The application of evaporative cooling technique is getting more and more attention. The aim of the work is to propose a hybrid air-conditioning system. The hybrid system employs an indirect evaporative heat exchanger (IEHX) as a pre-cooling unit that is operated in tandem with conventional air handling unit. The present work has developed a numerical model by considering the pre-cooling effect of the IEHX. The IEHX is able to adopt the room exhaust air as its working air. In addition, the mathematical formulation for the conventional cooling coil has been developed to study the influence of the pre-cooling effect on the chilled water temperature. The calculated results have demonstrated the ability of the evaporative pre-cooling unit to cool and dehumidify the ambient air under humid tropical climates. The chilled water supply temperature can be also raised due the pre-cooling process. Consequently, an improvement on the coefficient of performance for the chiller is achieved. The hybrid system is able to obtain a potential energy saving as a result of the pre-cooling effect and the enhanced efficiency.

A hybrid air-conditioning system has been proposed by integrating an indirect evaporative pre-cooling unit. In the proposed system, the room exhaust air is employed in the indirect evaporative cooler (IEC) to pre-condition the ambient intake air. The mathematical formulation has been judiciously established for the pre-cooling IEC. The validation of the numerical model has been conducted by comparing the simulated results with the experimental data in terms of the outlet temperature and the heat flux along the heat exchanger surface. The pre-cooling performance of the IEC is theoretically investigated for the climate in representative cities selected from five different climate zones. The psychrometric illustration of the air conditioning variation has indicated that the ambient air can be pre-cooled and pre-dehumidified through the IEC. The possibility of water vapor condensation depends on the humidity ratio of the ambient intake air. The simulation result demonstrates the capability of the pre-cooling IEC to fulfill part of the cooling load of the ambient intake air resulting in a marked energy saving potential.