Abstract: Fresh inlet air is precold by the cool air discharging from the enclosure by the means of a heat exchanger to become still colder as the result of evaporation inside the evaporative cooler so producing useful air colder and with less water than conventional evaporative cooler. A heat exchanger is disclosed which comprises of numerous exhaust and suction canals adjacent to each other in which is provided aluminium lace for the purpose of exchanging the heat. The cool discharged air passes through the exhaust canals and leaves the heat exchanger cool to outside space and inlet fresh air passes through the suction canals separately relationship with discharged air and after becoming cool leaves the heat exchanger inside the evaporative cooler to effect evaporation.