of ice lowers the temp by 3 degrees when done at night. and a cover when not being used. I have seen people use the under ground method with success too.

[BABAR]

It's blue, but it is a motorized cover (looks like a solid sheet of vinyl.) No cells. My guy feeling is that even if it is medium color blue, the sun is heating up the cover and the cover heats the water, so I think it probably hurts more than helps.

[scsager]

My pool is 91 degrees.

Goal is to cool off the pool...

Depending upon where you live (climate) your goal may not be practical. Almost anything can be achieved with enough cash.

You need to remove heat from the pool. To do this, shade the pool from the sun. For the maximum effect enclose the pool in a building with a 10 ton AC unit.

One other idea is to replace the hot water in the pool with cold water. Start with 50-100 10# bags of ice tossed into the pool after the sun goes down. This should reduce the pool temp by a few degrees as the ice melts.

Good luck

[aditat2]

the other thing about evaporative cooling that needs to be taken into account is the humidity of the air - not just the temperature. The more humidity the less evaporation of the spray so less cooling. Thats why swamp coolers work in the western US - less humidity - and not in the south east or anywhere else that the humudity tends to be higher.

[bobkrech]

Tom

You need to do 2 things to keep your pool cool.

Cover the pool area with a white tarp so the sunlight will not heat the water. The noon sun has a radiative heat flux of 1 BTU per square foot per second. Water weighs 62.5 pounds per cubic foot so in round numbers, in 1 minute in full summer sun, you will raise 1 cubic foot of water 1 F in 1 minute! Since the average pool is 5' deep, the temperature could increase 12 F in 1 hour around local noon! In reality it is less because not all the energy is absorbed (some is reflected and some is scattered), and the soil or ari around the pool take away heat, and importantly, some of the water evaporates and cools the surface. If the air is dry, and the pool is covered, and their is a breeze, you could have substantial evaporative cool, with the minimum temperature being the local dew point.

Example: http://www.tarpsonline.com/tarps/white.aspx

A fountain in a covered pool might be effective, but an evaporatative cooling tower is the way to go. We chill our process water with an evaporative cooler and it works great. The worst case is where the humidity is high so the water is only cooled to the low 70's. You can easlily process 60 to 100 gpm via this process. Imagine a 3600 to 6000 gph flow of 75 F water into the pool. A standard 20' x 40' x 5' pool has 30,000 gallons so you will keep the temperature down to a comfortable level.

http://en.wikipedia.org/wiki/Evaporative_cooler In the Southwest, this is how you cool the air in your house.

http://en.wikipedia.org/wiki/Cooling_tower This is how you cool water for industrial applicartions.



They work great. Are cheap to run, and are fairly maintenance free.

You might be able make an inexpensive pool water chiller by making a double wall structure with a spray bar spraying both internal walls. Let the cooler return water flow back inside the pool. You would need a few air inlets on one side to set up a convective air flow, but the wall would not need mortar, fan or pump since the return flow from the filter is pressurized. Painting the concrete block white on the outside white will keep them cool.

Get clever with the ehaxust air and you might be able to cool the patio as well.

Bob

[RadManCF]

+1 on the evaporative cooling tower, but I would not recomend a reflective cover, these can hinder the effectiveness of pool chemicals. I've taken care of pools before, I know what a pain it can be...

[BABAR]

For the record, the physicists are correct. No change in pool temperature.

Will have to look at cooling tower. Humidity in Tennessee runs a bit high.

Wondering if my pool cover (it is a motorized unit) can get replaceable covers, a silver/reflective one for summer and a black (retentive) one for spring and fall.



Thanks!

Tom