Abstract: A system for controlling environmental conditions in greenhouses having a plurality of crop beds. The system comprises sensors stationed over crop beds comprising an aspirated enclosure and means therein for generating analog electrical signals indicative of wet bulb and dry bulb temperatures. The system comprises a microcomputer located within the greenhouse having a central processing unit with associated scratch memory and program memory sections; an analog to digital input section for receiving the analog electrical signals from the sensors; an output section for converting the computer logic signals to electrical signals at power levels to operate electromechanical apparatus; and serial digital pathway means for connecting the central processing unit, input section and output section.