Ventilation systems can utilize 80 percent of the total thermal-energy requirements for a livestock confinement building. Optimizing energy expenditure or environmental control is not possible with conventional controls. Improper adjustment of thermostats can result in ventilation rates above the minimum while the supplemental heater is operating. Thermostats can provide undesirable environmental fluctuations. Variable-speed fan controls have difficulties with accuracy and reliability. Operators avoid the use of complex control systems because of their inability to set the controls properly;A single-board microcomputer was selected to provide logical control of the livestock environment. Inside and outside dry-bulb temperature inputs utilize a semiconductor sensor whose current output varies with absolute dry-bulb temperature. A dew-point temperature sensor measures the moisture content of the environment. The static pressure transducers include diaphragms and linear Hall effect sensors. Fan speeds are counted with pulses from digital Hall effect sensors. Operator inputs, the desired dry-bulb temperatures, are attained with the adjustment of the potentiometers. An 8-bit analog-to-digital converter is interfaced to the microcomputer;Solid state relays control the power to single-speed fans, supplemental heater solenoids, and air inlet motors for air distribution. Eight-bit digital-to-analog converters provide signals to prototype speed controllers which manipulate variable-speed fans. The direction of the air inlet motors is controlled by electromagnetic relays. The operator adjusts the minimum ventilation rate of the variable-speed fans;Software, located in erasable programmable read-only-memory, presents a rational correlation between the ventilation, supplemental heating, and air distribution systems. The ventilation and supplemental heating systems attempt to provide the desired temperatures. The degree of change in ventilation rates is determined by the outside temperature. Variable-speed and single-speed fans function logically together to reduce abrupt fluctuations in airflow. The dew-point temperature is monitored to limit the relative humidity. The micrcomputer utilizes the fan rpm sensors to prevent winds from stalling variable-speed fans. Static pressure is regulated by the air inlets to maintain uniform air distribution. Fans, for summer ventilation, are utilized only during stressful weather conditions, thus conserving electrical energy. The software is written in mnemonic code and converted to machine language with an assembler;The controller, installed in a swine farrowing and nursery room, is operational and entering the system testing phase. Intensive testing is required before the reliability of the design is proven.