These blades can be forward curved, straight, or backward curved. Centrifugal fans should be used for handling relatively clean air because dirt accumulation on centrifugal fan blades affects efficiency and airflow capacity. Centrifugal fans are commonly used in grain drying and forced air heating systems where high static pressures are required. A ventilating system is used to control the environment. Ventilation capacity is based primarily on the amount of air exchange needed to remove moisture in the winter and excess heat in the summer.
Airflow requirements vary with animal size and outside weather conditions.
Ideally, ventilation air must vary from just enough air to maintain good air quality during very cold weather up to a maximum rate to eliminate heat stress during hot weather. Cold weather ventilation is the minimum continuous rate that provides enough air to remove excess moisture. Cold weather fans run continuously with an emergency shut-off thermostat. Mild weather ventilation increases the air exchange rate to modify temperature and remove moisture. Mild weather fans are typically turned on and off with thermostats to maintain a desired air temperature.