How Desiccant Dehumidification Works

Date: 12-02-2013
In a typical dry desiccant system, the desiccant is mounted on a rotating wheel.   As the wheel turns, the desiccant passes alternately through the incoming process air where the moisture is adsorbed and through a “regenerating” zone where the desiccant is dried and the moisture expelled.  The wheel continues to rotate and the adsorbent process is repeated. 

Typically, about three-fourths of the desiccant wheel is exposed to the incoming air throughout the process.  During regeneration, the desiccant is heated by a direct-fired gas burner or indirect-fired water or steam coil.
dry_wheel.jpg (5774 bytes) Process Inlet—Air to be dried.  May be outside air, inside air or, more commonly, a mixture of air with high humidity content.

Process Outlet—Air is dried by desiccant wheel.  May be cooled, filtered or otherwise handled.  Relative humidity is substantially lower and temperature slightly raised.

Reactivation Inlet—Air flow, usually outside air, that drives moisture off wheel.   Reactivation air is heated by direct-fired gas burner or indirect-fired water or steam coils.

Reactivation Outlet—Hot, wet air from wheel is exhausted outside or passed through an air-to-air heat exchanger.  Using a heat exchanger to preheat incoming process air offers substantial savings in northern climates.