The method uses a secondary air flow to cool a primary air flow. The secondary air flow is humidity charged during humidifying, at least up to the saturation line of 100 per cent relative air humidity. The secondary air flow during humidifying may be charged or supersaturated with non-wetting cold steam. The supersaturation amounts to 10-50 per cent, and preferably 2 per cent of the respective water content which corresponds to the operating point of the secondary air flow on the saturation line.
