variavel0=<b>JOSÉ RUI CAMARGO</b> - rui@engenh.mec.unitau.br UNITAU/UNESP-FEG
<b>CARLOS DANIEL EBINUMA</b> - ebinuma@feg.unesp.br UNESP-FEG
<b>Abstract.</b> Air conditioning systems are responsible for the increase in man`s efficiency at the work due to a more comfortable working environment. Presently, the most used system is the mechanical vapor compression system. However, in many cases, evaporative cooling can be an economical alternative in place of conventional system, under several conditions, or as a pre-cooler in the conventional systems. This leads to a reduction in operational cost, in comparison with systems using only mechanical refrigeration. Evaporative cooling operates using natural phenomena, through induced processes, where water and air are the working fluids. It consists in water evaporation, induced by the passage of an air flow, thus decreasing the air temperature. The main characteristic of this process is the fact that it is more efficient when the temperatures are higher, that is, when more cooling is necessary for thermal comfort. This work presents, initially, the basic principles of air conditioning systems based on the evaporative cooling process for human thermal comfort. It also presents the principles of operation for direct and indirect evaporative cooling systems and the mathematical development of the equations of thermal exchanges, allowing the determination of heat transfer convection coefficients for primary and secondary air flow. In addition an analysis of the cooling effectiveness for direct and indirect systems is performed, concluding that such effectiveness can be determined if primary and secondary air flow and their specific heats are known.
<b>Keywords.</b> evaporative cooling, air conditioning, heat and mass transfer.