It has been observed that indirect evaporative cooling (IEC) is, in fact, a form of solar air-conditioning. This is because the refrigerant (water) is evaporated in the conditioner to provide a cooling effect and re-condensed by the atmospheric (rain) cycle to a liquid refrigerant. Thus the rain cycle is employed in preference to the energy consuming compressor and condenser of a conventional vapour compression (VC) system.

As a consequence, early in 2008 two IEC systems were installed in an air-conditioning plant room area at the University of Technology, Sydney (UTS). These units cool outside air supplied to the main UTS building.

Traditional direct evaporative coolers operate by humidifying air and only produce comfort in hot dry climates. Therefore they are not ideal for moderately humid climates like Sydney, because they allow too much moisture in the supply air. However IEC systems produce energy efficient conditioning of the outside air without adding any moisture.

Extensive testing under mildly warm summer conditions showed that the coefficient of performance of the IEC units exceeded the performance of traditional air-cooled HVAC systems by a factor of 3. It is envisaged that performance will be better under hot summer conditions, further demonstrating the benefits of employing the solar atmospheric cycle in place of traditional compressor systems.