The Best Design for a Direct Evaporative Cooling System Based on Pressure Drop at Desired Saturation Efficiency: A Cost–Benefit Optimization

In this study, saturation efficiency and pressure drop, two critical parameters for the direct evaporative cooling phenomenon, were numerically investigated and optimized. For this purpose, the direct evaporative cooling process was simulated at inlet air velocities in the range of 1–3 m/s on different thicknesses of CELdek 7090 evaporative cooling pad from 100 to 300 mm. The mathematical model of pressure drop and saturation efficiency was developed by analyzing variance at R-squared values of 99.53% and 99.99%, respectively. Finally, the non-dominated sorting genetic algorithm II (NSGA-II) was applied to minimize the pressure drop while maximizing the saturation efficiency simultaneously. The results indicate that applying mathematical models makes it possible to predict the saturation efficiency and pressure drop of direct evaporative cooling systems with a 4% and 7.9% deviation, respectively. It can also be concluded that the pad thickness effect is more significant on the saturation efficiency than on the pressure drop. On the other hand, the inlet velocity has a greater impact on the pressure drop. NSGA-II optimization demonstrated that, regardless of the pad thickness, optimal saturation efficiency and pressure drop were obtained at the inlet air velocity of 1 m/s. Accordingly, when using direct evaporative cooling systems, efficiency and pressure drop can be optimized whenever the fan is set at a low speed. Depending on the researchers’ and designers’ goals, the findings of this research can be used in the design of direct evaporative cooling systems for different applications to achieve maximal saturation efficiency at the minimum possible energy consumption.