Johnson Controls 40 25 TON, Installation Operation & Maintenance

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JOHNSON CONTROLS
5276178-JIM-C-0118
Start-up
TABLE 41 - BLOWER SPEED RATE OF CHANGE
CHANGE IN
RPM
CHANGE IN
CFM TSP
BHP AND
MOTOR
AMPS
.90 .90 .81 .73
.93 .93 .86 .79
.95 .95 .90 .86
.98
.98 .95 .93
1.00 1.00 1.00 1.00
1.03 1.03 1.05 1.08
1.05 1.05 1.10 1.16
1.08 1.08 1.16 1.24
1.10 1.10 1.21 1.33
1.13
1.13 1.27 1.42
1.15 1.15 1.32 1.52
1.18 1.18 1.38 1.62
1.20 1.20 1.44 1.73
Use the following tables and the PD calculated per the
previous equation to select a new motor sheave.
EXAMPLE
•
A 30 ton unit was selected to deliver 12,000 CFM
with a 20 HP motor and an 856 RPM drive, but
the unit is only delivering 11,000 CFM per Figure
15.
•
Use the equation to determine the required PD
for the new motor sheave (12,000 CFM/11,000
CFM X 6.7” = 7.3091 inch).
• Use the 30 ton table to select a Browning 2B5V74
which will increase the speed of the unit’s drive
and its supply air CFM to 111.9%. Thus select
the 7.5” PD at 112% increase over standard.
•
New drive speed = 1.1194 X 856 = 958.2
RPM.
•
New supply air = 1.1194 X 11,000 = 12,313
CFM
•
Re-use the existing belts and blower sheave.
New motor BHP = (speed increase)
3
x estimated motor
BHP at original start-up with 11,000 CFM and 856
RPM = (1.119)
3
x 11 BHP = 1.4012 x 11 BHP = 15.41
BHP New motor amps = (speed increase)
3
x measured
motor amps at original start-up with 11,000 CFM and
856 RPM.