**2.1 All-air systems**

In these systems air alone is used as working fluid to produce cooling or heating in air-conditioned zones; besides that air is responsible for controlling the zones' humidity level and provide the required ventilations to air-conditioned zones. In addition, in all-air systems, air is used for aromatizing purposes. Therefore, only air as working fluid is responsible for providing comfort, i.e., cooling, heating, controlling of humidity and ventilation odor, and thus these systems are called all-air systems [1–5].
