This paper investigates a mathematical simulation and optimization of the heat and mass transfer processes in the indirect evaporative air cooler. The heat exchanger uses a novel combined parallel and regenerative counter-flow arrangement. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process. Mathematical model was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented unit. The exchanger was compared with the conventional regenerative unit. The results of comparison show, that the presented unit is characterized by higher effectiveness. The impact of the selected unitless operating factors on the performance of the investigated heat exchanger was established. The conducted multi-criteria optimization allowed to establish Pareto-optimal operating conditions and preferable climatic zones for the presented heat exchanger. (C) 2014 Elsevier Ltd. All rights reserved.