In HVAC design the fundamental requirement is to identify the processes that is being performed on the air. These processes can be plotted on a psychrometric chart.
A psychrometric chart is a graphical representation of the thermodynamic properties of moist air at a pressure of one atmosphere. Using this chart, engineers can solve problems without having to do long and tedious calculations.
The psychrometric charts shows the quantities of:
dry bulb temperature
wet bulb temperature (also known as saturation temperature)
dew point temperature
moisture content (also known as humidity ratio)
enthalpy (also known as total heat)
specific volume (the inverse of density)