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Method two
1.
Drill two 5/16 inch holes, one in the return air duct as close
to the inlet of the unit as possible, and another in the supply
air duct as close to the outlet of the unit as possible.
2.
Using the hole drilled in step 1, insert eight inches of 1/4
inch metal tubing into the airflow of the return and supply
air ducts of the unit.
Note: You must insert the tubes and hold them in a position
perpendicular to the air flow so that velocity pressure
does not affect the static pressure readings.
3.
Use an inclined manometer or Magnehelic® to determine
the pressure drop across the unit. This is the external static
pressure (ESP). In order to obtain an accurate
measurement, verify that the air filters are clean.
4.
Determine the number of turns the variable motor sheave
is open.
5.
Select the correct blower performance table for the unit
from Tables 17 and 18. Tables are presented for side and
bottom duct configuration.
Figure 28: Dry coil delta P
Johnson Controls Ducted Systems
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
6.
Determine the unit measured CFM from the blower
performance table, external static pressure, and the
number of turns the variable motor sheave is open.
7.
To adjust measured CFM to required CFM, see Supply air
drive adjustment on page 40.
8.
After you note the reading, remove the tubes and seal the
holes.
9.
Tighten the blower pulley and motor sheave set screws
after any adjustments. Re-check the set screws after 10-12
hours run time.
Note: You must repeat this procedure with the addition of
field-installed accessories.
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
Airflow (CFM)
5835254-YIM-A-1119
ZZ15
39
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