ABSTRACT Aprototype desiccant dehumidifier was built utilizing a horizontal, rotating drum containing solid desiccant. Outlet relative humidity was controlled by a microcomputer responding to various dehumidifier settings and environmental conditions. The system was tested using constant temperature and humidity inlet air. A steady state heat and moisture transfer model was developed to identify the parameters needed to predict drum reotation as a function of outlet air humidity and temperature. The simulation model predicted increased sensitivity of outlet air humidity at higher temperatures.