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Thread: Evaporation

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    meatloaf's Avatar
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    Evaporation

    Does anybody know approximently how much water an inground pool (420 sq ft) will lose due to evaporation during the winter in Arizona? I did a search but couldn't find anything. Thanks
    My pool is a 10,500 gallon (420 Sq Ft ) kidney shape. A hand made sheer decent waterfeature. STA-RITE HRPB30, Sand filter 30" 98 GPM,
    1 HP Maxi-Glas 2 pump, BBB Method, Taylor K-2005 test kit, 50 Watt 12V low-voltage pond light illuminates the pool at night for a nice soft glow.
    250 gallon stand-alone hot tub. Got it FREE!

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    mas985's Avatar
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    Re: Evaporation

    There are a lot of factors involved with estimating evaporation. If you use a solar cover, it should be almost zero. If you use a heater without a cover, it will be quite large.

    If you don't have a cover and no heating, plus the water temp is about 52 deg F and fairly little wind, then I would estimate evaporation to be around 0.1"/day. But that is based upon a few other assumptions such as full sun exposure.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Evaporation

    Map of annual evaporation rates (in inches):
    http://www.grow.arizona.edu/images/water/panevap.gif

    You'd expect the bulk of it to be in the summer, of course. You could try poking around that website and see if they have data broken down by month, or something.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Evaporation

    Just a personal observation, but it seems that I lose more water during dry windy periods, than during hot, humid, still days.
    17,000 Gallon plaster pool. Hayward Perflex EC65 DE Filter. 3/4 HP Hayward Superpump converted to dual speed. CircuPool RJ45. Skimmer, floor drain, two returns.

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    Re: Evaporation

    Quote Originally Posted by jparr
    Just a personal observation, but it seems that I lose more water during dry windy periods, than during hot, humid, still days.
    That makes perfect sense. The formula for evaporation from pools has a factor for wind and another for the difference between the saturation vapor pressure (at water temp) and the actual vapor pressure (at air temp). So there is more evaporation with more wind and with dryer warmer air and with warmer water temperature. The sun does not directly cause evaporation, but it indirectly increases it by warming the temperature of the surface of the water.

    Here are some specific examples.

    Water Temp: 85ºF
    Air Temp: 75ºF
    Relative Humidity: 66%
    Wind: 0
    Evaporation: 0.20 inches/day

    Same as above, but with wind of 5 MPH: 0.62 inches/day
    Save as above, but with wind of 10 MPH: 1.06 inches/day
    NOTE: wind is measured near the water surface so is generally lower than general wind speed

    Same as above (no wind), but with relative humidity of 20%: 0.32 inches/day

    Same as above, but with water and air temp at 50ºF: 0.04 inches/day

    The evaporation rate during the day and at night is actually somewhat similar (assuming the same wind) because the relative humidity rises at night as the temperature cools, basically keeping the same amount of water in the air. You just see the evaporation effects more readily when the air is cooler since its increased saturation means there will be more visible "steam" as the water condenses.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Evaporation

    Glad I found this discussion. I was thinking that maybe there is a leak somewhere. After all the rain and wind storms that we got in northern California during the past few months, I did not expect the water level in the pool to be 1' to 1.5" lower than normal. There is an auto fill but it was turned off for the winter assuming that it was not needed. After reading this info on evaporation, I need to make sure that it is turned on in the winter when it gets windy.
    IG pebbletec pool: size of pool: 27,000 gal; filter: cartridge - Hayward Superstar Clear; pump size: 1.5 HP; TF 100 Test kit - got it on 7-29-10; The Pool Cleaner-4-wheel suction model; Pool calculator: http://www.poolcalculator.com/; bleach calc: http://troublefreepool.com/files/BleachCalc262.exe

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    Re: Evaporation

    I just saw this. I live in NW Florida, in the panhandle, and I had noticed quite a drop in the water level of my pool. It has been very sunny and windy lately, so could this be it? I did fill it about a half an inch, then like I said, it got windy, next thing, I noticed it dropped another inch! The mornings are a little cooler, and I do see the evaporation rising from the pool, so I hope this is it. Never noticed the water level drop like this before, and we haven't been in the pool since September.
    15x36 oval vinyl liner pool. IC40 intellichlor swg, pentair intelliflo vsp, Pentair clean and clear plus cartridge filter, 14,300 gallons

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    Re: Evaporation

    Welcome to TFP!

    You can do a bucket test as described in the Pool School article Leak Detection to make sure you don't have a leak.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    X-PertPool's Avatar
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    Re: Evaporation

    I always use a bucket test to make sure of leaks like chem geek mentioned but there is also this online thingy to gauge evaporation
    http://www.leaktools.com/professional/evaporation.php
    -Kevin
    X-Pert Pool Service
    x-pertpool.com
    X-Pert Pool on Facebook and @XPertPoolServic on Twitter
    22,000 gal / 16' x 32' / Vinyl / Hayward s244t /Pentair SuperFlo 1 hp

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    Re: Evaporation

    In the process of doing the bucket test, but I did the online thingy ("0) and was quite surprised at the results! checked the weather forecast on weather underground for that period of time, and the water evaporation was pretty high in comparison to what it would be like on a day like today. Thanks for that! I'm sure the results are just going to show it was evaporation "0)
    15x36 oval vinyl liner pool. IC40 intellichlor swg, pentair intelliflo vsp, Pentair clean and clear plus cartridge filter, 14,300 gallons

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