I want to cool my pool in the summer. The water heats up to 91 degrees.
I am thinking of burying 900 ft. of 4in. thin waled pvc pipe 6ft down where the ground temp is 76 degrees.
Any idea of the rate of flow I would need to run through the system to cool my pool down to 80-84 ?
I will use my pool pump that runs 12hrs at night plus 4hrs during the day.
The pool heats up about 4-4.5 degrees a day so I wont have to run the system all the time but I could.  And in the winter I could warm it from the low 50s.
Just a home owner with an idea I think will work .
ANY help or advise would be great,
Thanks
Dan

Forgot to add that thesystem would hold 585 US gallons when full
Thanks
Dan

SORRY
And the pool is 23,000 gallons

Without a heat pump I don't think you'll see much benefit. Basically your adding 940 square feet of ground contact to whatever you already have from the bottom of the pool. You'd probably get more benefit with a pool cover.

How about making a pool cover from reflective radiant barrier? Reflect the sun light back into the atmosphere instead of absorbing it with the pool. The reflective barrier made with bubble wrap would float quite nicely, I would think.

I want to pump pool water through the buried pipe in hopes of cooling the water like earth tubes are used to cool air. The pool is used almost all day so covering it is not an option. Any suggestions on where to find info.on heat transfer rates and weather or not the ground would heat up and loose its cooling capacity.
Thanks
Dan

The best thing I can think of would be to download every water-to-water heat pump installation manual you can find and glean them for information about ground loops. You'll have to translate the Btuh transfer rates for heat pumps and their ground loops to the parameters of the pool water.

First, though, you don't want to use 4" pipe, but rather something in the range of 3/4" to 1 1/2". There's a reason heat pump loops use this size, better heat transfer. You want to maximize as much as practical the surface contact area for the water flowing through the piping. Also, use the same material as the heat pump systems use. Experience has shown that it's the best considering life, heat transfer, cost, and ease of installation.

Do you have any data on how quickly the pool heats up? If you know how many degrees in how many days you can calculate how much heat you have to remove to keep the temperature stable. That's a fundamental number you need to start with. Otherwise you might be tempted, based on a seat of the pants estimate, to install 1000' of pipe when maybe all you need is 100'.

76F ground temp is pretty high. Are you sure that's what it is? If so, you should consider going deeper, like down to 5 to 6 feet, to where summer soil temp is closer to 55 or 60F. Also, the deeper you go the better the heat will get carried away down into the earth. The soil could warm up from the pool heat, but not enough I don't think to be an issue. It will also cool off during the winter.

Hope this helps, some at least.

I found this insulated pool kit site. http://insulatedpoolkits.com/design.asp

I'd think that would make your pool much hotter in the summer since it is insulated from the ground contact. yes? no?

I think he's down in south Florida where the average ground temps are actually mid 70s even 20 feet down. There's really no way to do this cheap upfront. A heatpump system can operate pretty cheaply but will cost some bucks upfront. 

I am in South Texas, southeast of San Antonio.

Hello All; In response to your question on pool cooling: the most efficient, effective and affordable solution is to apply a well established and mature technology, i.e., 'evaporative cooling' processes, to the needs of both the residential and commercial pool cooling markets. The technology works well, and quickly without the involvement of freon or gas; in both dry and humid climates. Evaporative cooling systems will reduce your pool water from bathtub temperatures down some 12°- 15° within 12 to 14 hours of installation. The systems work for both fresh and salt water pools. For information on these state of the art and affordable pool cooling systems, see http://swimcoolsystems.com.

