5567611-BIM-B-1218
Johnson Controls Ducted Systems
57
4.
Use the pressure drop indicated by the manometer and the
graph in Figure 28 to determine the unit CFM. In order to
obtain an accurate measurement, verify that the air filters
are clean.
5.
To adjust measured CFM to required CFM, see
6.
After you note the readings, remove the tubes and replace
the dot plugs.
7.
Tighten the blower pulley and motor sheave set screws
after any adjustments. Re-check the set screws after 10-12
hours run time.
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 19 and 20. Tables are presented for side and
bottom duct configuration.
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
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.
Figure 28: Dry coil delta P
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
1000
2000
3000
4000
5000
6000
7000
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Nominal CFM
supply
air
Pressure drop (IWG)
Pressure drop across a dry indoor coil versus
supply air CFM for all Z
s
unit tonnages
Z
sͲϬϲ
Z
sͲϬϳ
to
Z
sͲϭϮ
