and working back toward the fan. (See fig. 13-12.)
The type of diffuser and the air delivery design
of each outlet should be noted.
3. Obtain data pertinent to motors, fans,
diffusers, and grilles that are not given on
drawings. This can usually be taken from the
manufacturers identification plate located on the
component. This information is useful during the
balancing process for comparing measured results
with design conditions.
4. Make a visual check of the system to
ascertain that all fans are rotating correctly. Also,
that air filters are clean and properly installed.
5. Place all dampers in the open position. This
includes volume balancing dampers, splitter
dampers, outlet dampers, and fire dampers.
6. Check all necessary instruments prior to
starting the balancing procedure. Always follow
the manufacturers recommendations for check-
ing the calibration of instruments.
PROCEDURES FOR BALANCING
The procedures required for balancing most
systems are similar. Balancing is a rigorous tech-
nique that, if properly done, yields excellent
results. As with any set of procedures, each opera-
tion is necessary and must be performed in the
correct sequence. The following procedures are
general in nature and apply to most systems.
Determine Fan Performance
The first step of the procedure is to determine
fan performance. The purpose for this is to
ensure that there is sufficient static pressure
and air volume being handled at the fan before
balancing is started. The fans revolutions per
minute (rpm), the voltage and amperage of the
fan motor, the fan static pressure, and the
systems total airflow are indications of fan
The fan rpm can be measured by a tachometer
as shown in figure 13-13. You should take several
readings to ensure an accurate reading. The results
can be compared with the design conditions to
You should use a multimeter to determine if
the operating voltage and amperage of the fan
motor are within the range of rated voltage and
amperage indicated on the motor nameplate. The
measured results can either be compared or used
to calculate the brake horsepower. Use the
manufacturers recommended calculation to
determine the brake horsepower.
You can determine the fan static pressure by
attaching a velometer and static pressure probe
to test tap holes located on the inlet and discharge
duct of the fan, as shown in figure 13-14. Fan
static pressure is the static pressure at the outlet
minus the total pressure in the fan inlet. This
Figure 13-12.Duct system working sketch.