Indirect evaporative cooling is an effective way to increase energy efficiency of air conditioning systems. This technology is particularly suitable for data centers applications, where the indoor temperature can be higher than the one adopted in residential and commercial buildings. In this work an indirect evaporative cooling system based on a cross flow heat exchanger has been widely tested. The system has been designed in order to minimize water consumption, with water mass flow rate between 0.4% and 4% of the secondary air one. On the whole, 112 experiments have been carried out in different working conditions of data centers. The effects of variation of water flow rate, humidification nozzles setup and secondary air temperature, humidity and flow rate have been widely investigated. Results put in evidence that performance is slightly dependent on nozzles number and size but it is strongly influenced by the water flow rate. In addition, nozzles in counter flow arrangement perform better than in parallel flow configuration. Depending on working conditions and equipment setup, the wet bulb effectiveness varies between 50% and 85%. (C) 2016 Elsevier B.V. All rights reserved.