At the University of Michigan, DDC is typically used to control fan systems, namely the supply and return fan speeds, fresh-air mixing dampers, heating and cooling coils and humidification systems, all to maintain the desired fan discharge temperature and humidity and ultimately the occupied spaces of buildings. Additionally, BAS may control and/or monitor fume hood exhaust fan and energy recovery controls (using the available heating/cooling from the exhaust air to heat/cool the outside air that's being drawn into the building by the supply fans). CO2 monitoring also provides for controls that adjust fresh air to auditoriums as the occupancy level changes. BAS also controls complex chilled water systems, including primary/secondary/tertiary chilled water loops, cooling towers start/stop and where available variable-speed controls, free-cooling systems, as well as outside and inside lights, hot water pumps and a rapidly growing number of individual DDC room controls.