Psychrometrics is used to analyze the change in properties and the thermal characteristics of the air-conditioning process and cycles. Dalton's law is summarized from the experimental results and is more accurate at low gas pressure. Dalton's law can be extended, as the Gibbs-Dalton law, to describe the relationship of internal energy, enthalpy and entropy of the gaseous constituents in a mixture. The sensible heat of moist air is the thermal energy associated with the change of air temperature between two state points. The dew point temperature is the temperature of saturated moist air of the moist air sample having the same humidity ratio at the same atmospheric pressure. A psychrometric chart is a graphical presentation of the thermodynamic properties of moist air and various air-conditioning processes and air-conditioning cycles. A psychrometric chart helps in calculating and analyzing the work and energy transfer of various air-conditioning processes and cycles.