The present paper aims to describe the experimental study developed to characterise an indirect evaporative cooling system made of polycarbonate, designed and manufactured by the Thermal Engineering Group of the University of Valladolid; as well as to introduce the main results obtained. The prototype is characterised by a total heat exchange area of 6 m(2), and is installed in a heat recovery cycle in the experimental setup constructed in the laboratory. This setup mainly consists of: an AHU that enables the reproduction of the different climatic conditions to be tested; a climatic chamber where comfort conditions are to be achieved; a circuit to supply water during one of the operating modes; and the due ducts and measurement probes to properly connect the whole system and register the evolution of the interesting parameters. Two operating modes are performed. In the first one, exhaust air from the climate chamber, in comfort conditions, goes through one side of the heat exchanger, producing heat transfer from the outdoor air stream through the plastic walls of the system. In the second case, an evaporative cooling mode is implemented by supplying water to the exhaust airstream. Results obtained show that heat transfer through the heat exchanger polycarbonate wall improves in the evaporative cooling mode. Furthermore, both cooling capacity and thermal effectiveness of the system also increase in the second case. Moreover, global heat transfer coefficient and cooling capacity are improved by higher outdoor air volume flow rates. Finally, higher outdoor air temperatures imply better cooling capacities and thermal effectiveness. (C) 2011 Elsevier Ltd. All rights reserved.