Formula to calculate expected Pool Water Temperature???

[TheG$]

Does anyone know the formula to calculate the expected Pool Water Temperature (approximately of course)?

Specifically, assume the following inputs. I am not sure which of them are actually pertinent, but I assume someone has a simple formula for forecasting a "unheated, uncovered pool" expected temperature if you know the following pieces of information.

Overnight Low Air Temp
Daily High Air Temp
Relative Humidity
Size of Pool in gallons (probably not needed)
Average Depth
Surface Area (probably not needed)

EXAMPLE (not real data!): My pool is 9000 gallons, 4 feet deep, with a 370 sf surface area. The daily high for the next five days will be (f) 97, 99, 100, 96, 98. The overnight low will be 65, 69, 68, 66, 66. The magic formula predicts in 5 days the water temp will be .... 77 degrees.

Anybody have any guesses?

[chem geek]

If one ignores the factors of heating from sunlight, cooling from evaporation, and ground temperatures, then the pool water should average around the average temperature over the 24 hour period assuming there aren't huge temporary spikes or drops in such temperatures. That gives you a baseline -- it doesn't tell you how long it takes to get to this average if you are starting with water at a different temperature.

If you cover the pool at night (or use a clear cover all day and night), then you create an asymmetry where more heat is gained during the day than is lost at night and this can easily add 10F or more to the pool temperature.

My own pool over the winter pretty much averaged out to the average temperature throughout the day and night -- perhaps a little higher than that -- and I had an opaque cover on it almost all of the time. The lowest it dropped was to 45F when the daytime temp was in the low 50's and the nighttime temps was in the high 30's. During the spring/summer/fall (part of those times, at least) we use solar heating and keep the pool at 85-88F with daytime temps of 70-90F and nighttime temps at 50-65F.

Richard

[mas985]

This software takes into account your local condition averages to give you an expected water temp. You can include solar, gas, electric heating as well plus if you have a solar cover. It is about the best method I have found for determining water temp. One more thing, it will do a business case for you to determine if solar is worth it.

http://www.canren.gc.ca/tech_appl/index.asp?CaId=5&PgID=484