Port-A-Cool SERIES 2000 - Manual (Page 5)

PORT-A-COOL® Hazardous Location Units *
The following table demonstrates the BTU’s removed from the air based on a given amount of water
evaporated in an hour by the PORT-A-COOL® unit.
For actual temperature drops refer to Appendix A.
In simple terms, evaporative cooling is nature’s way of cooling. The PORT-A-COOL® unit utilizes the
same phenomenon, but in an extremely efficient manner.
B. Humidity and Evaporative Cooling.
A given 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 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 amount of water vapor the air can hold.
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 moisture. That is to say that in the morning the humidity
may be high, but as the day passes and the temperature increases the relative humidity will naturally decrease.
The extent to which relative humidity decreases through the day can be affected by local weather sys-
tems and proximity to large bodies of water. If an increase in temperature accompanied by a weather system
containing moisture moves in, then 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 mois-
ture-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 moisture 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 rela-
tive 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 will allow an evaporative cooling device to work more effectively.
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 (cooling the
air) at a given relative humidity. 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.
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