Determine the pressure in the vicinity of the fan. Measure the dry-bulb and wet-bulb temperatures within the fan inlet airflow passage. Temperatures must be measured across the cross-section; all such data are used to determine the air density at the relevant planes.
Characteristic parameters for the fan (including those with inlet guide vanes) must be established, covering the operating state where the guide vanes are in the fully open position. Variable inlet guide vanes are considered an integral part of the fan. To enable a comparison between test results and the fan's characteristic parameters, the guide vanes must be fixed in the fully open position during testing.
Record all relevant nameplate data for the fan motor, including voltage and rated load current. Measure the fan rotational speed as well as the motor's amperage, voltage, and wattage. If the three-phase current method is used to estimate the motor's output power, direct measurement of the motor's power input may not be required. If the motor operates far from its rated load point, it may be necessary to disconnect the drive mechanism and measure the no-load current.
For fans with unrestricted inlets, the sum of the static and dynamic pressures at the inlet can be considered equivalent to the sum of static and dynamic pressures measured at a point sufficiently far from the inlet-where static pressure is zero and dynamic pressure in still air is also zero.
Insufficient length of the discharge duct on the fan outlet side creates additional system resistance. To calculate the value of this additional resistance, it is necessary to measure the length of the discharge duct, the fan outlet area, and the fan's discharge area.
