Fan Controller-Variable Speed fan controls

Thermostatic ventilating system controllers are electronic decision makers that adjust fans, heaters, sprinklers and mixing fans based on control settings and a measured temperature. Controller adjustments impact the temperature, relative humidity and airborne contaminate concentrations in the barn. They also impact energy costs if supplemental heat is used. Most dairy ventilating systems do not use heaters so this article assumes no supplemental heat is being added.

All mechanically ventilated dairy barns with exhaust fans, including tunnel and cross ventilated barns, need ventilating system controllers to turn fans on and off or adjust variable fan speeds. Thermostatic controllers use a measured temperature and the controller's logic to decide when to turn fans on and off. More sophisticated controllers can make decisions based on time and additional sensor inputs when relative humidity, ammonia or carbon dioxide sensors are used.

Common single stage thermostats turn one fan on or off based on the temperature measured. Multi stage thermostats control two or more devices and programmable controllers can adjust variable speed fans.