The reason 100 or so gallons of water can heat or cool a home is because of amplification/extraction of heat energy through the refrigeration process. While you could make it work without, the foot print would have to be huge (just a guess, we'd be talking 3/4"X miles).
Much easier would be some sort of cooling tower/swamp cooler set-up, or an ASHP pool heater/cooler (~$5,000). If it would be practical you could also look at water to water system that cools your house and the pool.......
Good luck,
Joe

I would first try evaporative cooling before either the underground or heat pump options. I just checked San Antonio weather and see that you have slightly higher dry bulb temps than we have in FL but dewpoints a bit lower. The lower dewpoint may prove helpful

For just a few bucks you can gin up an experimental system - HomeDepot sells for about 2 bucks green plastic ring sprinklers that work on fairly low pressure. Temporarily rig 2-4 of them to the pump discharge so that the float in or otherwisespray entirely into the pool. Place them to maximize distance water travels in air before returning to pool. The water passing through air in thin streams will increase evaporation and cooling. Run this for a day and see if it helps. I think you might be suprised how well it does work. Every gallon of water evaporated removes enough heat to cool 100 gallons of water 8 degrees or so.

An additional benefit is that the system is a 'water feature' attractive to children using pool.

Downsides to this (or any evaporative system) will be water consumption, hardening of the pool water, and increased pool chemical use.

I have a 600 gal kiddie pool I fill with 90 degree water off my open loop geo. A shower head with the flow restrictor removed happens to produce the right flow at my system conditions. If the pool becomes too warm I can bungee the showerhead to a porch rail such that the water passes through air a few feet before hitting pool. It loses 5 or so degrees in that process, and our dewpoints are mid 70s, higher than yours.

I agree just buy a floating pool fountain that hooks up to your return lines and let it run. As it sprays in the air it will cool down the water a lot. You could make up your own or even try it by just adding a line to one of your returns and somehow spray it up or at an angle and falling back in the pool.

A ground loop would help, but be messy and likely only "help" not fix the problem.

My second choice after a fountain would be an air source heat pump. Just search heat pump and pool, just make sure it is reversible and if you’re cooling, do it at night when the ambient temps are the lowest and for heating when it is warmest out.

What color is the pool? If it is dark next time you have to refinish it, pick a very light color.

They also do make reflective pool covers you could use during the day, but leave it uncovered at night.

The fountain idea works, I have used it myself. You can only use it at night after air temps have gone down, Running it during the day will only increase evaporation and heat the water. If you have a polaris type pool cleaner you can attach a hose to the polaris fitting and run the fountain using the booster pump,

Looks like around $5/day to run a heat pump for your required btu.

A:  Increase evaporation, yes- it's the heat-of-vaporization extracted from the remaning liquid water that is providing the cooling effect.  Without the evaporation there's at an order of magnitude less heat exchange going on- the evaporation is what's working.

B: Heat up the water during the day- don't think so (or at least, not much. See A: )

Another approach to pool cooling that works is to use unglazed solar collectors designed for pools as nighttime radiant-coolers (pumping the water through them based on differential thermostat control.)  Unglazed pool heaters have low stagnation temps and self-cool to ambient rapidly. At night under a clear sky they run COLDER than the ambient air.  In NM & AZ solar pool heaters do double duty- heating during the cooler shoulder seasons, night-cooling all summer long.

They've even been adapted as radiant emitters for night-sky-cooling buildings. See:

http://zomeworks.com/files/double-play/SteveBaer/Cooling_PoolHeaters_7-1-02.pdf

Radiant-sky cooling works best in clear-sky low-humidity regions (like the southwest), but still some even in hazy areas.

With a sprinkler, I wonder how much of the cooling cools the air and how much cools the water falling back into the pool.

I like the above idea of an insulating cover with a reflective surface that is on during the day and off at night. Helps with chlorine and debris too.

jonr

Suggest you read up on the enthalpy of moist air and the relationship between dry bulb, wet bulb and dewpoint temperatures. Latent heat of vaporization informs as well.

It is possible, indeed likely, for 90 degree water to fall through 90 degree air and for both to become cooler as a result.

Thanks Engineer, but I'm quite familiar with this issue - enough even to know that your figure is noticeably low (it's over 10 degrees) - "every gallon of water evaporated removes enough heat to cool 100 gallons of water 8 degrees or so.".

Your latter statement is true; but it's not very applicable here.. 85 degree water through 95 degree air would be more applicable and of course it will depend on relative humidity, etc. Yes, with some set of conditions, spraying water through the air does heat the water up.