Most dehumidifiers use a refrigerant direct expansion (D/X) technology that the airstream flows across. The refrigerant makes the evaporator coil very cold and then condenses water from the air moving over it.  This technology is used for 45% to 65% relative humidity targets. 

Desiccant wheel systems use a specialty absorption type of wheel to remove humidity in applications requiring low humidity ranges below 40% RH.  After the water is absorbed by the wheel it rotates to second air stream that uses heat to remove the water.