Checking Supply Air CFM
To check the supply air CFM after the initial balancing has been
completed:
1.Remove the two ¼ inch dot plugs in the duct panel.
2.Insert at least 8 inches of ¼ inch tubing into each of these
holes for sufficient penetration into the airflow on both sides of
the indoor coil.
3.Using an inclined manometer, determine the pressure drop
across the dry evaporator coil. Since the moisture on an evapo-
rator coil may vary greatly, measuring the pressure drop across
a wet coil under field conditions would be inaccurate. To ensure
a dry coil, the compressors should be deactivated while the test
is being run.
4.Knowing the pressure drop across a dry coil, the actual CFM
through the unit can be determined from the curve in Coil Delta
P vs. Supply Air CFM figure.
WARNING! Failure to properly adjust the total system air quan-
tity can result in extensive system damage.
After readings have been obtained, remove the tubes and rein-
stall the two ¼ inch plugs removed in Step 1.
NOTE: De-energize the compressors before taking any test
measurements to ensure a dry indoor coil.
Unitary Products Group
7
035-16703-001-A-0202
D1NA Coil Delta P vs Airflow
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
400
600
800
1000
1200
1400
1600
1800
2000
2200
Airflow (CFM)
ID
C
oil
D
elt
a
P
D1NA024-30
D1NA036
D1NA042
D1NA048-60
D1NA018
Linear (D1NA024-30)
Linear (D1NA036)
Linear (D1NA042)
Linear (D1NA048-60)
Linear (D1NA018)
D1NA048-60
D1NA042
D1NA024
D1NA018
D1NA036
