Figure 7-3.Comfort zone chart.
saturated (maximum water vapor at that temperature)
and the temperature of that air falls, a point is finally
reached at which the air is saturated for the new and
lower temperature, and condensation of the moisture
begins. This is the dew-point temperature of the air for
the quantity of water vapor present.
Relationship of Wet-Bulb, Dry-Bulb, and
A definite relationship exists between the wet-bulb,
dry-bulb, and dew-point temperatures. These
relationships are as follows:
When the air is not saturated but contains some
moisture, the dew-point temperature is lower
than the dry-bulb temperature, and the wet-bulb
temperature is in between.
As the amount of moisture in the air increases,
the amount of evaporation (and, therefore,
cooling) decreases. The difference between the
temperatures becomes less.
When the air becomes saturated, all three
temperatures are the same and the relative
humidity is 100 percent.
To HUMIDIFY air is to increase its water vapor
content. To DEHUMIDIFY air is to decrease its water
vapor content. The device used to add moisture to the
air is a humidifier, and the device used to remove the
moisture from the air is a dehumidifier. The control
device, sensitive to various degrees of humidity, is
called a HUMIDISTAT.
Methods for humidifying air in air-conditioning
units usually consist of an arrangement that causes air
to pick up moisture. One arrangement consists of a