the commonest technique is by evaporation. Water is absorbed into a pad or filter, and a fan is used to speed the evaporation process. This strategy is simple and natural, and has been about for a long time. The only drawback is the noise of the fan.

Another technique which has been developed lately uses a spinning disk to encourage the water into the air. These ‘impeller’ models make a load less noise than a fan, which is a massive advantage.
the third type uses ultrasonic sound. This may sound like something from science fiction, but it is actually quite an effective strategy. To the human ear, these models are effectively silent! (more…)