A psychrometric chart is a graph of the physical
properties of moist air at a constant pressure (often equated
to an elevation relative to sea level). The chart graphically
expresses how various properties relate to each other, and is
thus a graphical equation of state. The thermophysical properties
found on most psychrometric charts are:
- Dry-bulb temperature (DBT)
- Wet-bulb temperature (WBT)
- Relative Humidity (RH)
- Humidity Ratio
- Specific Enthalpy
- Specific Volume
How to read the chart
The most common chart used by practitioners and students
alike is the "w-t" (omega-t) chart in which the
dry bulb temperature (DBT) appears horizontally as the abscissa
and the humidity ratios (w) appear as the ordinates.
In order to use a particular chart, for a given air pressure
or elevation, at least two of the six independent properties
must be known.
However it is quite tedious to note down exact values from
a give chart. This is where our software comes in.
Typically in the industry practices, one always knows the
dry bulb temperature, and one of the two values of wet bulb
temperature or relative humidity of air. Two values determine
exactly the property of air at a given point, and the remaining
physical properties can be jotted down.
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