Regenerative indirect evaporative cooling (RIEC) systems are an interesting alternative to conventional air-cooling systems based on direct expansion units. In the present work, the main objective was to experimentally determine the performance of a RIEC air-cooling system under different inlet air conditions. Moreover, a mathematical RIEC model based on modified ε-NTU numerical method was developed and validated. The experimental RIEC results showed high cooling capacity, with dew point effectiveness values up to 0.91. The accuracy obtained of the mathematical model was more than acceptable. Therefore, it can be used properly to study the global behaviour of a RIEC. These air-cooling systems would contribute to achieve the European objectives of nZEB.