Experimental evaluation of one, two, and three stage evaporative cooling systems

The thermal performance of four different arrangements of evaporative air coolers have been evaluated experimentally during the hot summer of Kuwait. The systems include one-stage direct evaporative cooling (DEC), one-stage indirect evaporative cooler (IEC) linked to an external cooling tower, two-stage indirect/direct evaporative coolers (IEC/DEC), and three-stage system of evaporative cooling and mechanical vapor compression (IEC/DEC-MVC). Two variables are used to evaluate the system thermal performance, the thermal effectiveness and the energy efficiency ratio (EER). The data show that the IEC/DEC has the highest EER, followed by the DEC, IEC/DEC-MVC, and IEC. The DEC has the lowest effectiveness, succeeded by the DEC/IEC, IEC, and IEC/DEC-MVC. Coupling MVC with IEC/DEC extends the cooling range and can cool the ambient air dry bulb temperature over a range of 40degreesC to 15degreesC at any value of ambient air wet bulb temperature. Two experimental correlations have been developed for each one of the tested systems. The first one relates the effectiveness to water to air mass flow ratio (L/G) or Reynolds number (Re), while the second correlation relates the EER with effectiveness and L/G and/or Re. These relationships are very important in designing and optimizing the studied evaporative cooling units.