Balancing of a Water and Air System (PDF

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can be used. If these become too expensive or unwieldy, measure the flow by Pitot tube
traverse.
Taps for Pitot tube traverses can be installed in either vertical or horizontal pipe runs. As
illustrated in Figure 13.7, the taps must be perpendicular to the pipe and at 90" from one
another. Adequate clearance [roughly the pipe diameter, plus three feet (1 m)] must be
available at each tap to install and position the Pitot tube.
If make-up enters or blow down leaves the tower or the system at a point where it will
affect any of the measured test values, they must either be shut off for the duration of the
test or the flow rates measured. Usually, these measurements lend themselves to a
volumetric or bulk measurement procedure. In many instances, a water meter will have
been installed in the make-up line and can be used for this purpose. In virtually all
instances, the blow down can be valved off during the test period.
Fan Motor Power
Most cooling tower fans are driven by electric motors of 480V or less. The preferred
method for measuring power is to use a calibrated, clamp-on wattmeter to measure the
KW input to the motor(s) and convert this to
Horse power output using the motor manufacturer's efficiency values. Brake horsepower
can be calculated.
Wind Velocity
When a cooling tower test is run under conditions of little or no wind, the parties to the
test often may agree to forego measurement of wind velocity. Strict compliance with the
test code, however, requires that wind velocity be measured with a meteorological
anemometer and wind vane. For towers with an overall height of less than 20 feet (6 m),
the point of measurement is 5 feet (1.5 m) above the basin curb at a distance 50 to 100
feet (15-30 m) upwind of the tower.
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