Energy and exergy analyses of an experimental open-cycle desiccant cooling system

Abstract

A procedure is developed for the energy and exergy analyses of open-cycle desiccant cooling systems and it is applied to an experimental unit operating in ventilation mode with natural zeolite as the desiccant. The same procedure and formulations may easily be applied to the units operating in recirculation mode. Energy-based performance parameters such as the coefficient of performance (COP) of the unit and the effectiveness’ of system components are presented. Exergy destruction and exergy efficiency relations for the system and its components as well as the reversible COP of the system are derived. The energy and exergy formulations are applied to the experimental unit using the data collected during a typical operation of the unit. The unit has a COP of 0.35, a reversible COP of 3.11, and an exergy efficiency of 11.1%. Desiccant wheel has the greatest percentage of total exergy destruction with 33.8% followed by the heating system with 31.2%. Rotary regenerator and evaporative coolers account for the remaining exergy destructions. The analysis shows that an exergy analysis can provide useful information with respect to the theoretical upper limit of the system performance, which cannot be obtained from an energy analysis alone. The analysis allows us to identify and quantify the sites with the losses of exergy, and therefore showing the direction for the minimization of exergy losses to approach the reversible COP.