Civil Engineering Reference
In-Depth Information
Fig. 13.3
An example of a psychrometric chart as suggested by ASHRAE
13.2.1 Typical Air Conditioning Processes
Most of the typical air conditioning processes (dehumidification, humidification,
adiabatic mixing, etc.) can be described using the basic principles discussed above
and psychrometric charts.
When necessary to lower the relative humidity, dehumidification is gen-
erally implemented by a cooling section followed by a re-heating section.
There are also other methods of dehumidification, such as chemical
absorption by salts.
In a dehumidification process by a cooling section (see Fig.
13.4
), the moist air
stream (point 1) is cooled below its dew-point temperature, so that the initial water
vapor condenses. A saturated moist air mixture (with relative humidity 100 % in
ideal operating conditions and lower humidity ratio) leaves the dehumidification
section (point 2) at the saturation temperature below the dew point (the final partial
pressure of water vapor at point 2 is lower than the initial partial pressure of water
vapor in the mixture, because condensate has been removed). This moist airstream
must generally be re-heated in a following section in order to bring it to a condition
most occupants would consider comfortable. This last phase occurs at constant
