Use and Care Manual

20
The following example illustrates the use of the psychrometric chart as it relates to
evaporative cooling. Since all of the items described above are properties, any two of them
describe a state point on the psychrometric chart. Once this point is determined, the values of
all the other properties can be read from the chart. Figure 5 below shows a Mollier type
psychrometric chart for atmospheric pressure.
The dot shown in Figure 5 is a state point. The following properties are known about the
air/water mixture at this state.
dry-bulb temperature: 97°F dew-point temperature: 71°F
wet-bulb temperature: 78°F relative humidity: 43%
The COOL-SPACE® unit is a high-
efficiency portable evaporative cooler.
The unit draws air across water saturated
high-efficency cooling pads which
forces the air to evaporate the water, thus
removing energy from the air.
Take the air/water mixture described by
the state point above, with a dry-bulb
temperature of 97°F and 43% relative
humidity, for example. As the air passes
through the cooling media on the
COOL-SPACE® unit, moisture is added
to the air increasing the relative
humidity. This increase in relative
humidity brings a decrease in dry bulb
temperature. When the relative humidity
is raised to 70%, the dry bulb
temperature has dropped to 86°F. When
the humidity level approaches 100%, the
dry bulb temperature has dropped nearly
20°F to 78°F.