Abstract: Systems and methods for Indirect Evaporative Cooling and for Two Stage Evaporative Cooling for conditioning fluids such as air are disclosed. The Indirect Evaporative Cooling Systems comprise scalable indirect evaporative heat exchangers formed with polymer substrates that have been treated to render one surface substantially hydrophilic while the other is substantially hydrophobic, with channels for passage of primary (cooled) an secondary (cooling) air streams between them. The Two Stage Evaporative Cooling System comprise an indirect evaporation component where the fluid is pre-cooled indirectly with the abovementioned scalable heat exchangers, followed by a direct evaporation stage where the pre-cooled fluid is further cooled directly by adiabatic evaporative cooling. The device employing these systems is scalable, energy-efficient, uses aseptic materials, filters/clean incoming fluids (e.g. air), circulates disinfected evaporating liquid (e.g. disinfected water and has enhanced performance efficiency.