SPONSORED BY GROWERSELECT
The starting point of designing a livestock or poultry ventilation system is to select fans with known air deliveries expressed as cubic ft. per minute (CFM), at normal static pressures developed in livestock buildings. This data allows us to create systems that regulate air speed for tunnel ventilation systems, determine the proper amount of evaporative cooling pads, establish the number of inlets, and calculate the minimum amount of air needed for moisture removal in the winter.
We rely on fan manufacturers to develop performance data based on standardized testing to optimize environments for our livestock and poultry. Fan companies produce this information by using a device known as Airflow Performance Test Chamber, or as it is more commonly known, a Wind Tunnel.
A Wind Tunnel consists of four separate chambers pressurized by a larger blower fan.
As air enters the first chamber, it meets a set of mesh straighteners that remove its turbulence. In the second chamber, it is forced through a nozzle wall consisting of metal cones that can be opened and closed to change the amount of square inches available according to the size of the test fan.
The air passes through the second wall of mesh straighteners before reaching the fourth chamber where the test fan is mounted.
Two devices, called Differential Pressure Transmitters, measure and record the static pressure differential on each side of the nozzle wall. The transmitters are calibrated monthly to maintain precise accuracy and are also returned to the manufacturer for a factory re-calibration once per year.
The testing begins by activating the test fan and adjusting the blower fan to achieve .0 inches of static pressure. The blower fan speed is then reduced to typical negative pressures such as .05, .10, .15 and the fan delivery is recorded. Engineers can test different combinations of motors, blades, pulleys and housing designs to achieve the most efficient design for a particular fan.
Although most fan manufacturers maintain a wind tunnel for in-house testing, the final authority for agricultural fans is BESS Laboratory at the University of Illinois. BESS Labs publishes a test booklet of fan performance data that includes air-moving capacity (cfm), efficiency ratings (cfm/watt) and air flow ratio that measures the ability of the fan to operate at high static pressure. More information can be found on online at http://bess.illinois.edu/