Abstract: A system provides a flexible control of heating, ventilation and air conditioning (HVAC) for enclosed areas. The apparatus and method of the present invention measures selected internal environmental variables in the enclosed area including data from a motion sensor indicating the occupancy status of the area for automatically controlling the operation of the HVAC system. Control settings are made to meet desired temperature and energy consumption levels. A logic algorithm and microcomputer determine humidity levels. The humidity levels are controlled to minimize the occurrence of mold and mildew. Algorithm timing strategies optimize air drying initiated by an occupancy sensor.