The following table demonstrates the BTU’s removed from the air based on a given
amount of water consumed in an hour by the PORT-A-COOL® unit.
In simple terms, evaporative cooling is nature s way of cooling. The PORT-A-COOL®
unit utilizes the same phenomenon, but in the most efficient manner possible.
B. Humidity and Evaporative Cooling.
A cubic volume of air at a certain temperature and pressure has the ability to absorb
and hold a certain amount of water vapor. If that volume~ne of air contains 50% of the
amount of moisture that it is capable of holding, it said to be at 50% relative humidity.
The higher the temperature of the air, the higher the amount of moisture it is capable of
holding. Any change in the temperature without a corresponding change in the pressure
results in an increase or decrease in the ability of the air to contain water vapor.
If the temperature increases without an increase in the pressure, the result is a decrease
in the relative humidity, and thus an increase in its ability to hold more moisture. That is
to say that in the morning the humidity may be high, but as the day passes and the tem-
perature increases the relative humidity will naturally decrease.
The extent to which relative humidity decreases through the day can be affected by local
weather systems and proximity to large bodies of water. If an increase in temperature
accompanied by a weather system containing moisture moves in, the drop in humidity
will not be as great Nevertheless, the fact remains that relative humidity does drop as air
temperature increases. In fact, for every 20°F rise in temperature, the moisture-holding
ability of air doubles. For instance, if the temperature of the air was 70°F and the relative
humidity was 100% at 5 a.m., and the temperature increased to 90°F at noon, the mois-
ture holding ability of the air would double As a result, the air would now be holding only
half of the moisture it is capable of holding, and the relative humidity of the air would
drop to 50%.
The hotter the day, the drier the air becomes, and the more cooling that can take place
through the evaporation of water. This means that when the day gets hot enough to
require cooling, the relative humidity will be much lower than in the morning and allow
an evaporative cooler to work well.
Since any evaporative cooling device must evaporate water to achieve cooling, more
water vapor is put into the air. As the ambient relative humidity increases, it becomes
more difficult to put moisture into the air. The efficiency of any evaporative cooling
device is directly related to its ability to evaporate water (cool) at a given relative humid-
ity. A unit with low efficiency will cool only at low relative humidity levels, while a unit
with high efficiency can achieve effective cooling at much higher humidity levels.
8
U. S. Gallons / Hour Total BTU’s Removed
10 (37.8 liters or 8.3 Imperial Gallons) 87,000
12 (45.4 liters or 10.0 Imperial Gallons) 104,400
14 (53.0 liters or 11.7 Imperial Gallons) 121,800
