This paper aims at developing an analytical model for the Coupled heat and mass transfer processes in indirect evaporative cooling under real operating conditions with parallel/counterflow configurations. Conventionally, one-dimensional differential equations were used to describe the heat and mass transfer processes. In modeling, Values of Lewis factor and surface wettability were not necessarily specified as unity. Effects of spray water evaporation, spray water temperature variation and spray water enthalpy change along the heat exchanger surface were also considered in model equations. Within relatively narrow range of operating conditions, humidity ratio of air in equilibrium with water surface was assumed to be a linear function of the surface temperature. The differential equations were rearranged and an analytical solution was developed for newly defined parameters. Also, performances with four different flow configurations were briefly discussed using the analytical model. Through comparison, results of analytical solutions were found to be in good agreement with those of numerical integrations. (c) 2005 Elsevier Ltd. All rights reserved.