BASIC TERMINOLOGY
VENTILATION - Moving air from one area to another.
CIRCULATION - The moving of air within a given area.
CFM - The volume of air moved by a fan expressed in cubic feet per minute.
SP / STATIC PRESSURE - The resistance to flow in any air moving system, expressed in inches of water column (IN. W.G.). Fans are rated in CFM at various static pressures.
HP / HORSEPOWER - The most common measurement of mechanical power of a motor.
BHP - The horsepower required to drive the fan at a given RPM and Performance Point.
VELOCITY - The speed, expressed in FPM (feet per minute), of air moving through a given area such as a duct, face area of a hood, air intake opening or cross section of a room or booth, or from an air circulator.
AIR CHANGES - The time required for a complete air change in given space. Normally expressed in minutes per change.
VENTILATION PRINCIPLES
AIR CHANGE METHOD - Probably the most common form of ventilation. Normally used for general ventilation of a building or an area in a building. Determine the volume of the area by multiplying the LENGTH X WIDTH X HEIGHT of the area, then divide the volume by the frequency of air change to determine the required CFM airflow. Determine the frequency of air change from the table below.
Several factors will affect your selection of air change frequency, a warmer climate will require a more frequent change than a more temperate one. Larger rooms often require less frequent air changes.
CAUTION - When ventilating an area that contains hazardous (explosive) fumes or dust in the air, specify a fan with an explosion proof motor and spark resistant construction.
INTAKE AIR - You cannot exhaust air without an intake air source, the air you exhaust from a building has to be replaced, a source of intake air located on the end of the building opposite the fan provides the best ventilation. Intake air velocity should be kept below 500-FPM velocity. Divide the CFM rating of the fan by the required velocity to determine the minimum square feet of face area for proper intake air (CFM / Velocity = Area). Bird screen in an air intake has a negligible effect on the open area, but insect screen reduces the open area by 50%. Louvers will also reduce the actual open area, see the louver data for actual open area. AIR CHANGE METHOD - Probably the most common form of ventilation. Normally used for general ventilation of a building or an area in a building. Determine the volume of the area by multiplying the LENGTH X WIDTH X HEIGHT of the area, then divide the volume by the frequency of air change to determine the required CFM airflow. Determine the frequency of air change from the table below.