Fan User Manual

VI. EVAPORATIVE COOLING
The PORT-A-COOL® unit is a fully self-contained, portable, high efficiency evaporative cooler.
The PORT-A-COOL® unit is proudly made in America at our Center, Texas factory.
A. What is Evaporative Cooling?
When trying to understand evaporative cooling, it may be best to think of air as being like
a sponge. Similar to a sponge, air has an ability to absorb moisture that it comes in contact
with. The amount of moisture that the air will absorb depends on the condition of the
air, or specifically, how much moisture the air already contains and the temperature of
the air. If the air is warm and contains only a small amount of moisture, it will more read-
ily absorb moisture. As air cools, its volume decreases, and with it, its ability to absorb
moisture decreases. After all, how easily you can clean up a spill depends on how dry the
sponge is that you are using.
The term “relative humidity” describes the quantity of water in the air in relation to its
total capacity. Any volume of air at any given temperature has an ability to hold a certain
quantity of moisture. If the air contains 20% of its total capacity to hold moisture, the rela-
tive humidity is said to be 20%. Whereas, a humidity of 100% indicates that the air at this
temperature and pressure is holding all the moisture it can. If the air has a low relative
humidity when entering the PORT-A-COOL® unit, then it has the ability to hold more
moisture, and will thus evaporate more water and cool more effectively.
When describing the amount of moisture in the air, the term relative humidity is used
because the “sponginess” of air changes relative to air temperature. The warmer the air,
the more spongy it becomes, and the more water it can hold. That is to say that air that
has a 100% relative humidity can hold no more water vapor. However, if the air is heated’
it expands, and as a result the relative humidity decreases even though the total amount of
water vapor in the air has not changed. As a result, we must describe the level of humid-
ity relative to the condition of the sponge we are talking about. Is it a 50°F sponge or an
80°F sponge? An 80°F sponge will hold more water at 50% humidity than a 50°F sponge.
How is cooling produced? In order to evaporate water, heat (energy) is required. In fact,
the evaporation of one gallon of water requires almost 8,700 BTU’s of heat. Where does
this heat come from? From whatever the water is in contact with as it evaporates. This
could be a hot sidewalk, your body, a tree, from the air itself or a wet cooling pad As the
heat is removed from an object, the temperature of that object is decreased - in this case,
the air.
It is important to realize that the temperature of the water does not have a great effect
upon the cooling produced through the evaporation. If you were to place a gallon of 50°F
water on a warm sidewalk, it would produce 9,000 BTU’s of cooling by consuming the
heat to perform the evaporation. A gallon of 90°F water would produce 8,700 BTU’s of
cooling, only a three percent difference. After all, if you were sprayed with water at either
of these temperatures on a hot day, you would still feel much cooler.
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