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Evaporation Loss
Name: Lawrence
Status: other
Age: 60s
Location: N/A
Country: N/A
Date: 1999-2001
Question:
Does water evaporate faster(inchs per day) from a smaller
surface area
ie. a spa vs a larger surface area ie. a swimming pool? My spa (7 ft dia)
loses 1 1/2 in. per day while my swimming pool (22' x 42') loses 1/2 in.
per day. My pool builder says that is normal!
Replies:
No, water doesn't evaporate from a smaller surface area than a larger one.
There may be a couple different reasons why the spa loses more than the pool
though!
1. If the spa is heated it will evaporate faster.
2. If the bubble jets are on (if the spa is equipped with them, I am
guessing it is like a hot tub?)
3. If the spa is smaller than the pool and is painted with a dark color,
the water will warm faster in the spa than the pool water would warm, this
would just be the sunlight heating two different volumes of water.(this
would occur regardless of color but would be more apparent if the paint was
dark) The only thing I could suggest is leave a thermometer in both and
compare the temperatures throughout the day and see if they vary by much.
Hope this helps
Dr. Baldwin
Isn't your spa warmer than your pool? If so, this is the reason its water
evaporates faster.
Tim Mooney
Lawrence,
I'm going to guess that in general you keep your spa warmer than your
pool. Water evaporation is related to temperature, so that would explain a
lot of it.
If they're being used by the same number of people each day, the spa will
also lose water faster, as the water absorbing in the suits and hair and
skin of each user will be the same, but since the spa is smaller, each bit
lost represents a larger percentage of the total volume.
Donald Yee Ph.D.
San Francisco Estuary Institute
180 Richmond Field Station,
1325 South 46th St. Richmond, CA 94804
Dear Lawrence-
There are several factors affecting the rate of evaporation of a liquid.
Probably the most important two factors are the temperature of the liquid
that is evaporating, and the humidity of the air into which the water is
evaporating.
If the air is "dry," the water will evaporate faster than if the air is very
humid. And warmer water evaporates faster than cold water. Probably the
temperature of the spa water is warmer than that of the swimming pool. And
possibly the air around the spa is drier than that over the swimming pool.
Other factors being equal, the size of the container of the water should
not matter.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
Hello,
There are many factor the can affect the rate of evaporation from a
pool: volume, surface area, wind, location, chemistry of water, air
temperature and moisture, color of the pool walls (different colors
absorb at different rates), etc.
Water is heated up by the sun and by the warm walls of the pool.
Infrared radiation is absorbed by water, mostly in the top 0.1 mm or so,
while the visible light goes deeper in water. Warm water -having lower
density- moves to the surface when it is further heated and evaporated.
The mechanism is complex, however, it is not difficult to understand why
the SPA loses more water than a pool - the question you posed.
SPA has a smaller volume of water than the pool. As such, for the same
amount of sunlight impinging on the surfaces of the pool and the SPA,
the water in the SPA is warmer, leading to more evaporation. Warm
ground may make additional heat contribution. In fact, you can measure
the water temperature at regular interval in the two reservoirs and
correlate the results with evaporation rates.
AK
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